Neutral-to-ground voltage shocked me today; cause?

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brantmacga

brantmacga

Señor Member
Location
Georgia
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Former Child
I had a situation today that I haven't encountered before:

Job was to install track lighting opposite of existing tracklight. With the circuit off, I found the switchleg in the attic and started to make a tap. When took hold of the cable end going to the existing light, I got shocked. I only had my wiggy in my back pocket and took a quick reading. The cable end going to the switch was dead as it was supposed to be. The cable end going to the light measured just under the 120v line, so lets assume it was somewhere around 100v (it felt weaker than 120v but I could be wrong).

I went back into the room where I was adding the light. I took the bulbs out of the existing track light and had the same voltage reading. Below this light was a receptacle with a computer plugged in through a surge protector (apparently on the switch leg). I uplugged the surge protector and checked voltage at the lampholder again: nothing. The voltage was coming from the surge protector itself. It was called a Panamax Max 4.

Was a capacitor discharging discharging and passing through and MOV or something? I haven't seen this before, so I'm just unsure how it got between the neutral and ground.
 
thats called "back feed" remember neutrals carry current under load. unless you turn off both circuits, or remove the load on the live circuit sharing the neutral, you have a potential for a jolt.......
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oh yeah, in case you wonderd about the lower voltage, thats most likely due to being back feed through a motor or light fixture or other device having a resistence....
 
When you open a neutral (that is carrying current) one side of it becomes hot. Not sure just what you were up against today but I'ld bet thats what happened. I learned this lesson rather painfully years ago in a motor control panel!:grin:
 
I doubt the surge protector is a power source, did you check the output recepts on the surge protector before and after unplugging it?

I'd say it's a misswired circuit - bad makeup somewhere, somebody did a homeowner improvement before you were there :D
 
brantmacga said:
When took hold of the cable end going to the existing light, I got shocked.
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The shock came from the end of the switch leg going to the fixture and receptacle.


brantmacga said:
I uplugged the surge protector and checked voltage at the lampholder again: nothing.
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I think this pretty much makes it impossible to theorize I was feeling shocks from a multi-wire branch circuit neutral.

brantmacga said:
The voltage was coming from the surge protector itself.
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So does this. :D

However, I didn't specify in the OP that i actually put the wiggy to the cord end of the surge protector and measured voltage.
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edit: The computer equipment was still connected to the surge protector when I measured voltage. I did not find a battery-backup connected to it either, and if it was there, most likely the surge protector would've been connected to it and then feeding the computer equipment. Connected devices were: Laptop power supply, printer, small stereo speakers, scanner.

another edit:

brantmacga said:
Connected devices were: Laptop power supply
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hmmm.
 
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I would check Pierre's suggestion first, before considering surge protector / device transients.

MOV's don't store energy, just open or close a circuit. Circuits with surge protectors connected to computer peripherals always show voltage with a DVM, but not usually with a solenoid, wiggy, or Fluke T+ Pro.

I've never seen a warning or discussion about transients released by de-energized, rectified-power supplies, their capacitors, or by capacitance stored in power-limited recepticle xfmrs, when the de-energized circuit is grounded or shorted.

These devices are often connected to the surge protector, but I've nevery read or heard of them posing a hazard after being powered down. (That does not mean it's not possible).

Tick tracers do not detect common mode / ground voltage. They don't beep or light up, because the reference to ground is either zero or something well below 50 volts. If the circuit breaker is still on, there's too many ways for the power company's transformers to find a parallel path to ground thru your body. If you refuse to use LOTO, then get some gloves (PPE).
 
yursparky said:
I still don't think this is your problem, I would guess swapped wires somewhere in the circuit, where your white conductor is actually carrying line voltage
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No. Read my posts:

brantmacga said:
. . . . .i actually put the wiggy to the cord end of the surge protector and measured voltage.
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brantmacga said:
Was a capacitor discharging discharging and passing through and MOV or something? I haven't seen this before, so I'm just unsure how it got between the neutral and ground.
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I have never heard of this happening with a surge strip, if that is the source of power, comming from a capacitor, its still backfeed through the computer as a load, and how it got on the neutral, and if you get between the backfeed on the neutral and ground, you will get tweeked....
 
brantmacga said:
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edit: The computer equipment was still connected to the surge protector when I measured voltage. I did not find a battery-backup connected to it either, and if it was there, most likely the surge protector would've been connected to it and then feeding the computer equipment. Connected devices were: Laptop power supply, printer, small stereo speakers, scanner.
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Was any of it "on" and running?

Is it possible the receptacle is fed somehow else, another splice to a different/ or same circuit ahead of your j-box?
 
So, you're saying voltage on the plug end of the Powermax device?

That IS very strange, hope they kept their receipt for that one....




edit: plug end
 
ramsy said:
If you refuse to use LOTO, then get some gloves (PPE).
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Please read the entire thread before making such insults.

yursparky said:
So, you're saying voltage on the plug end of the Powermax device?

That IS very strange, hope they kept their receipt for that one....




edit: plug end
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YES!



ramsy said:
MOV's don't store energy, just open or close a circuit.
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yes i understand that, i was just thinking of possible paths for the electrons. I don't know how this thing is connected inside, i was pulling at strings because i have no other explanation.
 
For a capacitor to provide voltage and current for AC circuits, there would have to be an inverter to convert the DC cap voltage to AC sine wave voltage. I doubt a surge protector would do this. A UPS system, yes. Surge protector = no.

To get shocked from a multi-wire BC neutral, there has to be a load connected to the other circuit. Unplugging the surge protector would have removed the load on the neutral.
 
brantmacga said:
The cable end going to the light measured just under the 120v line, so lets assume it was somewhere around 100v (it felt weaker than 120v but I could be wrong).
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Your statement above suggests some expeirence in measuring voltage by feel. If I was off base here, my apology; otherwise its open season for being whiped on and thumped on, from all directions.
 
ramsy said:
Your statement above suggests some expeirence in measuring voltage by feel. If I was off base here, my apology; otherwise its open season for being whiped on and thumped on, from all directions.
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i can be far from specific sometimes. when i say measuring by feel, i mean by vibration of the solenoid tester. there was no way for you to know that i guess. your comment suggested to me that you think i purposely work in unsafe conditions, which is certainly not the case. but i can see the confusion.
 
ramsy said:
Whipings and thumpings withdrawn. Soory if there was any bruising.
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No bruising, I just don't want you to think I'm completely stupid; contrary to what my wife thinks.
 
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