## Example Calculation

A single line diagram is provided below to illustrate how to calculate arc flash arcing current. The bolted fault current is calculated using MVA method for simplicity.

**Given:**

K = -0.097 *(Box Configuration)*

I_{bf} = 34.73 kA

log I_{bf} = 1.540704783

V = 0.46 kV

G = 25 *(LV MCC from Table 2)*

log I_{a} = -0.097+0.662log(34.73)+0.0966x0.46+0.000526x25+0.5588x0.46xlog(34.73)-0.00304x25xlog(34.73)

log I_{a} = 1.259474086

**I _{a} = 18.17498605 kA**

For low-voltage applications, under 1 kV, a reduced arcing fault current which is 85% of the arcing fault current I_{a} is required to be calculated to allow a second calculation needed due to variation in arc current. For cases where the arc current falls on the steep part of the time-current curve or falls near a step change, the variation in arc current could cause a significant error in protective-device tripping or operating time.

**I _{a} = 85% x 18.17498605 = 15.4487 kA**

On the next post, we will be calculating the Incident Energy and PPE using the provisions of NPFA 70E.

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