Unknown cure for hot and ground reversed

[Bob_Sacamano]

I went to a customer's garage who complained that his GFCI on his work bench wasn't holding, in turn knocking out every outlet tapped off of it. When I inserted my plug tester it read "Hot and Ground reversed". I freed the outlet from the box and tested between the wires (mind you ground is bare): Hot & Ground - 0V; Hot & Neutral - 0V; Ground and Neutral - 120 V.

The customer insisted it was a bad GFCI and of course he was standing over my shoulder. So I changed the GFCI since he paid for it anyway, and of course the problem still existed. I started opening up boxes up the line looking for an incorrect splice. In the panel the neutral and the ground went to the same bar. I found one splice where the wires were pulling taught on the wire nuts and the wire nuts were oversized. However the wires weren't mixed up, hots went to hots and so forth. I opened up the splices and of course they weren't twisted with kliens, just stabbed in. The tips of the copper looked charred a little. I took the reading at this box and they were the same at the GFCI. I got some slack from the romex and went about redoing all 3 splices and used the proper sized wire nut. This fixed the problem! Suddenly all my reading were correct, the plug tester read fine, the GFCI held, and the plug tester tripped it as it should. I'm puzzled as to what problem exactly did I fix?

What splice had to be open to get that hot and ground reversed reading?

 

[480sparky]

Did you take actual voltmeter readings, or just use a plug-in tester?

Sometimes, certain testers will give incorrect readings if there's an open neutral.

Also, the only approved method to test a GFCI is the built-in test button. I've had cases where plug-in testers will not trip a properly-wired GFCI.

 

[synchro]

One possibility is that there was an open splice on the neutral after the panel, followed by a L-N load that puts 120V on the neutral wire, and then an open splice on the hot and so it no longer has 120V. Then neutral to ground would be 120V and the hot to either neutral or ground would be 0V, at least if you used a low impedance tester such as a Wiggy.
If you used a high impedance meter then it still might show a non-zero "phantom" voltage on a hot wire with an open connection earlier in the chain, due to coupling between wires.

 

[ActionDave]

Plug in testers lie. I'm not saying I don't use them. I am saying don't trust them when it comes to serious troubleshooting.

 

[480sparky]

UL White book:

OUTLET CIRCUIT TESTERS (QCYU)
GENERAL
This category covers portable devices with fixed attachment-plug blades, or probes attached to flexible leads, used to indicate various wiring conditions in 15 or 20 A branch circuits by a pattern of lights or other similar means along with markings or instructions to identify the probable wiring
conditions which cannot be determined by the tester.
The devices may include provisions for checking the functions of a ground-fault circuit interrupter (GFCI) connected to the branch circuit, or for indicating that a branch circuit is connected to an arc-fault circuit interrupter (AFCI).
AFCI indicators operate by producing a waveform similar to an arc fault. Since these devices cannot produce an actual arc fault, an AFCI indicator
may not trip every AFCI. AFCI indicators are provided with markings or instructions that state the following or equivalent: ‘‘CAUTION: AFCIs recognize characteristics unique to arcing, and AFCI indicators produce characteristics that mimic some forms of arcing. Therefore the indicator may provide a false indication that the AFCI is not functioning properly. If this occurs, recheck the operation of the AFCI using the test and reset buttons.
The AFCI button test function will demonstrate proper operation.’’
These devices are not intended for use as comprehensive diagnostic instruments.

 

[Eddie702]

@Bob_Sacamano

I had a similar issue and it was a bad splice upstream.

I hate Scotch lock wire nuts, can't get them off

 

[augie47]

The particular tester I use shows hot & ground reversed when there is no equipment ground.
Time to get a real tester out

 

[grich]

The particular tester I use shows hot & ground reversed when there is no equipment ground.
Time to get a real tester out

So does mine.

That tester usually sinks to the bottom of the tool bag so I'm more likely to use a meter for outlet testing anyhow.

 

[sameguy]

Ideal Industries 61-040 Test-Glo Circuit Tester, 80-600 VAC
I have this tester for 40 years ok a couple not just the one.