A/C Variations

[gaoneal02]

The argument of how to represent watts or amps on a panel schedule has heated up. On a 2-pole breaker that powers up a total of 25 amps, even though current has variations across the poles, on the panel schedules I have only know it to show the 25A divided across the 2 poles on the panel schedule, so each pole would show 12.5 amps, as opposed to showing 25A on each pole. What is the max allowed variations of amps from pole to pole?

 

[mivey]

The argument of how to represent watts or amps on a panel schedule has heated up. On a 2-pole breaker that powers up a total of 25 amps, even though current has variations across the poles, on the panel schedules I have only know it to show the 25A divided across the 2 poles on the panel schedule, so each pole would show 12.5 amps, as opposed to showing 25A on each pole. What is the max allowed variations of amps from pole to pole?

Can you please provide an example of the loads and panel schedule you are talking about?

You can load each pole up to its rating however it is generally good practice to balance the loads.

 

[gaoneal02]

Can you please provide an example of the loads and panel schedule you are talking about?

You can load each pole up to its rating however it is generally good practice to balance the loads.

For example, the attached panel schedule shows 25A across circuits 19 & 21 but the total amp is 25A, I have only known to put 12.5 on each circuit for not only a balanced load, but for the total load which is actually 25A total for circuits 19 & 21, not 50A

 

[just the cowboy]

current in current out

current in current out

For example, the attached panel schedule shows 25A across circuits 19 & 21 but the total amp is 25A, I have only known to put 12.5 on each circuit for not only a balanced load, but for the total load which is actually 25A total for circuits 19 & 21, not 50A

If cir 19 has 25a out, cir 21 has 25a back. You are useing these numbers to total amps per phase in the bottom so total load per phase is 25a that gets added to each phase.

 

[gaoneal02]

but Circuit 19 & 21 are using only a total of 25a, so this should be split across the two circuits 19 L would have 1.5A and circuit 21 L2 will have 12.5a, o when you total them together, they= the 25A of total consumption?

 

[gadfly56]

It looks like the heaters are set up as 277 volt MWBC's. Do I understand correctly?

 

[gaoneal02]

480V

 

[mivey]

For example, the attached panel schedule shows 25A across circuits 19 & 21 but the total amp is 25A, I have only known to put 12.5 on each circuit for not only a balanced load, but for the total load which is actually 25A total for circuits 19 & 21, not 50A

I wonder if in the past you have seen a panel schedule with VA instead of just A. With a 2-pole load, you would split the load's total VA across the poles.

We do not do it the same way with amps. A balanced load's amps is the same for all of the poles it uses.

 

[mivey]

but Circuit 19 & 21 are using only a total of 25a, so this should be split across the two circuits 19 L would have 1.5A and circuit 21 L2 will have 12.5a, o when you total them together, they= the 25A of total consumption?

Double-check the loads and make sure that is the case.

For example:

A single-phase 480 volt 20 amp load would have 20 amps on both poles.

A three-phase 480 volt 20 amp load would have 20 amps on three poles.

A 277 volt 20 amp load would have 20 amps on one pole and 20 amps returning on the neutral. Put two of these loads on separate poles and you have 20 amps on both poles and 20 amps on the neutral. Its a vector thing, don't sweat it but if you want consider why the two 277 volt legs do not sum to 554 volts.

Put three of these loads on separate poles and you have 20 amps on three poles and 0 amps on the neutral. Again a vector thing but now it looks the same as one 20-amp 480 volt 3-phase load. For this case, the current that goes out on one pole returns on the other two (they are continuously rotating these duties to different degrees).

Its a little different for 240/120 but let me know if you want to hear that story also.

 

[gaoneal02]

Well, I am not agreeing with this panel schedule they have at all. I am used to seeing it in VA as well. This particular panel schedule in the way they set it up is only useful to see the description of a load on circuit. The calculation part is all screwed up. #1. the actual schedule calculates in amps, then the little summary box calculates in watts.

 

[Smart $]

... then the little summary box calculates in watts.

...and that little summary box is in error, not only in that it uses watts instead of VA, the value is calculated from the sum of odd and even line totals then multiplied by 480V. Where line amps are used, the total VA is calculated by multiplying the sum by the line-to-neutral voltage (actual for wye system or virtual for delta).