I'm doing a loose look at a temporary service in which I have a 150 Kva and a 300 Kva XFMR both 480V feeds. I need to put the circuits in a panel schedule but not sure how much Kw to carry for them. The amps off the chart seem high.
Calculating the Kw of a XFMR for a panel schedule.
- Thread starter Hale5761
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JoeStillman
Senior Member
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- Electrical PE
What will the transformers feed? If it's only temporary service, just use the loads that are on the transformers. For permanent installations, I always try to allow upstream capacity for the transformers to be loaded all the way up in the future.
They both feed panels. The 300 Kva XFMR has a load of just under 500 amps, and the 150 has a 200-amp load. Also consider I was very conservative on my loads. For example, construction trailers with a 70-amp panel I allotted 33 amps, I know that's probably twice what I need. What I did was take the load of each panel, add 25% and carry that back as my XFMR load.
ggunn
PE (Electrical), NABCEP certified
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150kVA is ~180A @ 480/277V; 300kVA is about 360A.
Spot on.
petersonra
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I have no idea where you came up with your numbers but I kind of agree that the NEC load calculations are very conservative so for a temporary service I would not be opposed to something more realistic.
Since you did not say I am guessing that the transformers are 480 V primary and 208-120 secondary.
A construction trailer allotted 33 A at 208 V 3 phase is 12 kW which seems more than adequate to run an electric heater or A/C, a coffee pot, and some lights and receptacles. Maybe not suitable for the three EVs they plan to charge up from it though.
Since you did not say I am guessing that the transformers are 480 V primary and 208-120 secondary.
A construction trailer allotted 33 A at 208 V 3 phase is 12 kW which seems more than adequate to run an electric heater or A/C, a coffee pot, and some lights and receptacles. Maybe not suitable for the three EVs they plan to charge up from it though.
ggunn
PE (Electrical), NABCEP certified
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- Austin, TX, USA
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- Consulting Electrical Engineer - Photovoltaic Systems
I was thinking he meant MV to 480/277V.
petersonra
Senior Member
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- Semi-retired engineer
Why would you run 480 to a construction trailer?
I mean, it's a really nice construction trailer though.
ggunn
PE (Electrical), NABCEP certified
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- Austin, TX, USA
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- Consulting Electrical Engineer - Photovoltaic Systems
I have no idea, but 300kVA and 150kVA at 208/120V is about 1250A total; that seems like a lot of current for a construction trailer. But I don't work in construction, so I dunno about that, either.
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