Technical information

CONTROL CIRCUITS

circuit and can be either devices suitable for the branch circuit (UL508), or

protections called “supplementary”: in particular “supplementary fuses” and

“supplementary protector” (miniature circuit breaker,for example in

accordance with UL1077, such as the 1492-SP).

2) Control Circuit derived directly from the feeder

The control circuit is derived directly from the general powering (feeder) of

the panel. In accordance with the North American standard definitions,the

derivation is a power circuit (branch circuit) that,in its turn has the control

circuit as a “load”

The rules require to install a protection, of branch circuit, against the short

circuit: the real control circuit begins down line from the BCP in which both

devices suitable for the branch circuits or supplementary protections can be

installed.

The BCP connected to the feeder should have a rating that is not more than 20 A.

Inside the control circuit the standards require the use of an overcurrent

protection (either branch or supplementary) in given points:

•in the case of a Control Circuit derived from the BCP,down line of the

pre-existing branch circuit;

•al

w a ys, in the derivation points of conductors with a smaller cross-section.

The rating of the protections is chosen on the basis of:

–specific circuit requirements (as in the low-voltage limited energy circuits);

–control circuit conductor capacity;

–restrictions on the markings of the devices down line.

It is not necessary for a single protection to meet all the conditions listed, but it is

possible to co-ordinate several protections to achieve this purpose, vertically and

horizontally.

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