Provision in Philippine Electrical Code
Section 3.10.1.4 Conductors in Parallel, states that aluminum, copper-clad aluminum, or copper conductors of size 50 mm² and larger, comprising each phase, polarity, neutral, or grounded circuit conductor, shall be permitted to be connected in parallel (electrically joined at both ends).
Conditions to Comply
The paralleled conductors in each phase, polarity, neutral, or grounded circuit conductor shall comply with all of the following:
(1) Be the same length
(2) Have the same conductor material
(3) Be the same cross sectional area of the conducting material
(4) Have the same insulation type
(5) Be terminated in the same manner
Where run in separate raceways or cables, the raceways or cables shall have the same physical characteristics. Where conductors are in separate raceways or cables, the same number of conductors shall be used in each raceway or cable. Conductors of one phase, polarity, neutral, or grounded circuit conductor shall not be required to have the same physical characteristics as those of another phase, polarity, neutral, or grounded circuit conductor to achieve balance.
Differences in inductive reactance and unequal division of current can be minimized by choice of materials, methods of construction, and orientation of conductors.
Where equipment grounding conductors are used with conductors in parallel, they shall comply with the requirements of this section except that they shall be sized in accordance with 2.50.6.13. Conductors installed in parallel shall comply with the provisions of3.10.1.15(b)(2)(a).
Exceptions
There are several exceptions in the PEC for the use of parallel conductors as per Section 3.10.1.4
- As permitted in 6.20.2.2(a)(1). This provision allows conductors size lesser than 50mm².
Lighting Circuits. For lighting circuits: Copper 2.0 mm2 (1.6 mm dia.). Copper 0.50 mm2 (0.80 mm dia.) or larger conductors shall be permitted in parallel, provided the ampacity is equivalent to at least that of 2.0 mm2 (1.6 mm dia.) copper. - Exception No. 2: Conductors in sizes smaller than 50 mm2 shall be permitted to be run in parallel to supply control power to indicating instruments, contactors, relays, solenoids, and similar control devices, provided all of the following apply:
- They are contained within the same raceway or cable.
- The ampacity of each individual conductor is sufficient to carry the entire load current shared by the parallel conductors.
- The overcurrent protection is such that the ampacity of each individual conductor will not be exceeded if one or more of the parallel conductors become inadvertently disconnected.
- Conductors in sizes smaller than 50 mm2 shall be permitted to be run in parallel for frequencies of 360 Hz and higher where conditions (a), (b), and (c) of Exception No. 2 are met.
- Under the supervision of a licensed electrical engineer, grounded neutral conductors in sizes 30 mm2 and larger shall be permitted to be run in parallel for existing installations.
Why Use Parallel Conductors
Conductors connected in parallel are treated by the PEC as a single conductor with a total cross-sectional area of all conductors in parallel.
The use of parallel conductors is a practical and cost-effective means of installing large-capacity feeders or services. Using conductors larger than 500 mm² in raceways is neither economical nor practical unless the conductor size is governed by voltage drop.
The ampacity of larger sizes of conductors would increase very little in proportion to the increase in the size of the conductor. Where the cross-sectional area of a conductor increases 50 percent (e.g. from 500 to 750 mm²), a type THW conductor ampacity increases only 80 amperes (less than 15 percent). A 100-percent increase (from 500 to 1000 mm²) causes an increase of only 120 amperes (approximately 22 percent). Generally, where cost is a factor, installation of two (or more) paralleled conductors per phase may be beneficial.
The parallel connection of two or more conductors in place of using one large conductor depends on compliance with 3.10.1.4 to ensure equal current division in order to prevent overloading any of the individual paralleled conductors.
Where individual conductors are tapped from conductors in parallel, the tap connection must include all the conductors in parallel for that particular phase. tapping into only one of the parallel conductors would result in unbalanced distribution of tap load current between parallel conductors, resulting in one of the conductors carrying more than its share of the load, which could cause overheating and conductor insulation failure. For example, if a 125 mm² conductor is tapped from a set of two 250 mm² conductors in parallel, the splicing device must include both 250 mm² conductors and the single 125 mm² tap conductor.