# #6 romex



## Shawn23 (Jan 5, 2011)

Our local AHJ have allowed us to use 6-2wg romex to feed Air Handler units with 10k heat strips forever and now they are saying its not allowed. My question is what is it rated for? #6 thhn is rated at 75 correct?


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## HackWork (Oct 2, 2009)

Shawn23 said:


> Our local AHJ have allowed us to use 6-2wg romex to feed Air Handler units with 10k heat strips forever and now they are saying its not allowed. My question is what is it rated for? #6 thhn is rated at 75 correct?


Romex isn't THHN. You use the 60 degree column for it.


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## HARRY304E (Sep 15, 2010)

Shawn23 said:


> Our local AHJ have allowed us to use 6-2wg romex to feed Air Handler units with 10k heat strips forever and now they are saying its not allowed. My question is what is it rated for? #6 thhn is rated at 75 correct?


334.80 Ampacity. The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The allowable ampacity shall not exceed that of a 60°C (140°F) rated conductor. The 90°C (194°F) rating shall be permitted to be used for ampacity adjustment and correction calculations, provided the final derated ampacity does not exceed that of 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 392.80(A).
Where more than two NM cables containing two or more current-carrying conductors are installed, without maintaining spacing between the cables, through the same opening in wood framing that is to be sealed with thermal insulation, caulk, or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a) and the provisions of 310.15(A)(2), Exception, shall not apply.
Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a).


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## Shawn23 (Jan 5, 2011)

So he highest 6-2 nm could be rated is 55?


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## BBQ (Nov 16, 2010)

Shawn23 said:


> Our local AHJ have allowed us to use 6-2wg romex to feed Air Handler units with 10k heat strips forever and now they are saying its not allowed. My question is what is it rated for? #6 thhn is rated at 75 correct?


Get yourself some nice aluminum SE and save some money.


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## BBQ (Nov 16, 2010)

Shawn23 said:


> So he highest 6-2 nm could be rated is 55?


Yes.


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## Shawn23 (Jan 5, 2011)

BBQ said:


> Get yourself some nice aluminum SE and save some money.


 
Now that the 6-2 will no longer be accepted I am looking for the next easiest way to make them pass. I have several HVAC friends who feed me work as they do system change outs and fail do to wire size.
When in conduit its easy. Most of them are residential so its attic work.


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## Dennis Alwon (May 9, 2009)

The problem is that the manufacturers of these units have up the ampacity from 52-54 amps up to 56-58 amps. Just enough to make it a major cost difference. 

Years ago a 6-2 NM would be compliant because those units were under 55 amps.


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## aftershockews (Dec 22, 2012)

Dennis Alwon said:


> The problem is that the manufacturers of these units have up the ampacity from 52-54 amps up to 56-58 amps. Just enough to make it a major cost difference.
> 
> Years ago a 6-2 NM would be compliant because those units were under 55 amps.


I thought when they went to seer 13?, the efficiency raised and the amps lowered. I do residential and have seen this to be true.


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## B4T (Feb 10, 2009)

It would help if the manufactures got off their asses and finally rated the conductors in NM..

We all know they are THHN... :whistling2::laughing:


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## BBQ (Nov 16, 2010)

B4T said:


> It would help if the manufactures got off their asses and finally rated the conductors in NM..
> 
> We all know they are THHN... :whistling2::laughing:


That would not change 334.80


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## B4T (Feb 10, 2009)

BBQ said:


> That would not change 334.80


No... but an exception would... :thumbsup:

There is no logical reason THHN in NM can't be rated using the 75 degree table....


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## Dennis Alwon (May 9, 2009)

aftershockews said:


> I thought when they went to seer 13?, the efficiency raised and the amps lowered. I do residential and have seen this to be true.


That is true with the a/c unit --seer has to do with the outdoor unit not the indoor heat strips and motor. They either put in a higher ampacity motor or a higher kw heat strip. Most 10 kw units do not have 10kw heat strips-- somewhere between 9.2 and 9.6 I think


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## Pete m. (Nov 19, 2011)

BBQ said:


> Get yourself some nice aluminum SE and save some money.


Most of the fan coils I have seen only accept copper conductors for whatever reason....

Pete


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## BBQ (Nov 16, 2010)

Pete m. said:


> Most of the fan coils I have seen only accept copper conductors for whatever reason....
> 
> Pete


No disconnects?


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## BBQ (Nov 16, 2010)

B4T said:


> No... but an exception would... :thumbsup:
> 
> There is no logical reason THHN in NM can't be rated using the 75 degree table....


You mean other than the testing they did that showed it getting too hot?


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## Pete m. (Nov 19, 2011)

what I have always suggested if the original branch circuit was aluminum is a mechanical butt-splice and a short piece of copper.

Pete


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## Pete m. (Nov 19, 2011)

BBQ said:


> No disconnects?


Some of the units have integral disconnects but still, for whatever reason, require a copper conductor for final connection. Seriously wish I knew why.

Pete


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## BBQ (Nov 16, 2010)

Pete m. said:


> Some of the units have integral disconnects but still, for whatever reason, require a copper conductor for final connection. Seriously wish I knew why.
> 
> Pete


I was figuring an external disco would solve the problem. Just use copper the last bit.


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## Shawn23 (Jan 5, 2011)

So what would be the next best Copper nm cable to meet the 60 amp requiremnet?


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## drspec (Sep 29, 2012)

#4 seu


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## Shockdoc (Mar 4, 2010)

Use 3/4 ENT and pull two 6s and a 8. OCPD @ 70 amps.


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## JHFWIC (Mar 22, 2012)

6-3 Romex is good for 55 amps, but that is not a standard breaker size so cant you use a 60 amp?


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## HackWork (Oct 2, 2009)

JHFWIC said:


> 6-3 Romex is good for 55 amps, but that is not a standard breaker size so cant you use a 60 amp?


Yes, but only if the load is less than 55a. I don't believe it would be for the 10k heat strip.


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## Shawn23 (Jan 5, 2011)

Shockdoc said:


> Use 3/4 ENT and pull two 6s and a 8. OCPD @ 70 amps.


I know i can do this but im trying to avoid it:thumbsup:


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## Shawn23 (Jan 5, 2011)

JHFWIC said:


> 6-3 Romex is good for 55 amps, but that is not a standard breaker size so cant you use a 60 amp?


I literally carry every size of every brand of breaker from 2p 15 up to 2p 60 on my truck so thats not a problem. The problem is the Name plate calls for a 60 so that is what the AHJ wants.


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## Shawn23 (Jan 5, 2011)

HackWork said:


> Yes, but only if the load is less than 55a. I don't believe it would be for the 10k heat strip.


Correct


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## ceb58 (Feb 14, 2009)

Shawn23 said:


> I literally carry every size of every brand of breaker from 2p 15 up to 2p 60 on my truck so thats not a problem. The problem is the Name plate calls for a 60 so that is what the AHJ wants.


Dose the name plate have a min. circ. amp stamped on it?


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## mgraw (Jan 14, 2011)

HackWork said:


> Yes, but only if the load is less than 55a. I don't believe it would be for the 10k heat strip.


It is very unusual to have a true 10k heat strip. I have only seen one in almost 40 years and it was rated at 208v. Usually they are 2- 4.8k strips or 9.6k.


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