Suspicious Polarity


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Old 06-26-22, 06:57 PM
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Suspicious Polarity

I have an older fridge in the garage, plugged into an outlet with a couple other recepticals on the same circuit. The fridge has worked fine for years and nothing has changed recently. Here's the issue that has me perplexed. My handy-dandy 3-prong plugin tester reports normal polarity at the receptical "before" the fridge but reversed polarity at the receptical "after" the fridge. Opening the receptical boxes, I see nothing wired white to black. The strange part is that if I unplug the fridge, then all the receptacles test normal polarity. In other words, the fridge seems to make the polairty reverse at downstream receptacles!

With the fridge plugged in, voltage at the downstream receptical is 117 V between neutral and ground (sorta confirming the polarity reversal). Unplug the fridge and that voltage drops to 8 volts (really) with 109 volts between between hot and ground or neutral.

Any wisdom out there on what might be the cause of
a). The polarity reversal with fridge plugged in
b). The unusual N-G voltage (8v) with the fridge unplugged



 
  #2  
Old 06-26-22, 08:17 PM
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voltage at the downstream receptical is 117 V between neutral and ground
You have an open neutral either in the fridge receptacle or the bad testing one.
 
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Old 06-27-22, 05:51 AM
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Thanks for prompt reply. I will do more testing to look for an open neutral. However, the N-G voltage drops when I unplug the fridge--can't imagine how that would reconnect the neutral since it is tied together by lugs on the socket. And I have the same issue if I plug the fridge into a different outlet.

Further, my plug-in tester does not report an open neutral when the fridge is unplugged. Is it possible that the fridge is energizing the ground, but not tripping a breaker?
 
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Old 06-27-22, 06:04 AM
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The problem is probably in the fridge receptacle. Does the fridge actually work?
The voltage is passing through the fridge motor onto the neutral. Since the neutral is open it has nowhere to return.
 
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Old 06-27-22, 09:26 AM
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Yes fridge works. As do all the other outlets whether or not the fridge is plugged in. Plus, same issue occurs if I plug the fridge into a different outlet.

Did some more voltage testing (fridge unplugged) and found 119 v between hot and neutral (thus, neutral NOT open), 85 volts between hot and ground, 30 volts between ground and neutral. The "first" outlet has a GFCI, but it's wired so the following outlets bypass that protection (i.e. the fridge continues to run when the GFCI is tripped). I'm now suspecting a faulty GFCI. Does that make any sense at all?
 
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Old 06-27-22, 03:19 PM
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Does the outlet with the reversed polarity function? If it does then it could be a bad grd. But voltage between neutral and grd has always been a bad neutral connection in my experience.
 
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Old 06-27-22, 05:32 PM
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85 volts between hot and ground, 30 volts between ground and neutral.
In this case you have a ground issue.
With a ground issue..... everything will work fine but there will be zero fault protection.
 
Dennis Miller voted this post useful.
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Old 06-27-22, 07:29 PM
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Joed: Several outlets report normal polarity when the fridge is unplugged and reverse polarity when the fridge is plugged in. They all work, regardless of whether the fridge is plugged in. As PJ suggests, I'm suspecting a ground issue (rather than open neutral). We'll see what happens when I checkout the GFCI.
 
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Old 06-27-22, 07:29 PM
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In this case you have a ground issue
My bet is on old style BX cable they have been known to glow bright orange in a serious fault (short circuit) condition high impedance ground will not trip the breaker or blow the fuse but the outer metal will glow like I said.
 
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Old 06-28-22, 10:35 AM
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Feeling somewhat brainless, here. I left yesterday with my tester indicating reverse polarity. Plugged it in this morning to resume testing and it shows normal polarity. Huh? Turns out the polarity flips NOT when the fridge is plugged in, rather when the compressor engages. Suggests a ground issue with the fridge, but doesn't explain unusual voltages with fridge unplugged.
 

Last edited by Dennis Miller; 06-28-22 at 11:08 AM.
  #11  
Old 06-28-22, 01:12 PM
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Not necessarily a fridge problem. Could be the load it presents to the circuit.
A meter would be a better test device.

Those plug in checkers are easily fooled.
 
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Old 06-30-22, 07:13 PM
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FYI, here is what played out. Multiple issues had me chasing my tail. First, the fridge is most certainly bad. Plugged it into another circuit and it tripped the GFCI. Plugged it into yet another circuit without the GFCI and it tripped the breaker. Yet the fridge worked on the "bad" circuit (though seeming to cause a reversed polarity condition). To unravel the mystery, read on...

I found 2 issues on the problem circuit. First, the groundwire at the fridge receptacle did not have continutity with the ground at the receptacle that fed it. Yet it did show continuity with neutral (and a slight voltage to boot). Turns out the last leg of the circuit is buried, serving a yard light. The second problem was a ground fault on that buried cable. Disconnecting that leg of the circuit returned all voltages to expected values and helped me isolate the ground discontinuity.

 
  #13  
Old 07-01-22, 10:40 AM
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I suspect in the old fridge here is a problem that could easily enough be in the old compressor where the neutral is shorted to ground. That would explain why the issue only shows itself when the fridge is plugged in and the compressor is running.
 
 

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