troubleshooting
- Thread starter Knack43
- Start date
- Status
- Occupation
- Licensed Electrician
Bad neutral to ground bond.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Even with that wouldn't the L-L voltage still be 480V?
I would guess a bad/lost phase and something is backfeeding to get a reading on the lost phase/leg.
ptonsparky
Tom
- Occupation
- EC - retired
New install?
POCO or Customer owned?
POCO or Customer owned?
Last edited:
oldsparky52
Senior Member
- Location
- Wilmington, NC USA
I've never heard of a 480V single phase service being used. Is this a PoCo supplied voltage or is this in house supplied (in other words, your transformers not PoCo's)?
- Occupation
- Licensed Electrician
I think single phase is set up line to ground, ie 0-480 not 240-0-240 and not single phase from a wye system where you have 277 to ground
- Occupation
- Licensed Electrician
All I've heare is that it is used for highway lighting
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
OP needs to clarify and be more specific. I am not exactly sure where and how is measurements are being taken and they make no sense.
Pretty common to have two legs of a 277/480 system to feed a single phase transformer. Or could be an SDS for a specific machine, in which case there would be a few choices depending on if the tranny had a CT.
Pretty common to have two legs of a 277/480 system to feed a single phase transformer. Or could be an SDS for a specific machine, in which case there would be a few choices depending on if the tranny had a CT.
ptonsparky
Tom
- Occupation
- EC - retired
We have POCO supplied single phase for use with phase converters where they cannot provide three.
growler
Senior Member
- Location
- Atlanta,GA
I think the OP could start out by stating what this is being used for.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Still don't think he should ever see 480 to ground, but that depends on exactly what his source is. I'm presuming 240 - 0 - 240. We have many those around here for irrigation systems where three phase primary lines isn't available and customer uses a phase converter to get three phase.
But does sound like one should make sure there isn't lost ungrounded conductor. Lost ungrounded conductor includes blown fuse - those can throw inexperienced people into confusion. Measure volts across the fuses, if they are good fuses there is no voltage drop across them, no more than a few millivolts anyway.
Beaches EE
Senior Member
- Location
- NE Florida
- Occupation
- Electrical Engineer / Facilities Manager
480 single phase IS common for highway lighting and as already stated, the OP should tell us about the application and the service configuration.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I'm guessing most places it has 240 volt center tap and that is what is grounded. It certainly would be more common here vs 480 volt two wire system.
Electricmo
Senior Member
- Location
- Missouri
- Occupation
- Lineman
We need more info. Possibly the POCO has a blown fuse on their transformer bank causing fluctuating voltage dependent on load. 480 volt single phase is weird.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Why?
You only need right number of turns on a transformer and you can get about any voltage imaginable.
480 single phase source maybe a little out of ordinary but it does exist as there are items out there that are designed to run on 480 single phase and won't care if connected to a single phase source or between two lines of a three phase system.
- Status