Insulation Ratings

[Brandon Loyd]

Is it true that wire of different insulation ratings can share the same encloure, if the lesser rated wire is used for metering purposes? I found a couple of branch panel with 24V wire installed on CT's for the main feeders, which was not rated for 600v like the rest of the wire in the enclosure. I thought this was illegal, but was told it was ok if used for metering.

 

[Dennis Alwon]

You mean different voltage ratings, don't you? If they are both the same voltage rating then there should not be an issue with insulation types. There could be other factors depending on what class wiring it is.

 

[Brandon Loyd]

Yes. Different voltage ratings. The 24v wiring is not rated for 600v.

 

[Dennis Alwon]

Yes. Different voltage ratings. The 24v wiring is not rated for 600v.

Look at 300.3(C) in the 2008 NEC. Basically if the 24V wiring has an insulation rated equal to that of the voltage applied to the maximum circuit. Thus if this is a 240V system then no conductor in that enclosure will have a voltage higher than 120V . Many low voltage wire have an insulation rated 300 v. Other than photovoltaic I see no exception.

It does not have to equal the rating of the insulation of the high voltage conductor just equal the voltage that would be on that conductor.