Wire Question.

[eddie1278]

The NEC does not permit using nameplate data for supply conductors.

You use 430.248

 

[Kevin C]

I'm a little lost on what you're saying about the motor plate saying 15A vs the specs saying to run it on a minimum 15A circuit. The two don't jive. If the motor plates says 15A then it needs to be on a 20A circuit. 15A X 1.25 = 18.75A so 20A circuit.

Edit: I'd use the motor plate amps. The HP rating is most likely baloney.

No they dont jive... I was surprised to see the recommendation. I will post a screen shot of the manual.

Past that... Would I be required to use the NEC method for my 3 hp motor (It's stamped, 3 HP, 15 amps manf by DOER).

That would say that I should rate for: 17 amps (per the NEC Table) * 1.25 = 21 amps.

 

[G_P]

The NEC does not permit using nameplate data for supply conductors.

You use 430.248

I can get that. I have a vacuum that is labeled 17amps yet it runs fine on a 20a circuit with a large stereo system on it as well without tripping the breaker.
I assume some manufacturers label motors with the max amps if the motor stalls to make them sound more powerful.

Sent from my C5120 using Tapatalk 2

 

[pattenp]

As eddie1278 pointed out to be NEC compliant you need to size it as 3HP @ 17A. Since the motor data plate has 3hp on it that's what you should go by. If the data plate only listed the amps then the amps is what you'd use. I was thinking the 3hp was just the advertised hp printed on the compressor.

 

[Aceman]

As eddie1278 pointed out to be NEC compliant you need to size it as 3HP @ 17A. Since the motor data plate has 3hp on it that's what you should go by. If the data plate only listed the amps then the amps is what you'd use. I was thinking the 3hp was just the advertised hp printed on the compressor.

You got it mostly right. Read 430.6(A)1 starting about halfway down. If a motor is marked only in amperes, you are basically supposed to make a "best guess" on the motor horsepower and then select the ampacity from the motor tables.

 

[pattenp]

I see what you're saying. The ending of the sentence says to interpolate if necessary. Interpolation is a method of constructing new data points within the range of a discrete set of known data points. So 15A would be a little over 2 1/2 HP. So what's the point of interpolating? 2 1/2hp just brings you back to 15A. So I assume you are just to take the next highest value on the table which is 3hp. I never thought of it as a best guess when it says to interpolate. Oh well.. I guess I'm over interpolating this.

You got it mostly right. Read 430.6(A)1 starting about halfway down. If a motor is marked only in amperes, you are basically supposed to make a "best guess" on the motor horsepower and then select the ampacity from the motor tables.

 

[wyliesdiesels]

Ok for the armchair ec's

start at
334.80 then go to 310.16


I never stated a code section just the ampacity table 310.16. Type NM #12 in the 60 degree column has an ampacity of 25 amps. End of discussion.

By the way I'm on the 2008 code in PA

So i did a little more investigating and it turns out that pattenp, aceman, and I, as well as others were right! If the OP uses Southwire brand 12/2 NM, aka Romex, then you are wrong about the 25a ampacity rating. This would violate Southwire's instructions and U/L listing which states to base the ampacity rating of 12/2 Romex off the 60c deg column in the 2011 NEC, table 310.15, WHICH IS 20 AMPS!

So it looks like u need to get yourself a new code book....that is...if u care about code!....which u supposedly do based on your previous comments!

And just for reference, in case u still don't agree, u can read Southwire's own pdf data sheet on Romex:

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet6