Ground/neutral voltage

Status
Not open for further replies.
D

Dpaps12

Member
Location
San Diego
Occupation
Electrician
Hey guys. 17 yrs in this trade, looking for ideas...

1800a service at 480Y...490V on A B and C to utility neutral...after the main, I’m getting weird voltages to ground...A-N 465V. B-N 475. And 485V C-N. It also varies quite a bit. I’m also getting 14.5-15.5 volts from after the main neutral to my building steel, and concrete grounding Electrode. I also get 0.2 amps on these ground. I’ve checked my building steel connection and other ground on MAIN. all seems good and at both locations and all the lugs and bus bolts and other breakers have been torqued on a recent shut down at all main gear..

what is strange and the other guys say it’s fine, is in getting a decent ark in my 480v panels when I go N to ground with my screw driver...I know there is something up with the neutral..any ideas? Lights keep burning out, power packs keep burning up LCP trans smoked...
Any other things I should check? I haven’t contacted the utility company yet because they are giving me nice clean power..
All my 120/208 (through trans) see no issue. (Bonded to building steel as well)

Thanks I’m Advance.
 
Welcome to the forum. This sounds like a classic floating, unbonded neutral to me.

I would check the neutral-to-building-steel voltage at the main service, and if it's 0v, check each point until that changes.
 
LarryFine said:
Welcome to the forum. This sounds like a classic floating, unbonded neutral to me.

I would check the neutral-to-building-steel voltage at the main service, and if it's 0v, check each point until that changes.
Click to expand...
Indeed sounds like it might be an unbonded neutral, but more likely a high resistance neutral somewhere past the bond point to the building GES. If the neutral is not compromised, then it being unbonded to GES and also unbonded at POCO secondary could produce odd line to ground voltages but would not burn out equipment.
I suspect that was actually what Larry was trying to say, but the words did not come out right, IMHO.
 
Thanks for the rapid response...

My bad guys, I was up late after a long weekend writing this..it is 480/277 and voltages are 265v a-n 275 b-n : 285 c-n. and 280v all phases to ground.
Thanks guys. Ill start testing in the gear to see where it starts having an issue.
 
Dpaps12 said:
Thanks for the rapid response...

My bad guys, I was up late after a long weekend writing this..it is 480/277 and voltages are 265v a-n 275 b-n : 285 c-n. and 280v all phases to ground.
Thanks guys. Ill start testing in the gear to see where it starts having an issue.
Click to expand...
Ok whew, thats better. It does seem like your voltage N-G is a little high. As others have said, seems like you may have a neutral issue somewhere. TI would check your neutral grounded condutor and ask the POCO to check things on their side. You could try to load only one phase to neutral and see what happens with the voltage, but be careful and do it only in a controlled manner to avoid burning something up.
 
Also think you likely have bad neutral somewhere. More balanced your 277 volt load is the more stable voltage will be, the more unbalanced the 277 volt load is the more each phase will vary.

Neutral to ground measured volts is result of voltage drop across the bad spot, coupled with balancing of all three phases.

Your 208/120 loads aren't effected because the transformer primary does not utilize the neutral - is it 480 volts delta winding and is still seeing ~480 volts between each input line.
 
Thanks for all replies. I followed the neutral after the service, end up after the utility pull section (they) never connected the neutral to the house panels gear. Thanks for the replys, measured the busing and getting the proper bus coupling made, shut down to follow. It’s been like this for 20+ years..

Thanks gents
 
Status
Not open for further replies.
Top