Heat load calculation HELP.

[kiss]

Can enyone help with this please.
I need to install additional capacity to feed 120 electric heating units rated
208Volts 1Phase 16.0Amps each
all units will run at the same time for more than 3 hours
Service available is 3phase 4wire 120/208volts
If you can help me calculate the additional service needed, and how you got it it will be appreciated.

 

[Mr. Bill]

208V * 16A = 399.36kVA

399kVA / 3 / 120V = 1109A at 3-phase if balanced.

Just because they're on all the time doesn't mean they'll run for more than 3 hours. Kiln manufacturers get around the continuous load requirements because the heating element is cycled on and off to maintain the set temperature. Think of your electric oven at home. It is likely that these electric heaters would not be continouos loads. But if they really are.

1109A / 0.8 = 1386.7A

On the plus side you won't have any harmonics.

 

[kiss]

Thanks for the reply. When I did the math I came up with a 1111 amps at 3phase, and I thought I did something wrong. Thanks

 

[bob]

It is likely that these electric heaters would not be continouos loads. But if they really are.

1109A / 0.8 = 1386.7A

On the plus side you won't have any harmonics.

If it truely electric strip heating, the pf is likey = 1.0.

 

[infinity]

If it truely electric strip heating, the pf is likey = 1.0.

Sounds like he was calculating this for a hypothetical continuous load, hence the .8 multiplier.