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Old 06-17-2008, 12:33 PM   #1
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AC Outlet voltage diagnosis


An exterior outlet on my recently purchased house was non-functional. It had supposedly been repaired prior to sale, and there is a new GFCI outlet and a new outdoor outlet cover. But the outlet still didn't actually work.

I took it apart today, and found that the hot and neutral were connected to the load, instead of to the line side of the GFCI. I switched it, and now the outlet works.

In the process of fixing this, I measured the line voltages and found
Hot-Neutral: 117V AC
Hot-Ground: 47V AC
Neutral-Ground: 46V AC

What's the diagnosis?

My guess is that the ground wire, is uh, well, not really grounded. Nearby, the outlet on the interior wall has roughly the same voltages. I've found at least two different circuits with suspicious voltages, as well as several circuits with normal voltages. (This is a 1920's house, luckily all the wiring is modern, but I have not yet mapped out all the circuits)

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Old 06-17-2008, 12:49 PM   #2
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AC Outlet voltage diagnosis


Poor Neutral possibly. Call an electrician, before you have further problems, and go from there.

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Old 06-17-2008, 01:50 PM   #3
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AC Outlet voltage diagnosis


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Originally Posted by gregzoll View Post
Poor Neutral possibly. Call an electrician, before you have further problems, and go from there.
The electrician hired by the seller is who installed the GFCI incorrectly (I've got the receipts, obviously this particular company won't get repeat business from me)

If the problem were with the neutral wire, I would expect to still see about 120V across hot-ground. Is that incorrect?
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Old 06-17-2008, 05:57 PM   #4
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AC Outlet voltage diagnosis


If both the neutral and ground were terminated under the same screw in the buss then the reading could be similar.
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Old 06-17-2008, 07:13 PM   #5
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AC Outlet voltage diagnosis


Problem is you are using a digital meter and the ground is open. You are measuring phantom voltage.
If this is a GFCI then it is fine under code. It should have a little sticker that says no ground.
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Old 06-18-2008, 11:17 AM   #6
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AC Outlet voltage diagnosis


Measure from hot to neutral, not from hot to ground. This reading to ground is what confuses so many of us. Just stick to the power reading.

Try using an induction tester. They are less expensive then some meters and really work well for the homeowner. google "Wiggy".
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Old 06-18-2008, 11:21 AM   #7
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AC Outlet voltage diagnosis


The exterior outlet is GFCI, but there are also standard interior outlets on the same circuit (with the same, or very similar voltage measurements).

I'm going to figure out which outlets are on this same circuit and look for any loose connections.
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Old 06-18-2008, 11:44 AM   #8
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AC Outlet voltage diagnosis


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Originally Posted by J. V. View Post
Measure from hot to neutral, not from hot to ground. This reading to ground is what confuses so many of us. Just stick to the power reading.
See original post: Hot-Neutral measures 117V

Measuring to ground in addition to measuring hot-neutral is a way to check if the hot and neutral lines have been swapped. (Just manually doing what one of those plug-in testers will do for you)

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Try using an induction tester. They are less expensive then some meters and really work well for the homeowner. google "Wiggy".
I've got a cheap radio-shack multimeter, a nice Fluke multimeter, and a tektronix oscilloscope. Hopefully that's good enough
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Old 06-18-2008, 01:26 PM   #9
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AC Outlet voltage diagnosis


If the cheap RS meter is an analog one with a needle, that is the one to use. The fluke will give phantom readings.

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