Proper Phasing of Panels

[jonny1982]

I noticed some existing panels where phased from left to right (A,B,C) instead of from right to left (A,B,C) when I hooked up my rotation meter. The colors where also off (B phase correct being orange) but the other two (Brown and Yellow) flip flopped.

It got me thinking, is there actually a code that says panels must be phased a certain way?

With phase rotation, does phasing really matter unless working with motors? Like, if replacing a panel, I see how it is important to re install the new one just like the old one because if there are motor loads connected, they have all been running the correct rotation with the existing phasing in the panel.

But is it safe to say that if the phasing is off in a new panel that there isn't much to worry about (except a bit of confusion) because all new motor circuits will most likely be bump tested after install?

Thanks

 

[Smart $]

Code required in 408.3...

(E) Bus Arrangement.

(1) AC Phase Arrangement. Alternating-current phase ar-
rangement on 3-phase buses shall be A, B, C from front to
back, top to bottom, or left to right, as viewed from the
front of the switchboard, switchgear, or panelboard. 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.

Exception: Equipment within the same single section or
multisection switchboard, switchgear, or panelboard as the
meter on 3-phase, 4-wire, delta-connected systems shall be
permitted to have the same phase configuration as the metering
equipment.

Informational Note: See 110.15 for requirements on marking
the busbar or phase conductor having the higher voltage
to ground where supplied from a 4-wire, delta-connected
system.

(2) ...

 

[jonny1982]

Code required in 408.3...

Do you know of a 3 phase rotation meter that determines exactly what is A, what is B, and what is C? The one I used only shoes roation. In other words, if I know already what phase A, B, and C are if I connect L1 to A, L2 to B, and L3 to C it says I have proper rotation. If I connect L1 to B, L2 to C, and L3 to A, it also says I have proper rotation. If I connect L1 to C, L2 to A, and L3 to B, again, it says I have proper rotation.

What if I have a scenario where I don't know which one is A, which one is B, and which one is C. Do I just have a cheap meter?

Thanks

 

[Smart $]

Do you know of a 3 phase rotation meter that determines exactly what is A, what is B, and what is C? The one I used only shoes roation. In other words, if I know already what phase A, B, and C are if I connect L1 to A, L2 to B, and L3 to C it says I have proper rotation. If I connect L1 to B, L2 to C, and L3 to A, it also says I have proper rotation. If I connect L1 to C, L2 to A, and L3 to B, again, it says I have proper rotation.

What if I have a scenario where I don't know which one is A, which one is B, and which one is C. Do I just have a cheap meter?

Thanks

That's all you'll get from a rotation meter. To know exactly which one is which, you have to trace one wire all the way back to the generators at power plants. I wouldn't be surprised at all if POCO's actually have 'em rotated somewhere. As far as NEC implementation, base it on the arrangement in the meter or CT cabinet.

 

[electricalist]

I was taught a,b,c is brown orange yellow and if i need to swap any wires for rotation , switch the outside wires and the reason i dont know, i assumed keeping the b phase in the center for the systems with higher voltage. Here in a meter base if there is a high leg it has to be landed on c phase and from there i run c phase to b phase at the 1st service equipment.In austin b phase is purple to avoid the confusion of 277/480 being b o y and the requirement to mark hi leg as orange..

 

[kwired]

NEC says left or top bus is designated as A, center is B, and right or bottom is C.

Nowhere does NEC specify the rotation though.

Even if you have a "high leg" system you will know per NEC that the high leg should be landed on the B phase bus of equipment - but you still don't know if the POCO considers the high leg to be B or C as their metering generally requires the high leg to be in the C position of the metering. Also if it is an open delta system it can be derived from any two "phase" leads plus the neutral of the primary system - yet the secondary has three "phase" leads.

 

[don_resqcapt19]

...
Even if you have a "high leg" system you will know per NEC that the high leg should be landed on the B phase bus of equipment - but you still don't know if the POCO considers the high leg to be B or C as their metering generally requires the high leg to be in the C position of the metering. Also if it is an open delta system it can be derived from any two "phase" leads plus the neutral of the primary system - yet the secondary has three "phase" leads.

It is my understanding that even though the utility wants the high leg landed in the C phase position in the meter, it is B phase as far as rotation is concerned.

 

[iceworm]

Discussion limited to 3ph, 4W, Y

408.3.E.1 leaves me completely cold as to what exactly they want. I've asked two nationally recognized code experts and essentially got blank looks.

Them: "Well it means you put phase A on the left or top"
Me: "Which one is A? Don't say, 'the one on the left' "
T: Okay it is the one coming from the left transformer stud
M: And if the xfm studs are arranged in a triangular pattern?
T: Uhhh ....

M: Okay, are they implying CCW rotation? One might infer that ABC is left to right.
T: Absolutely not. Use any rotation you want.

So, there is no requirement which lead is A. There is no requirement for any specific rotaation.

Personal Opinion: The NEC is after consistency. Pick any one you want for A, B, and C. What ever you mark them at the first disconnect sets the rotation and is now the standard through the plant.

ice

 

[kwired]

Personal Opinion: The NEC is after consistency. Pick any one you want for A, B, and C. What ever you mark them at the first disconnect sets the rotation and is now the standard through the plant.

ice

My conclusion as well. You don't even get same rotation from one service to the next from most POCO around here on a new service - maybe if you specify rotation you can get what you want, or if they are replacing/upgrading existing they will make sure they replace with same rotation, but new service is a crapshoot - but with 50% odds.

 

[don_resqcapt19]

...
Personal Opinion: The NEC is after consistency. Pick any one you want for A, B, and C. What ever you mark them at the first disconnect sets the rotation and is now the standard through the plant.

ice

The code making panel agrees with you. blue = proposed new text

_______________________________________________________________
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

_______________________________________________________________

 

[iceworm]

The code making panel agrees with you. blue = proposed new text ...

Wow - a code panel that agrees with me. I wonder if the earth's magnetic field has swapped.

I don't recall when the requirement came into being - it was in the 1996 as 384.3.f. I'm pretty sure it was after 1980. I recall AB marketed back-to-back MCC that used a common bus. The rotation was flipped between the two sides. It was only available for a few years - during that time period. As I recall it went away when the NEC changed.

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.

I supose anything past that is a design consideration. All of my customers work at having the rotation consistent through the plant and keeping the phasing the same on the load side of each transformer. But that is design, not safety.

Still, I am mildly surprised the panel did not jump at a chance to add a design requirement.

ice

 

[meternerd]

As a POCO, we wire all of our service panels ABC CW. If the customer needs reverse rotation, he has to rewire his equipment. The exception is on older services where a rewire would be unreasonable. If we do wire it ABC CCW, we put a BIG sticker on the panel indicating it. Pretty rare, though. On a 3P 4W Delta meter panel, the "power" leg is usually located on the right hand phase (C phase), even though at the weather head it will be B phase. Don't know why the meter is wired with C phase as the "high leg", but it's not likely to change. Newer solid state meters don't care.

 

[electricalist]

Is there a chance that the power leg- hi leg is on c phase due to how older meters we built? Seems all the other mechanical connection s are created equal.