wire types

[wyatt]

I fore the most part only get to play with romex in my job. but I was looking at some thhn and on the wire is printed (thwn-2 or thhn)is most thhn like this and means that it is ok for wet loaction?

 

[bphgravity]

Re: wire types

Yes, it is good for a wet location but is limited to 75?. The thhn insulation gives the conductor a 90? rating in dry locations.

 

[bdarnell]

Re: wire types

Bryan, doesn't the -2 designation give it a 90 deg. rating, wet or dry ?

 

[LarryFine]

Re: wire types

Wyatt, the designation must have a "W" in it for wet locations.

 

[bphgravity]

Re: wire types

Yes, you are correct per Not 4 of the Table. Good catch...

 

[Matt Harp]

Re: wire types

related question, what is the insulation type commonly used on the conductors in type NM and NM-B cable? Apparently, NM-B has a 90C rating.

 

[bassphisher]

Re: wire types

334.80 Ampacity.
The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60?C (140?F) conductor temperature rating. The 90?C (194?F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60?C (140?F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.
I believe that this code section applies to your question.
Gretna Inspector
Paul

 

[pierre]

Re: wire types

Wyatt
If you have a code book, take a look at Tables 310.13 Conductor Application and Insulations, 400.4 Flexibe Cords and Cables, and 402.3 Fixture Wires.

These will help you to become more familar with some of the different types of conductor and cable type available.
Then go to page 3 of the '02 or '05 NEC and look at the left column. Those are Chapter 3 cable types also. Read each of the Articles and you can become familar with those as well. That should give you something to do for a while

Good Reading