GROUNDED B PHASE

[bobboan]

The wiring appeared to be in it's original position. Wires on load side of contactor were marked left to right 1/2/3. I switched 1&2 around and the amps leveled out. My only theory is that the electric co. switched two phases around. Be a reciprocating compressor rotation was not a concern.

On a side note. Yesterday i got a no cooling call on a Heil dry unit i installed last year. This is at the same shopping center where i had the blower motor problem that started this thread. Get this i check the unit and found the phase monitor flashing. Panal cover says phase problem. I reversed two phases and the light stops flashing. Runs a few seconds and shuts down. I then switch it back and same thing again. I can not get the board to reset. I call tech support and explan. He tells me it will not work with this B phase ground and has me install a Carrier CLO ( compressor lockout ) Yet it ran all last summer no problem.

Interesting. I don't think I've ever seen a corner grounded secondary Delta used at a shopping center. The obvious reason being that a grounded neutral would be necessary for 120v loads and it would not seem make sense to have a separate corner grounded system to supply relatively small to medium hvac loads. But, I haven't seen everything either.

Are you certain it was corner grounded or could there have been a fault in a phase? Could someone have changed something not realizing the type of system it was?

I doubt if the poco would have changed phasing. They are very careful about that and one of their standard tools is a phase rotation meter.

[bobboan]

Are the transformers pole mounted? If so, can you post some pics of them clearly showing their wiring?

[VTP99]

Interesting. I don't think I've ever seen a corner grounded secondary Delta used at a shopping center. The obvious reason being that a grounded neutral would be necessary for 120v loads and it would not seem make sense to have a separate corner grounded system to supply relatively small to medium hvac loads. But, I haven't seen everything either.

Are you certain it was corner grounded or could there have been a fault in a phase? Could someone have changed something not realizing the type of system it was?

I doubt if the poco would have changed phasing. They are very careful about that and one of their standard tools is a phase rotation meter.

The tenant spaces have two electric meters. One for three phase and one for single phase. It's easy to identify the grounded B phase because you will get no voltage to ground on that phase.

[VTP99]

Are the transformers pole mounted? If so, can you post some pics of them clearly showing their wiring?

Yes pole mounted with 3 high voltage wires and no ground wire. Getting pictures is no problem. My problem is knowing how to post them here.

[timebuilder]

Yes pole mounted with 3 high voltage wires and no ground wire. Getting pictures is no problem. My problem is knowing how to post them here.

How many transformers in the group?

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[stanbyyourword]

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[wolfdog]

I'm not sure what you are trying to say by "maintain that standard."

The B phase is only grounded at the transformer. Are you saying that the B phase is always in second position? I would agree with that.

What I don't get in the thread is the assertion that a motor was fried because motor leads were swapped where one lead was for the B phase. Electricity has taught me nothing that says the B phase lead cannot be swapped with the A or C phase for motor reversal.

So, some piece of this situation is still missing.

Don't make anything out of my statement beyond what I said.
The transformer is grounded at "B" phase and IF "standards are maintained", every "B" phase throughout the system will have ZERO potential to ground. If you change the load wires at the motor contactor\ starter to change rotation - no harm, no foul. If you swap the grounded "B" phase somewhere else in the system, you have created a hazard for the next poor shmuck that has to work on this thing, because ZERO potential to ground on a live phase is now where it is not supposed to be. (assuming the poor shmuck understands what he is dealing with to start with)

[timebuilder]

Don't make anything out of my statement beyond what I said.
The transformer is grounded at "B" phase and IF "standards are maintained", every "B" phase throughout the system will have ZERO potential to ground. If you change the load wires at the motor contactor\ starter to change rotation - no harm, no foul. If you swap the grounded "B" phase somewhere else in the system, you have created a hazard for the next poor shmuck that has to work on this thing, because ZERO potential to ground on a live phase is now where it is not supposed to be. (assuming the poor shmuck understands what he is dealing with to start with)

So, you were saying that A B and C should be kept in their expected positions? I agree with that.

I'm still curious about the connection being made in this thread between the presence of a grounded B and a fried motor due to a phase reversal using two wires to achieve a change in rotation.

[stanbyyourword]

me too, regardless of type of power supply , 3 phase is 3 phase right? Definitely a phase reversal in running mode is a no no , this sounds different, and on inspection one leg high amps , after switching 2 all ok? stan?