NM terminating in exterior box (here we go again)

[Jim W in Tampa]

Then what good are these types of boxes?

And why are these made?

They are designed for that and you will be using ul listed fittings.
Believe i do under the thinking of the holes but an inspector should tag it.

 

[jaylectricity]

try table 310.13

It doesn't really describe the letter designations.

 

[480sparky]

It doesn't really describe the letter designations.

INSULATION MATERIAL
C = Cotton
FEP = Fluorinated Ethylene Propylene
MI = Mineral (magnesium oxide)
PFA = Perfluoroalkoxy
R = Rubber (sometimes Neoprene)
S = Silicone "rubber"
SA = Silicone-asbestos
T = Thermoplastic
TA = Thermoplastic-asbestos
TFE = Polytetrafluoroethylene ("Teflon")
X = Cross-linked synthetic polymer
Z = Modified ethylene tetrafluoroethylene


HEAT RATING
H = 75 degrees Celsius
HH = 90 degrees Celsius


OUTER COVERING ("JACKET")
N = Nylon


SPECIAL SERVICE CONDITIONS
U = Underground
W = Wet
-2 = 90 degrees Celsius and wet



Therefore, a "THWN" conductor has Thermoplastic insulation, is Heat resistant to 75? Celsius, is rated for Wet conditions, and comes with a Nylon outer jacketing.

 

[goldstar]

Wouldn't they need to be marked THWN?

You are correct Ty. Sometimes THHN conductors are often dual rated (THHN/THWN) if marked as such. After doing a little research I found the following definitions :

THWN stands for "Thermoplastic High Water-resistant Nylon-coated." THWN is a designation for a specific insulation material, temperature rating, and condition of use (wet locations) for electrical wire and cable.

THHN stands for "Thermoplastic High Heat-resistant Nylon-coated." THHN is a designation for a specific insulation material, temperature rating, and condition of use (suitable for dry and damp locations) for electrical wire and cable.

So I guess we'll have to ask ourselves if the area inside a fixture whip or w/p junction box is condisered a wet location or a damp location. IMHO it's a damp location. On the other hand wiring inside buried PVC is a wet location and THWN should be used but I'm sure THHN is used just as often.

 

[Sharpie]

I guess the manufacturers should be able to make nm cable with wet location wires and some type of non-wicking material. I know that they make UF. I personally hate working with the stuff (especially stripping it). I don't know, I guess I'm just thinking out-loud (so to speak).

Or maybe they could make UF that is easier to strip.

 

[cpal]

It doesn't really describe the letter designations.

Well
actually the table is quite informative it may require a little further investigation but to the trained eye it usually gives all the application information needed for a compliant installation.
T= thermoset insulation
W= cross link poly
R= Rubber
M= Machine wire
H= 75 deg C
HH= 90 Deg C
No H = 0 deg C
W= Wet Locations Use
HH, is a 90 Deg Conductor The foot notes add to your knowlege base (- 2) conductors have Temp ratings in wet or dry locations some of the insulation types don't.

Don't forget that the restrictions on the use of a conductors (insulation actually) beyond material is determined by the operating temperature of the insulation, and the conditions of use of the insulation.
I probably missed a few things I'm looking at the Code Book, but that should give you an idea. The UL wire marking guide is also helpful it can be downloaded from their site.

So an XHH

 

[480sparky]

...........No H = 0 deg C.....................

Kinda limits it's use, doesn't it?

(I think you mean 60 deg C)

 

[jaylectricity]

INSULATION MATERIAL
C = Cotton
FEP = Fluorinated Ethylene Propylene
MI = Mineral (magnesium oxide)
PFA = Perfluoroalkoxy
R = Rubber (sometimes Neoprene)
S = Silicone "rubber"
SA = Silicone-asbestos
T = Thermoplastic
TA = Thermoplastic-asbestos
TFE = Polytetrafluoroethylene ("Teflon")
X = Cross-linked synthetic polymer
Z = Modified ethylene tetrafluoroethylene


HEAT RATING
H = 75 degrees Celsius
HH = 90 degrees Celsius


OUTER COVERING ("JACKET")
N = Nylon


SPECIAL SERVICE CONDITIONS
U = Underground
W = Wet
-2 = 90 degrees Celsius and wet



Therefore, a "THWN" conductor has Thermoplastic insulation, is Heat resistant to 75? Celsius, is rated for Wet conditions, and comes with a Nylon outer jacketing.

Thanks, that's exactly what I was looking for.