3 Phase 240 V Panel?

[cgardner1]

Hello,

I have recently encountered a breaker panel that is giving results that are unfamiliar to me when measuring voltage.

The panel appears to be a 3 phase panel, it has three lines entering the terminals at the top of breaker. When measuring voltage across each phase to ground (A,B,C) voltage is 125V through each phasehowever when measuring voltage across phases A to C reads 250V, B to C reads 250V, but phase A to B gives a reading of 1V; practically nothing.

I want to know if anyone has encountered this situation before, and/or what is likely the reason for this?

Customer intends to install industrial compressor with magnetic starter, low voltage wiring of motor calls for 3 phase 240V connection. With all wires connected there is again, a missing reading across one of the incoming lines to starter much like the the reading from panel between phase A to B.

Also, the panel is wired with breakers set in a formation that is odd to me, where it appears whomever installed it intentionally skipped a slot and set-in breakers two in a row and skips and continues all the way down in this same pattern. I may be able to post pictures of panel as well

 

[cgardner1]

https://flic.kr/p/2kXL9cg

 

[cgardner1]

https://flic.kr/p/2kXHnrY

 

[cgardner1]

https://flic.kr/p/2kXMPfR

 

[infinity]

Looks like you have a 3Ø, 4-wire Delta system. The B phase is the high leg of 208 volts that's why there are no single pole CB's being used on the B phase. Did you measure the voltage from each phase to the neutral?

 

[cgardner1]

Yes, I already considered the possibility of a high leg, but as stated, the voltage read for each phase to neutral is 125V, no reading of 208V. My main issue is the phase to phase voltage between A and B not reading 250V like B to C, or A to C, or of at least 240V.

 

[ptonsparky]

OP states 125 to ground On all three.

It appears that A&B are same potential. Makes me wonder if the 3 phase Delta has been discontinued at some point in time.

 

[augie47]

From your readings 125v on "B" phase is likely from feedback thru the one "B" phase breaker at the bottom or, at the source, ,someonr has has tied "A" & "B" under the same supply. .
I would say the way the breakers are laid out, "B" was never supplied power.

 

[Hv&Lv]

Look out on the pole. The power XF has a blown fuse.
The way the coils are connected in the transformers is why you get 120 to G and nothing between B&C

 

[ptonsparky]

There Appears to be a two pole breaker on the bottom right. Turn that breaker off and check voltage again.

Augie47 caught it.

 

[cgardner1]

Agreed, I had a fellow journeyman come out and take a look for me and he believes it is backfed somewhere as well. We did remove the double pole breaker, as well the one above it, turned off all other breakers, and set in a 3 phase 40A breaker as a sort of test for the compressor, and similar to the terminals coming in; between phases the readings on the breaker itself on each leg to neutral would read 125V, but between each other for instance line 2 and 3 had not shown 250V as 1 to 2 and 1 to 3 did.

Also, I did also start to think that B had not been powered as well, but at the same time how would that be the case if I have power reading from the incoming B terminal to ground of 125V, and a reading of 250V between B and C as well? Kind makes me believe that there is indeed power there just possibly back fed somewhere as you mentioned.

All in all we believe it to be something in error on the service side coming in just unsure of what it is. Told customer to call power company and explain the possible “loss” of B phase inside panel for them to troubleshoot and find the error. Should get an answer within a day or two just was feeling anxious/curious to know what some other experienced electricians could derive from this scenario. Thanks for the response.

 

[infinity]

I would turn off the main and check all the voltage combinations one the line side of the main. That will tell you if it's a POCO problem.

 

[Hv&Lv]

Agreed, I had a fellow journeyman come out and take a look for me and he believes it is backfed somewhere as well. We did remove the double pole breaker, as well the one above it, turned off all other breakers, and set in a 3 phase 40A breaker as a sort of test for the compressor, and similar to the terminals coming in; between phases the readings on the breaker itself on each leg to neutral would read 125V, but between each other for instance line 2 and 3 had not shown 250V as 1 to 2 and 1 to 3 did.

