I'm hooking up a dishwasher and failed to check wiring before I removed the old one.

Black - Red = 120v Black - White = 120v Red - White = 0v.

So obviously Red and white are Neutral and Ground. How can I tell? If the Red were Green or Bare, I wouldn't worry, but seeing as the original installer used the wrong wire, I need to question everything.

Is there a simple way of telling the two apart? Keep in mind that I'm in Canada, where the code does not allow grounding to Neutral.

-- Resolved. I ended up tracing back to the panel, Opening the panel and seeing that Red went into the rat's nest of bare copper. So, IN THIS CASE ONLY, Red was ground.

However, this leads us to the greater problem of Contractors using non-standard parts because they happen to be laying around. If I couldn't get to the panel, how could I determine the difference. I was think that a continuity check between a known ground and (test)neutral should be open, and known ground to test ground should be closed. Is that a correct assumption?

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    Re. the update: I can't speak for Canadian wiring, but in the US, ground and neutral are bonded together at the service panel, so your test would show them as closed. – Niall C. Feb 5 '11 at 15:48
  • In Canada, Neutral is provided by the supplier, and ground is a heavy copper spike driven into the (literal) ground or bonded to the water supply inlet. And you're not allowed to switch them anywhere along the way. – Chris Cudmore Feb 5 '11 at 16:10
  • The system works the same in both USA and Canada, and although the codes are separate (NEC and CEC), they are very similar. Neutral comes from the center-tap of the transformer, and is bonded to ground at the service panel only. They are not allowed to be connected anywhere else, and never switched. Ground is a safety feature, it is supposed to carry current to earth in the event of a fault instead of it going your body. Normally ground will not be conducting any current. See also: en.wikipedia.org/wiki/Electrical_wiring_in_North_America – gregmac Feb 6 '11 at 18:09
  • @Niall, I expect that in the USA and Canadian like the UK both systems are in use along with a few other eathing systems depending on when your bit of the network was installed etc. – Walker Feb 6 '11 at 22:23
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    scary that your red was ground. NEC allows recoloring a wire at the ends. If your ends aren't recolored, consider putting a little green tape or paint on them to make it obvious. – Jay Bazuzi Jun 23 '11 at 4:38

Can you trace the cable back to the service panel or to another outlet (if there is another one on that circuit) and do a visual inspection of the wires?

Failing that, you could temporarily wire in a GFCI, guessing at which wire should be neutral and which ground. Plug in an appliance, turn it on, and if the GFCI trips, you got ground and neutral the wrong way around.

  • There may also be testers that check for that condition, but mine doesn't. – Niall C. Feb 5 '11 at 15:16
  • Accepted for Traceback. – Chris Cudmore Mar 8 '11 at 17:06

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