mistermudd
Senior Member
- Location
- Washington State
Does the NEC allow 4/0 SE cable supplying the total load of a dwelling unit to be installed indoors, through insulation, and be protected at 200 amps?
SE cannot be used more than a short distance inside if it is being used as a service conductors (upstream of the service disconnect/OCPD.)Does the NEC allow 4/0 SE cable supplying the total load of a dwelling unit to be installed indoors, through insulation, and be protected at 200 amps?
Does the NEC allow 4/0 SE cable supplying the total load of a dwelling unit to be installed indoors, through insulation, and be protected at 200 amps?
Informational Note No. 1: The conductor ampacity may
require other correction or adjustment factors applicable to
the conductor installation.
The 2014 requires that the feeder be sized at 83% of the entire load. According to the IN No. 1: adjustment factors would apply if the wiring method required it, such as SE cable within insulation.
Does the NEC allow 4/0 SE cable supplying the total load of a dwelling unit to be installed indoors, through insulation, and be protected at 200 amps?
Isn't that if it's over 12" of insulation ? Which would not be the case if just passing from outside to inside, in most cases .
Does the NEC allow 4/0 SE cable supplying the total load of a dwelling unit to be installed indoors, through insulation, and be protected at 200 amps?
OP only mentioned SE cable - this would include both SEU and SER unless he specifies otherwise.
Before 2014 NEC 310.15(B)(7) did not have any requirement to make ampacity adjustments, just select conductor size and go with it no matter what other adjustments may be otherwise required in other situations. With 2014 they did away with the table and went with the 83% ampacity otherwise required but the catch is you must also apply ampacity adjustments like you would any other conductor.
I think this is somewhat a bigger issue for conductors that may be on a rooftop where ambient temp can make a big difference in adjustment values. Otherwise most other instances you end up with same conductor size you did before 2014.
So before the change how do you go about ampacity adjustments? all you had was a table that told you overcurrent protection level and a corresponding copper or aluminum cable that was acceptable to use at that overcurrent protection level, you were not in any way determining conductor ampacity, you didn't even need to consider conductor insulation rating, it was a same size fits all kind of situation, all that was different was they did recognize different sizes depending on if you used copper or aluminum.Actually I would argue that NEC 310.15(B)(7) did not have to make any mention about the adjustments and corrections because 310.15 already had that covered. I believe it was the notion that corrections and adjustments did not apply in which spawned the removal of the table along with attempting to simplify the idea of a "main power feeder".
We all know that an elevated ambient temperature does affect the ampacity of a conductor so to be honest with you I believe (I honestly do) that 310.15(B)(2) always applied and 310.15(B)(7) did not need to make mention of it. But so many people thought the table was a CATCH ALL that it was part of the debate to push for the change.
Just my thoughts on it...
I would argue (and not sure why I am) that when you selected 4/0 AL from 310.15(B)(7) that you treated the internal conductors as you would in NM-B and use the 90 degree value as given in 310.15(B)(16) and then made the adjustment. The application without the table is no different in my opinion.
In the 2011 NEC you can choose your conductor (if applicable) per 310.15(B)(7) and then if you had to apply any adjustments or corrections as specified in 310.15(B) then you would do so accordingly. The size from the chart to me was just a starting point. I actually sat in on the discussions regarding this at the ROC in Redondo Beach, CA and I never got the sense that they did not feel 310.15(B) applied. That was part of the reasons for the change to make sure the message was clear that it did apply.
Prior to 2014, I would have selected an applicable conductor per 310.15(B)(7) and if any of the conditions in 310.15 apply I would then have to go to the relevant ampacity value in 310.15(B)(16) and do it just like any other cable would. I just now that thermal dynamics are going to take place and blindly choosing a CATCH ALL was not the intent.
But again.....we can agree to disagree...I'm ok with that as I am quite happy with how the 2014 NEC made it clear.
Prior to 2014, I would have selected an applicable conductor per 310.15(B)(7) and if any of the conditions in 310.15 apply I would then have to go to the relevant ampacity value in 310.15(B)(16) and do it just like any other cable would. I just now that thermal dynamics are going to take place and blindly choosing a CATCH ALL was not the intent.
In the case of SE (SER) cable in insulation, 338.10 would still limit us the 60? ampacity after all is said and done (ignoring 310.15(A)(2) for discussions sake)
Correct ?
As Dennis can confirm, I had a terrible time with 310.15(B)(6) vs 338.10 in the '08 & '11.
Well actual you had the right thought on it all and your thinking on it is what the 2014 is now saying. The problem was in the past the wording wasn't there to support what you and many of us assumed would be what they meant. Now there is no question IMO
IMO the old Table 310.15(B)(7) did not make prevision for ampacity adjustment. Common sense did but the NEC did not.