Technical information

FEEDER AND BRANCH CIRCUITS

EXAMPLE

As in the previous example a feeder protection and switch with circuit breaker

(series 140U) is taken up again.

The switching function requires a size of no less than 40 A but the calculation of

the value a) as overcurrent protection requires the size not to be more than:

22 + 8 + 4 = 34 A

The incompatibility of the design data is clear

Three solutions are proposed

1. Foregoing the protection function and sizing the 140U only as a switch. In

this case it will be necessary to install another device with a size no greater

than 35A to perform the function of the protection;

Modifying the equipment to raise value a) from 35 to a value greater than 40 A

Prot 22 + 8+ 4 <= 34 A

Sect. 1.25 x (22 + 8 + 4) >=42.5 A

Cond. 1.25 x 22 + 1.25 x 8 + 4 > = 41.5 A

AWG 8 (50A)

Prot 35 + 8+ 4 <= 47A

Sect. 1.25x (22 + 8 + 4) >=42.5 A

Cond. 1.25 x 22 + 1.25 x 8 + 4 > = 41.5 A

AWG 8 (50A)