CQD: 5/30/2016

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Monday, May 30, 2016

Question:

I have a code question. I believe this is the correct forum, rather than asking UL folks.

If my math is right, for a solidly grounded 480 wye system, the ungrounded conductors achieve voltages of:

1) 277V RMS to ground

2) 480V RMS to each other

3) 391V absolute to ground (ex. @ 90 degrees phase A peaks)

4) 588V absolute between each other (ex. @ 90 degrees phase A peaks, phases B and C are at 1/2 negative peak)

Normal, small wire connectors (ex. Ideal 71B and 72B Wire-Nuts) are rated 300V. Can they be used to terminate small 480 volt motors?

For components rated ###V, is that

1) volts RMS to ground?

2) volts RMS to adjacent components?

3) volts absolute to ground?

4) volts absolute to adjacent components?

Howard S.

Answer:

Hey Howard thanks for your question. No, the voltage used is that at which the circuit operates as stated in 110.4. Connectors rated at 300 volts are not allowed to be used at 480 volts. Voltage, Voltage, Nominal and Voltage to Ground are all defined in Article 100. Examples of nominal voltages are provided in 220.5(A).But there is also nothing wrong with asking UL and the manufacturer for clarification.

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