Primary protection for LV lighting

[Ponchik]

Suppose a 200VA low voltage lighting transformer that is cord connected to a 15Amp circuit. If the transformer does not have a 5Amp fuse inside, is this installation in violation of table 450.3(b)

200 va /120 v = 1.66 Amps, maximum ocpd can not exceed 300%, so 1.66 x 300% = 5 Amps

 

[kwired]

Suppose a 200VA low voltage lighting transformer that is cord connected to a 15Amp circuit. If the transformer does not have a 5Amp fuse inside, is this installation in violation of table 450.3(b)

200 va /120 v = 1.66 Amps, maximum ocpd can not exceed 300%, so 1.66 x 300% = 5 Amps

I don't see that anything in art 450 applies. If this is a low voltage lighting transformer you have to apply art 411 in which 411.3 tells us you must either use a complete listed system, or a system assembled from listed parts - and those parts must be listed for use as part of the same identified lighting system. If your transformer is listed for the purpose it is acceptable whether it has fuses or not, chances are it has some kind of overcurrent protection built in though.

 

[Ponchik]

Thanks.

I also found 411.6 talks about branch circuits limited to 20Amps.

 

[kwired]

Thanks.

I also found 411.6 talks about branch circuits limited to 20Amps.

Not really sure why. But if you had a transformer rated 20 amps @ 120 volt input you would have 200 amps @ 12 volts output. (and probably a very heavy unit)

You generally never see any LV lighting transformers over 240VA or 20 amps @ 12 volts. You do see 480 VA units but they are essentially two 240 VA units in one, and/or can be used as a 20 amps @ 24 volt supply.