Control transformer, mandatory or not?

[dmitri]

In Industrial Control Panel acc. to UL508A (or NFPA79), the use of control transfromer supplying control circuit is mandatory or not?

In which case the idea of control circuit common, which seems not to use transformer, can be applied?

Pls. advise.

Thank you

 

[jim dungar]

In Industrial Control Panel acc. to UL508A (or NFPA79), the use of control transfromer supplying control circuit is mandatory or not?

In which case the idea of control circuit common, which seems not to use transformer, can be applied?

Pls. advise.

Thank you

No, a "control transfromer" is not required. The control voltage can come from any source whether internal or external to the panel. The control can also be tapped directly off of the supply voltage, however many codes and standards discourage control circuits above 120VAC. Control circuits originating external to the panel require their own disconnecting means although it can be separate from the main power disconnect.

 

[petersonra]

In which case the idea of control circuit common, which seems not to use transformer, can be applied?

what does this mean?