240.4 d

[zappy]

I thought that it applied to 14,12,10awg NM-B cable only. But does it apply to MC cable size 14,12,10awg also?

Also when you go to HD there's a sign over there wire rack that says "8-2 NM-B cable 40 amps, 6-2 NM-B cable 50amps". But 310-16 says 8awg 50amps, 6awg 65amps. So which one is it? The asterisk is only next to the 14, 12, 10 awg at 310-16

Thank you for your help.

 

[ActionDave]

Ooops.......

 

[ActionDave]

1) Yes.

2) Check out 334.80

 

[iwire]

I thought that it applied to 14,12,10awg NM-B cable only. But does it apply to MC cable size 14,12,10awg also?

Also when you go to HD there's a sign over there wire rack that says "8-2 NM-B cable 40 amps, 6-2 NM-B cable 50amps". But 310-16 says 8awg 50amps, 6awg 65amps. So which one is it? The asterisk is only next to the 14, 12, 10 awg at 310-16

Thank you for your help.

Zappy, if you are interested in the NEC do not let anything posted in a store even enter your head.

HD is foolish to put up ampacities as there are many things in the NEC change the ampacity.

• The ampacity of 8 AWG NM is different than the ampacity of 8 AWG THHN run in conduit.
  
• The terminal ratings of the equipment the conductors connect to can change the ampacity of the conductors.
  
• The ambient temperature of the area the conductors are run in change the ampacity of the conductors.
  
• The number of conductors run together effect the ampacity of the conductors.

There are likely more that I have forgotten ....


In closing, believe nothing that the pros at HD tell you.

 

[chris kennedy]

In closing, believe nothing that the pros at HD tell you.

Also a good idea to change out of your lettered work shirt before you go in.

 

[infinity]

I thought that it applied to 14,12,10awg NM-B cable only. But does it apply to MC cable size 14,12,10awg also?

Here's the code section you've mentioned. It would apply to NM, conduit and wire and MC cable. But as Bob pointed out there is no blanket statement answer that applies to every installation.

(D) Small Conductors. Unless specifically permitted in 240.4(E) or (G), the overcurrent protection shall not exceed that required by (D)(1) through (D)(7) after any correction factors for ambient temperature and number of conductors have been applied.
(3) 14 AWG Copper. 15 amperes
(4) 12 AWG Aluminum and Copper-Clad Aluminum. 15 amperes
(5) 12 AWG Copper. 20 amperes
(6) 10 AWG Aluminum and Copper-Clad Aluminum. 25 amperes
(7) 10 AWG Copper. 30 amperes

 

[LarryFine]

Also a good idea to change out of your lettered work shirt before you go in.

Or, offer a business card with the statement that "My license and insurance do not allow me to tell you how to do electrical work. They only cover work I do. Please call me if I can be of any service to you." or something similar.

I just made that up, so take it with the proverbial grain of salt.

 

[zappy]

Here's the code section you've mentioned. It would apply to NM, conduit and wire and MC cable. But as Bob pointed out there is no blanket statement answer that applies to every installation.

Ok I just got a e-mail from southwire, and it states that 8-3 AWG, NM-B cable is rated for 40amp, 60c. And 8-3AWG, M/C cable is rated for 50AMPS 75c.

So where in the NEC does it say 8awg nm-b cable is rated for40a., 60c. And 8-3awg, M/C cable is rated for 50a. 75c.?

 

[iwire]

Ok I just got a e-mail from southwire, and it states that 8-3 AWG, NM-B cable is rated for 40amp, 60c. And 8-3AWG, M/C cable is rated for 50AMPS 75c.

It sounds like they gave a decent answer but in general I would not ask them for the rating.

For instance if you ask Southwire what their 4/0 copper portable power cable is rated for they may say 400 amps at 150C but there will not be an NEC application that allows you to run it as 150C, you would be limited to 75 C and about 200 amps.

So where in the NEC does it say 8awg nm-b cable is rated for40a., 60c. And 8-3awg, M/C cable is rated for 50a. 75c.?

You will not find anything that direct.

I would start at 110.14(C) which talks about terminal and equipment temperature limitations.

I would move on to 240.4 and then to 310.15 and Table 310.16.

Beyond that for NM specifically you need to look at 334.80 which limits NM to the 60 C column of 310.16

 

[roger]

So where in the NEC does it say 8awg nm-b cable is rated for40a., 60c. And 8-3awg, M/C cable is rated for 50a. 75c.?

Did you read the section Dave gave you in post #3?

Roger