Mike Holt Master/Contractor Simulated Exam, part 3, question 15, pg 18 -2008 NEC

[Finite10]

This question is regarding the Calculations section of Mike's book;
What is the code reference that tells me to use the nameplate rating FLA, and not the NEC Table 430.248 FLC?

The answer key says to use the nameplate FLA, not FLC.

I've dug around and can't find it. Confused, please help.

 

[Finite10]

(too late to edit so I'll add this post)

(too late to edit so I'll add this post)

This isn't stated in the question but is the only thing I can come up with to use nameplate rating;

" For a listed motor-operated appliance, use the FLC marked on the nameplate of the appliance (rather than the horsepower rating) to determine the ampacity (or rating) of the disconnecting means, branch-circuit conductors, controller, and branch-circuit short-circuit and ground-fault protection [430.6(A)(1) Ex 3]. "

The question wants to find the conductor size to feed the motor @ 115V w/in Vd tolerance in NEC's FPN.

cmil = 12.9 x 56A x (2 x 110') / 3.45V


3.45V is the 3% Vd that the FPN in the NEC suggests (5% Vd is for feeder + branch)
12.9 is the k value for Cu @ 75 degrees
110' is the length (x 2 conductors)
56A is the FLC

5hp motor; I used Table 430.248 1ph 115V = 56A (not 52A FLA on nameplate)
No big deal but I'd like to get straightened out.

 

[Dennis Alwon]

Can you give the exact wording. If it is an appliance then 422.10(A) tells us the branch circuit cannot be less then the marked rating of the appliance.

 

[Finite10]

Sure, thanks for the reply

Sure, thanks for the reply

A 1ph 5hp motor that's 110' from panel.
Nameplate says 115/230V and FLA is 52/26A.

What size conductor for 115V operation?
Apply NEC recommended Vd limit.

(The question doesn't talk about motor type or utilization)

 

[Little Bill]

A 1ph 5hp motor that's 110' from panel.
Nameplate says 115/230V and FLA is 52/26A.

What size conductor for 115V operation?
Apply NEC recommended Vd limit.

(The question doesn't talk about motor type or utilization)

Finite10,
As to your question about code ref. saying to use the nameplate rating rather than Table 430.248, I don't believe there is a code ref. for this in what the question is asking. I'm studying Mike Holt's Electrical Exam Prep. too. In the text book he is just showing how to figure VD. He is giving examples of known values on a nameplate ie: current and voltage, then he gives the distance so that you can use the formula that you stated. I suppose using the nameplate listing is so that you don't have to bother to look it up in the table. After you use the formula, look at Chpt.9 Table 8 and find the wire size for the CMIL you came up with. Make sure the wire size is large enough for 125% of the 52A listed.
Hope this helps.

 

[Finite10]

Thanks Little Bill

Thanks Little Bill

I was looking at 430.6(A)(1) and figured I might be overlooking an exception that applied to it.

Other than for motors built for low speeds (less than 1200 RPM) or high torques, and for multispeed motors, the values given in Table 430.247, Table 430.248, Table 430.249, and Table 430.250 shall be used to determine the ampacity of conductors or ampere ratings of switches, branch-circuit short-circuit and ground-fault protection, instead of the actual current rating marked on the motor nameplate

 

[rbalex]

I was looking at 430.6(A)(1) and figured I might be overlooking an exception that applied to it.

Other than for motors built for low speeds (less than 1200 RPM) or high torques, and for multispeed motors, the values given in Table 430.247, Table 430.248, Table 430.249, and Table 430.250 shall be used to determine the ampacity of conductors or ampere ratings of switches, branch-circuit short-circuit and ground-fault protection, instead of the actual current rating marked on the motor nameplate

Don't know what the question actually was but you need to read the next Subsection for an example when the nameplate value is used. [430.6(A)(2)]

 

[Little Bill]

Don't know what the question actually was but you need to read the next Subsection for an example when the nameplate value is used. [430.6(A)(2)]

See post #4, the question is asking for conductor size given the nameplate listing and to include the VD calculations to size the conductor for the VD.

 

[Finite10]

Don't know what the question actually was but you need to read the next Subsection for an example when the nameplate value is used. [430.6(A)(2)]

Thanks rbalex, yeah I did see that but didn't want to sidetrack into OL's - I even deleted a reference to that I was going to mention. I will use the tables I think as it's not a listed motor-operated appliance, or other NPR appliance, in the question.