Distribution panel sizing

[ElliotM]

Hi,

In advance, thank you for your help.

In the plant I currently have 1200A, 600V, 3P, 4W main panel. I would like to place a distribution panel which would feed a # of outlets which are estimated to draw 116 AMPs total at 120V, split between 12 breakers (3x15amp and 5x20amp)

116AMP is 80% FLA (planning for future) -> resulting in 145 AMP. I don't know the actual draw, but assumed maximum allowed on each breaker -> 12AMP * 1.25 = 15AMP, 16AMP *1.25 = 20AMP.

What size of a panel do I need for 120/208 Wye, 3PH ? If I load the phases, I get 55A, 35A, 35A (distributing buckets as evenly as possible) -> does that mean I should be looking at 100AMP panel ? OR 145AMP total would push me to 200AMP panel.

This is where I get confused with the 3 phase vs single phase and panel requirements.

Once, settled, the question than becomes, do I need a 45KVA transformer --> 45000/120/1.732 = 216 or 30KVA would be sufficient ? Main goal is to understand the logic and some math behind the selection.

 

[JoeStillman]

Welcome to the forum Elliot.

What is the electrical code where you work? I wouldn't want to give you an answer based on the NEC if that doesn't apply.

 

[ElliotM]

Welcome to the forum Elliot.

What is the electrical code where you work? I wouldn't want to give you an answer based on the NEC if that doesn't apply.

Hi Joe,

Since I live in Canada, Ontario. I am working with Ontario Building Code, but they are quite similar, but please don't reference NEC, since I don't have access to the CODE itself.

 

[augie47]

Canadian or US wattage is wattage
You have your estimated load of 116 amps @ 120v.
You probably would do well to look at everything in terms of kw and not worry that much about "amps" as you are going to be distributing over a 3 phase network.
You load is only 14 kw so with a 30kw transformer you will have twice the "needed" capacity.

(as a side note since you are working at a plant.. your situation may be different but when I first started installing "plant" work I learned real quick that 1 month after I installed a 100 amp panel, it was too small . They normally don't "pick" at price and you might be doing them a favor by installing a 45kva)

 

[kwired]

How many of your loads will not run simultaneously? In food processing plant for example, you might have loads that run while processing, but different loads that will run during cleaning operations, but never all of them at one time - pick the largest load that will run at any given time for feeder and service type calculations.

How many will run simultaneously?

How many have a "duty cycle" or other characteristic that makes them not run continuously and possibly can be considered at a lower demand rate?

 

[kingpb]

In the plant I currently have 1200A, 600V, 3P, 4W main panel. I would like to place a distribution panel which would feed a # of outlets which are estimated to draw 116 AMPs total at 120V, split between 12 breakers (3x15amp and 5x20amp)

As a rule, it is best to work in kW/KVA and then calculate amps. Causes less confusion in designing of system.:thumbsup: