Am I understanding THHN de-rating correctly?

[GarageGuy89]

I need to run a 50 amp breaker roughly 50' max to the 14-50R outlet. Reason I am asking this question is I think, based on my pricing, THHN is about half the cost, so my main objective is cost savings.

This is going in a garage in seattle, WA, breakers are Eaton type BR (which correct me if I'm wrong rated at 76C?)

If I de-rate THHN to 75C is it acceptable to run it on the 50 amp circuit?
Does it need to be in conduit or does it just hang loose, do you need to tape it together every 10' or something?

What's the DL on de-rating?

 

[wyliesdiesels]

Why are u derating?

I think youre confused. No need to derate anything if all youre doing is running 4-wires(2 ungrounded conductors, 1 grounded conductor and 1 grounding conductor) in the same pipe.

You would use the 75* c ampacity for THHN.

So for 50a circuit u can use #8.

Derating would be for either high temperature or excess # of conductors in same pipe.

Yes THHN needs to be in conduit for the entire run from panel to j box.

 

[manwithtools]

I'm thinking the OP is referring to "derating" from 90C column to 75C column. This is sometimes confusing because while the wire might be rated for 90C operation, the termination points are only rated for 75c and therefore one would need to use the 75C column for amperage values and wire size selection.

In realty it's not derating, it's choosing from the right column for the application. It's a terminology thing. Derating is a factor that is applied to account for ambient temperature or other factors beyond the numbers shown in the ampacity tables.

 

[rockwithjason]

I need to run a 50 amp breaker roughly 50' max to the 14-50R outlet. Reason I am asking this question is I think, based on my pricing, THHN is about half the cost, so my main objective is cost savings.

you never said what size wire you were wanted to run

This is going in a garage in seattle, WA, breakers are Eaton type BR (which correct me if I'm wrong rated at 76C?)

75 degC

If I de-rate THHN to 75C is it acceptable to run it on the 50 amp circuit?
Does it need to be in conduit or does it just hang loose, do you need to tape it together every 10' or something?

derate it from what? you never said. will this be in conduit? will it be in a wall? it sounds like you want to run thhn loose in the wall and that is a no no. thhn must be in conduit. the added cost of the conduit generally makes cable assemblies more cost effective

What's the DL on de-rating?

when groups of wires are run together they tend to build up heat. the increase in heat makes the insulation less effective, so we derate where we are running many wires together. how and when to derate depends on many factors

 

[GarageGuy89]

Thank you for the responses. I did not realize it had to be in conduit, and I guess I don't really understand the derating process in general. So, as you all have stated I think the conduit plus the wire will just about even out the cost between the two, plus I don't want to have to install conduit.

I'll just run the Romex....

 

[mike93lx]

Thank you for the responses. I did not realize it had to be in conduit, and I guess I don't really understand the derating process in general. So, as you all have stated I think the conduit plus the wire will just about even out the cost between the two, plus I don't want to have to install conduit.

I'll just run the Romex....

If the romex is unprotected, it could also require conduit, depending on its placement.

 

[pattenp]

Using Romex you need to rate it at 60 deg C. So you need #6 Romex for 50A. Also to sleeve it in conduit is only needed if the Romex is run in an exposed location where it may be subject to damage.