Philippine Electrical Code Part 1/Chapter 2. Wiring and Protection/Article 2.40 - Overcurrent Protection

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Article 2.40 - Overcurrent Protection

DISCLAIMER
This is not an official copy of the Philippine Electrical Code. This is a Design Guide according to the provisions of the Philippine Electrical Code. It also provides interpretation and annotations of the clauses of the Philippine Electrical Code. Any information, interpretation and/or annotation presented herein are based on personal opinion of the authors and does not represent the official interpretation of the Philippine Electrical Code.


While the authors have used good faith and efforts to ensure that the information and instructions contained in this work are accurate, the authors disclaim all responsibility for errors or omissions, including without limitation responsibility for damages resulting from the use of or reliance on this work. Use of the information and instructions contained in this work is at your own risk. If any contents or other technology this work contains or describes is subject to open source licenses or the intellectual property rights of others, it is your responsibility to ensure that your use thereof complies with such licenses and/or rights

Note: This is a work in progress...

Contents


2.40.1 General

2.40.1.1 Scope.

Parts 2.40.1 through 2.40.7 of this article provide the general requirements for overcurrent protection and overcurrent protective devices not more than 600 volts, nominal. Part 2.40.8 covers overcurrent protection for those portions of supervised industrial installations operating at voltages of not more than 600 volts, nominal. Part 2.40.9 covers overcurrent protection over 600 volts, nominal.

FPN: Overcurrent protection for conductors and equipment is provided to open the circuit if the current reaches a value that will cause an excessive or dangerous temperature in conductors or conductor insulation. See also 1.10.1.9 for requirements for interrupting ratings and 1.10.1.10 for requirements for protection against fault currents.

2.40.1.2 Definitions.

Current-Limiting Overcurrent Protective Device. A device that, when interrupting currents in its current-limiting range, reduces the current flowing in the faulted circuit to a magnitude substantially less than that obtainable in the same circuit if the device were replaced with a solid conductor having comparable impedance. Supervised Industrial Installation. For the purposes of Part 2.40.8, the industrial portions of a facility where all of the following conditions are met:

(1) Conditions of maintenance and engineering supervision ensure that only licensed electrical practitioner or non licensed electrical practitioner under the supervision of a licensed electrical practitioner monitor and service the system.
(2) The premises wiring system has 2500 kVA or greater of load used in industrial process(es), manufacturing activities, or both, as calculated in accordance with Article 2.20.
(3) The premises has at least one service or feeder that is more than 150 volts to ground and more than 300 volts phase-to-phase. This definition excludes installations in buildings used by the industrial facility for offices, warehouses, garages, machine shops, and recreational facilities that are not an integral part of the industrial plant, substation, or control center.

Tap Conductors. As used in this article, a tap conductor is defined as a conductor, other than a service conductor, that has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 2.40.1.4.

2.40.1.3 Other Articles.

Equipment shall be protected against overcurrent in accordance with the article in this Code that covers the type of equipment specified in Table 2.40.1.3.

2.40.1.4 Protection of Conductors.

Conductors, other than flexible cords, flexible cables, and fixture wires, shall be protected against overcurrent in accordance with their ampacities specified in 3.10.1.15, unless otherwise permitted or required in 2.40.1.4(a) through (g).

(a) Power Loss Hazard. Conductor overload protection shall not be required where the interruption of the circuit would create a hazard, such as in a material-handling magnet circuit or fire pump circuit. Short-circuit protection shall be provided.

FPN: See NFPA 20-2003, Standard for the Installation of Stationary Pumps for Fire Protection.

(b) Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:

(1) The conductors being protected are not part of a multioutlet branch circuit supplying receptacles for cord-and-plug-connected portable loads.
(2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).
(3) The next higher standard rating selected does not exceed 800 amperes.


Table 2.40.1.3 Other Articles
Equipment Article
Air-conditioning and refrigerating equipment 4.40
Appliances 4.22
Assembly occupancies 5.18
Audio signal processing, amplification, and reproduction equipment 6.40
Branch circuits 2.10
Busways 3.68
Capacitors 4.60
Class 1, Class 2, and Class 3 remote-control, signaling, and power-limited circuits 7.25
Closed-loop and programmed power distribution 7.80
Cranes and hoists 6.10
Electric signs and outline lighting 6.0
Electric welders 6.30
Electrolytic cells 6.68
Elevators, dumbwaiters, escalators, moving walks, wheelchair lifts, and stairway chair lifts 6.20
Emergency systems 7.0
Fire alarm systems 7.60
Fire pumps 6.95
Fixed electric heating equipment for pipelines and vessels 4.27
Fixed electric space-heating equipment 4.24
Fixed outdoor electric deicing and snow-melting equipment 4.26
Generators 4.45
Health care facilities 5.17
Induction and dielectric heating equipment 6.65
Industrial machinery 6.70
Luminaires (lighting fixtures), lampholders, and lamps 4.10
Motion picture and television studios and similar locations 5.30
Motors, motor circuits, and controllers 4.30
Phase converters 4.55
Pipe organs 6.50
Receptacles 4.6
Services 2.30
Solar photovoltaic systems 6.90
Switchboards and panelboards 4.8
Theaters, audience areas of motion picture and television studios, and similar locations 5.20
Transformers and transformer vaults 4.50
X-ray equipment 6.60

(c) Devices Rated Over 800 Amperes. Where the overcurrent device is rated over 800 amperes, the ampacity of the conductors it protects shall be equal to or greater than the rating of the overcurrent device defined in 2.40.1.6.

