Insulation Type

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Grouch

Grouch

Senior Member
Location
New York, NY
Hey guys,
I've come across this situation in a prior project, and I want to try to make sure there's no mistake.

In the attached pic you'll see the main feeder coming into the lugs of an MLO panel (the red and black wires). It's a 120/208 volt, single phase, three wire copper feeder. The feeder insulation has no print on it unfortunately. With a caliper I measured the diameter of each wire, and it matches with #8 AWG.

My question is, does the insulation look to be type TW, forcing me to use the 60 deg. C column of the ampacity table 310.15(B)(16)?

Or does it look to be something else, such as type THWN / THW / THHW or THHN, allowing me to use the 75 deg. C column, and therefore a higher amperage rating for the wire?

I'm afraid to use the higher ampacity rating in a load calculation. If the insulation happens to be TW, I have to use the lower ampacity rating for the wire.

Thanks for the help!

IMG_9466.jpg
 
LarryFine said:
Unfortunately, as a cable, the printing is on the sheath. I can't tell by looking at a pic.
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yeah I got it. I could not find any print on the sheath unfortunately. I was hoping there's a minute difference between TW and other types that can be seen that I'm not aware of.
 
Odd that there is no printing on it. Is it pulled through conduit or is there AC cable coming into the panel which wouldn't have printing on the conductors?
Grouch1980 said:
I was hoping there's a minute difference between TW and other types that can be seen
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Types THWN / THW / THHW or THHN will have a clear nylon jacket over the insulation and be so marked.

-Hal
 
I misunderstood what Larry wrote. I do believe it is a cable. Here's a pic of where the feeder enters the panel, on the top right. Plus, this panel, which is for an apartment, is on the 17th floor of an old building. I really doubt they used conduit.

This is as much access as I had. I could not access the cable sheath unfortunately, since it's behind the walls.

IMG_9469.jpg
 
It’s very common on NM cable that there is no printing on the individual conductors, partially because even it it were THHN inside, it must still be used under the 60C column, because it is NM cable.
 
You don't have additional access behind the walls, but do you have access to the electrical room at the supply end?

You need everything in the chain to be rated for 75C to use the 75C ampacity. You need 75C or 90C conductors and 75C terminals.

It is plausible that you have that situation, but need to check before you depend on it.
 
See 110.14 (C)(1)(a)(1) You can always use the rule of thumb there. If the lugs for termination are rated for #14 through #1 or the circuit is rated 100A or less, figure the entire circuit as 60 C. max.
 
Grouch1980 said:
So these conductors would be TW type? Or no way to definitely tell?
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It's type AC so there will be no markings on anything. You would need to measure the insulation diameter and look up the size Chapter 9, Table 5 that has TW conductor properties.
 
Thanks everyone. Something I learned on this thread... in a cable the conductors have no markings 😭. I would've thought they have markings.
 
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