Conductor Insulation and Uses

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sjp42051

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Electrical Contractor
I'm purchasing wire for a job and looking at pricing and it occurred to me that most everything I use is THHN/THWN-2. Thermoplastic wrap good for heat and moisture. I forget what the N stands for. Anyway, I was wondering who out there can explain applications and uses for the various types of conductor insulation and if they are even commonly used anymore. XHHW, RHW, THHW and their variations specifically. I come across these ones on existing systems, but are they commonly installed on new projects? Thanks for the input.
 
The N stands for nylon which is the outer covering on the insulation. XHHW is considered by many to be superior to THHN/THWN-2 because it's made from a different material. For normal use I don't see a problem with the basic THHN/THWN-2.

Welcome to the Forum. :)
 
sjp42051 said:
I'm purchasing wire for a job and looking at pricing and it occurred to me that most everything I use is THHN/THWN-2. Thermoplastic wrap good for heat and moisture. I forget what the N stands for. Anyway, I was wondering who out there can explain applications and uses for the various types of conductor insulation and if they are even commonly used anymore. XHHW, RHW, THHW and their variations specifically. I come across these ones on existing systems, but are they commonly installed on new projects? Thanks for the input.
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I am not sure if this table has been relocated. In the 2020 NEC look at table 310.4(a).
 
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