THWN Vs THWN-2

Magnettica

What's the difference in insulation besides the columns used for derating?

I've seen THWN-2 written on large wires like 2/0 copper, but is there such an animal for say #12 copper?

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480sparky

The difference is obvious in reading T310.13(A).

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Magnettica

Thank you. I should have known it was just a temperature rating.

THWN is good for a maximum operating temperature of 167ºF and THWN-2 is good for up to 190ºF.

Thanks again.

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JohnJ0906

Also, the -2 can be derated from the 90° column, where THWN would have to be derated from the 75° column.

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John from Baltimore
"One Day at a Time"
All replies based on the 2008 NEC

Magnettica

But even still, the 'W' is abbreviated for water, so can the THWN-2 rating be derated from the 90º column if used as an underground conductor in a conduit?

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JohnJ0906

Yes.

Check out the 310.13(A) table.
THWN is 75°, THWN is 90°.

As a comparison, take a look at THHW. The temp listings change with the location. 90° in a dry location, 75° in a wet location.

From the looks of 310.13(A), a -2 designation seems to mean that the conductor holds the 90° rating in a wet location, as opposed to dropping from 90° to 75°

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John from Baltimore
"One Day at a Time"
All replies based on the 2008 NEC