Ampacity

[George Newman Jr.]

Question: What is the ampacity of a 12/2 NMB Cable?
How do you answer this when taking a Master Electrician's Exam?

 

[chris kennedy]

Question: What is the ampacity of a 12/2 NMB Cable?
How do you answer this when taking a Master Electrician's Exam?

Sorry!....

 

[ibew441dc]

Question: What is the ampacity of a 12/2 NMB Cable?
How do you answer this when taking a Master Electrician's Exam?

Yikes! I don't know what NMB is? I'd play it safe and say 20 amps.

 

[iwire]

Per 334.80 we must use the 60 C column so the ampacity is 25 amps.

And we can use it at 25 amps for motors, HVAC equipment and many other applications.

240.4(D) limits the use of 12 AWG to 20 amps for some installations like branch circuits but that does not change the rating of the cable just how we use it.

 

[iwire]

Yikes! I don't know what NMB is? I'd play it safe and say 20 amps.

NM-B is Nonmetallic Sheathed cable type B ............ in other words regular old Romex. :smile:

 

[ibew441dc]

NM-B is Nonmetallic Sheathed cable type B ............ in other words regular old Romex. :smile:

That would be that old cloth stuff??? I don't recall ever seeing NM-B in the NEC.

I thought maybe that is what the OP was trying to point out:smile:

 

[480sparky]

Type NM-B:

Wierd stuff, I tells ya! They can't even decide what color to make it. Some's white.... some's yeller, some's that icky orange. And when it's real thick, it's black as coal!

 

[Dennis Alwon]

That would be that old cloth stuff??? I don't recall ever seeing NM-B in the NEC.

I thought maybe that is what the OP was trying to point out:smile:

nm-B is what we use today- It is what most of us call romex or NM cable.

 

[ibew441dc]

334.112 Insulation. The insulated power conductors shall
be one of the types listed in Table 310.13(A) that are suitable
for branch-circuit wiring or one that is identified for
use in these cables. Conductor insulation shall be rated at
90?C (194?F).
FPN: Types NM, NMC, and NMS cable identified by the
markings NM-B, NMC-B, and NMS-B meet this
requirement.

Well would ya looky there......duuuhhhh:roll:

 

[chris kennedy]

Question: What is the ampacity of a 12/2 NMB Cable?
How do you answer this when taking a Master Electrician's Exam?

I agree it is a poorly worded question. I my post #2, I quoted 334.80 because I thought the question read "How do you answer this when talking to a master electrician?" I retracted that because as Bob pointed out, there is more than one answer.

 

[ibew441dc]

nm-B is what we use today- It is what most of us call romex or NM cable.

I always call it Romex or NM cable....never even thought of NM-B.....I thought the OP's question was a curve ball.....I failed:roll:

 

[iwire]

I retracted that because as Bob pointed out, there is more than one answer.

I did?

Then I did not type what I think. :smile:

IMO there is only one answer and that is 25 amps.

240.4(D) is not a 'rating'

 

[ibew441dc]

Question: What is the ampacity of a 12/2 NMB Cable?
How do you answer this when taking a Master Electrician's Exam?

Answer = 20 amps....shuuuuhh! good thing I played it safe
http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet6

 

[ibew441dc]

I did?

Then I did not type what I think. :smile:

IMO there is only one answer and that is 25 amps.

240.4(D) is not a 'rating'

I think it is 20......and remember iwire....No Questioning!:grin:

 

[iwire]

I think it is 20......and remember iwire....No Questioning!:grin:

So many questions.

What does T310.16 tell us?

What circuits does 240.4(D) apply to and did the question specify what type of circuit?

Where do you see anything about a 'rating' in 240.4(D)?

Article 240 does not have to do with conductor ratings it has to do with over current protection and 240.4(D) tells us what size OCPD we must use with 12 AWG in some applications. Article 240 can not change a conductors rating, only how we protect it.

 

[ibew441dc]

So many questions.

What does T310.16 tell us?

What circuits does 240.4(D) apply to and did the question specify what type of circuit?

Where do you see anything about a 'rating' in 240.4(D)?

Article 240 does not have to do with conductor ratings it has to do with over current protection and 240.4(D) tells us what size OCPD we must use with 12 AWG in some applications. Article 240 can not change a conductors rating, only how we protect it.

I'm catch'n what your throw'in as far as the directive stated in 334.80 but take a look at this http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet6

although it may be unintended...it says 20 amps is the ampacity of 12/2.

Using the Southwire Brand Romex type NM-B, I think 110.3(B) comes into play.

 

[chris kennedy]

Using the Southwire Brand Romex type NM-B, I think 110.3(B) comes into play.

This is a test question, and as the question reads, I agree with Bob.

 

[infinity]

I'm catch'n what your throw'in as far as the directive stated in 334.80 but take a look at this http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet6

although it may be unintended...it says 20 amps is the ampacity of 12/2.

Using the Southwire Brand Romex type NM-B, I think 110.3(B) comes into play.

Even though is says 20 amps, according to the NEC that is incorrect as Bob has pointed out.

 

[480sparky]

I'm with Bob on this one. Ampacity is based on 310.16, where it says it's 25. 240.4(D) is about overcurrent protection, not ampacity.

It's the same thing when it comes to the top speed of a car, as opposed to the speed limit.

 

[ibew441dc]

This is a test question, and as the question reads, I agree with Bob.

Don't get me wrong, I agree with Bob too. I mean come on I was questioning the existence to NM-B at the beginning of this thread, and came to the conclusion that I knew what it was, but did not call it appropriately. Anytime I look something up for Romex, I'm think'n NM not NM-B....

For the sake of conversation though....based on the Southwire info what do you think the ampacity is for 12/2 NM-B?:smile: