kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
rattus said:
Ah, a real world simplified approach, and look Ma, no phase angles!!!
Single Phase Load Calculations on Three Phase system
- Thread starter jbwhite
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Ah, a real world simplified approach, and look Ma, no phase angles!!!
Wow five pages... lol
I thought I was asking a simple question for engineers.
I do appreciate eveyone for helping me out.
Someone hit the nail on the head when they said that we electricians think in amps not VA or KVA. We get confused easy when we need to start doing calcs on 3 phase stuff. I for one have a major stumbling block when someone mentions vectors. It is as if they have started speaking klingon.
This is just a way for me to get a rough but safe guess. In my real job we would have something like this given to us from an engineering firm.
Thanks again to everyone for your help.
I thought I was asking a simple question for engineers.
I do appreciate eveyone for helping me out.
Someone hit the nail on the head when they said that we electricians think in amps not VA or KVA. We get confused easy when we need to start doing calcs on 3 phase stuff. I for one have a major stumbling block when someone mentions vectors. It is as if they have started speaking klingon.
This is just a way for me to get a rough but safe guess. In my real job we would have something like this given to us from an engineering firm.
Thanks again to everyone for your help.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
jbwhite said:
Lingosh Lama Bavok!
Hey guys I ran into a similar issue today at an Apartment complex. 100 amp single phase MB panels for each unit. Three units being fed by one 100 amp three phase breaker at switch gear. I was asked to complete load calculation on the units. I came up with 12.5 KVA per unit. Now by using the formula:
12,500 x 3 = 37,500 KVA / 208V x 1.73 = 104 amps. By this calculation the main breaker is undersized for this load. Am I missing something?
12,500 x 3 = 37,500 KVA / 208V x 1.73 = 104 amps. By this calculation the main breaker is undersized for this load. Am I missing something?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
johnpm said:
It is hard to know if you arrived at the 12.5KVA/ unit correctly. Could Art. 220.84 come into play.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
12.5 Kva should be just above 50a.
morepower
morepower
This is a pretty neat question. Please, allow me to throw my two cents worth in. I'm attaching a spreadsheat (or trying to) that I developed for use in my classes, and so far it has not failed me. I use it for sizing panels, but is just as useful here. I've used 208v instead of the 240v presented because the only time I have run into 240v three phase has been on a high leg delta system, and that would change my calcs tremendously. I have also not accounted for continous duty either.Ed
morepower
This is a pretty neat question. Please, allow me to throw my two cents worth in. I'm attaching a spreadsheat (or trying to) that I developed for use in my classes, and so far it has not failed me. I use it for sizing panels, but is just as useful here. I've used 208v instead of the 240v presented because the only time I have run into 240v three phase has been on a high leg delta system, and that would change my calcs tremendously. I have also not accounted for continous duty either.Ed
The forum does not permit the attachment of spreadsheet file formats.morepower said:
Perhaps you can upload it to a file sharing site such as QuickSharing.com, then post the url here.
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