range calculations

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vinman

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I am taking the an Inspecters exam and I had a few questions I froze on.
Here they are
1) 16 12kw ranges what is the unbalanced load?
I am having trouble even with using the back of the book. examples.
2) A # 6 NM cable ampacity. I went to 334.80 and I still can not figure it out. What is the insulation of the conductors in NM cable?
 
Re: range calculations

1. Use Table 220.19 to determine calculated load for the 16 ranges. Then use 220.22 to determine the neutral load.

2. Per 334.80, the conductors are rated at 90? however, the final ampacity cannot exceed that of the 60? column of 310.16
 
Re: range calculations

For the 16 12KW ranges I see that 31kw is the demand. I would take the 31000 x 140% then divide by 240 volts? Is that correct
 
Re: range calculations

It's 70%, not 140%. The 140% only applies to "two phase systems," and these are rare. Also, if this were to give you a neutral current above 200 amps (in this case, it does not), then there is a further reduction allowed. See 220.22 (2002 version).
 
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