Lighting Transformer

[skm]

Is it necessary to employ a lighting transformer to feed the lighting distibution board from a 3P4W (TPN) source?

I understand that lighting transformer is used for reducing the fault level on the lighting DBs so that MCBs (typicall 9kA) can be used. This reduction in the rated fault level of the DB can also be achieved using a suitably rated fuse in the feeder.

Thanks and regards,



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[tommom]

If I understand your question, you want to know if you need to install a transformer prior to a panel which is to feed lighting.

If you are using lighting control relays which have a low-withstand rating such as GE R-7 (I think they're called), you might need to use some way to reduce the avail. short-circuit current.

If your panel doesn't feed any relays or contactors, you can use either fully-rated molded-case circuit breakers for the system, or you can use series-rated breakers as allowed by NEC 240.

The other option if you need to remotely control the lighting is to use either Cutler-Hammer or Square D remote control breakers, which are series-ratable themselves - but you'll have to check with the mfr to identify which upstream devices they series-rate with.