Calculating loads on 208Y120 panel with mixed 1ph & 3ph loads

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bryanbdp

Member
Location
Avon CT
Occupation
General Contractor
Hi. As part of my ongoing effort to rough out the electrical system at our space, I have recreated a panel schedule spreadsheet I saw in an older post.
Seems to work fine for 240 volt 1ph (2p) and 3ph (3p) loads.
Now I'm trying to figure out how to calculate a combination of 120v 1ph (L-N) loads and 208 3ph loads (L-L-L) and 208 1ph loads (L-L) and make the spreadsheet work.
What is throwing me a bit is with the 2 & 3 phase loads, I have divided the total load (circuit amps * voltage) by the number of poles to help balance the load on the panel.

example: 60A 3ph load = 60*208 = 12,480 VA divided by 3ph = 4160 per phase
Later, I add up all VA on each phase, and divide by 208x1.73 to get the total ampere load. (ignoring continuous calcs and reductions)

Now, when I start to add 120v loads, do I just put the entire load on the single phase for that circuit?
example: 15a 1ph load at 120v = 1800va = load on that phase?

If so, can I go ahead and just add up all the loads on each phase of my chart and divide by 208x1.73, or do I have to keep track of 208v and 120v loads separately, then divide by the 120v or 208x1.73 value?

I have attached a pdf file of what my panel schedule chart looks like, with some sample loads. I think the 208 1ph and 3ph loads calculate correctly.
I am not sure about the 120v loads... If they need to be tabulated separately, I have to figure out a way to automate that in the spreadsheet...

I'd be happy to share this spreadsheet with anyone that wants a copy once we get it to work correctly!
Thanks,
Bryan
 

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  • panel sched example 208Y120.pdf
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charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
I think you have the basic concept.
  • For a single phase, 120 volt load, put 120 times the current on the applicable phase.
  • For a single phase, 208 volt load, put 208 times the current, then divided by two, onto each of the two phases.
  • For a three phase, 208 volt load, put 208 times the current, then times 1.732, then divided by three, onto each of the three phases.
  • For each phase, add the total VA. See how well it balances. Adjust the circuit assignments, if needed.
  • The panel needs to be rated for a current that is equal to the total VA on all three phases divided by 208, and then divided by 1.732.
 

bryanbdp

Member
Location
Avon CT
Occupation
General Contractor
OK, thank you. The example I was looking at had only 1ph 2p loads. So I DO have to multiply the initial VA calculation by 1.73 for 3ph loads?
I don't think I have to change my worksheet, just remember to calculate the VA correctly before dividing.
My sample sheet is wrong then for the 3ph loads, since they are entered without the extra 1.73...
The 3 inputs should be 2639VA rather than 1525VA, correct?

But the 120v loads will calculate OK?

Thank you!
Bryan
 

kayjay

New User
Location
Colorado
Hi. As part of my ongoing effort to rough out the electrical system at our space, I have recreated a panel schedule spreadsheet I saw in an older post.
Seems to work fine for 240 volt 1ph (2p) and 3ph (3p) loads.
Now I'm trying to figure out how to calculate a combination of 120v 1ph (L-N) loads and 208 3ph loads (L-L-L) and 208 1ph loads (L-L) and make the spreadsheet work.
What is throwing me a bit is with the 2 & 3 phase loads, I have divided the total load (circuit amps * voltage) by the number of poles to help balance the load on the panel.

example: 60A 3ph load = 60*208 = 12,480 VA divided by 3ph = 4160 per phase
Later, I add up all VA on each phase, and divide by 208x1.73 to get the total ampere load. (ignoring continuous calcs and reductions)

Now, when I start to add 120v loads, do I just put the entire load on the single phase for that circuit?
example: 15a 1ph load at 120v = 1800va = load on that phase?

If so, can I go ahead and just add up all the loads on each phase of my chart and divide by 208x1.73, or do I have to keep track of 208v and 120v loads separately, then divide by the 120v or 208x1.73 value?

I have attached a pdf file of what my panel schedule chart looks like, with some sample loads. I think the 208 1ph and 3ph loads calculate correctly.
I am not sure about the 120v loads... If they need to be tabulated separately, I have to figure out a way to automate that in the spreadsheet...

I'd be happy to share this spreadsheet with anyone that wants a copy once we get it to work correctly!
Thanks,
Bryan

Hi Bryan, Did you finish your spreadsheet? I would like a copy if you wouldn't mind sharing, I could use it to double check my calculations on a panel. Ken
 
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