Panel Calculation 200A 480/3ph

[Rfoster66]

Good morning, I am an electrician at a WWTP. I have a 200A panel that is full, and it has been requested to add a 480V 45kw 54A water heater.

There is a power monitor unit (20A) that we plan to remove in order to make room for the water heater breaker. However reviewing the power meter, I see it keeps the highest KW value, this was 69.9kw. Using 220.87 I think found I found that adding the 45kw unit will be over loading the rated service.

Max load at 125% plus new load must not exceed the rating of the service (200A).

I would like confirmation on my calculations.

W/V+25%+new load Amps= full load amps

69900W/467=149.67 x 25% = 37.42

149.67A + 37.42= 187.09A

187.09A + 54A = 241.09A

41A over 200A rated main.

Thanks for all input.

 

[Rfoster66]

Panel

 

[electrofelon]

Looks like you forgot the 1.732 factor for you existing load. You should be fine.

 

[tortuga]

Yeah 69900 / (480 * 1.732) = 84.1 A presuming all the 480V loads are balanced, I also like to check the highest loaded leg.
Also is the new water heater single phase or 3 phase?

 

[wwhitney]

Also is the new water heater single phase or 3 phase?

"480V 45kw 54A" implies 3 phase, as 54*480*sqrt(3) = 44.9 kW.

Cheers, Wayne

 

[Rfoster66]

Yeah 69900 / (480 * 1.732) = 84.1 A presuming all the 480V loads are balanced, I also like to check the highest loaded leg.
Also is the new water heater single phase or 3 phase?

It is 3 ph.

 

[Rfoster66]

Looks like you forgot the 1.732 factor for you existing load. You should be fine.

Ok that’s what I wasn’t sure about since I had 69kw from the power meter. Thanks for the input.

 

[Rfoster66]

Yeah 69900 / (480 * 1.732) = 84.1 A presuming all the 480V loads are balanced, I also like to check the highest loaded leg.
Also is the new water heater single phase or 3 phase?

Thank you. They are all balanced. 3 ph water heater.

 

[Rfoster66]

Looks like you forgot the 1.732 factor for you existing load. You should be fine.

So full load amp is 86A + 25% to equal 125%

107A + 54A = 161Amps this makes more sense.

Thanks

 

[tortuga]

Yep for simple (balanced) calculations I keep all my numbers in 'VA' and then convert to amps at the end:

Existing Load​	69900​
25% Of existing Load​	17475​
New Load​	45000​
Total Load​	132375​
Amps = Total load / (480 * SQRT 3)​	159​