# Load calculation



## Morg12345 (Jan 22, 2016)

Goodmorning
Putting in a new 3 phase 480 V/277 service service having to figure out a load for The service
I have 277 volt lighting...277 volts heat pumps ect... Figuring the load with the 3 phase isn't a problem Wattage/480×1.73=amps
My question is what about the 120/240 V stuff that's coming off the dry Transformers....480 prim...240 secondary.......is this figured 480 volt 3 phase also..with secondary wattage??
Thanks a little confused...morg


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## backstay (Feb 3, 2011)

Wattage divided by volts divided by 1.73


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## SWDweller (Dec 9, 2020)

Use the primary wattage on your transformers. If you have more than one transformer move the primary's from A-B to B-C and so on. 

277 volt heat pumps? You have 3 phase why not use it.
Over 1000 amps you need ground fault


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## HertzHound (Jan 22, 2019)

> is this figured 480 volt 3 phase also..with secondary wattage??


wattage of the primary is equal to wattage of the secondary. A 75KVA transformer is 75 KVA on the primary and 75KVA on the secondary. What changes is the voltage and amps on the primary and secondary.


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