wirenuts11
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How do I calculate the necessary size for a three phase main breaker where there will be single phase loads as well as three phase loads?
Three Phase Main Breaker Sizing
- Thread starter wirenuts11
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That's certainly a "loaded" question... :wink:
Unfortunately there is no easy answer. Going by NEC requirements, the sizing will differ according to the type of occupancy and the type or types of loads.
Suggest you first become familiar with Article 220 ? Branch Circuit, Feeder, and Service Calculations and attempt to understand the methodology used in the Annex D examples. A good start is to list and convert all loads to KVA. However, I should note the results of calculation by the NEC will be the minimum size required... so there is no restriction to sizing the components larger than required [AFAIK].
We can better assist you with more detailed information.
Unfortunately there is no easy answer. Going by NEC requirements, the sizing will differ according to the type of occupancy and the type or types of loads.
Suggest you first become familiar with Article 220 ? Branch Circuit, Feeder, and Service Calculations and attempt to understand the methodology used in the Annex D examples. A good start is to list and convert all loads to KVA. However, I should note the results of calculation by the NEC will be the minimum size required... so there is no restriction to sizing the components larger than required [AFAIK].
We can better assist you with more detailed information.
- Location
- Lockport, IL
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- Retired Electrical Engineer
The "short answer" is that you convert all of your load information into units of VA, add up all the VA, and then convert to amps. So long as you make a reasonable attempt to balance the loading among the three phases, it will not matter that some loads are single phase and others are three phase.
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