sizing feeder for sub-panel at commercial laundry

[Cleveland Apprentice]

Thanks for taking the time to read this. I am stumped on this and may be obvious to others on this forum. I do not conduct a lot of load calculations and a little rusty. My math is not the best as well. If I am missing something from my calculations, please let me know. I checked sections 220, 430, and Annex D and I am still kind of lost.

I am installing a Square D, 3 phase S/P fed by a 240/120 volt 3 phase Delta service. This is a commercial laundry shop so my understanding is that everything is calculated at 100% demand. The new circuitry added is as follows:

1. Two 3 phase, 240 volt commercial washers with FLA of 22.5 amps. The minimum size CB per specs is 40 amp per unit on these units. My calculation for this is: 22.5 amps x 240 x 1.73 = 9,342 VA; There are total of two washers connected to this S/P, so total VA on this will be 18,684.

2. One single phase, residential dryer (not sure why he wants a residential dryer). This is 5,000 VA I believe. (Also I realize this must be wired to A and C phase, as the motor is 120 volts to ground).

3. One 3 phase, 240 volt gas dryer. FLA 6 amps x 240 x 1.73 = 2,491 VA.

Total VA among the 4 appliances is 26,175 VA/240 = 109 amps. So feeder protected by 110 amp 3 pole CB?

These are non-continous loads so I don't need to multiply by 1.25. I feel that I am missing something and if someone could guide me to the right code section, it would be greatly appreciated.

Thank you and Happy Easter!

 

[augie47]

You need to calculate your 3 phase loads using 240 X 1.732

 

[shortcircuit1]

Thanks for taking the time to read this. I am stumped on this and may be obvious to others on this forum. I do not conduct a lot of load calculations and a little rusty. My math is not the best as well. If I am missing something from my calculations, please let me know. I checked sections 220, 430, and Annex D and I am still kind of lost.

I am installing a Square D, 3 phase S/P fed by a 240/120 volt 3 phase Delta service. This is a commercial laundry shop so my understanding is that everything is calculated at 100% demand. The new circuitry added is as follows:

1. Two 3 phase, 240 volt commercial washers with FLA of 22.5 amps. The minimum size CB per specs is 40 amp per unit on these units. My calculation for this is: 22.5 amps x 240 x 1.73 = 9,342 VA; There are total of two washers connected to this S/P, so total VA on this will be 18,684.

2. One single phase, residential dryer (not sure why he wants a residential dryer). This is 5,000 VA I believe. (Also I realize this must be wired to A and C phase, as the motor is 120 volts to ground).

3. One 3 phase, 240 volt gas dryer. FLA 6 amps x 240 x 1.73 = 2,491 VA.

Total VA among the 4 appliances is 26,175 VA/240 = 109 amps. So feeder protected by 110 amp 3 pole CB?

These are non-continous loads so I don't need to multiply by 1.25. I feel that I am missing something and if someone could guide me to the right code section, it would be greatly appreciated.

Thank you and Happy Easter!

Couple of questions
1.I am assuming this is a 240/120v high leg delta..? If so then your single phase dryer is 240v you can connect it between A and C but you are saying the motor is 120v to ground...If it is 120v to ground then you should connect between A and neutral or C and neutral...
2.For the total VA among 4 appliances you cant just total VA/240 cause loads are combination of 3 phase and single phase..You can simply use the amps you have and add them up...

 

[JFletcher]

Thanks for taking the time to read this. I am stumped on this and may be obvious to others on this forum. I do not conduct a lot of load calculations and a little rusty. My math is not the best as well. If I am missing something from my calculations, please let me know. I checked sections 220, 430, and Annex D and I am still kind of lost.

I am installing a Square D, 3 phase S/P fed by a 240/120 volt 3 phase Delta service. This is a commercial laundry shop so my understanding is that everything is calculated at 100% demand. The new circuitry added is as follows:

1. Two 3 phase, 240 volt commercial washers with FLA of 22.5 amps. The minimum size CB per specs is 40 amp per unit on these units. My calculation for this is: 22.5 amps x 240 x 1.73 = 9,342 VA; There are total of two washers connected to this S/P, so total VA on this will be 18,684.

2. One single phase, residential dryer (not sure why he wants a residential dryer). This is 5,000 VA I believe. (Also I realize this must be wired to A and C phase, as the motor is 120 volts to ground).

3. One 3 phase, 240 volt gas dryer. FLA 6 amps x 240 x 1.73 = 2,491 VA.

Total VA among the 4 appliances is 26,175 VA/240 = 109 amps. So feeder protected by 110 amp 3 pole CB?

These are non-continous loads so I don't need to multiply by 1.25. I feel that I am missing something and if someone could guide me to the right code section, it would be greatly appreciated.

Thank you and Happy Easter!

You are forgetting to divide by 1.732. Work the math backward (check the answer).

You have 2 3ph washers @ 22.5A ea (45 total),
a 3ph gas dryer @ 6A,
now you're at 51A.
51A x 240V x 1.732 = 21,200VA,
+ 5000VA for the 1ph 240V dryer =
26,200VA

Your 240V 5000VA dryer isnt pulling 58A, more like 25A on A and C leg. 76A, 51A, and 76A on A, B, C phases.

Any chance of HVAC, exhaust fans, or a linen press being installed as well?