(d) Small Conductors. Unless specifically permitted in 2.40.1.4(e) or 2.40.1.4(g), the overcurrent protection shall not exceed 15 amperes for 2.0 mm 2 (1.6 mm dia.), 20 amperes for 3.5 mm 2 (2.0 mm dia.), and 30 amperes for 5.5 mm 2 (2.6 mm dia.) copper; or 15 amperes for 3.5 mm 2 (2.0 mm dia.) and 25 amperes for 5.5 mm 2 (2.6 mm dia.) aluminum and copper-clad aluminum after any correction factors for ambient temperature and number of conductors have been applied. (e) Tap Conductors. Tap conductors shall be permitted to be protected against overcurrent in accordance with the following:

(1) 2.10.2.1(a)(3) and (a)(4) Household Ranges and Cooking Appliances and Other Loads
(2) 2.40.1.5(b)(2) Fixture Wire
(3) 2.40.2.2 Location in Circuit
(4) 3.68.2.8(b) Reduction in Ampacity Size of Busway
(5) 3.68.2.8(c) Feeder or Branch Circuits (busway taps)
(6) 4.30.4.3(d) Single Motor Taps

(f) Transformer Secondary Conductors. Single-phase (other than 2-wire) and multiphase (other than delta-delta, 3-wire) transformer secondary conductors shall not be considered to be protected by the primary overcurrent protective device. Conductors supplied by the secondary side of a single-phase transformer having a 2-wire (single- voltage) secondary, or a three-phase, delta-delta connected transformer having a 3-wire (single-voltage) secondary, shall be permitted to be protected by overcurrent protection provided on the primary (supply) side of the transformer, provided this protection is in accordance with 4.50.1.3 and does not exceed the value determined by multiplying the secondary conductor ampacity by the secondary to primary transformer voltage ratio.

(g) Overcurrent Protection for Specific Conductor Applications. Overcurrent protection for the specific conductors shall be permitted to be provided as referenced in Table 2.40.1.4(g).


Table 2.40.1.4(g) Specific Conductor Applications
Conductor Article Section
Air-conditioning and refrigeration equipment circuit conductors 4.40.3, 4.40.6
Capacitor circuit conductors 4.60 4.60.1.8(b) and 4.60.2.2(a)–(d)
Control and instrumentation circuit conductors (Type ITC) 7.27 7.27.1.9
Electric welder circuit conductors 6.30 6.30.2.2 and 6.30.3.2
Fire alarm system circuit conductors 7.60 7.60.2.3, 7.60.2.4, 7.60.3.1, and Chapter 9, Tables 12(a) and 12(b)
Motor-operated appliance circuit conductors 4.22.2
Motor and motor-control circuit conductors 4.30.3, 4.30.4, 4.30.5, 4.30.6, 4.30.7
Phase converter supply conductors 4.55 4.55.17
Remote-control, signaling, and power- limited circuit conductors 7.25 7.25.2.3, 7.25.2.4, 725.41, and Chapter 9, Tables 11(a) and 11(b)
Secondary tie conductors 4.50 4.50.1.6


2.40.1.5 Protection of Flexible Cords, Flexible Cables, and Fixture Wires.

Flexible cord and flexible cable, including tinsel cord and extension cords, and fixture wires shall be protected against overcurrent by either 2.40.1.5(a) or (b).

(a) Ampacities. Flexible cord and flexible cable shall be protected by an overcurrent device in accordance with their ampacity as specified in Table 4.0.1.5(a) and Table 4.0.1.5(b). Fixture wire shall be protected against overcurrent in accordance with its ampacity as specified in Table 4.2.1.5. Supplementary overcurrent protection, as in 2.40.1.10, shall be permitted to be an acceptable means for providing this protection.

(b) Branch Circuit Overcurrent Device. Flexible cord shall be protected where supplied by a branch circuit in accordance with one of the methods described in 2.40.1.5(b)(1), (b)(2), (b)(3), or (b)(4).

(1) Supply Cord of Listed Appliance or Portable Lamps. Where flexible cord or tinsel cord is approved for and used with a specific listed appliance or portable lamp, it shall be considered to be protected when applied within the appliance or portable lamp listing requirements.
(2) Fixture Wire. Fixture wire shall be permitted to be tapped to the branch circuit conductor of a branch circuit in accordance with the following:
a. 20-ampere circuits — 18 AWG, up to 15 m of run length
b. 20-ampere circuits — 16 AWG, up to 30 m of run length
c. 20-ampere circuits — 2.0 mm 2 (1.6 mm dia.) and larger
d. 30-ampere circuits — 2.0 mm 2 (1.6 mm dia.) and larger
e. 40-ampere circuits — 3.5 mm 2 (2.0 mm dia.) and larger
f. 50-ampere circuits — 3.5 mm 2 (2.0 mm dia.) and larger
(3) Extension Cord Sets. Flexible cord used in listed extension cord sets shall be considered to be protected when applied within the extension cord listing requirements.
(4) Field Assembled Extension Cord Sets. Flexible cord used in extension cords made with separately listed and installed components shall be permitted to be supplied by a branch circuit in accordance with the following:
20-ampere circuits — 16 AWG and larger
2.40.1.6 Standard Ampere Ratings.

(a) Fuses and Fixed-Trip Circuit Breakers. The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 amperes. Additional standard ampere ratings for fuses shall be 1, 3, 6, 10, and 601. The use of fuses and inverse time circuit breakers with nonstandard ampere ratings shall be permitted.

