Cross Phasing between Panels

[Do You Like Ham]

Hi... does the NEC permit panel phases to be cross connected.. what I mean is Panel has three phase busses: Phase A, B, C... typically Phase A on the left, B in the middle, and C on the right. Say Panel A is connected in this way, but then feeds Panel B and lands the Phase A conductor on the middle bus, then Phase B conductor on the right bus, and phase C on the left bus. Is that, or any such variation allowed? If allowed, have you ever come across it in practice? What would the reason for doing so be?

 

[MAC702]

... What would the reason for doing so be?

Every motor coming from one subpanel needed to be rotation reversed.

 

[ptonsparky]

Back before marking tape was invented conductors weren’t always landed in a particular order. It didn’t mean much when it was mostly lighting and GP receptacles. The occasional motor was hit and miss for direction.

 

[roger]

See 408.3(E)

Roger

 

[Do You Like Ham]

See 408.3(E)

Roger

Thanks, Roger.. 408.3(3) (sorry, I'm not a practicing EE... just a software guy... and my book may be dated - 2005).. just says the other arrangements may be permitted and marked.. it gives an exception for meter equipment... but it doesn't really say if one could somewhat arbitrarily mix and match the phasing.

the section says "other busbar arrangements shall be permitted for additions to existing installations and shall be marked"... I'd interpret that if a system is phased, say BAC, that additions would follow suit.... would you interpret this to allow (for some reason) someone to connect from an BAC panel to something downstream as ABC?

 

[roger]

the section says "other busbar arrangements shall be permitted for additions to existing installations and shall be marked"... I'd interpret that if a system is phased, say BAC, that additions would follow suit.... would you interpret this to allow (for some reason) someone to connect from an BAC panel to something downstream as ABC?

In an existing installation I would ignore new code mandates, with that said I would not consider changing phase arrangements from different panels or switchboards within a facility a safe or acceptable practice.

Roger

 

[hillbilly1]

One place you cannot do it, at least with “B” phase is with a delta system with a high leg. High leg is a required to be the center or “B” phase (except at the meter, where it is on “C” phase for proper meter operation)

 

[jim dungar]

High leg is a required to be the center or “B” phase ...

Again, this is only for relatively new installations. Facilities built decades ago may not have had this requirement. They used to just need to be marked with a specific color, which is why they may still be referred to as 'red-leg' systems.

 

[kwired]

Again, this is only for relatively new installations. Facilities built decades ago may not have had this requirement. They used to just need to be marked with a specific color, which is why they may still be referred to as 'red-leg' systems.

And I believe if the existing system has high leg on the C bus, you are still permitted to use the C bus as the high leg on any new feeders you would add, might create more dangers to try to change that on just limited portions of an existing install.

 

[kwired]

All 408.3(E) tells us is that ABC within a particular panel is a reference for bus from front to back, left to right, or top to bottom in any particular panelboard. Other than the high leg requirements it doesn't tell us which supply conductor must connect to each bus. There is no A,B or C in the supply until you designate it. There is phase rotation to the supply. NEC does not designate any particular rotation arrangement for buses either.

Now if you have more than one voltage system on the premises and need to apply 210.5(C)(1) and/or 215.12(C)(1) you are likely going to carry same conductor identification to each panel, I don't know that any wording specifically requires bus A in panel 2 to have same conductor landed on it as bus A in panel 1 though. Most people are probably going to keep them the same however.