Single Phase Commercial Load Calculations

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admiralporklung

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Hello, and thanks in advance for your help.

I am a Master and am working up a sketch for permit to add an X-Ray at a small Vet Clinic. The service is single phase 120/240V with a 200A Panel.

There have been multiple do-it-yourselfers in the panel, and none of the work has been inspected.

The existing panel load calculation, per art. 220 is minimal, roughly 31.9 kVA.

I want to add a 100a 2pole breaker for the x-ray machine. There is no kVA rating on the X-ray specs, I just need to provide 100a feeder to a disconnect line, from which the vendor will hook up the machine.

Do I just do 100a X 240v=24kVA and add this to 31.9kVA?

How do I find my total connected amps?

Is there enough ampacity for this load?



In a three phase scenario I would find kVA per phase, divide by 120V to find the amperage per phase, then, I would average the three phases for my connected Amps.

I am very confused. PLEASE HELP ME!!!
 
Your answer lies in 220.87. You can either use a year's worth of utility bills (if they show peak demand per month, and not just the total KWH consumed) or install a meter that reads the peak demand every 15 minutes for a month. That will give you the existing load. To that value you add 25% (for conservatism), and then add your new load. If you are within the capacity of the service and the panel in question, you can do the install.

By the way, I would never do any of the math in units of amps. Convert everything to VA (or KVA), do the addition, and convert back to amps as the very last step.
 
The MFG will usually provide requirements for the machine. These requirements are more that the NEC would require. NEC 517 may provide information. There should be a name plate on the machine to give you additional information. You need to know that the Xray operates in milli seconds and does not really load the service. But the MFG requirements are what you need to address.
 
The nameplate really gives no information.

Just for kicks, what needs to be done to add any 100A load, such as a mechanical load? I am confused what the math is.

I am in a bit of a rush, as always on this little project.
 
just like bob said, since the xray peak demand is momentary, the code allows you to use 50% of the peak demand for your calculations. getting that number from the manufacturer can be easy, or not. If the doctor is buying thru a distributor, they can be very insular with that information. They're kind of hoggy like that.
 
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