(b) Adjustable-Trip Circuit Breakers. The rating of adjustable- trip circuit breakers having external means for adjusting the current setting (long-time pickup setting), not meeting the requirements of 2.40.1.6(c), shall be the maximum setting possible.

(c) Restricted Access Adjustable-Trip Circuit Breakers. A circuit breaker(s) that has restricted access to the adjusting means shall be permitted to have an ampere rating(s) that is equal to the adjusted current setting (long-time pickup setting). Restricted access shall be defined as located behind one of the following:

(1) Removable and sealable covers over the adjusting means
(2) Bolted equipment enclosure doors
(3) Locked doors accessible only to qualified personnel 2.40.1.8 Fuses or Circuit Breakers in Parallel. Fuses and circuit breakers shall be permitted to be connected in parallel where they are factory assembled in parallel and listed as a unit. Individual fuses, circuit breakers, or combinations thereof shall not otherwise be connected in parallel.

2.40.1.9 Thermal Devices.

Thermal relays and other devices not designed to open short circuits or ground faults shall not be used for the protection of conductors against overcurrent due to short circuits or ground faults, but the use of such devices shall be permitted to protect motor branch-circuit conductors from overload if protected in accordance with 4.30.3.10.

2.40.1.10 Supplementary Overcurrent Protection.

Where supplementary overcurrent protection is used for luminaires (lighting fixtures), appliances, and other equipment or for internal circuits and components of equipment, it shall not be used as a substitute for required branch-circuit overcurrent devices or in place of the required branch-circuit protection. Supplementary overcurrent devices shall not be required to be readily accessible.

2.40.1.12 Electrical System Coordination.

Where an orderly shutdown is required to minimize the hazard(s) to personnel and equipment, a system of coordination based on the following two conditions shall be permitted:

(1) Coordinated short-circuit protection
(2) Overload indication based on monitoring systems or devices

FPN: The monitoring system may cause the condition to go to alarm, allowing corrective action or an orderly shutdown, thereby minimizing personnel hazard and equipment damage.

2.40.1.13 Ground-Fault Protection of Equipment.

Ground-fault protection of equipment shall be provided in accordance with the provisions of 2.30.7.6 for solidly grounded wye electrical systems of more than 150 volts to ground but not exceeding 600 volts phase-to- phase for each individual device used as a building or structure main disconnecting means rated 1000 amperes or more.

The provisions of this section shall not apply to the disconnecting means for the following:

(1) Continuous industrial processes where a nonorderly shutdown will introduce additional or increased hazards
(2) Installations where ground-fault protection is provided by other requirements for services or feeders
(3) Fire pumps

2.40.2 Location

2.40.2.1 Ungrounded Conductors.

(a) Overcurrent Device Required. A fuse or an overcurrent trip unit of a circuit breaker shall be connected in series with each ungrounded conductor. A combination of a current transformer and overcurrent relay shall be considered equivalent to an overcurrent trip unit.

FPN: For motor circuits, see Parts 4.30.3, 4.30.4, 4.30.5, and 4.30.9.

(b) Circuit Breaker as Overcurrent Device. Circuit breakers shall open all ungrounded conductors of the circuit both manually and automatically unless otherwise permitted in 2.40.2.1(b)(1), (b)(2), and (b)(3).

(1) Multiwire Branch Circuit. Except where limited by 2.10.1.4(b), individual single-pole circuit breakers, with or without identified handle ties, shall be permitted as the protection for each ungrounded conductor of multiwire branch circuits that serve only single-phase line-to-neutral loads.
(2) Grounded Single-Phase and 3-Wire dc Circuits. In grounded systems, individual single-pole circuit breakers with identified handle ties shall be permitted as the protection for each ungrounded conductor for line-to-line connected loads for single-phase circuits or 3-wire, direct-current circuits.
(3) 3-Phase and 2-Phase Systems. For line-to-line loads in 4-wire, 3-phase systems or 5-wire, 2-phase systems having a grounded neutral and no conductor operating at a voltage greater than permitted in 2.10.1.6, individual single-pole circuit breakers with identified handle ties shall be permitted as the protection for each ungrounded conductor.

(c) Closed-Loop Power Distribution Systems. Listed devices that provide equivalent overcurrent protection in closed-loop power distribution systems shall be permitted as a substitute for fuses or circuit breakers.

2.40.2.2 Location in Circuit.

Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their supply except as specified in 2.40.2.2(a) through (g). No conductor supplied under the provisions of 2.40.2.2(a) through (g) shall supply another conductor under those provisions, except through an overcurrent protective device meeting the requirements of 2.40.1.4.

(a) Branch-Circuit Conductors. Branch-circuit tap conductors meeting the requirements specified in 2.10.2.1 shall be permitted to have overcurrent protection located as specified in that section.

(b) Feeder Taps. Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder as specified in 2.40.2.2(b)(1) through (b)(5). The provisions of 2.40.1.4(b) shall not be permitted for tap conductors.

(1) Taps Not Over 3 000 mm Long. Where the length of the tap conductors does not exceed 3 000 mm and the tap conductors comply with all of the following:
a. The ampacity of the tap conductors is
1. Not less than the combined calculated loads on the circuits supplied by the tap conductors, and
2. Not less than the rating of the device supplied by the tap conductors or not less than the rating of the overcurrent-protective device at the termination of the tap conductors.
b. The tap conductors do not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply.
c. Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway, which shall extend from the tap to the enclosure of an enclosed switchboard, panelboard, or control devices, or to the back of an open switchboard.
d. For field installations where the tap conductors leave the enclosure or vault in which the tap is made, the rating of the overcurrent device on the line side of the tap conductors shall not exceed 10 times the ampacity of the tap conductor.

