Delta Wye Transformer - motor rotation

[Besoeker]

If you're swapping leads on the primary, I'd check all branch circuits on the secondary and track down all motors on the secondary that are 3-phase and not operating through a vfd, and just swap 2 on those motors. Then test to verify rotation.

Use a phase rotation meter.

Any issues doing this?

If you just swap two phases on the primary only you must know that all the three phase fixed speed motors on the secondary will run in the reverse direction.
So why not swap two phases on the secondary? Issue avoided and job's a good 'un.
Seems to me like the simplest fix.........
Other than the "do nothing" option to fix a problem that doesn't appear to exist.

 

[don_resqcapt19]

While I agree with others that flopping two primary conductors will necessitate flopping secondary conductors, that presents a problem if you flop secondary at the transformer terminals. Let me explain...

Let's say your primary conductor-terminal pairings are ABC-BAC and your secondary terminal-conductor pairings are abc-abc. When you flop, you'll end up with ABC-ABC and abc-bac. The problem this presents is the NEC requires busing phase arrangement in distribution equipment to be ABC (or abc regarding the secondary), top to bottom, front to back, or left to right.

The only way to correctly do this is to flop primary and affected motors individually. Do not flop secondary even though that would provide the correct motor rotation.

I am not really sure what the ABC phase arrangement is intended to mean.

9-139 Log #3652 NEC-P09 Final Action: Reject
(408.3(E))
_______________________________________________________________
Submitter: Donald A. Ganiere, Ottawa, IL
Recommendation: Revise text to read as follows:
(E) Phase Arrangement. The phase arrangement on 3-phase buses shall be so that when the leads of a phase rotation meter are connected A, B, C from front to back, top to bottom, or left to right, as viewed from the front of the switchboard or panelboard that the phase rotation meter shall indicate a clockwise rotation. The B phase shall be that phase having the higher voltage to ground on 3-phase, 4-wire, delta-connected systems. Other busbar arrangements shall be permitted for additions to existing installations and shall be marked.

Substantiation: As this section is currently written it has no meaning. It appears that the intent is to require a clockwise rotation. If this is not the intent, then the section does not accomplish anything as the terms A, B and C are only arbitrary terms and the section should be deleted from the code.

Panel Meeting Action: Reject
Panel Statement: 408.3(E) is intended to be a construction requirement for panelboards and switchboards as a matter of consistency. The proposal is a design consideration for connected equipment which is not the purpose of this section.

Number Eligible to Vote: 12
Ballot Results: Affirmative: 12

(blue text = proposed new text)

 

[kwired]

If you have a significant amount of single phase load, A/B/C might actually mean something to you when it comes to trying to achieve balance.

If you mostly have three phase load rotation is really all that matters in most instances.

If you have a high leg or a grounded phase that one leg is important to keep identified, but other then that rotation is your bigger concern most instances.

 

[Smart $]

I am not really sure what the ABC phase arrangement is intended to mean.

(blue text = proposed new text)

I agree ABC is the result of an arbitrary assignment. However, once that assignment is made at one point on a system, I believe the same arrangement throughout the system is prudent... and Code makes it warranted where bus is involved. Phase indication is also required for ungrounded conductors in some instances.

 

[don_resqcapt19]

I agree ABC is the result of an arbitrary assignment. However, once that assignment is made at one point on a system, I believe the same arrangement throughout the system is prudent... and Code makes it warranted where bus is involved. Phase indication is also required for ungrounded conductors in some instances.

I don't see the code as requiring anything other than an A, B, C marking. It has no real meaning.

 

[dkidd]

The problem this presents is the NEC requires busing phase arrangement in distribution equipment to be ABC (or abc regarding the secondary), top to bottom, front to back, or left to right.

Can you give the reference?

 

[Smart $]

I don't see the code as requiring anything other than an A, B, C marking. It has no real meaning.

Code only requires marking when other than the stipulated ABC bus arrangement is used.

You are correct in that Code does not define what A, B, and C are or mean. I suppose this somewhat relates back to 90.1(A) second sentence: This Code is not intended as a design specification or an instruction manual for untrained persons.

We both know an ABC assignment isn't kept in the strictest manner from the power source, i.e. the power plant generators or national grid, all the way to loads. In fact, where delta-wye or wye-delta transformers are used, there's a 30° phase shift, but engineering standards (using that term loosely) dictate which terminals correlate to ABC (albeit by an abc designation).

Regardless, we both know it is at the very least a trade practice to track and align the phase arrangement throughout a system. There are only a few instances for which we must deviate. One instance is a high leg system in which the utility makes the high leg other than B, and flopping the arrangement is a matter of Code compliance. The most common is, of course, to obtain proper motor rotation. Code does not cover the issue of how to accomplish such, so strictly a design decision. I feel it should be handled at the motor circuit level... but JMO.

 

[Smart $]

Can you give the reference?

408.3(E)

 

[don_resqcapt19]

The problem is that the A, B, C is just a set of letters with no real meaning per the CMP's comment and there is nothing to even suggest that the A, B, C in one panel has to be the same as the A, B, C in the panel next to it.

 

[Besoeker]

I don't see the code as requiring anything other than an A, B, C marking. It has no real meaning.

Except that the B crossing from negative to positive will conventionally be 120 deg later than the A crossing point.

 

[don_resqcapt19]

Except that the B crossing from negative to positive will conventionally be 120 deg later than the A crossing point.

But that would mean that ABC = a specific rotation and the code making panel says the rule does not mean that.

 

[Smart $]

The problem is that the A, B, C is just a set of letters with no real meaning per the CMP's comment and there is nothing to even suggest that the A, B, C in one panel has to be the same as the A, B, C in the panel next to it.

And this is where common trade practice enters into it. Code infers a conductor connected to an A-phase bus or perhaps an A-phase-bus-connected breaker pole is connected to an A-phase terminal or bus on the other end. Without the unwritten context, I agree the requirement is totally superfluous.

 

[don_resqcapt19]

And this is where common trade practice enters into it. Code infers a conductor connected to an A-phase bus or perhaps an A-phase-bus-connected breaker pole is connected to an A-phase terminal or bus on the other end. Without the unwritten context, I agree the requirement is totally superfluous.

The rule should just say that all of the switchgear, swithboards, panel boards and MCCs in a building, or a set of buildings under common ownership, shall be connected so as to give the same rotation when connected left to right, top to bottom or front to back.

 

[Smart $]

The rule should just say that all of the switchgear, swithboards, panel boards and MCCs in a building, or a set of buildings under common ownership, shall be connected so as to give the same rotation when connected left to right, top to bottom or front to back.

But ABC, BCA, and CAB all provide the same rotation. What if you had multiple voltage systems requiring phase identification throughout the wiring? Wiring one panel on a system ABC and another on the same system BCA would be... well, pretty messed up IMO.

 

[don_resqcapt19]

But ABC, BCA, and CAB all provide the same rotation. What if you had multiple voltage systems requiring phase identification throughout the wiring? Wiring one panel on a system ABC and another on the same system BCA would be... well, pretty messed up IMO.

Not a problem for someone who knows what they are doing

 

[kwired]

Not a problem for someone who knows what they are doing

I agree. If you have mostly three phase loads, rotation is all that matters to you. You won't really care if one panel is ABC and the next is BCA - they both still have same rotation. If you have a lot of single phase load, knowing which phase has what loads on it may be more important for load balancing, should be a design issue though not a code requirement IMO.

 

[Besoeker]

But that would mean that ABC = a specific rotation and the code making panel says the rule does not mean that.

Yes, that would be the meaning. Conventionally, as I said.

I was addressing your comment
"It has no real meaning."