code question: CT allowed inside disconnect?

[BrianEngPME]

Hello,

Code question! Is a current transformer (CT) allowed inside a fused disconnect/fused safety switch? Seems like the NEC doesn't say... I've looked in article 312 and article 404.

Also, if the CT is allowed inside the FSS, would a tap for the voltage (for a power meter) also be allowed inside the FSS? My brain is telling me that a CT is a little different from a voltage tap because the CT operates by electromagnetic induction & doesn't require direct connection.

Basically it looks like someone is trying to avoid having a separate CT cabinet for the meter.

Thanks,

Brian

 

[busbar]

If the CTs/PT taps are for revenue metering, it’s unlikely that the serving utility wound permit them installed in other than a separate sealed compartment.

 

[alehman]

I don't think the NEC directly addresses CT's. If the voltage tap is sharing a lug with the main conductor, you may have a violation if the lug is not listed for more than one wire.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[rcw retired EE]

Some inspectors might consider the CT's are part of the "listed" equipment for that enclosure.

I know of several installations where small metering CT's were placed in fused disconnects because that was a convenient place to connect the metering for monitoring some processes. I can't say if it was according to code. I did not find a definitive answer when I investigated one of those installations.

IMHO, the installation was safe, but that opinion would never stand up in court if something happened inside the switch.

 

[alehman]

Good point on violating the listing. IMO, it would be a stretch to say a small properly installed CT should be a problem for the listing of the switch, but as rcwilson suggested, you never know how a jury will see it.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[BrianEngPME]

Thanks for the advice, folks!