FPN: For overcurrent protection requirements for lighting and appliance branch- circuit panelboards and certain power panelboards, see 4.8.3.7(a), (b), and (e).

(2) Taps Not Over 7 600 mm Long. Where the length of the tap conductors does not exceed 7 600 mm and the tap conductors comply with all the following:
a. The ampacity of the tap conductors is not less than one-third of the rating of the overcurrent device protecting the feeder conductors.
b. The tap conductors terminate in a single circuit breaker or a single set of fuses that will limit the load to the ampacity of the tap conductors. This device shall be permitted to supply any number of additional overcurrent devices on its load side.
c. The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.
(3) Taps Supplying a Transformer [Primary Plus Secondary Not Over 7 600 mm Long]. Where the tap conductors supply a transformer and comply with all the following conditions:
a. The conductors supplying the primary of a transformer have an ampacity at least one-third the rating of the overcurrent device protecting the feeder conductors.
b. The conductors supplied by the secondary of the transformer shall have an ampacity that is not less than the value of the primary-to- secondary voltage ratio multiplied by one-third of the rating of the overcurrent device protecting the feeder conductors.
c. The total length of one primary plus one secondary conductor, excluding any portion of the primary conductor that is protected at its ampacity, is not over 7 600 mm.
d. The primary and secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.
e. The secondary conductors terminate in a single circuit breaker or set of fuses that limit the load current to not more than the conductor ampacity that is permitted by 3.10.1.15.
(4) Taps Over 7 600 mm Long. Where the feeder is in a high bay manufacturing building over 11 m high at walls and the installation complies with all the following conditions:
a. Conditions of maintenance and supervision ensure that only licensed electrical practitioner or non licensed electrical practitioner under the supervision of a licensed electrical practitioner service the systems.
b. The tap conductors are not over 7 600 mm long horizontally and not over 30 m total length.
c. The ampacity of the tap conductors is not less than one-third the rating of the overcurrent device protecting the feeder conductors.
d. The tap conductors terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors. This single overcurrent device shall be permitted to supply any number of additional overcurrent devices on its load side.
e. The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.
f. The tap conductors are continuous from end-to-end and contain no splices.
g. The tap conductors are sized 14 mm 2 copper or 22 mm 2 aluminum or larger.
h. The tap conductors do not penetrate walls, floors, or ceilings.
i. The tap is made no less than 9 000 mm from the floor.
(5) Outside Taps of Unlimited Length. Where the conductors are located outdoors of a building or structure, except at the point of load termination, and comply with all of the following conditions:
a. The conductors are protected from physical damage in an approved manner.
b. The conductors terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the conductors. This single overcurrent device shall be permitted to supply any number of additional overcurrent devices on its load side.
c. The overcurrent device for the conductors is an integral part of a disconnecting means or shall be located immediately adjacent thereto.
d. The disconnecting means for the conductors is installed at a readily accessible location complying with one of the following:
1. Outside of a building or structure
2. Inside, nearest the point of entrance of the conductors
3. Where installed in accordance with 2.30.1.6, nearest the point of entrance of the conductors

(c) Transformer Secondary Conductors. Each set of conductors feeding separate loads shall be permitted to be connected to a transformer secondary, without overcurrent protection at the secondary, as specified in 2.40.2.2(c)(1) through (c)(6). The provisions of 2.40.1.4(b) shall not be permitted for transformer secondary conductors.

FPN: For overcurrent protection requirements for transformers, see 4.50.1.3.

(1) Protection by Primary Overcurrent Device. Conductors supplied by the secondary side of a single-phase transformer having a 2-wire (single-voltage) secondary, or a three-phase, delta-delta connected transformer having a 3-wire (single-voltage) secondary, shall be permitted to be protected by overcurrent protection provided on the primary (supply) side of the transformer, provided this protection is in accordance with 4.50.1.3 and does not exceed the value determined by multiplying the secondary conductor ampacity by the secondary to primary transformer voltage ratio. Single-phase (other than 2-wire) and multiphase (other than delta- delta, 3-wire) transformer secondary conductors are not considered to be protected by the primary overcurrent protective device.

(2) Transformer Secondary Conductors Not Over 3 000 mm Long. Where the length of secondary conductor does not exceed 3 000 mm and complies with all of the following:

a. The ampacity of the secondary conductors is
1. Not less than the combined calculated loads on the circuits supplied by the secondary conductors, and
2. Not less than the rating of the device supplied by the secondary conductors or not less than the rating of the overcurrent- protective device at the termination of the secondary conductors, and
3. Not less than one-tenth of the rating of the overcurrent device protecting the primary of the transformer, multiplied by the primary to secondary transformer voltage ratio
b. The secondary conductors do not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply.
c. The secondary conductors are enclosed in a raceway, which shall extend from the transformer to the enclosure of an enclosed switchboard, panelboard, or control devices or to the back of an open switchboard.

FPN: For overcurrent protection requirements for lighting and appliance branch- circuit panelboards and certain power panelboards, see 4.8.3.7(a), (b), and (e).

