480v Question
- Thread starter 360Youth
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I would.360Youth said:
I'm with Roger on this one. You have a corner grounded delta service. It will read 0, 480, and 480 line to ground and 480, 480, and 480 line to line. When you switch to gen' power, that corner is no longer grounded because your switching to 480Y/277, and should get readings of 277 each line to ground and 480 line to line. While on gen' power [manually switched], check the service line side of the transfer switch. It should still measure 0, 480, and 480 line to ground.
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quogueelectric
Senior Member
- Location
- new york
no hv lighting
no hv lighting
[QUOTE There is no such lighting. 480v motors with step down transformers handling 120v controls, lighting, and basic receptacles. Proper grounding is present at receptacles.[/QUOTE]
My next suspicion would be a bugnut at a motor termination grounding to the peckerhead.
Most likely would be a larger sized wire that someone had to alligator wrestle into the small enclosure.
After I wrap the bugnuts I like to cut out a small piece of plastic milk carton material and line the inside of the cover so that it can never short to the cover.
This would be my next most logical suspicion. The ground is going to be on your 480v equipment.
no hv lighting
[QUOTE There is no such lighting. 480v motors with step down transformers handling 120v controls, lighting, and basic receptacles. Proper grounding is present at receptacles.[/QUOTE]
My next suspicion would be a bugnut at a motor termination grounding to the peckerhead.
Most likely would be a larger sized wire that someone had to alligator wrestle into the small enclosure.
After I wrap the bugnuts I like to cut out a small piece of plastic milk carton material and line the inside of the cover so that it can never short to the cover.
This would be my next most logical suspicion. The ground is going to be on your 480v equipment.
- Location
- Illinois
- Occupation
- retired electrician
It can't be a corner grounded system...the "0" reading goes away with the main breaker off. There must be a ground fault on the load side of the main.
Don
480 system
480 system
Thank you, Don. I didn't feel like going through all that again, however, I am still puzzled by something 360 said....You and I agree if the fault clears when the main is off, and he measures line to ground voltages, it isn't a corner grounded system, but, he said when its on generator, the readings are "normal",,assuming that means 277 to ground...if that is accurate, it would seem the fault woud have to be between the main and the transfer switch.
If the generator neutral is connected, anything after the transfer would result in a short.
360, are you sure the building readings are "normal" (277 phase to ground) when you are on generator ?
(edited to correct an ungodly number of typos)
480 system
Thank you, Don. I didn't feel like going through all that again, however, I am still puzzled by something 360 said....You and I agree if the fault clears when the main is off, and he measures line to ground voltages, it isn't a corner grounded system, but, he said when its on generator, the readings are "normal",,assuming that means 277 to ground...if that is accurate, it would seem the fault woud have to be between the main and the transfer switch.
If the generator neutral is connected, anything after the transfer would result in a short.
360, are you sure the building readings are "normal" (277 phase to ground) when you are on generator ?
(edited to correct an ungodly number of typos)
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360Youth
Senior Member
- Location
- Newport, NC
augie47 said:
The generator voltage readings are normal when transfered by throwing main. I assume utility voltages return to "normal" at that time because they have done so every time we turn of the main and check readings line side. I have not checked utility voltage when transfering manually. I will have to try. I do believe our next step is to check each load individually. And hopefully narrow down the fault.
roger said:
We have not got that far yet in troubleshooting. If I had to guess now, I believe it is a pole mounted transformer. To be honest I am not sure where meter cabinet is.
- Location
- Illinois
- Occupation
- retired electrician
augie,
Don
My guess is that it is not a solid fault....that is a fault that can't carry much current. It doesn't take much of a ground to change the voltage readings on an ungrounded system. I would expect that if the system is left on generator power for a length of time the fault will make its location known. I am not recommending this as there will be damage at the point of the fault.
Don
360Youth
Senior Member
- Location
- Newport, NC
I don't know if I am making this more difficult than it is because I am unfamiliar with 480v systems (we've worked on them, but not much, and very little if any troubleshooting, especially a 4-wire). One of the things I have been pondering is the moisture build-up. It is a water station and the motor feeds are run into slab. I believe everything is RMC, but they love to paint everything, so at first glance it appears to be pvc.
quogueelectric
Senior Member
- Location
- new york
does the generator pick up the entire bldg load??
does the generator pick up the entire bldg load??
This is unusual that the gen picks up the entire bldg load so it is possible that the fault is on a feeder that is not on emergency power this may be why the generator does not seem to be damaged.
does the generator pick up the entire bldg load??
This is unusual that the gen picks up the entire bldg load so it is possible that the fault is on a feeder that is not on emergency power this may be why the generator does not seem to be damaged.
My WAG is, asuuming the only EGC for the loads is the conduit, there is a short to ground on the load side of a deteriorated underslab conduit.360Youth said:
I was once called out to a major retail store after the fire department had been called because the floor was "red hot" (a quote, but not my words). Turned out a #12 on a 20A circuit had been pinched between a raised cover and a 4 sq. box under the front counter. The previous electrician used an existing underslab feed which used only the conduit as the EGC. The conduit had deteriorated beneath the slab to the point where the conductive path was earth. Conducting power at a less-than-trip-level current, the soil around the deteriorated section of conduit acted like a heating element.
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360Youth
Senior Member
- Location
- Newport, NC
quogueelectric said:
I will have to check that. I do not remember if we did. Under transfer to the generator, all readings are normal. I think augie hinted at/suggested that earlier. We need to manually transfer the load and see if the fault disappears at the line side lugs of ATS of if fault remains. We had more than anticipated struggles pulling that feed, so I pray there are no problems.
quogueelectric
Senior Member
- Location
- new york
augie is pretty sharp
augie is pretty sharp
augie is pretty sharp
Good luck tommorow you have a lot to look at I wish I could be there I love this stuff.360Youth said:
360Youth
Senior Member
- Location
- Newport, NC
To be honest we have not. Right now I am backed up about 3 weeks on installs and trim outs. When last there, though the problem remained we checked the safety of everything before we left (the job is about an hour away, so unfortunately is is not one we can just pop-in). We could not locate any voltage or curent to ground. No load imbalances. Grounding present at lighting and receptacle outlets.
eric stromberg
Senior Member
- Location
- Texas
I've seen this type of problem three times now. The first was from a generator. One of the phase conductors had made contact with a cable tray rung as the cable was going around a corner. The other two times were cables that had been forced into LBs and the insulation was damaged.
barstowporter
Member
Need help with this thread......are there utility supplied 480 volt 3 phase delta systems with B phase intentionally grounded? If so, then aren't my 3 phase motors running with the motor frame as B phase?
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