Feeder calc for dummies.

[darekelec]

Hello everyone.
I did not go thru a course of commercial calculations yet so I would like to ask a simple for you question.
Can somebody explain like to a 10 year old boy )) how to size a feeder in commercial kitchen?
Actually I would like to max out a 100 Amp 3 phase + neutral feeder (3 awg preferably) 100' long for a breaker box.
I would like to connect
9 pcs remote refrigeration compressors @ 15A 120V (sorry I don't have better info on name plate... and 'they just want 20A breaker')
1 pcs split system air conditioning compressor @ 208V single phase 16A MCA
2 pcs 3 phase split system air conditioning compressors @ 208V 3 phase 21A MCA

If you gave me formula that would be the best because I can supply some of the equipment from different panel.
Thank you very much and let me tell you guys you are the best professionals in the country.

 

[charlie b]

Do all the work in units of VA, not in units of amps. Take the single phase 120 volt loads, multiply the current times 120 volts, and set that number aside. Take the single phase 208 volt loads, multiply the current times 208 volts, and set that number aside. Finally, take the three phase 208 volt loads, multiply the current times 208 volts and multiply the result by 1.732 (i.e., the square root of 3). Now add the three answers to get a total VA. Divide that result by 208 volts, and divide the result by 1.732, and you will have the total amps that will be supplied by the panel.

 

[kwired]

Hello everyone.
I did not go thru a course of commercial calculations yet so I would like to ask a simple for you question.
Can somebody explain like to a 10 year old boy )) how to size a feeder in commercial kitchen?
Actually I would like to max out a 100 Amp 3 phase + neutral feeder (3 awg preferably) 100' long for a breaker box.
I would like to connect
9 pcs remote refrigeration compressors @ 15A 120V (sorry I don't have better info on name plate... and 'they just want 20A breaker')
1 pcs split system air conditioning compressor @ 208V single phase 16A MCA
2 pcs 3 phase split system air conditioning compressors @ 208V 3 phase 21A MCA

If you gave me formula that would be the best because I can supply some of the equipment from different panel.
Thank you very much and let me tell you guys you are the best professionals in the country.

You need to get actual rated loads if you want more accuracy. Those 9 15 amp units could be 8 amps could be 14, starts to add up after 9 of them. MCA is for sizing conductors and is not the actual load either. It should be 125% of the largest motor (probably the compressor) plus other loads on that unit, reducing that MCA to 80% should get you pretty close to actual full load if there is minimal aux load.

Using those values will not leave you undersized, but will leave you short of what you possibly could run.