Phasing

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If you are referring to single phase loads, i.e. one hot plus neutral, no there is not a formula. It is probably best determined by use of a schedule whereby you can try to balance the load among phases as best as possible.
 
Divide the circuit number by 3.
  • If the remainder is 1, you are on phase A.
  • If the remainder is 2, you are on phase B.
  • If the remainder is 3, you are on phase C.

Example: Circuit #17.
  • 17 divided by 3 is 5, with a remainder of 2.
  • Therefore circuit 17 is on phase B.

If you are using a calculator to do the division, then a "remainder of 1" will show up as a series of threes after the decimal point, a "remainder of 2" will show up as a series of sixes after the decimal point,a "remainder of 0" will show up as a series of zeroes after the decimal point.
 
charlie b said:
Divide the circuit number by 3.
  • If the remainder is 1, you are on phase A.
  • If the remainder is 2, you are on phase B.
  • If the remainder is 3, you are on phase C.

Example: Circuit #17.
  • 17 divided by 3 is 5, with a remainder of 2.
  • Therefore circuit 17 is on phase B.

If you are using a calculator to do the division, then a "remainder of 1" will show up as a series of threes after the decimal point, a "remainder of 2" will show up as a series of sixes after the decimal point,a "remainder of 0" will show up as a series of zeroes after the decimal point.
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Charlie, #17 should be C phase.

Here is what I was taught.

Divide circuit number by 6.

If remainder is 1 or 2, A phase

If remainder is 3 or 4, B phase

If remainder is 5 or 0, C phase
 
Depends on how the panel is numbered (e.g. odd on one side) and whether it is numbered based on half-size breaker slots.
It is risky to blindly depend on any formula.

Tapatalk!
 
I don't do remainders well. :ashamed1:

I simply try to find the nearest multiple of 6 and figure out what phase I am on based on that.

For example, 73 is a phase down and left from 72, so it has to be A.

123 is two phases down from 120, so it must be B.
 
George Stolz said:
I don't do remainders well. :ashamed1:

I simply try to find the nearest multiple of 6 and figure out what phase I am on based on that.

For example, 73 is a phase down and left from 72, so it has to be A.

123 is two phases down from 120, so it must be B.
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But as GD noted, this assumes the circuits are numbered odd left, even right, and top down. I've been in enough panels to know this numbering schema is not always used. Then there's the bastards ones that use this schema, but a bottom fed panel with spaces not divisible by 6... such as a 40 space 3? panel, the top left breaker would be B?.
 
Smart $ said:
but a bottom fed panel with spaces not divisible by 6... such as a 40 space 3? panel, the top left breaker would be B?.
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I guess the installer should not bottom feed that panel type.

408.3 Support and Arrangement of Busbars and Conductors.

(E) Phase Arrangement. The phase arrangement 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 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 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.
Click to expand...
 
It is uncommon enough to be ignored. When someone does not know a standard procedure for determining phasing in a conventional panel, I see no benefit to confusing the fundamentals with uncommon gear. JMO.

The first step is to learn to quickly ascertain phasing on a conventional system, which after much practice with conventional panels can be adapted when oddball gear is occasioned upon.

The end result of introducing "it could be anything" is learning nothing.
 
George Stolz said:
It is uncommon enough to be ignored. When someone does not know a standard procedure for determining phasing in a conventional panel, I see no benefit to confusing the fundamentals with uncommon gear. JMO.

The first step is to learn to quickly ascertain phasing on a conventional system, which after much practice with conventional panels can be adapted when oddball gear is occasioned upon.

The end result of introducing "it could be anything" is learning nothing.
Click to expand...
You can approach teaching and learning from whatever perspective you deem is correct.
 
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