(3) Industrial Installation Secondary Conductors Not Over 7 600 mm Long. For industrial installations only, where the length of the secondary conductors does not exceed 7 600 mm and complies with all of the following:

a. The ampacity of the secondary conductors is not less than the secondary current rating of the transformer, and the sum of the ratings of the overcurrent devices does not exceed the ampacity of the secondary conductors.
b. All overcurrent devices are grouped.
c. The secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

(4) Outside Secondary Conductors. Where the conductors are located outdoors of a building or structure, except at the point of load termination, and comply with all of the following conditions:

a. The conductors are protected from physical damage in an approved manner.
b. The conductors terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the conductors. This single overcurrent device shall be permitted to supply any number of additional overcurrent devices on its load side.
c. The overcurrent device for the conductors is an integral part of a disconnecting means or shall be located immediately adjacent thereto.
d. The disconnecting means for the conductors is installed at a readily accessible location complying with one of the following:
1. Outside of a building or structure
2. Inside, nearest the point of entrance of the conductors
3. Where installed in accordance with 2.30.1.6, nearest the point of entrance of the conductors

(5) Secondary Conductors from a Feeder Tapped Transformer. Transformer secondary conductors installed in accordance with 2.40.2.2(b)(3) shall be permitted to have overcurrent protection as specified in that section.

(6) Secondary Conductors Not Over 7 600 mm Long. Where the length of secondary conductor does not exceed 7 600 mm and complies with all of the following:

a. The secondary conductors shall have an ampacity that is not less than the value of the primary-to-secondary voltage ratio multiplied by one-third of the rating of the overcurrent device protecting the primary of the transformer.
b. The secondary conductors terminate in a single circuit breaker or set of fuses that limit the load current to not more than the conductor ampacity that is permitted by 3.10.1.15.
c. The secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

(d) Service Conductors. Service-entrance conductors shall be permitted to be protected by overcurrent devices in accordance with 2.30.7.2.

(e) Busway Taps. Busways and busway taps shall be permitted to be protected against overcurrent in accordance with 3.68.2.8.

(f) Motor Circuit Taps. Motor-feeder and branch-circuit conductors shall be permitted to be protected against overcurrent in accordance with 4.30.2.8 and 4.30.4.3, respectively.

(g) Conductors from Generator Terminals. Conductors from generator terminals that meet the size requirement in 4.45.1.13 shall be permitted to be protected against overload by the generator overload protective device(s) required by 4.45.1.12.

2.40.2.3 Grounded Conductor.

No overcurrent device shall be connected in series with any conductor that is intentionally grounded, unless one of the following two conditions is met:

(1) The overcurrent device opens all conductors of the circuit, including the grounded conductor, and is designed so that no pole can operate independently.

(2) Where required by 4.30.3.6 or 4.30.3.7 for motor overload protection.

2.40.2.4 Change in Size of Grounded Conductor.

Where a change occurs in the size of the ungrounded conductor, a similar change shall be permitted to be made in the size of the grounded conductor.

2.40.2.5 Location in or on Premises.

(a) Accessibility. Overcurrent devices shall be readily accessible and shall be installed so that the center of the grip of the operating handle of the switch or circuit breaker, when in its highest position, is not more than 2.0 m (6 ft 7 in.) above the floor or working platform unless one of the following applies:

(1) For busways, as provided in 3.68.2.3.
(2) For supplementary overcurrent protection, as described in 2.40.1.10.
(3) For overcurrent devices, as described in 2.25.2.11 and 2.30.7.3.
(4) For overcurrent devices adjacent to utilization equipment that they supply, access shall be permitted to be by portable means.

(b) Occupancy. Each occupant shall have ready access to all overcurrent devices protecting the conductors supplying that occupancy.

'Exception No. 1: Where electric service and electrical maintenance are provided by the building management and where these are under continuous building management supervision, the service overcurrent devices and feeder overcurrent devices supplying more than one occupancy shall be permitted to be accessible to only authorized management personnel in the following:


"(1) Multiple-occupancy buildings

"(2) Guest rooms or guest suites of hotels and motels that are intended for transient occupancy

Exception No. 2: Where electric service and electrical maintenance are provided by the building management and where these are under continuous building management supervision, the branch circuit overcurrent devices supplying any guest rooms or guest suites shall be permitted to be accessible to only authorized management personnel for guest rooms of hotels and motels that are intended for transient occupancy.

(c) Not Exposed to Physical Damage. Overcurrent devices shall be located where they will not be exposed to physical damage.

FPN: See 1.10.1.11, Deteriorating Agents.

(d) Not in Vicinity of Easily Ignitible Material. Overcurrent devices shall not be located in the vicinity of easily ignitible material, such as in clothes closets.

(e) Not Located in Bathrooms. In dwelling units and guest rooms or guest suites of hotels and motels, overcurrent devices, other than supplementary overcurrent protection, shall not be located in bathrooms.

2.40.3 Enclosures

2.40.3.1 General.

(a) Protection from Physical Damage. Overcurrent devices shall be protected from physical damage by one of the following:

(1) Installation in enclosures, cabinets, cutout boxes, or equipment assemblies

(2) Mounting on open-type switchboards, panelboards, or control boards that are in rooms or enclosures free from dampness and easily ignitible material and are accessible only to qualified personnel

(b) Operating Handle. The operating handle of a circuit breaker shall be permitted to be accessible without opening a door or cover.

2.40.3.3 Damp or Wet Locations.

Enclosures for overcurrent devices in damp or wet locations shall comply with 3.12.1.2(a).

2.40.3.4 Vertical Position.

Enclosures for overcurrent devices shall be mounted in a vertical position unless that is shown to be impracticable. Circuit breaker enclosures shall be permitted to be installed horizontally where the circuit breaker is installed in accordance with 2.40.7.2. Listed busway plug-in units shall be permitted to be mounted in orientations corresponding to the busway mounting position.

