Technical information

The protection device must have size/regulation that does not exceed the

product “current x coefficient”, but if the value calculated does not coincide with

a standard size/regulation, the use of the one immediately above is acceptable.

Take for example a 10 A motor: using rapid fuses (nontime-delay) the coefficient

is 300% and the product is equal to 10 A x 300% = 30 A, standard size.On the

contrary when (time-delay o dual element) delayed fuses are used, the

coefficient is 175% and the product equals 17.5 A that is not the standard size: in

this case fuses up to 20 A can be used.

If the values indicated in the table are not sufficient to guarantee the start up of

the motor without the slow intervention of the protection, the tabulated values

can be used up to:

•fuses without delay or CC class up to 600 A: 400%

•fuses without delay over 601 A: 300%

•(dual element delayed fuse: 225%

•automatic thermomagnetic cutout not above 100 A: 400%

•automatic thermomagnetic cutout not above 100 A: 300%

•magnetic cutout for Design B, C or D motors: 1300%

•magnetic cutout for Design E motors: 1700%

Use of instantaneous trip (magnetic only) breakers must be part of a listed

combination of MCP + Contactor + O/L Relay. Alternatively, UL panel shops can have

combinations procedure described.

EXAMPLE

Furthermore it is assumed that the

restrictions of the contactor and the

thermal relay are negligible for the

purposes of choice and scaling of

the BCP.

a) Not-delayed fuses: the maximum

size is 7.6 A x 300% = 22,8 A that

is not the maximum standard for

which the use of fuses up to 25

A is legitimate. CC fuses (dim.

10x38) are chosen. The suitable

fuse holder is the 1492-FB3C30

or 140F-03C-C30.

b) automatic circuit breaker: the

maximum size is 7.6 A x 250% =

19 A that is not the standard size

so the use of a 20A circuit

breaker is legitimate.

The thermo magnetic for this

use is the 140U-H2C3-C20,with

an interrupting capacity of 35 kA

at 240 V.

BRANCH CIRCUIT