2008 NEC Exam Preparation

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thortin simpson

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The NEC 2008 Exam preparation was just what the doctor order!!
But I do have a couple things that I just can't get my mind to grasp for instance:

1. Page 152 practice question ask: What size THHN conductor is required for a 50a circuit where the terminals are not marked with a temperature rating?
Answer c. 6 AWG...................................MYy dilema is that T.310.16. THHN is not under the 60C catergory it is under 90C ..........Please someone tell me what I'm doing wrong

2. Page 246 Figure 9-7. Accordingly to that diagram the receptcles that are located on the same wall as the entry door those receptacles are 6ft apart (which is code compliance) but why are receptacles on the opposite wall 12ft apart which I was under the assumption accordingly to sec 210.52(A)(2) that they shall be 6ft apart ..................Where is my thinking off?

3. Page 248 Figure 9-13 Accordingly to sec.210.52(C) (1) Receptacles shall be not more than 24in apart, here some receptacles are 24in (which is code compliance) but if you look at the figure on C wall they are 48in apart ..........Again someone please steer me in the right direction
 
Dennis Alwon

Dennis Alwon

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thortin simpson said:
The NEC 2008 Exam preparation was just what the doctor order!!
But I do have a couple things that I just can't get my mind to grasp for instance:

1. Page 152 practice question ask: What size THHN conductor is required for a 50a circuit where the terminals are not marked with a temperature rating?
Answer c. 6 AWG...................................MYy dilema is that T.310.16. THHN is not under the 60C catergory it is under 90C ..........Please someone tell me what I'm doing wrong
Click to expand...

Look at 110.14(C)(1)

2. Page 246 Figure 9-7. Accordingly to that diagram the receptcles that are located on the same wall as the entry door those receptacles are 6ft apart (which is code compliance) but why are receptacles on the opposite wall 12ft apart which I was under the assumption accordingly to sec 210.52(A)(2) that they shall be 6ft apart ..................Where is my thinking off?
Click to expand...

I think you mean 210.52(A)(1)-- it states that no space along the wall shall be further than 6' from a receptacle. That means if I place a lamp with a 6' cord I must be able to reach a receptacle. So if the receptacles are 12' apart I can set a lamp in the middle and still reach a receptacle.

The code requires an outlet within 6' of any opening for the same reasons.


3. Page 248 Figure 9-13 Accordingly to sec.210.52(C) (1) Receptacles shall be not more than 24in apart, here some receptacles are 24in (which is code compliance) but if you look at the figure on C wall they are 48in apart ..........Again someone please steer me in the right direction
Click to expand...

Again read it as I mentioned above with a 2' appliance cord.
 
roger

roger

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thortin simpson said:
Explain why........Do you have the book to see what I am trying to explain.
Click to expand...

No, I do not have the book but, as I said, going by the way you describe them they are correct.


In post #2 Dennis explained why they are correct.

In short, if you can reach a receptacle along a wall space with a 6' cord attached to a table top lamp 210.52(A)(1) has been met and for counter tops in kitchens it is 2'

Here is a graphic that may help for the counter top

1099601197_2.jpg


Roger
 
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roger

roger

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thortin simpson said:
Great this is identical to the one I was referring to look at (Wall C) the distance is 48in correct or no?
Click to expand...
That is correct, meaning if you put an appliance between the receptacles you would not be more than 2' away from one of them.

Roger
 
raider1

raider1

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1. Page 152 practice question ask: What size THHN conductor is required for a 50a circuit where the terminals are not marked with a temperature rating?
Answer c. 6 AWG...................................MYy dilema is that T.310.16. THHN is not under the 60C catergory it is under 90C ..........Please someone tell me what I'm doing wrong
Click to expand...

THHN has a temperature rating if 90 degrees, but 110.14(C)(1) limits you to using the ampacity listed in the 60 degree column of Table 310.16.

Chris
 
Dennis Alwon

Dennis Alwon

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thortin simpson said:
Duh!! I see what you mean I got it thanks alot
Not what about the THHN dilema ...... do you see what I am tryin to say?
Click to expand...

Thornton I tried to give you the explanation without giving the answer. Read my post and the related section and tell me what you don't understand.
 
Dennis Alwon

Dennis Alwon

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If you knew that the temperature rating of your terminals were 75C, as most are today, then you could use the 75C column. The 90C column is used when you have to derate for pipe fill or other reasons. You can start at the 90C rating but you generally cannot protect the wire higher than the weakest link.

Art. 110.14(C) tells if if the terminals are not known then we must use 60C for circuits sized 100 amps or less. Since you do not know the temp. rating of your terminals then the 60C column is used.

If I know my temperature ratings of my terminals were 75C then I could use #8 for the 50 amp circuit.

If I use THHN the wire is rated 90C. Suppose I have 4 current carrying conductors (CCC) in a conduit. According to Table 310.15(B)(2) I have to de-rate 80%.

An example, I have a #8 thhn wire with terminals rated 75C and 4 CCC in a conduit. I can use the 90C rating of #8-- 55amps -- and multiply by .8 from T. 310.15(B)(2) and get a conductor rated 44 amps. Now even though 75C column states the conductor is good for 50 amps, it no longer is because of the de-rating. So I would have to use a #6 in this case.
 
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