Understanding the nec volume 1 by mike holt

[Callaway]

I am continually getting the wrong wire size for the amperage calculated in practice questions. Mostly pages 147-151. There is usually a reference to where the book's answer came from but I am unable to see where they got the size from. There must be factors I'm not aware of?

 

[luckylerado]

Can you post an example with your answer

 

[Dennis Alwon]

I am continually getting the wrong wire size for the amperage calculated in practice questions. Mostly pages 147-151. There is usually a reference to where the book's answer came from but I am unable to see where they got the size from. There must be factors I'm not aware of?

We all don't have the book so if you want answers post the question and show us what you did.

 

[Callaway]

Examples

Examples

A 25 amp oven with 75 degree terminals gets #10. Why not #12? The answer mentions 110.14c1. Then in the diagram after it says #10 rated 30 amps at 60 degrees. Why did the question say 75 degree terminals and the answer say 60?

What ungrounded conductors are required for a 119 amp calculated load-3 wire single phase 120/240. Answer says #2 and mentions 215.2a4 and 310.15b7 Why not #1?

Another single phase 120/240 service/feeder calculated load says #4 for 97 amps. Same articles mentioned again.

 

[Dennis Alwon]

A 25 amp oven with 75 degree terminals gets #10. Why not #12? The answer mentions 110.14c1. Then in the diagram after it says #10 rated 30 amps at 60 degrees. Why did the question say 75 degree terminals and the answer say 60?

If the wiring is for an oven in a residence then the wiring method is usually nm cable. NM cable is rated 60C (art. 334.80). Regardless #10 can only use 30 amp overcurrent protective device in this situation. Look at the asterisk in the table for 10, 12, and 14 awg. The asterisk at the bottom of the table tells us to use 240.4(D)-- This section limits #10 to 30 amps even if the terminals and wiring methods are rated 75C

 

[Dennis Alwon]

What ungrounded conductors are required for a 119 amp calculated load-3 wire single phase 120/240. Answer says #2 and mentions 215.2a4 and 310.15b7 Why not #1?

I think this is for a single family dwelling
T. 310.15(B)(7) is an exeption table for single family dwellings only and only under certain conditions.

Another single phase 120/240 service/feeder calculated load says #4 for 97 amps. Same articles mentioned again

Again this is for a single family dwelling where #4 is good for 100 amps.

This Table is for the 2011 and before. The 2014 has deleted the table and has gone to a percentage method for SFD