THHN vs RHW

[peebee]

I have a project where THHN/THWN was specified for standard AC building wire, but RHW EPR was specified for a 125VDC system.

Any guesses why? I'm not familiar with RHW EPR. Any particular advantages to this over THHN/THWN?

 

[dpc]

I believe THHN/THWN is a thermoplastic insulation with a very thin nylon jacket. The RHW EPR is a rubber-based thermosetting material that is generally considered higher quality and will hold up better under fire or high-temp conditions. Probably used for the critical dc circuit to increase reliability.

Our normal standard is to specify THHN/THWN for small 120 V power circuit up to #8 AWG, then XHHW for anything larger. Same idea.

THHN is bottom of the barrel insulation as far as I'm concerned. I've often seen the nylon jacket scraped off when being pulled through a conduit body. It's OK for lighting and receptacles, but I wouldn't use it for anything I cared much about or for anything where reliability was a concern.

 

[advidana]

Ask the person that specified the job for your best answer.

 

[peebee]

Well I would have, but that's not exactly an option on this job.....

 

[alehman]

Some manufacturers use crosslinked poly for RHH/RHW.