208v 3 Phase Disconnect Sizing

[JDye]

Hello everybody and first off thank you for all the information that I've gathered over years as just a guest on the forums.

But to my main question. We are trying to calculate a service disconnect on a 3 Phase 208y/120. We are hooking up many appliances that are single phase loads. Our total appliance draw is 320,000 Watts. We need to know how to size the service disconnect and fuses.

Thank you all in advance.

 

[augie47]

In it's simplest ohm's law calculation it would be 888 amps (320,000/208X1.732).
Depending on the nature of the load (% continuous, size of motors) and how well you can balance the single phase loads, the next standard size fuse, 1000 amps, would likely be sufficient. (The next standard size switch would be a 1200 amp if you wanted more room for growth, also multiple disconnects might be a $$ advantage)
Can you expand on the loads.. largest motor, etc.

 

[infinity]

How did you come up with the calculated load was it per Article 220?

Welcome to the Forum.

 

[JDye]

Thank you for the fast response.

There are 200 units rated at 1600 watts continuous. With no start/stop applications.

 

[augie47]

Be easy to balance at least

 

[augie47]

(5) 200 amp 84 circuit panelboards.

 

[JDye]

I do apologize. I wasn't clear on the original question. Each unit pulls 1600 Watts and will be supplied 208v single phase double pole breaker.

 

[petersonra]

(5) 200 amp 84 circuit panelboards.

makes sense to me

 

[electrofelon]

. We need to know how to size the service disconnect and fuses.

Thank you all in advance.

(5) 200 amp 84 circuit panelboards.

What might work out economically is a 1000 amp MLO service rated panelboard containing 5 200 amp service disconnects serving those 5 panelboards.

 

[kwired]

Thank you for the fast response.

There are 200 units rated at 1600 watts continuous. With no start/stop applications.

Not even thermostatically controlled starting/stopping? IOW all 200 units always draw 1600 watts each at all times?

If so then your conductors and overcurrent protection also needs to be 125% of the load. If demand factors are allowed then you can reduce things.

More details are needed before one can go with less than 125% of what is described as a continuous load.