T 430.238

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jumper

jumper

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This is just a learning question, not an install.

How would you size the OCPD for a single phase 480V motor? It is not listed in T430.238, I suppose you could use the nameplate, but I thought you only used that for overload not SC/GF.
 
A 480V single-phase motor would most likely fall under 430.6 (A)(1) Exception No. 2. Use the nameplate FLC.
 
jumper said:
This is just a learning question, not an install.

How would you size the OCPD for a single phase 480V motor? It is not listed in T430.238, I suppose you could use the nameplate, but I thought you only used that for overload not SC/GF.
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Any motor not listed in 430 tables needs to use nameplate ratings for any calculation that would otherwise use values from those tables.

Run into non standard horsepower ratings quite frequently on things like blowers (somewhere between 7.5 and 10 or between 10 and 16 happen frequently with crop drying fans), and of course power tools.
 
cowboyjwc said:
Well it's a good thing those guys got in there before me, because I was gonna tell you to just take a WAG.:happyyes:
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It just popped into my head, all the 480V 1P motors I have worked on were condenser fans for RTUs and were part of a unit package, I just got curious on how to size it if if it was speced or part of the MCA of a unit.
 
I was looking for a code section to back up what I said and am not having much luck with finding anything that says what to do if the motor is not listed in the tables. Crop drying fans is one application I run into often. Seeing how these things are often wired from the manufacturer I doubt they are listed appliances, so that exception would not apply.

Closest things I could find were in 430.6. Other special purpose motors are mentioned but it says nothing about Hp ratings that are not in the tables. What else are you supposed to use besides nameplate is how I feel about it.

One could say use the next larger motor size in the chart - but there is no next size if the motor is larger than the largest one on the chart.

Smallest three phase motor on chart is 1/2 Hp. I have run into some smaller than that. Not a big deal on conductor sizing to use 1/2 hp values in this case, but FWIW it is not on the chart.

I do occasionally run into 480 volt single phase motors on irrigation equipment - there is no 480 volt colum in the chart for single phase motors.
 
jumper said:
It just popped into my head, all the 480V 1P motors I have worked on were condenser fans for RTUs and were part of a unit package, I just got curious on how to size it if if it was speced or part of the MCA of a unit.
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This just moved you into 440.6 and 7 depending on the actual application. It will generally (unfortunately, not always) be part of the MCA.
 
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