Wire insulation letters. Thhn

Status
Not open for further replies.
chuckgassmannm said:
Hey there. I can't find where in the code book it tells what the letters on conductor insulation. Like then. Thank you.

Sent from my Moto G (4) using Tapatalk
Click to expand...
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.
 
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."
 
al hildenbrand said:
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."
Click to expand...
The wires with "T" are thermoplastic and not thermoset.
 
Status
Not open for further replies.
Top