Weird voltage - Electrician Talk - Professional Electrical Contractors Forum

electron · 09-09-2009, 06:01 AM

Hi everybody, I been visiting this web site for a few weeks and I really like it

, so I decided to become a member, this is a little bit about me: I just pass my journeyman test and became license four months ago and I been working for a small company for the last four years doing residential and some commercial work.
I do not want to make this to long, so this is what I found today:
I was going to run a circuit from a 3 phase panel to a freezer and as a routine I checked the voltage which is phase A to neutral=0 volts, B to N=240 and C to N=240volts, from ground to neutral=120V. This is a sub panel being fed from a 100A panel, so what I did is star turning breakers off, one by one and when I turn off a 2 pole breaker feeding another freezer, the voltage went back to normal 208v between phases and 0V ground to neutral, I unplug the freezer to see if the was creating that but still doing the same even without any load, I did not have time to do anything else, but I will go back tomorrow
Any suggestions will help, thank you

Bob Badger · 09-09-2009, 06:28 AM

Quote:

Originally Posted by electron

I checked the voltage which is phase A to neutral=0 volts, B to N=240 and C to N=240volts, from ground to neutral=120V. This is a sub panel being fed from a 100A panel, so what I did is star turning breakers off, one by one and when I turn off a 2 pole breaker feeding another freezer, the voltage went back to normal 208v between phases and 0V ground to neutral,

You have a serous issue with the neutral (like it's not connected) if your before and after readings are correct.

480sparky · 09-09-2009, 09:06 AM

Yep......... yet another classic open neutral.

(Are they not teaching this is class any more?)

brian john · 09-09-2009, 04:03 PM

1. Neutral and A hase are crossed.

or

2. The system's neutral is not grounded and A phase is grounded/shorted.

vizzolts · 09-09-2009, 08:31 PM

My best guess is an open neutral in combination with A being shorted to N somewhere down the line from your 2 pole circuit breaker feeding the other freezer. Couldn't figure out how to factor in your 240V readings VS your 208V readings, unless that was just a typo.

If I'm talking out my ass I'd appreciate one of the old timers chiming in and correcting me.

BCSparkyGirl · 09-09-2009, 10:00 PM

Quote:

Originally Posted by 480sparky

Yep......... yet another classic open neutral.

(Are they not teaching this is class any more?)

Well, they do up here in BC..........

electron · 09-09-2009, 10:03 PM

I was tracking the freezer circuit and I found 2 J boxes with a few more circuits, at the second junction box the neutral was split to another circuit ( which I now is wrong since is a dedicated circuit should be by it self), but aside from that all joints are made properly, so I tried moving to another breaker and it when back to normal, but I still do not understand how is that happening.

The panel is being fed from a dry transformer delta 480, Y 208, but like vizzolts mention when I turn I getting readings of 240V to ground not 208V, I brought another multimeter just to make sure and I got the same readings, but something i didnt mention is that this panel is feeding more 110V circuits and all of them are "working properly" but still reading 110V between ground and neutral, and I try my gfci plug tester and all the lights came on, I test with my pen voltage tester and beep on the hot and on the neutral.
I am going to run a dedicated circuit for this circuit on saturday, but i still want to find out why is this happenig, plus we need to explain the customer what is going on, thank you for all of your advices.

vizzolts · 09-09-2009, 10:33 PM

I'd double check the transformer hookup (turn off primary), verify correct grounding/ bonding, verify that you have a neutral and that nothing is shorted or crossed at your panel. Trace out all that branch circuit wiring that came off the old freezer breaker while the panel is still dead (maybe with the secondary conductors lifted so you aren't reading through the transformer).

In fact the first thing I might do is kill power to the panel and ring out the conductors coming off that breaker or look through those J boxes. The answer is somewhere in there.

electron · 09-15-2009, 11:24 PM

I just got back to that job and I was surprise whit all the mess, the circuit for the freezer was getting power from two different panels on each phase, the neutral was shared with a 110v circuit, in some other outlets the ground was used as neutral, etc. So we rewired 14 circuits and everything work just fine, thanks everybody for their responses