Wire insulation letters. Thhn

[chuckgassmannm]

Hey there. I can't find where in the code book it tells what the letters on conductor insulation. Like then. Thank you.

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[iceworm]

Look at 310.104

 

[GoldDigger]

Note that thhn auto-corrects to then.

 

[480sparky]

You mean what the letters actually mean / stand for ?

 

[kwired]

Hey there. I can't find where in the code book it tells what the letters on conductor insulation. Like then. Thank you.

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310.104 gives you some idea but doesn't exactly tell you every detail either.

A few common things:

T: thrermoplastic
H: heat resistant
W: moisture resistant
N: Nylon jacket (mostly for gasoline and oil resistance)
X: cross linked polyethylene
M: machine tool wire
R: rubber

some combination examples:
TW = thermoplastic, moisture resistant
THW = thermoplastic, heat resistant (75C), moisture resistant
THHN = thermoplastic, double heat resistand (90C), moisture resistant
THWN = thermoplastic, heat resistant (75C), moisture resistant, nylon jacket

Then you find a -2 sometimes this turns THWN-2 into same thing as THWN but with a 90C rating. For some reason they'd rather do that than call it THHWN.

 

[chuckgassmannm]

Thank you. That does answer my question.

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[al hildenbrand]

The first place I can recall finding this being used goes back to the early decades of the 1900s and the NECs published then.

Rubber insulated conductors were being perfected, using a largely synthetic compound that was mandated to contain at least (something like) 13% real rubber. Three different identifiers were used: R, H and W

R = The basic 60 degree C, "rubber" insulation with a cotton weave slip that is impregnated with bituminous compounds and further coated with wax.
H = Rubber insulation "Heat" rated for 75 degree C.
HH = "High Heat" rubber insulation rated for 90 degree C.
W = "Wet" moisture rated rubber insulation.

The "T" came with the post World War II evolution of plastics and stands for "Thermoset Plastic."

 

[don_resqcapt19]

The first place I can recall finding this being used goes back to the early decades of the 1900s and the NECs published then.

Rubber insulated conductors were being perfected, using a largely synthetic compound that was mandated to contain at least (something like) 13% real rubber. Three different identifiers were used: R, H and W

R = The basic 60 degree C, "rubber" insulation with a cotton weave slip that is impregnated with bituminous compounds and further coated with wax.
H = Rubber insulation "Heat" rated for 75 degree C.
HH = "High Heat" rubber insulation rated for 90 degree C.
W = "Wet" moisture rated rubber insulation.

The "T" came with the post World War II evolution of plastics and stands for "Thermoset Plastic."

The wires with "T" are thermoplastic and not thermoset.

 

[480sparky]

"T" doesn't always mean thermoplastic. As in MTW (Machine Tool Wire).

 

[kwired]

"T" doesn't always mean thermoplastic. As in MTW (Machine Tool Wire).

Well then W doesn't always mean moisture resistant either

 

[480sparky]

Well then W doesn't always mean moisture resistant either

Absotively posilutely.