Troubleshooting

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nickelec

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Just came from my mother-in-law's house I'm pretty sure it's a utility issue but with the main breaker off on the line side of the breaker I get 208 as soon as I turn the breaker on I get 110

As I turn individual circuit breakers off the voltage starts to climb back up and increments to 208

To me it seems like a bad neutral from the street

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It's a 208 system I was testing phase a to phase b on breaker terminals

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Yes after further investigation I would agree. Is anyone inclined to agree with me that it's not a problem inside the premise it only happens when there's a load

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nickelec said:
Yes after further investigation I would agree. Is anyone inclined to agree with me that it's not a problem inside the premise it only happens when there's a load

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If you are checking on the line side of the breaker, then yes, sounds like a weak/intermittent connection north of that point. Maybe in meter socket or even further back.
 
If the service i single phase (two phases of a three phase 208Y/120 volt system) 208/120 volts, the measurements appear to happen due to a lost fuse. Curious to what you find.
 
nickelec said:
Yes after further investigation I would agree. Is anyone inclined to agree with me that it's not a problem inside the premise it only happens when there's a load

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Where is the utility point of delivery?
we have some check at the breakers only to find out it’s a bad SER cable between the Meterbase and the breaker or up the weather head to the drip loop.
Normally those are yours also.

Look up and see if there’s something obvious you can point to and tell them where it’s at.
 
Knuckle Dragger said:
Here in Mass.
It's the homeowners responsibility right up to the point of attachment.
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Here in NYC it's the same they. This happens to be and underground service. Coned came last night and checked the conductors.with a load tester they confirmed definitely a problem on there end. They also seem to not even know where the conduit goes.

So this should be a fun one, thankfully we don't need 220 service for a few we only really need it for AC's.

And yes this is two legs from a three phase service.

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nickelec said:
Here in NYC it's the same they. This happens to be and underground service. Coned came last night and checked the conductors.with a load tester they confirmed definitely a problem on there end. They also seem to not even know where the conduit goes.

So this should be a fun one, thankfully we don't need 220 service for a few we only really need it for AC's.

And yes this is two legs from a three phase service.

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But you still lost one leg coming in, if you checked individual circuits you probably have pretty stable 120 nominal on the good leg and a voltage that varies depending on loading conditions on the other leg. What happens is the "dead leg" ends up in series with a(ny) 208 volt load such as a heater or something and many things that normally draw low current may seem to be working ok, but the more load you put on that leg the less voltage they will see. Turn off all two pole breakers in your panel and all those items on the dead leg will stop working at all because no more back feed through 208 volt loads.
 
Exactly what I did, I first tested face to face on the line side with the main breaker off voltages were good 208 steady with all the individual circuit breakers on I turned on the main and immediately lost the one leg

Then I started turning off individual circuit breakers and as I turn them off of course the voltage on the bed leg started raising back to normal

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nickelec said:
Exactly what I did, I first tested face to face on the line side with the main breaker off voltages were good 208 steady with all the individual circuit breakers on I turned on the main and immediately lost the one leg

Then I started turning off individual circuit breakers and as I turn them off of course the voltage on the bed leg started raising back to normal

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You probably not using a low impedance meter to take readings. But even if you were, there might been high enough resistance in whatever failed that it allows some (though pretty low) current to flow. Take away all the load and there is no current therefore no voltage drop across that resistance - that is why you still see full voltage when not loaded.
 
You poor bastard... trying to help mom in law? :)
Tell her you fixed it, quit now while you can. She wont like you any better...
 
James L said:
🤔🤔
Two phases never equal one phase.
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Our LTN is completely 208Y/120 volt 4wire throughout the city. Requests for single phase service are satisfied by extending two phases and a neutral from the three phase system. To the customer, this is. A single phase 208/120 volt supply. It will not support three phase load as configured and is used accordingly. If the user understands that they are supplied by two phases of a three phase system they could connect a transformer bank as open Wye open Delta and it would allow them to supply three phase loads otherwise it is for all intents and purposes single phase.
 
NewtonLaw said:
Our LTN is completely 208Y/120 volt 4wire throughout the city. Requests for single phase service are satisfied by extending two phases and a neutral from the three phase system. To the customer, this is. A single phase 208/120 volt supply. It will not support three phase load as configured and is used accordingly. If the user understands that they are supplied by two phases of a three phase system they could connect a transformer bank as open Wye open Delta and it would allow them to supply three phase loads otherwise it is for all intents and purposes single phase.
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I think you missed my point.

Two legs does not equal two phases.

Phase and leg are not synonyms
 
NewtonLaw said:
Our LTN is completely 208Y/120 volt 4wire throughout the city. Requests for single phase service are satisfied by extending two phases and a neutral from the three phase system. To the customer, this is. A single phase 208/120 volt supply. It will not support three phase load as configured and is used accordingly. If the user understands that they are supplied by two phases of a three phase system they could connect a transformer bank as open Wye open Delta and it would allow them to supply three phase loads otherwise it is for all intents and purposes single phase.
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One thing to note is that with a balanced 3-phase load, the neutral supplying a pair of open-wye/open-delta connected transformers will draw 1.73 times the RMS current that's drawn on each of the two phase conductors supplying the transformers. And so the ampacity of the neutral conductor would need to be at least 1.73 times higher than that of the phase conductors. The reason for this is the currents thru the two open delta secondary windings are 120° apart from each other due to the 3-phase load, but the currents drawn by the open wye primaries are 60° apart because of the required polarity inversion thru one transformer vs. the other.
 
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