wireguy8169
Senior Member
- Location
- Southern Maine
Not to start a thread with in a thread but couldn't you protect it with an 80A 240.4(B)?
Derating SE type cables for service
- Thread starter howardrichman
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
You can as long as the calculated load is not greater than 75 amps.
wireguy8169
Senior Member
- Location
- Southern Maine
Thanks just did not know if there was something that trump Art 240 on this...funny I am on this job I took over and the have most of the materials there two sub panels going in two 100A breakers, well now that I read this (did not know this but now will never forget) instead of them eating the cut 2AL SER cable I will just have them return the breakers and get two 80 amp. Did the load calcs and they are bother under 50amp but never know what is going to be added. If this sounds like a bad way to go I am sure I will hear it. Just hate to have this customer eat the wire but hate more for the cable to melt.
side note I wonder how many times a feeder in this situation gets under sized ...
Thanks to the OP (and those that answered)
- Location
- New Jersey
- Occupation
- Journeyman Electrician
IMO you don't need to worry about melting. The conductors in the cable are rated for 90? C. The terminations are likely rated for 75? C. So in reality the cable can function forever at it's 75? C ampacity. It's only because someone thought that SE and NM cable should be used at the same 60? C ampacity that we're even discussing this.
howardrichman
Senior Member
My other question is: Does 334.80 for NM which also applies to SE cable supercede table 310.15(B)(6)??
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
See post #20.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
IMO, no.... In Gus' opinion Yes...:grin:
My feeling is that T. 310.15(B)(6) clearly states what type of wires are acceptable and article 310.15(B)(6) states the conditions etc. Nowhere in either of these does temperature of the wire come into play. Nowhere does it say to reference 334.80.
I do understand that all the individual conductors that are stated are either 75C or 90C however se cable is also listed. IMO, one may infer that since se is rated 60C when installed as a feeder inside therefore it does not comply. I see that and perhaps that is the intent however they never clarified that case. Perhaps T. 310.15(B)(6) should apply to any conductors rated 75C or more.
Unfortunately Nec 2011 does nothing to clear the air however it allows se cable to exclude 334.80 except where installed in thermal insulation.
howardrichman
Senior Member
Just saw it; Thanks. I'll be calling or meeting the inspector in the morn to confirm one way or the other. I think 338.10(4)(A) will rule; but I'll you know how it turns out.
HR
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tom kanzler
Member
- Location
- New York
This is big, at least as I think I understand it now, as it means that most applications of SER as a subpanel feeder (among other applications of SE cable that isn't actually service entrance duty) will allow use of the 75C ampacity, rather than the 60C, as long as it's not run in thermal insulation. Unless I'm wrong on this.
I was actually searching for discussions on this change, and came across this thread, which only grazed the topic.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
You are correct. However if it goes thru a touch of insulation then it could be considered to be 60C. What I don't understand is why 310.15(A)(2) does not come into play. IMO, it should but I have others state it does not. Basically this allows up to 10' of the run to be in insulation in a 100 foot run or more. Otherwise it would be limited to 10% of the run. 50' run would allow 5' to be in insulation.
Unfortunately the way 338.10(B)(4) is written it appears that you cannot use this rule.
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