SE cable for feeders - temperature rating?

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74sparks

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338.10(B)(4)(a)(1) states "Type SE service-entrance cable used for interior wiring shall comply with the installation requirements of part II of Article 334, excluding 334.80.

Of course 334.80 is the Ampacity clause, stating we shall never exceed that of a 60°C rated conductor.

So, if an SE cable is marked 75°C, is that the ampacity one would use for installing it as a feeder in an unfinished basement? If not, I'm seeing no benefit to even considering SE, as going to 60°C rating on it actually pushes the cost above NM-B.

In this case, I'm evaluating a 50A feeder, the SE (or NM-B AWG-6/3+G) comprising a run from breaker to junction with THWN-2 at AWG-8.
 
From your link, look at #3:

(4) Installation Methods for Branch Circuits and Feeders​


Informational Note No. 1: See 310.14(A)(3) for temperature limitation of conductors.

Informational Note No. 2: For the installation of main power feeder conductors in dwelling units refer to 310.12.

(a) Interior Installations.

  1. In addition to the provisions of this article, Type SE service-entrance cable used for interior wiring shall comply with the installation requirements of Part II of Article 334, excluding 334.80.
  2. Where more than two Type SE cables containing two or more current-carrying conductors in each cable are installed in contact with thermal insulation, caulk, or sealing foam without maintaining spacing between cables, the ampacity of each conductor shall be adjusted in accordance with Table 310.15(C)(1).
  3. For Type SE cable with ungrounded conductor sizes 10 AWG and smaller, where installed in contact with thermal insulation, the ampacity shall be in accordance with 60°C (140°F) conductor temperature rating. The maximum conductor temperature rating shall be permitted to be used for ampacity adjustment and correction purposes, if the final ampacity does not exceed that for a 60°C (140°F) rated conductor.
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If this is not residential keep in mind that section also loops in 334.10(3)
 
This is residential. At this amperage, going 75C on the SE means you'd be using the same gauge wire in SE (at 75C) as you would in NM-B (at 60C). In that case, there is a small cost savings to going with aluminum, although arguably still not enough to settle the peace of mind that comes with an all-copper system.

If having to hold SE at 60C, that would have required a larger gauge, and thus higher cost for Al SE versus Cu NM-B. Again, at this (50A - 60A) amperage, I'm sure that changes as size increases.
 
74sparks said:
This is residential. At this amperage, going 75C on the SE means you'd be using the same gauge wire in SE (at 75C) as you would in NM-B (at 60C). In that case, there is a small cost savings to going with aluminum, although arguably still not enough to settle the peace of mind that comes with an all-copper system.
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How can two conductors of the same size and material have the same ampacity at both 60° C and 75° C?
 
infinity said:
How can two conductors of the same size and material have the same ampacity at both 60° C and 75° C?
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Sorry if I was to cryptic there. Not the same material, I was referring to Al SE versus Cu NM-B.

The 50A feeder would require AWG-6 in Cu NM-B (60°C rating), but would also use AWG-6 in Al SE (75°C rating). The too-oft repeated rule of aluminum requiring one gauge increment larger than copper for a given feeder doesn't hold, if the aluminum SE is jacketed at 75C, and one is permitted to rate the SE accordingly.

Personally, I think I'll be sticking with Cu NM-B, either way.
 
At 50A, 8awg Cu is good at 75C but 6awg Cu is required at 60C. So 8awg CU SER might be a good choice if you can get it a better price. Lately I've been finding some sizes of SER at better prices than NM-B, apparently because people don't know better. Oh, wait...You didn't hear that! ;)

But don't forget to check that all the equipment your terminating to has 75C rated terminals, or else you don't comply with 110.14(C).
 
tortuga said:
Ben your buying copper SER? I have not seen that in over a decade.
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It's funny, the aluminum SE types are so ubiquitous in the old houses I work on, that I automatically associated the two, as "SE" = "Al". I can't even recall having ever seen Cu SER installed in any old house, and I think it could be that many sources will only sell full spools of Cu SER, not by the foot. If you're buying SER by the foot, it seems aluminum is much easier to find.

But both mine and others assertion that Cu SER might be the cost effective path didn't pan out, in grabbing some quick pricing online. Here's how it shakes out:

feeder wire.jpg

Perhaps if copper SER 8-8-8-8 was available , it would have been cheaper, but I didn't find it at any of my usual sources. Hence the "NA" in that slot.

So hopefully the conversation and costing exercise is useful for someone coming across this thread in future searches. For nearly the same price, I'll probably just do a 55A feed on NM-B AWG-6, since I just don't love using aluminum. Since I already have a spare 50A breaker in this panel, it will go on there, I don't think I've ever even seen a CH255 breaker anyway.
 
Several consecutive code cycles in the 2000s kept changing the rules--including ampacity--on SE cable. For a while it was strictly limited to the 60° degree column. I think it was some cycle in the 20-teens where they settled on the current restrictions regarding small gauges and contact with insulation.
 
frofro19 said:
I just bought some #3 SER CU for a F150 truck charger. Charger is 80 amps and ran #3 SER and terminated on a 100 amp breaker.
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Yeah, I should have said that in the 8-8-8-8 and 6-6-6-6, it's hard to find Cu SER by the foot, around here. In some other gauges, it does appear to be more commonly available.
 
This thread appears to be a DIY how too so it's time to close it. Hopefully the OP got some help.
 
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