Technical information

The conductors to the primary and the secondary should have a capacity of

no less than the rating of the relative protection.

1.8.1 Protections Allowed

The protection should be made with suitable components at the point of

installation of the transformer/auto transformer.The most common can be

specified

•self transformer on input to the panel to adapt the v oltag e: as already

mentioned in the chapter on power circuits, the transformer is inserted inside

the feeder and should therefore be protected with:

–primary: fuses for the power circuits (for example CC or J fuses and relative

fuse holders 140F, 1492-FB) or molded case circuit breakers (e.g. 140-U);

–secondary: as for the primary unless the protection is the sum of the branch

circuit protections (BCP).

•control transformer pow ered b y the f eeder:

–primary: the protection of the transformer is for all intents and purposes a

BCP,but special components cannot be used for motor starting such as

combination motor controller or manual motor controller;

–secondary: we are inside the control circuit, thus all components can be used

including the supplementary protection (e.g. the miniature circuit breakers

1492-SP).

•the control transformer powered down line with an existing branch circuit

transformer: primary and secondary are already part of the control circuit thus

all the components can be used including the supplementary protection (e.g.

the miniature circuit breakers 1492-SP). The protection to the primary can be

omitted if the rating if the pre-existing BCP satisfies the sizing indicated above.

CONTROL CIRCUITS