71v from switch yoke to ground switch leg in BX

[BCES]

Here's my question. Doing a job this weekend, house it mostly old BX. Discovered light box in kitchen was hot from box to neutral using my neon tester. Put the volt meter on it, getting 71 volts. Isolated it to the BX switch leg going down. Getting the same voltage on the switch yoke to the bare frame of the refrigerator which is plugged into a new and grounded outlet.

My concern is that this is more than "Ghost voltage" and my friend who I apprenticed under years ago and who was helping me said its normal for the old BX to "bleed through" and why it will light the bulb on a neon tester but 71 volts is high. My concern is that if, worse case scenario, some touches one of the plate screws and the fridge, they could get popped. My friend said I have two options. Nylon plate screws or re-feed the switch leg.

Would like to hear some opinions. Thanks in advance

 

[rlundsrud]

Try using a low impedance meter, I think you will read zero volts if you do. This sounds like capacitive coupling to me.

 

[kwired]

Here's my question. Doing a job this weekend, house it mostly old BX. Discovered light box in kitchen was hot from box to neutral using my neon tester. Put the volt meter on it, getting 71 volts. Isolated it to the BX switch leg going down. Getting the same voltage on the switch yoke to the bare frame of the refrigerator which is plugged into a new and grounded outlet.

My concern is that this is more than "Ghost voltage" and my friend who I apprenticed under years ago and who was helping me said its normal for the old BX to "bleed through" and why it will light the bulb on a neon tester but 71 volts is high. My concern is that if, worse case scenario, some touches one of the plate screws and the fridge, they could get popped. My friend said I have two options. Nylon plate screws or re-feed the switch leg.

Would like to hear some opinions. Thanks in advance

I'd say between you and your friend you are both partly right and partly wrong.

If you measured with a low impedance meter you will eliminate any "ghost voltatge".

Sounds likely there is no EGC to the old BX and what you are measuring is capacitive coupled "ghost voltage", non contact voltage testers work on detecting capacitive coupled voltage and will indicate voltage when testing non grounded items that typically are supposed to be bonded to equipment grounding conductor.

So a test with a low impedance meter will likely eliminate the voltage reading to a good ground, if not then you do have an ungrounded conductor faulting to this isolated metal armor of the old AC cable - and everything else bonded to it, but I would guess if that had happened you would be measuring much closer to full 120 volts instead of 71 volts.

 

[BCES]

I'd say between you and your friend you are both partly right and partly wrong.

If you measured with a low impedance meter you will eliminate any "ghost voltatge".

Sounds likely there is no EGC to the old BX and what you are measuring is capacitive coupled "ghost voltage", non contact voltage testers work on detecting capacitive coupled voltage and will indicate voltage when testing non grounded items that typically are supposed to be bonded to equipment grounding conductor.

So a test with a low impedance meter will likely eliminate the voltage reading to a good ground, if not then you do have an ungrounded conductor faulting to this isolated metal armor of the old AC cable - and everything else bonded to it, but I would guess if that had happened you would be measuring much closer to full 120 volts instead of 71 volts.

Would a cheap analog meter from Radio Shack or Wal Mart work? I would have thought the bulb in my neon tester (Klein part# 69105) would have put a bit of a load on it or not?

 

[jumper]

Would a cheap analog meter from Radio Shack or Wal Mart work? I would have thought the bulb in my neon tester (Klein part# 69105) would have put a bit of a load on it or not?

Not.

I would suggest a Volcan or Knopp tester, or you can experiment with load tests using a 100W incandescent bulb and such for a load.

 

[gadfly56]

Try using a low impedance meter, I think you will read zero volts if you do. This sounds like capacitive coupling to me.

Then again, maybe not. I had this exact situation when I was changing out an overhead light socket to one with a 5-15 socket built in. I had plugged in a radio and cranked it up while I went into the basement and started unscrewing fuses. When the radio quit I took that fuse all the way out. While dropping the old socket I got bit. There was almost the same voltage (70) as the OP reports. When I looked at the panel again, it seemed someone had double tapped that fuse position. I wasn't in the mood to trouble-shoot so I just unscrewed everything to complete my work.

 

[GoldDigger]

Would a cheap analog meter from Radio Shack or Wal Mart work? I would have thought the bulb in my neon tester (Klein part# 69105) would have put a bit of a load on it or not?

A neon tester may have a 100,000 ohm resistor in series, so less than 1ma from 120V source. [(120-67)/100,000.]
That is not a heavy enough load to rule out capacitive coupling, although insulation leakage would be a more likely source in a short run of wire.

Sent from my XT1585 using Tapatalk

 

[BCES]

A neon tester may have a 100,000 ohm resistor in series, so less than 1ma from 120V source. [(120-67)/100,000.]
That is not a heavy enough load to rule out capacitive coupling, although insulation leakage would be a more likely source in a short run of wire.

Sent from my XT1585 using Tapatalk

I did find my old Square D Wiggy that my friend gave me this past summer. I've never used it before other than putting 120 on it to make sure it still functioned That should do it, right? Either way, I will know shortly and will report back

 

[BCES]

I did find my old Square D Wiggy that my friend gave me this past summer. I've never used it before other than putting 120 on it to make sure it still functioned That should do it, right? Either way, I will know shortly and will report back

The Wiggy did the trick. No voltage from the yoke to ground. Whatever is inside it, the solenoid and the thing that makes it vibrate, puts a good small load on the circuit from the arc it was creating when touched to the screw terminal on the switch.

Thanks for the help

 

[kwired]

The Wiggy did the trick. No voltage from the yoke to ground. Whatever is inside it, the solenoid and the thing that makes it vibrate, puts a good small load on the circuit from the arc it was creating when touched to the screw terminal on the switch.

Thanks for the help

It don't take much load to short out "ghost voltage". But a typical digital volt meter has a really high impedance and not enough load to short out the "capacitor" that such voltage comes from.

You can test from a live line to your bare hand with a high impedance meter and read full 120 volts if you are grounded well enough, and not feel a thing, but replace that meter with a wiggy or other low impedance meter and it will shock you real good - though the current may still only be a few milliamps.