colorado masters renewal

[Riograndeelectric]

I renewed my Masters License but 2 questions I was not quite clear on .

what is the minimum size SOW cord that may be used to supply a 30HP 3-phase 460 Volt motor.
A. 4 AWG B. 6 AWG C. 8 AWG D. 10 AWG
my answer was 6 awg.

also what is the minum size Copper NM cable that may be used to supply a 5 Gallon 2000W ,120V storage type water heater.

A. 14AWG b. 12 AWG. C. 10AWG D> 8AWg. My answer was 12 awg.
I would like to know what every one else thinks.
Thanks.


I did pass my renewel test..

 

[Jljohnson]

I answered them bot the same way you did. I also passed.

 

[Charles R. Miller]

Congratulations Riograndeelectric and Jim on passing. If you or others see these or similar questions, the answers are as follows:

1. What is the minimum size SOW cord that may be used to supply a 30-hp, 3-phase, 460-volt motor?
A. 4 AWG B. 6 AWG C. 8 AWG D. 10 AWG

The full-load current of a 30 hp, 3-phase, 460-volt motor is 40 amperes. (Table 430.250)
Next, in accordance with 430.22(A), multiply the motor?s FLC by 125 percent. 40 x 125% = 50 amperes.
The allowable ampacity for Type SOW cable is in the ?A+? column of Table 400.5(A).
A 6 AWG cord only has an allowable ampacity of 45 amperes. The correct answer is 4 AWG.


2. What is the minimum size copper NM cable that may be used to supply a 5-gallon, 2000 watt, 120-volt storage type water heater?

A. 14 AWG B. 12 AWG C. 10 AWG D. 8AWG

Start by calculating the current of the water heater. 2000/120 = 16.67 amperes
Since this load is considered continuous as specified in 422.13, multiply by 125 percent. 16.67 x 125% = 20.8 amperes
The ampacity of Type NM cable must not exceed that for a 60 degree rated conductor. (334.80)
The smallest 60-degree conductor, from Table 310.16, permitted to carry 20.8 amperes is 12 AWG.

Charles

 

[Riograndeelectric]

Charles , Thank you very much for your answers.I was wrong on the 30HP motor, but right on the water heater.

It is sometimes hard to really understand the intent of the questions sometimes.
Great to be able to have a place where one can come with these types of questions for advice.

Thanks.
Cameron

 

[COMaster]

I would agree with the path you took to come up with the SOW cord size, but because of 240.4(D), I would size the NM cable for the water heater at #10. Do you see something wrong with my interpretation?

 

[davizaud]

I would agree with the path you took to come up with the SOW cord size, but because of 240.4(D), I would size the NM cable for the water heater at #10. Do you see something wrong with my interpretation?

I too concure were #12 is good for 1920 Watts and #4 on the SOW question.