2.40.4 Disconnecting and Guarding

2.40.4.1 Disconnecting Means for Fuses.

A disconnecting means shall be provided on the supply side of all fuses in circuits over 150 volts to ground and cartridge fuses in circuits of any voltage where accessible to other than licensed electrical practitioner or non licensed electrical practitioner under the supervision of a licensed electrical practitioner, so that each circuit containing fuses can be independently disconnected from the source of power. A current-limiting device without a disconnecting means shall be permitted on the supply side of the service disconnecting means as permitted by 2.30.6.13. A single disconnecting means shall be permitted on the supply side of more than one set of fuses as permitted by 4.30.9.2, Exception, for group operation of motors and 4.24.3.4(c) for fixed electric space-heating equipment.

2.40.4.2 Arcing or Suddenly Moving Parts.

Arcing or suddenly moving parts shall comply with 2.40.4.2(a) and (b).

(a) Location. Fuses and circuit breakers shall be located or shielded so that persons will not be burned or otherwise injured by their operation.

(b) Suddenly Moving Parts. Handles or levers of circuit breakers, and similar parts that may move suddenly in such a way that persons in the vicinity are likely to be injured by being struck by them, shall be guarded or isolated.

2.40.5 Plug Fuses, Fuseholders, and Adapters

2.40.5.1 General.

(a) Maximum Voltage. Plug fuses shall be permitted to be used in the following circuits:

(1) Circuits not exceeding 125 volts between conductors

(2) Circuits supplied by a system having a grounded neutral where the line-to-neutral voltage does not exceed 150 volts

(b) Marking. Each fuse, fuseholder, and adapter shall be marked with its ampere rating.

(c) Hexagonal Configuration. Plug fuses of 15-ampere and lower rating shall be identified by a hexagonal configuration of the window, cap, or other prominent part to distinguish them from fuses of higher ampere ratings.

(d) No Energized Parts. Plug fuses, fuseholders, and adapters shall have no exposed energized parts after fuses or fuses and adapters have been installed.

(e) Screw Shell. The screw shell of a plug-type fuseholder shall be connected to the load side of the circuit.

2.40.5.2 Edison-Base Fuses.

(a) Classification. Plug fuses of the Edison-base type shall be classified at not over 125 volts and 30 amperes and below.

(b) Replacement Only. Plug fuses of the Edison-base type shall be used only for replacements in existing installations where there is no evidence of overfusing or tampering.

2.40.5.3 Edison-Base Fuseholders.

Fuseholders of the Edison-base type shall be installed only where they are made to accept Type S fuses by the use of adapters.

2.40.5.4 Type S Fuses.

Type S fuses shall be of the plug type and shall comply with 2.40.5.4(a) and (b).

(a) Classification. Type S fuses shall be classified at not over 125 volts and 0 to 15 amperes, 16 to 20 amperes, and 21 to 30 amperes.

(b) Noninterchangeable. Type S fuses of an ampere classification as specified in 2.40.5.4(a) shall not be interchangeable with a lower ampere classification. They shall be designed so that they cannot be used in any fuseholder other than a Type S fuseholder or a fuseholder with a Type S adapter inserted.

2.40.5.5 Type S Fuses, Adapters, and Fuseholders.

(a) To Fit Edison-Base Fuseholders. Type S adapters shall fit Edison-base fuseholders.

(b) To Fit Type S Fuses Only. Type S fuseholders and adapters shall be designed so that either the fuseholder itself or the fuseholder with a Type S adapter inserted cannot be used for any fuse other than a Type S fuse.

(c) Nonremovable. Type S adapters shall be designed so that once inserted in a fuseholder, they cannot be removed.

(d) Nontamperable. Type S fuses, fuseholders, and adapters shall be designed so that tampering or shunting (bridging) would be difficult.

(e) Interchangeability. Dimensions of Type S fuses, fuseholders, and adapters shall be standardized to permit interchangeability regardless of the manufacturer.

2.40.6 Cartridge Fuses and Fuseholders

2.40.6.1 General.

(a) Maximum Voltage — 300-Volt Type. Cartridge fuses and fuseholders of the 300-volt type shall be permitted to be used in the following circuits:

(1) Circuits not exceeding 300 volts between conductors
(2) Single-phase line-to-neutral circuits supplied from a 3-phase, 4-wire, solidly grounded neutral source where the line-to-neutral voltage does not exceed 300 volts

(b) Noninterchangeable — 0–6000-Ampere Cartridge Fuseholders. Fuseholders shall be designed so that it will be difficult to put a fuse of any given class into a fuseholder that is designed for a current lower, or voltage higher, than that of the class to which the fuse belongs. Fuseholders for current-limiting fuses shall not permit insertion of fuses that are not current-limiting.

(c) Marking. Fuses shall be plainly marked, either by printing on the fuse barrel or by a label attached to the barrel showing the following:

(1) Ampere rating
(2) Voltage rating
(3) Interrupting rating where other than 10,000 amperes
(4) Current limiting where applicable
(5) The name or trademark of the manufacturer

The interrupting rating shall not be required to be marked on fuses used for supplementary protection.

(d) Renewable Fuses. Class H cartridge fuses of the renewable type shall only be permitted to be used for replacement in existing installations where there is no evidence of overfusing or tampering.

2.40.6.2 Classification.

Cartridge fuses and fuseholders shall be classified according to voltage and amperage ranges. Fuses rated 600 volts, nominal, or less shall be permitted to be used for voltages at or below their ratings.

