# continuity from main lug to panel



## steampunk2309 (Nov 22, 2016)

3 phase 400 amp sub panel with power off is getting continuity between back of panel and the supply wires coming in. Only thing I have done to this panel is add another tap at the bottom to run to a disconnect from. I did this by drilling and tapping into the bars of all three phases. All plastic protection and isolating means are still in place. What could be wrong ? Note there is not a ground wire pulled only two sets of 4 wire pulls

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## glen1971 (Oct 10, 2012)

Filing shorting to ground?

What breakers are open when you measure? What are you using to determine continuity? What reading are you seeing? Where are you measuring in the system?

Something downstream has a neutral that is bonded to ground? Heat trace? Control Transformer? Short in one of your new wires? Crescent wrench on a lug?


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## steampunk2309 (Nov 22, 2016)

Thanks for your reply
All breakers are on with power off.
All shavings are blown out.
Fluke multimeter is used to test.
All new wires were ohmd before connecting. 
This problem was discovered right after installation of lugs .
Next step is to turn off breakers till continuity stops? 
Panel has been there for years not sure why it would not have a bonding wire from the map. Was this an older addition to the nec?

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## gpop (May 14, 2018)

Not enough info

You said that the phases are ohming low to the ground of the case on the incoming side of the breaker. So how did you turn off the incoming supply before testing.

If all 3 are ohming low and they are connected to a Y transformer (incoming) that would make sense as the neutral would be bonded (poco meter?)


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## eddy current (Feb 28, 2009)

Did it actually trip when energized or are you just taking readings before energizing? I bet it was like that before you started. 

There is most likely a resistive device somewhere downstream wired phase to neutral. Because the neutral is grounded, your reading through the device to ground.


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## steampunk2309 (Nov 22, 2016)

gpop said:


> Not enough info
> 
> You said that the phases are ohming low to the ground of the case on the incoming side of the breaker. So how did you turn off the incoming supply before testing.
> 
> If all 3 are ohming low and they are connected to a Y transformer (incoming) that would make sense as the neutral would be bonded (poco meter?)


I turned off the breaker feeding the panel and discovered this while homing that there was continuity between the feeds and the metal of the enclosure.

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## steampunk2309 (Nov 22, 2016)

eddy current said:


> Did it actually trip when energized or are you just taking readings before energizing? I bet it was like that before you started.
> 
> There is most likely a resistive device somewhere downstream wired phase to neutral. Because the neutral is grounded, your reading through the device to ground.


I'm taking these measurements while the power is off. How would it not shock someone when touching the case ? 

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## eddy current (Feb 28, 2009)

steampunk2309 said:


> I'm taking these measurements while the power is off. *How would it not shock someone when touching the case ? *
> 
> Sent from my SM-N950U using Tapatalk


Because it would not be hot on the grounded side of the circuit. 

Of course, you can not measure this continuity when the power is on.

Imagine a 120 volt heater for instance. Power leaves a phase conductor, goes through the element and comes back on a neutral. The neutral is connected to the ground at the main panel making it a grounded conductor. All is good.

Now you have the Power off to the panel. Using an ohm meter your measuring continuity from the phase conductor, through the metal element, back up the neutral that is eventually connected to ground and the enclosure. 

If you turned the branch circuit breakers off one at a time while measuring the continuity from phase to ground, you will eventually clear it and see which circuit is the one giving you the continuity reading from phase to ground. 

My money is on a heater of some kind.


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## steampunk2309 (Nov 22, 2016)

Thanks alot everyone I will update tomorrow when I find the culprit

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