I'm learning and need some help

[EnemyOf1]

I was told power was 120/208v 3ph. Trying to hook up a condenser unit, rated at 208-230vac 60hz. When I took meter readings this is what I found.
Line to Neutral & Ground were both the same
A phase reads 120v
B phase reads 123v
C phase reads 176v

Phase to phase reads
A to B is 243v
A to C is 282v
B to C is 115v

Is this 240 3ph High Leg?

I have no idea how to make this work, I've only been doing it for 4 years and still learning.

Thanks!

 

[Ponchik]

your voltage readings are not correct.

Check the input side of the breaker and see if get consistent reading.
If not, check the mail panel of the unit/building and see if you get good reading.

Keep going up the ladder till you find good voltage reading then start troubleshooting backwards to see why you have bad voltage readings.

 

[under8ed]

Are you replacing a unit that failed feeding from that panel? Those voltages appear out of the norm, I'm not very familiar with these "high leg"systems. From what I've seen here though, phase to phase is usually consistent. I'm wondering if a failing transformer has not caused the problem.

 

[EnemyOf1]

That's why I'm asking. Those readings were taken at the Main lugs of the panel. So now I'm wondering WTH is going on. Putting new batteries in my Fluke, I can check again, but I've don't it twice and they were the same both times. This is my first venture into anything 3 phase outside of 120/208, so I was, and am, completely baffled. Great!

Thanks for the replies.

 

[ActionDave]

That's why I'm asking. Those readings were taken at the Main lugs of the panel. So now I'm wondering WTH is going on. Putting new batteries in my Fluke, I can check again, but I've don't it twice and they were the same both times. This is my first venture into anything 3 phase outside of 120/208, so I was, and am, completely baffled. Great!

Thanks for the replies.

Main panel or sub panel? If it is a sub check at the service.

 

[GoldDigger]

That's why I'm asking. Those readings were taken at the Main lugs of the panel. So now I'm wondering WTH is going on. Putting new batteries in my Fluke, I can check again, but I've don't it twice and they were the same both times. This is my first venture into anything 3 phase outside of 120/208, so I was, and am, completely baffled. Great!

Thanks for the replies.

Your line to neutral and line to line voltages are not even, AFAIK, consistent with a true 3 phase (as in 120 degree phase offset) system, and they are certainly not consistent with any standard wye or delta transformer configuration.

What it might be would be a center tapped delta made up of two or three mismatched voltage single transformers, or at least transformers with incorrect tap wiring. But even then the relation between A-C and B-C is not explainable.

The one sure thing is that with A-N +B-N = A-B those two windings are either part of a single center tapped winding or are precisely in phase with each other.
You might have a center tapped 120/240 connected from A-B and then a 90 degree out of phase 115V winding connected from B to C. The hypotenuse of the resulting triangle would give close to 280 for A-C and ~160 from C to N. Not great, but closer than anything you could get with three phase vectors
Maybe there is a hidden Scott-T and then some really bad miswiring?

OK, here is something that just might work well enough with just three phase:

A-N-B is a single phase 120/240. There is one additional phase of a three phase supply driving a 115V secondary transformer which connects B to C BUT it is wired with reverse polarity (not reverse rotation). The result is that from N to C adds the 120V vector to a sixty degree vector that takes C farther from the neutral point rather than back toward it.
The equations would be (N-C)² = (N-B plus 115/2)² plus (115 sqrt(3)/2)². Nope. That is even worse than the two-phase (quadrature) solution.

I really want to see the voltages on a scope!

Maybe we do not have sinusoids????

 

[epr212005]

It sounds like a problem at the transformer feeding your panel i wouldnt worry to much about the rest while it is interesting to know why its giving you bad voltage readings i would focus on a remedy if it was a high leg your high voltage would be on b phase and it would be 277 volts to ground not 176 on c phase to ground if this building is fed with 277/480 check for the right voltage at the breaker feeding your stepdown transformer if everything is ok there you know you have a problem transformer

 

[Little Bill]

It sounds like a problem at the transformer feeding your panel i wouldnt worry to much about the rest while it is interesting to know why its giving you bad voltage readings i would focus on a remedy if it was a high leg your high voltage would be on b phase and it would be 277 volts to ground not 176 on c phase to ground if this building is fed with 277/480 check for the right voltage at the breaker feeding your stepdown transformer if everything is ok there you know you have a problem transformer

If you're talking about a high leg delta 240/120V, then the high leg would be 208V give or take a few volts. It would not be 277V.

 

[epr212005]

Yea sorry what bill said is correct