2.40.7 Circuit Breakers

2.40.7.1 Method of Operation.

Circuit breakers shall be trip free and capable of being closed and opened by manual operation. Their normal method of operation by other than manual means, such as electrical or pneumatic, shall be permitted if means for manual operation are also provided.

2.40.7.2 Indicating.

Circuit breakers shall clearly indicate whether they are in the open “off” or closed “on” position.

Where circuit breaker handles are operated vertically rather than rotationally or horizontally, the “up” position of the handle shall be the “on” position.

2.40.7.3 Nontamperable. A circuit breaker shall be of such design that any alteration of its trip point (calibration) or the time required for its operation requires dismantling of the device or breaking of a seal for other than intended adjustments.

2.40.7.4 Marking.

(a) Durable and Visible. Circuit breakers shall be marked with their ampere rating in a manner that will be durable and visible after installation. Such marking shall be permitted to be made visible by removal of a trim or cover.

(b) Location. Circuit breakers rated at 100 amperes or less and 600 volts or less shall have the ampere rating molded, stamped, etched, or similarly marked into their handles or escutcheon areas.

(c) Interrupting Rating. Every circuit breaker having an interrupting rating other than 5000 amperes shall have its interrupting rating shown on the circuit breaker. The interrupting rating shall not be required to be marked on circuit breakers used for supplementary protection.

(d) Used as Switches. Circuit breakers used as switches in 120-volt and 277-volt fluorescent lighting circuits shall be listed and shall be marked SWD or HID. Circuit breakers used as switches in high- intensity discharge lighting circuits shall be listed and shall be marked as HID.

(e) Voltage Marking. Circuit breakers shall be marked with a voltage rating not less than the nominal system voltage that is indicative of their capability to interrupt fault currents between phases or phase to ground.

2.40.7.6 Applications.

A circuit breaker with a straight voltage rating, such as 240V or 480V, shall be permitted to be applied in a circuit in which the nominal voltage between any two conductors does not exceed the circuit breaker’s voltage rating. A two-pole circuit breaker shall not be used for protecting a 3-phase, corner-grounded delta circuit unless the circuit breaker is marked 1–3 to indicate such suitability.

A circuit breaker with a slash rating, such as 120/240V or 480Y/277V, shall be permitted to be applied in a solidly grounded circuit where the nominal voltage of any conductor to ground does not exceed the lower of the two values of the circuit breaker’s voltage rating and the nominal voltage between any two conductors does not exceed the higher value of the circuit breaker’s voltage rating.

FPN: Proper application of molded case circuit breakers on 3-phase systems, other than solidly grounded wye, particularly on corner grounded delta systems, considers the circuit breakers’ individual pole-interrupting capability.

2.40.7.7 Series Ratings.

Where a circuit breaker is used on a circuit having an available fault current higher than the marked interrupting rating by being connected on the load side of an acceptable overcurrent protective device having a higher rating, the circuit breaker shall meet the requirements specified in (a) or (b), and (c).

(a) Selected Under Engineering Supervision in Existing Installations. The series rated combination devices shall be selected by a licensed professional engineer engaged primarily in the design or maintenance of electrical installations. The selection shall be documented and stamped by the professional engineer. This documentation shall be available to those authorized to design, install, inspect, maintain, and operate the system. This series combination rating, including identification of the upstream device, shall be field marked on the end use equipment.

(b) Tested Combinations. The combination of line-side overcurrent device and load-side circuit breaker(s) is tested and marked on the end use equipment, such as switchboards and panelboards.

(c) Motor Contribution. Series ratings shall not be used where

(1) Motors are connected on the load side of the higher-rated overcurrent device and on the line side of the lower-rated overcurrent device, and

(2) The sum of the motor full-load currents exceeds 1 percent of the interrupting rating of the lower-rated circuit breaker.

2.40.8 Supervised Industrial Installations

2.40.8.1 General.

Overcurrent protection in areas of supervised industrial installations shall comply with all of the other applicable provisions of this article, except as provided in Part 2.40.8. The provisions of Part 2.40.8 shall be permitted only to apply to those portions of the electrical system in the supervised industrial installation used exclusively for manufacturing or process control activities.

2.40.8.3 Location in Circuit.

An overcurrent device shall be connected in each ungrounded circuit conductor as required in 2.40.8.3(a) through (d).

(a) Feeder and Branch-Circuit Conductors. Feeder and branch- circuit conductors shall be protected at the point the conductors receive their supply as permitted in 2.40.2.2 or as otherwise permitted in 2.40.8.3(b), (c), or (d).

(b) Transformer Secondary Conductors of Separately Derived Systems. Conductors shall be permitted to be connected to a transformer secondary of a separately derived system, without overcurrent protection at the connection, where the conditions of 2.40.8.3(b)(1), (b)(2), and (b)(3) are met.

(1) Short-Circuit and Ground-Fault Protection. The conductors shall be protected from short-circuit and ground-fault conditions by complying with one of the following conditions:

a. The length of the secondary conductors does not exceed 30 m and the transformer primary overcurrent device has a rating or setting that does not exceed 150 percent of the value determined by multiplying the secondary conductor ampacity by the secondary-to- primary transformer voltage ratio.

b. The conductors are protected by a differential relay with a trip setting equal to or less than the conductor ampacity.

FPN: A differential relay is connected to be sensitive only to short-circuit or fault currents within the protected zone and is normally set much lower than the conductor ampacity. The differential relay is connected to trip protective devices that will de-energize the protected conductors if a short-circuit condition occurs.

c. The conductors shall be considered to be protected if calculations, made under engineering supervision, determine that the system overcurrent devices will protect the conductors within recognized time vs. current limits for all short-circuit and ground-fault conditions.

