OK a little background. I have a 30 KVA transformer, Primary is corner grounded delta 480v , secondary is 120/208 center grounded wye. Now the problem; without load my power is clean 120/208+ no problem, after putting standard 120 volt load on I have a loss of power on one hot leg (0 volts) and the neutral becomes the hot leg?? all connections and taps have been triple checked help. yes i typed this right without load x1-120 x2-120 x3-120 x0-0, with load x1-0 x2-120 x3-120 x0-120 or else an odd one like x1-98 x2-120 x3-120 x0-28 ANY help woul be great
nasty three phase problem
- Thread starter mixedbag
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electricman2
Senior Member
- Location
- North Carolina
- Occupation
- Retired Electrical Contractor
Re: nasty three phase problem
Need more information. Are you saying that the leg you connect the load to goes to 0V and the others stay at 120? What is the reference point for your measurements? Is this true of all legs or just one? Also have you connected 208V loads?
Need more information. Are you saying that the leg you connect the load to goes to 0V and the others stay at 120? What is the reference point for your measurements? Is this true of all legs or just one? Also have you connected 208V loads?
Re: nasty three phase problem
Let me get long winded here. This is in a computer room at the industrial plant where I work. I was called in by the comp tech when he installed new UPS units, as they were fault coding "improper wired receptacle". Using a standard "quick check" hot/nuetral/ground tester, it showed reversed polarity on the grounded/hot wires. I checked all wires to the panel to see if colors/ polarity had been reversed and found nothing. So I checked the incoming wiring and found the neutral to be 120 volt (Isolated ground). I promptly shut the main breaker off and retested, all incoming wiring is now OK 120 volt on each leg. I shut off all branch circuit breakers and turned on the main - still OK. I turned on the receptacle breaker and switheroo the hot is now 0 volts and the nuetral is 120 volts.
Let me get long winded here. This is in a computer room at the industrial plant where I work. I was called in by the comp tech when he installed new UPS units, as they were fault coding "improper wired receptacle". Using a standard "quick check" hot/nuetral/ground tester, it showed reversed polarity on the grounded/hot wires. I checked all wires to the panel to see if colors/ polarity had been reversed and found nothing. So I checked the incoming wiring and found the neutral to be 120 volt (Isolated ground). I promptly shut the main breaker off and retested, all incoming wiring is now OK 120 volt on each leg. I shut off all branch circuit breakers and turned on the main - still OK. I turned on the receptacle breaker and switheroo the hot is now 0 volts and the nuetral is 120 volts.
Re: nasty three phase problem
oh, didn't answer your question totally. No 208 loads are in this panel, I have no idea why the original electrician installed a 120/208 three phase panel. 120 loads are lights in three offices, general receptacles in two offices and two designated circuits in the computer room.
oh, didn't answer your question totally. No 208 loads are in this panel, I have no idea why the original electrician installed a 120/208 three phase panel. 120 loads are lights in three offices, general receptacles in two offices and two designated circuits in the computer room.
electricman2
Senior Member
- Location
- North Carolina
- Occupation
- Retired Electrical Contractor
Re: nasty three phase problem
I am still trying to get a handle on this. Are you taking the voltage measurements at the panel at the load side of the breaker? When you say the neutral is 120V where is the reference point,i.e 120V to what? Is voltage at receptacles on the other two phases correct polarity?
I am still trying to get a handle on this. Are you taking the voltage measurements at the panel at the load side of the breaker? When you say the neutral is 120V where is the reference point,i.e 120V to what? Is voltage at receptacles on the other two phases correct polarity?
Re: nasty three phase problem
The problem seems to be just on the one leg, and just with the receptacles in the computer room. I have not torn into the lghting circuit, and other receptacles do not seem to have the same problem (which may mean they are not on that phase, or that I just haven't had any problem with it)!
The problem seems to be just on the one leg, and just with the receptacles in the computer room. I have not torn into the lghting circuit, and other receptacles do not seem to have the same problem (which may mean they are not on that phase, or that I just haven't had any problem with it)!
- Location
- Illinois
- Occupation
- retired electrician
Re: nasty three phase problem
mixedbag,
Don
mixedbag,
What other type of panel would be installed on a 3 phase system?
Does the equipment connected between X1 and X0 work? I expect that it does. It is my opinion, as dillon said earlier, that you are missing the connection between X0 and the grounding system.
Don
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: nasty three phase problem
I am totally unworthy to add to this, but I'm going to anyway.
I had a similar event in a (don't laugh) apartment. No load, everything was fine. Whenever there was a load applied, I'd get hot-neutral reverse. The problem was a loose neutral in the service where the meter banks coupled to the disconnect.
Have you checked all of your connections?
I am totally unworthy to add to this, but I'm going to anyway.
I had a similar event in a (don't laugh) apartment. No load, everything was fine. Whenever there was a load applied, I'd get hot-neutral reverse. The problem was a loose neutral in the service where the meter banks coupled to the disconnect.
Have you checked all of your connections?
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