Also, I did also start to that B had not been powered as well, but at the same time how would that be the case if I have power reading from the incoming B terminal to ground of 125V, and a reading of 250V between B and C as well? Kind makes me believe that there is indeed power there just possibly back fed somewhere as you mentioned.

All in all we believe it to be something in error on the service side coming in just unsure of what it is. Told customer to call power company and explain the possible “loss” of B phase inside panel for them to troubleshoot and find the error. Should get an answer by Monday just was feeling anxious/curious to know what some other experienced electricians could derive from this scenario. Thanks for the response.

Again, look outside at the POCO pole. There’s probably a fuse hanging out.
Maybe even a squirrel at the base of the pole

 

[paulengr]

Sounds like it WAS 208/120 but has been changed to 240/120 with the extra phase ties to another phase.

If it was a blown fuse on the high or low side you would not be seeing 240 V. If it’s grounded somewhere you would normally trip or see low voltages.

Don’t assume that labels or wire markings are correct when troubleshooting. When you walk up on one use everything you know but trust measurements over everything then name plates then what someone says and finally drawings in that order. If there are any inconsistencies discount the last two.

 

[gar]

210510-0837 EDT

cardner1:

In your photo there appears to be a neutral bus on the right side with a heavy wire connected to it.

On the left is there appears to be an EGC bus.

What is the voltage difference between each of these bus bars? My guess is very close to zero.

From what I believe is the neutral bus what are the voltages to each of the hot incoming lines?

On your pole how many transformers are on the pole?

You read 125 V from the neutral bus to A, B, or C. This is 1/2 of 250. If you have a 3 phase delta supply you can not have two center taps of different phases connect together.

If you have a 3 phase wye, and line to neutral is 125, then you can not read 250 line to line.

From your voltage measurements it looks like a center tapped single phase source is connected to a 3 phase panel. One third of the breaker slots are not used because there is no third phase. When you look at the pole and what transformers are there and how they are connected, then you may get a better idea of what is the source circuit.

.

 

[infinity]

In your photo there appears to be a neutral bus on the right side with a heavy wire connected to it.

On the left is there appears to be an EGC bus.

What is the voltage difference between each of these bus bars? My guess is very close to zero.

There are neutrals terminated on both the bus on the left and on the right and there appears to be a bar at the bottom connecting the two buses together. There also appears to be a black conductor taped green terminated on the bus on the left which is likely the GEC.

 

[synchro]

Again, look outside at the POCO pole. There’s probably a fuse hanging out.

Agree that's a possible scenario.
If it's an open delta, the teaser transformer is connected to the A and B phases, and the fuse supplying the teaser is blown, then it would show the symptoms described by the OP.

 

[zbang]

Sure looks like it was wired for 3-phase at one time, then backed to single and all the B phase breakers removed. Except for the pesky 2-pole at the bottom.

Any time I see panel where there are regular missing breakers, the "This is not wye-fed" flag pops up; almost always it's either a 3-phase panel used for single or it's a high-leg delta. (Like others said, turn off the panel's main and meter the line side. If it looks weird, trace back the feeder 'til you find why its weird.)

 

[Hv&Lv]

Sounds like it WAS 208/120 but has been changed to 240/120 with the extra phase ties to another phase.

If it was a blown fuse on the high or low side you would not be seeing 240 V. If it’s grounded somewhere you would normally trip or see low voltages.

Don’t assume that labels or wire markings are correct when troubleshooting. When you walk up on one use everything you know but trust measurements over everything then name plates then what someone says and finally drawings in that order. If there are any inconsistencies discount the last two.

If it were an open delta you would.

 

[LarryFine]

If it were an open delta you would.

Right. The high-leg secondary would still be intact, and that line will read the same as the line (phase) it's connected to.