Conductor size for 100 amp sub panel?

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Conductor markings

Conductor markings

Just talked with my brother who sold for wire manufacturer Southwire for years... (Biggest customer was GM in the old days) He says ALL wire in NM sheath is marked (or should be) by either printing or having been embossed... (Makes sense since at the time the individual conductors are manufactured, no one knows what it's final application will be... ie no one knows it might end up inside a NM sheathed cable...) Will check marks again tomorrow, however... The embossing is hard to read...
 
Vliposky, if you do find that the conductors inside the sheath are identified as of conductor type please let us know who the manufacturer of this NM is.

I have heard others say they have seen conductors marked as THHN/THWN inside NM only to find after closer examination they were not.

Roger
 
vliposky said:
If not here, where would the #4 be usable for 100 AMPS?
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If the cable you were using was a copper service entrance cable- 4 wire- then you would be able to apply Table 310.15(B)(6).

I have been told by the wire manufacturer that NM cable does in fact use THHN insulation. This, however would not fly without it being labeled on the wire or the jacket of the cable.

I have made a complete turnaround, (no surprise) in my thinking on this. I realize that you may have grounds to stand on, as George has said, if the cable were marked THHN. The fact is the NM cable is not listed in Table 310.15(B)(6) and if it were I still do not believe the NEC's intent is to use NM for Table 310.15(B)(6).

Why? Because if you look at Table 310.15(B)(6) you will see that the NEC lists conductors as well as cables at the top. So pretend that NM cable has THHN wire and is marked. The table still does not list NM.

Maybe it is an unintentional omission you may say. I say this--SE cable is listed and most SE cable has XHHW-2 conductors inside and it is marked on the sheathing. Table 310.15(B)(6) list THHN but not NM cable yet it lists xhhw-2 and it also list SE cable. That would be redundant if they wanted us to use the conductor insulation as a basis for this table.

I believe the NM was intentionally left off Table 310.15(B)(6) because it's temp rating should be used only at 60C.

I would still love to know why NM is only listed as 60C-- I was also told by the wire manufacturer that the jacket on NM is the same insulation as the wire, thus it is rated 90C.

The only way we know that the conductors of NM cable are 90C is because the NEC says it must be art.334.112. The NEC does not specify what temperature the jacket insulation should be.
 
vliposky said:
If not here, where would the #4 be usable for 100 AMPS?
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IMO....If your cable was one of the types listed in 310.15(B)(6), you could use #4 copper in your application.
I've stripped a lot of NM and I've never seen any insulation markings on the conductors.
steve
 
NM Conductor Marks

NM Conductor Marks

Cannot verify conductor marks or absence thereof... Cable is now installed and not stripped enough to read.... CAPEX brand cable manufacturer not located.... Another cable & wire sales guy says NM is probably THHN inside but probably not marked....
 
vliposky said:
Cannot verify conductor marks or absence thereof... Cable is now installed and not stripped enough to read.... CAPEX brand cable manufacturer not located.... Another cable & wire sales guy says NM is probably THHN inside but probably not marked....
Click to expand...

And this fact takes you back to the conductors only being allowed to be used at 60 deg.

310.11, (the key here) 334.80, and 334.112

Roger
 
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