Tap Question

[don_resqcapt19]

deputygrsmith,

Once I select the proper wire size, do I take the wire's max ampacity per 310.16 and size the OCPD to either equal or less than it's max ampacity?

That is exactly what the code requires.

If this is true, then 400a(1/3) = 133a and is a #1/0 which it's max ampacity is 150a and I should be able to use the standard OCPD of 150a? I should not have to use 125a OCPD as the book states, correct?

You are correct, the book is wrong. The wire can be protected at 150 amps. Note I am assuming that the wire is 75?C wire as that is the only way a 1/0 is large enough to satisfy the 1/3 part of the rule.

The book is applying different answers and is not consistent in it's calculations and the inconsistentcy is throwing me off.

You can't believe everything you read in books, or even everything that you read on this forum. :twisted:

 

[deputygrsmith]

Thank all you for your time. I now have an understanding on the Tap OCPD question. :wink:

 

[GalwayElectric]

What size OCPD is required for a tap, over 10 ft but not more than 25 ft in length, that originates at a junction box supplied by a feeder circuit with a 500A OCPD?

That is a stupid question.
Don

That wasn't a very nice thing to say Don.

 

[don_resqcapt19]

don_resqcapt19 wrote:
Quote:
What size OCPD is required for a tap, over 10 ft but not more than 25 ft in length, that originates at a junction box supplied by a feeder circuit with a 500A OCPD?

That is a stupid question.
Don

That wasn't a very nice thing to say Don.

I guess not, but my comment is directed at the test question and not the poster. With the information given in the question, it cannot be answered.
Don

 

[jwelectric]

I agree that this is not a good question. I have a test generator that has a bank of 2500 questions that any number can be picked at random. One of the questions is similar to this question, to wit, it ask for the overcurrent protection of the tap that hits odd as this question does. The correct answer given is rounded down to the next fuse size and no wire size is mentioned.

I have glanced over the questions but I did not see the question. When I find it I will post it here.

 

[GalwayElectric]

don_resqcapt19 wrote:
Quote:
What size OCPD is required for a tap, over 10 ft but not more than 25 ft in length, that originates at a junction box supplied by a feeder circuit with a 500A OCPD?

That is a stupid question.
Don

That wasn't a very nice thing to say Don.

I guess not, but my comment is directed at the test question and not the poster. With the information given in the question, it cannot be answered.
Don

My mistake Don. I thought you were calling the poster stupid, which I thought was pretty rude and out of character. I should have known better!