Ser cable ampacity

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Smart $ said:
I disagree.

The exception starts, "Where two different ampacities apply to adjacent portions of a circuit, ..." This cannot include the entire run where there are two or more non-adjacent portions.



Why even bother having the exception in the NEC ? -- I mean please give me a real world example. -- the OCPD will always be set at the 60C amperage.
The exception appears to be a way of using the conductors at 75C ampreage therefore inceasing the OCPD used.
It seems 4/0 ser is most commonly effected as a feeder where 60C limits you to 150A OCPD & @ 75C will rate the conductors @ 180A resulting in a 200AOCPD being used. The limit of 10% designates 90% without thermal insulation and able to dissapate heat freely.
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The most common use for this exception that I have seen described has been for conduit passing through a roof and running a few feet to equipment (including both AC and DC for PV systems).
The combination of outside ambient and rooftop adder can result in a large ampacity correction.
Without the exception the two alternatives would be increasing the size of the entire run or switching wire size in a j-box below the roof.
Neither of these seem to be justified, hence the exception.

Applying this exception to rules relating to insulation coverage or particularly to fire caulked penetrations seems to be a recent topic.

Tapatalk!
 
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mwm1752 said:
Why even bother having the exception in the NEC ? -- I mean please give me a real world example. -- the OCPD will always be set at the 60C amperage.

...
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The OCPD and and associated equipment may and likely will be rated for 75?C operation.
 
augie47 said:
O.K. let's take it back to the OP.
In the '11 Code, SE cable in insulation must be installed at it's 60? ampacity.
I have a 60 ft run of SER cable, the 1st 5 ft leaving the panel is in insulation.
Since less than 10% and less than 10 ft is in insulation, can I use the 75? ampacity for the cable ?
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Not quite but yes. 10% of the 55 feet that is not in the insulation is equal to 5.5 ft. so the 5' that is in the insulation would be the exception and you could use 75C

However imo that exception although written it seems to be fact, is not the way it was meant and the exception should not be used according to all the authorities I have talked with including the Southwire member of the panel.
 
Dennis Alwon said:
...

However imo that exception although written it seems to be fact, is not the way it was meant and the exception should not be used according to all the authorities I have talked with including the Southwire member of the panel.
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The 310.15(A)(2) Exception or SE cable ampacity per 338.10(B)(4)?

Chances are the former will not get changed just for SE. IMO, until there's a revision to 338.10(B)(4), 310.15(A)(2) Exception can be applied. AHJ rejection is not supported by the current wording.
 
Smart $ said:
. AHJ rejection is not supported by the current wording.
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Smart I think I and you have both said that more than once. It is not always about what is written but about interpretation. As the AUTHORITY HAVING JURISDICTION of the state one has responsibilities that go beyond the actual words to find out what the intent was behind this article. Our state guy has done that and I was told by him, as stated in other post, that ser cannot use that exception. Once the state makes that decision based on talks with Southwire- apparently they did the studies, then that is the rule as ridiculous as it sounds. Not sure what other states do with that exception.
 
From the Southwest site

Table values reflect XHHW-2 conductors. +Allowable Ampacities:Allowable ampacities shown are for general use as specified by the National Electrical Code, 2011 Edition, Section 310.15.

60? C - When terminated to equipment for circuits rated 100 amperes or less or marked for 14 through 1 AWG conductors. See NEC Article 338.10(B)(4). 100A or less ? disagree

75? C - When terminated to equipment for circuits rated over 100 amperes or marked for conductors larger than 1 AWG. May not apply, see NEC Article Agree

338.10(B)(4).

90? C - Wet or dry locations. For ampacity derating purposes. Agree

Dwelling - For units, conductors shall be permitted at listed ampacities as 120/240-volt, 3-wire, single-phase services and feeders per NEC Article 310.15. Only in certain circumstances

310.15(A)(2) Exception310.15(A)(2) Exception is not mentioned -- Dennis do they have a written document to support your conversations?
 
mwm1752 said:


Dwelling - For units, conductors shall be permitted at listed ampacities as 120/240-volt, 3-wire, single-phase services and feeders per NEC Article 310.15. Only in certain circumstances

310.15(A)(2) Exception310.15(A)(2) Exception is not mentioned -- Dennis do they have a written document to support your conversations?
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I did not have any confirmation however after reading your post I wrote to Dave Mercier who is Southwires Technical Director for their electrical division.

Here is his email response

Dave Mercier said:
When used as a feeder or branch circuit, all rules for NM-B cable apply. There is no allowance for using 310.15(A)(2).
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So now we can continue to look at the NEC and say that the NEC does not say that-- I don't know what to tell you. Talk to the AHJ
 
Change in SE ampacity rules/2011

Change in SE ampacity rules/2011

334.80 applies to SE used as an interior branch circuit or feeder ONLY when applying the 2008 NEC, but does not apply in cycles following the 2008 NEC. In the 2011 and 2014 NEC, SE cable is specifically not subject to 334.80.
Also, you are allowed to use 310.15(A)(2)Exception in the 2011 and 2014 without further limitation by 334.80 (since it does not apply to SE cable). Therefore, if your cable is installed in thermal insulation for less than 10 ft or 10% of the run, you can use the higher ampacity of a 75C SE cable. In the 2008 NEC, the prohibition against using 310.15(A)(2)Exception applies only to more than two cables with two or more current-carrying conductors installed without maintaining spacing through openings in wood framing with fire- or draft-stopping.
 
Christel said:
334.80 applies to SE used as an interior branch circuit or feeder ONLY when applying the 2008 NEC, but does not apply in cycles following the 2008 NEC. In the 2011 and 2014 NEC, SE cable is specifically not subject to 334.80.
Also, you are allowed to use 310.15(A)(2)Exception in the 2011 and 2014 without further limitation by 334.80 (since it does not apply to SE cable). Therefore, if your cable is installed in thermal insulation for less than 10 ft or 10% of the run, you can use the higher ampacity of a 75C SE cable. In the 2008 NEC, the prohibition against using 310.15(A)(2)Exception applies only to more than two cables with two or more current-carrying conductors installed without maintaining spacing through openings in wood framing with fire- or draft-stopping.
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I agree with this but somehow it is not what southwire is saying.

The only correction I have to up above is the 10' or 10% whichever is less. So if you are 10' in insulation and your run is 60' then you need to use 60C
 
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