Conductors holding charge after insulation test

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Dsg319

Dsg319

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Wv Master “lectrician”
I have never personally received a shock from conductors after a megger test.

But have heard people say they have and read operating procedures on the web saying to “ground” the wire up to 4x the time of the applied test.

I know the conductor is basically just a capacitor.

So if I test a large conductor from it to ground, after the test with both ends “floating” from ground, will there be a potential difference “voltage” from the conductor to ground?
 
Dsg319 said:
I have never personally received a shock from conductors after a megger test.

But have heard people say they have and read operating procedures on the web saying to “ground” the wire up to 4x the time of the applied test.

I know the conductor is basically just a capacitor.

So if I test a large conductor from it to ground, after the test with both ends “floating” from ground, will there be a potential difference “voltage” from the conductor to ground?
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If it passes, yes. How long, IDK.

Back when my favorite tester was a Beha, later Greenlee, those conductors that passed would charge up like a capacitor and hold it. Reapplying the tester would not charge again. Those that failed either continued the tone or charge then drop off and charge again once the tester was reapplied.
 
ptonsparky said:
If it passes, yes. How long, IDK.

Back when my favorite tester was a Beha, later Greenlee, those conductors that passed would charge up like a capacitor and hold it. Reapplying the tester would not charge again. Those that failed either continued the tone or charge then drop off and charge again once the tester was reapplied.
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Even if I was doing a phase to phase instead of ground test would it still have a voltage relative to ground?
 
Dsg319 said:
Even if I was doing a phase to phase instead of ground test would it still have a voltage relative to ground?
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Probably not, (except for that caused by trace amounts of leakage resistance) but those two conductors would retain a charge and pose a hazard.

Isn't there a rule somewhere (OSHA? England?) that says to leave the megger in place until there's less than 50 volts on its terminals?
 
drcampbell said:
Probably not, (except for that caused by trace amounts of leakage resistance) but those two conductors would retain a charge and pose a hazard.

Isn't there a rule somewhere (OSHA? England?) that says to leave the megger in place until there's less than 50 volts on its terminals?
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The fluke that I use goes back to 0 volts right after the applied 500volts.

Maybe I will change it too voltage setting next time right after I megger a set and see if voltage still remains.
 
Some shielded medium voltage cable was shipped with a label on the spool that said to short the conductor to the shield before touching the cable because of the possibility of the conductor acting as a charged capacitor from the manufacturer's testing of the cable before shipping.
 
don_resqcapt19 said:
Some shielded medium voltage cable was shipped with a label on the spool that said to short the conductor to the shield before touching the cable because of the possibility of the conductor acting as a charged capacitor from the manufacturer's testing of the cable before shipping.
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Yes, and dielectric absorption in the cable insulation can cause the cable to recharge at least somewhat even if it was fully discharged before shipping. Capacitors often have a shorting bar or wire to prevent this from happening.
 
I can tell you from experience that shielded cables will hold a charge and give a good zap if not discharged. One day one cable didn't get grounded and we went to break. We forgot the far end of the cable never got grounded for discharge and it nailed one of my co-workers. It didn't injure him, but he made up an entirely new vocabulary of profanity that could be heard for several hundred feet.
 
K8MHZ said:
I can tell you from experience that shielded cables will hold a charge and give a good zap if not discharged. One day one cable didn't get grounded and we went to break. We forgot the far end of the cable never got grounded for discharge and it nailed one of my co-workers. It didn't injure him, but he made up an entirely new vocabulary of profanity that could be heard for several hundred feet.
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We were working with some stretched out on the ground under a primary. Snapped pretty dang good and didn't take long to charge up again.
 
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