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Why is >600V peak voltage allowed on 600V wiring?

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    Why is >600V peak voltage allowed on 600V wiring?

    Examples include ~800VDC pulses on VFD outputs and ~2000VAC pulses on ballast outputs.

    I know this is allowed because equipment manufacturers install 600V rated wire on the outputs of these devices.

    Why is this allowed?

    AC voltage ratings of cables are RMS. So a cable rated for 600VAC is already inherently capable of a peak voltage of 848V. But a cable insulation's capabilities to withstand pulses are different from the AC RMS voltage ratings as well. You need to look at the Dielectric rating of the insulation and the Corona Inception Voltage (CIV) factor. They are a lot higher.

    Still, in terms of the effects of standing waves created by PWM outputs, you have a point. That issue is covered pretty well in this paper from Belden.
    __________________________________________________ ____________________________
    Many people are shocked when they discover I am not a good electrician...

    I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.


      Unless otherwise stated, the voltage rating of wire may be assumed to be an AC RMS rating.
      That is 600 volt wire, if otherwise suitable, may be used on a 600 volt nominal AC system.
      A 600 volt RMS AC system will have a peak voltage of about 1.4 times the RMS rating, or say about 840 volts. No de-rating is required since the wire is designed for 600 volts RMS, and therefore by inference for up to 840 volts peak.
      Therefore the use of such wire for the output of a VFD should be fine provided that the RMS voltage does not exceed 600 volts RMS/about 840 peak volts.

      As regards high voltage pulses from the control gear for HID lamps, if the high voltage pulses are confined within a luminaire, then this is an appliance and outside the remit of the NEC. The luminaire should of course be UL listed or equivalent.

      If however an electrician uses standard wire to connect a remote ignitor to a lamp, than IMHO that is a violation.

      If a standard type of wire is supplied pre-wired by the manufacturer, then it could be argued that this is part of the appliance, and if the complete kit or assembly is sold for the purpose and UL listed, permitted.


        600Volt wire

        I agree with the previous posts and in addition remember you have two wires so the rating doubles. And the peak would be aprox 1700 volts.