I have 3 wires coming out of the wall where I need to install a dishwashwer. All 3 are black and one of them is ribbed.



Assuming the ribbed one is the positive wire, how do I use a multimeter to determine which of the other 2 is the negative and the ground (Dishwasher has the common black, white, and green wires)

The ribbed *should* be the neutral.

Hot should read about 120V to either of the other two. Neutral should read about 120V to the hot. Neutral should be really close to zero to the ground. Ground should be zero to another ground using an extension cord, or any other metal box, ground wire, etc.

Can test one wire to a known ground device. If you have another plug nearby, you can test that the ground to ground wire has minimal resistance. A hot should have high to infinite resistance; a neutral should have higher than ground resistance, but still low.

If you measure voltage, a ground and hot should give you a 120V; others should show 0.

~egon

Damn this thread is just further proof that I could really use a class on electricity

Once you identify your hot isolate it. Using an extension cord you shoulda be able to determine neutral and ground with an ohm meter. Look for continuity.

Kenneth_2003 said:

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Once you identify your hot isolate it. Using an extension cord you shoulda be able to determine neutral and ground with an ohm meter. Look for continuity.

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I hired an electrician and he was great. Showed me how to do it using his commercial grade tester. Still not sure I could do it on my own though with my 6.99 multimeter from Harbor Freight.

And yes we found the box nearby that the line was ran to and looked for continuity to find the neutral. Finding the hot was easy.

Dr. Doctor said:

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If you measure voltage, a ground and hot should give you a 120V; others should show 0.

~egon

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Hot to neutral is 120V