(2) Overload Protection. The conductors shall be protected against overload conditions by complying with one of the following:

a. The conductors terminate in a single overcurrent device that will limit the load to the conductor ampacity.

b. The sum of the overcurrent devices at the conductor termination limits the load to the conductor ampacity. The overcurrent devices shall consist of not more than six circuit breakers or sets of fuses, mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard. There shall be no more than six overcurrent devices grouped in any one location.

c. Overcurrent relaying is connected [with a current transformer(s), if needed] to sense all of the secondary conductor current and limit the load to the conductor ampacity by opening upstream or downstream devices.

d. Conductors shall be considered to be protected if calculations, made under engineering supervision, determine that the system overcurrent devices will protect the conductors from overload conditions.

(3) Physical Protection. The secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

(c) Outside Feeder Taps. Outside conductors shall be permitted to be tapped to a feeder or to be connected at a transformer secondary, without overcurrent protection at the tap or connection, where all the following conditions are met:

(1) The conductors are protected from physical damage in an approved manner.
(2) The sum of the overcurrent devices at the conductor termination limits the load to the conductor ampacity. The overcurrent devices shall consist of not more than six circuit breakers or sets of fuses mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard. There shall be no more than six overcurrent devices grouped in any one location.
(3) The tap conductors are installed outdoors of a building or structure except at the point of load termination.
(4) The overcurrent device for the conductors is an integral part of a disconnecting means or shall be located immediately adjacent thereto.
(5) The disconnecting means for the conductors are installed at a readily accessible location complying with one of the following:

a. Outside of a building or structure

b. Inside, nearest the point of entrance of the conductors

c. Where installed in accordance with 2.30.1.6, nearest the point of entrance of the conductors (d) Protection by Primary Overcurrent Device. Conductors supplied by the secondary side of a transformer shall be permitted to be protected by overcurrent protection provided on the primary (supply) side of the transformer, provided the primary device time– current protection characteristic, multiplied by the maximum effective primary-to-secondary transformer voltage ratio, effectively protects the secondary conductors.

2.40.8.4 Series Ratings.

Where a circuit breaker is used on a circuit having an available fault current higher than its marked interrupting rating by being connected on the load side of an acceptable overcurrent protective device having the higher rating, the circuit breaker shall meet the requirements specified in 2.40.8.4(a) or (b) and (c).

(a) Tested Combinations. The combination of line-side overcurrent device and load-side circuit breaker(s) is tested and marked on the end use equipment, such as switchboards and panelboards.

(b) Selected Under Engineering Supervision. The line-side device is selected under engineering supervision. This series combination rating, including identification of the upstream device, shall be field marked on the end use equipment.

(c) Motor Contribution. Series ratings shall not be used where

(1) Motors are connected on the load side of the higher-rated overcurrent device and on the line side of the lower-rated overcurrent device, and
(2) The sum of the motor full-load currents exceeds 1 percent of the interrupting rating of the lower-rated circuit breaker.

2.40.9 Overcurrent Protection Over 600 Volts, Nominal

2.40.9.1 Feeders and Branch Circuits.

(a) Location and Type of Protection. Feeder and branch-circuit conductors shall have overcurrent protection in each ungrounded conductor located at the point where the conductor receives its supply or at an alternative location in the circuit when designed under engineering supervision that includes but is not limited to considering the appropriate fault studies and time–current coordination analysis of the protective devices and the conductor damage curves. The overcurrent protection shall be permitted to be provided by either 2.40.9.1(a)(1) or (a)(2).

(1) Overcurrent Relays and Current Transformers. Circuit breakers used for overcurrent protection of 3-phase circuits shall have a minimum of three overcurrent relay elements operated from three current transformers. The separate overcurrent relay elements (or protective functions) shall be permitted to be part of a single electronic protective relay unit.

On 3-phase, 3-wire circuits, an overcurrent relay element in the residual circuit of the current transformers shall be permitted to replace one of the phase relay elements.

An overcurrent relay element, operated from a current transformer that links all phases of a 3-phase, 3-wire circuit, shall be permitted to replace the residual relay element and one of the phase-conductor current transformers. Where the neutral is not regrounded on the load side of the circuit as permitted in 2.50.10.5(b), the current transformer shall be permitted to link all 3-phase conductors and the grounded circuit conductor (neutral).

(2) Fuses. A fuse shall be connected in series with each ungrounded conductor.

(b) Protective Devices. The protective device(s) shall be capable of detecting and interrupting all values of current that can occur at their location in excess of their trip-setting or melting point.

(c) Conductor Protection. The operating time of the protective device, the available short-circuit current, and the conductor used shall be coordinated to prevent damaging or dangerous temperatures in conductors or conductor insulation under short-circuit conditions.

2.40.9.2 Additional Requirements for Feeders.

(a) Rating or Setting of Overcurrent Protective Devices. The continuous ampere rating of a fuse shall not exceed three times the ampacity of the conductors. The long-time trip element setting of a breaker or the minimum trip setting of an electronically actuated fuse shall not exceed six times the ampacity of the conductor. For fire pumps, conductors shall be permitted to be protected for overcurrent in accordance with 6.95.1.4(b).

(b) Feeder Taps. Conductors tapped to a feeder shall be permitted to be protected by the feeder overcurrent device where that overcurrent device also protects the tap conductor.




Other Pages in this Category: Chapter 2. Wiring and Protection

References