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This question is two fold:

I have a PrimeWeld 225x TIG welder and it calls for a 50amp/220v breaker and NEMA 6-50P.
I need to run 60 feet from NEMA 6-50P to breaker box (I have 200amp service). Googling, I think I should be using AWG 6/2 wire. This will be running indoor along exposed ceiling. So I assume conduit is a must.

My father-in-law is an electrician and he says I can use his AWG 8 (500' spool) ground wire to save money. He says I can run three 60' lengths of this wire through conduit to make 8/2 with ground.

I'm skeptical because the conduit would be mounted to wooden ceiling joist. So I want the 50amp breaker to do its job if for some reason the wires get too hot. He mentioned he has plenty of heavy duty plastic/metal conduit used for outdoor C/A units if I wanted to be extra safe.

Here is exactly (best I could read) what his wire has stamped on it:

"SOUTHWIRE E51583(UL)(AWG 8) 8,367mm2 CU TYPE MTW THWN-2 OR THHN OR GASOLINE AND OIL RESISTANT II OR AWM 600 VOLTS VW-1--CSA T90 NYLON OR TWN75 FT1 NOM-ANCE 90° C"

I'm used to only running Romex wire from Home Depot, so this multi-rated wire is so confusing to me and he was trying to explain it to me (language barrier), but I'm still not sure.

  1. Is this AWG 8 wire acceptable for my 50amp application?
  2. Can I use it along with conduit to make 8/2 (with ground)for my application?

6/2 MC wire runs about $3/ft, so it's great that he can save me a lot of money, but I hope someone can clarify if his idea would be safe and up to code.

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  • Can you post photos of the label on the inside of the breaker panel you're planning to run this circuit from? Oct 15, 2021 at 1:32
  • Label? What am I looking for? Do you mean just on the door or take the panel off?
    – foobash
    Oct 15, 2021 at 1:39
  • For most panels, it's on the inside of the door, yes Oct 15, 2021 at 1:39
  • By the way, pay close attention to the rules on duty cycle on welders... often they can be plugged into a surprisingly small circuit. Also note that electric vehicles are becoming all the rage, and home buyers are willing to pay a premium for houses with an EV receptacle. A 6-50 receptacle should be just fine for that! Oct 15, 2021 at 3:29

2 Answers 2

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#1. Anytime you're into #10 or larger copper, there are better alternatives.

#2. Use a receptacle that is rated for 75C thermal, and aluminum. There is nothing wrong with aluminum wire at these larger sizes (#6 and larger).

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Use Aluminum wire, AWG 6/2 or THHN or XHHW

This is rated for 50A if both terminals are 75C thermal rated (breakers are).

And well under a buck a foot for the whole cable, at least under normal market conditions.

If you want to run conduit the entire way (which you would have to in order to use your father's wires), feel free to use THHN or XHHW aluminum individual wires at about 20 cents a foot under normal market conditions.

Note that if you run EMT metal conduit (properly) the EMT provides the ground path and you don't need a ground wire.

If it is placed in conduit, this must be the only circuit in the conduit. See next section for details.

Or use that #8 copper...

... by selling it on Craigslist/Facebook Marketplace for what it will fetch, given the current shortages and market prices, it'll fetch well more than the aluminum wire will cost, so net profit! That spool lists for $250 right now.

If you must use it for social reasons, you must a) run in conduit the entire way (no gaps) and b) follow my advice about getting a socket with 75C thermal rating. The circuit breakers are 75C. THWN-2 wire is good for 90C. You are limited by the lowest temperature, that being 60C unless the socket is 75C.

#8Cu and #6Al are allowed 40A at 60C.
#8Cu and #6Al are allowed 50A at 75C. <-- Bingo!

However this only works if there is 1 circuit in the conduit. If 1-2 other circuits are in the conduit, the wires derate to 44A. With 3 other circuits, 38A. With 4 or more, don't ask.


What about ground? Use EMT, IMC or RMC metal conduit (properly) and no need to run a ground wire. Regardless, #8 black wire cannot be re-marked to be ground. (NEC 250.119).

You don't need neutral, but #8 black can't be re-marked to be neutral either. NEC 200.6.

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  • This wire is black. What's wrong with marking the black wire (say green tape on each end) ground? I do have a spool of green wire. Gotta see what gauge that is.
    – foobash
    Oct 15, 2021 at 2:58
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    @foobash Well that's good news. Remarking grounds smaller than #4 is a code violation. NEC 250.119. This circuit needs ground wire that is #10 CU or larger, or #8 AL or larger. Although, if it's done in EMT metal conduit, it does not need a ground wire AT ALL. Oct 15, 2021 at 3:07
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Can I use it along with conduit to make 8/2 (with ground)for my application?

What throws a lot of folks is that they tend to base amps off the rating for NM-B. Your 8/2 (plus ground) NM-B is only rated for 40 amps, because NEC says NM-B is considered 60° C rated. You cannot use this wire at all here. It must be 6/2 plus ground NM-B cable if you want cable here.

The free wire your father-in-law has is different. You said it says this

SOUTHWIRE E51583(UL)(AWG 8) 8,367mm2 CU TYPE MTW THWN-2 OR THHN OR GASOLINE AND OIL RESISTANT II OR AWM 600 VOLTS VW-1--CSA T90 NYLON OR TWN75 FT1 NOM-ANCE 90° C

The important things in that list are

  • CU (copper)
  • AWG 8 (8 gauge)
  • THWN-2 OR THHN (can be used for both wet and dry applications)
  • 90° C

THHN-2/THWN-2 is a single wire and counts as 90° C rated, which means you can run 55 amps through it. The catch is that, being wire and not cable, it must be run inside conduit. If you go through the hassle of running EMT (metal) conduit, that can also be your ground path. Since you have 500' and only need 60' (180' total for two hots + ground), you have enough to run in PVC instead and save money and hassle.

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  • He has plenty of conduit. MC and some plastic/metal reinforced that is used on outdoor on central air units. Even though it's rated at 90C, I gotta still go by 75C cause of my breaker, right? So this will cost me zero if it's safe/code.
    – foobash
    Oct 15, 2021 at 2:56
  • Can't run all 3 of this wire in PVC - it is black - ground needs to be EMT or a green ground. Oct 15, 2021 at 3:16
  • @foobash -- the "plastic/metal reinforced conduit" is called LFMC, btw Oct 15, 2021 at 4:23
  • @Machavity 90 degree, but my breaker/panel only gonna be rated at 75 degrees C. Is 75C still good for 50A?
    – foobash
    Oct 16, 2021 at 11:31
  • The breaker temp rating does not affect what wire you can use. Amps are the key measurement. The breaker is designed to trip when it reaches its limit of 50A (which I assume is 75C internally), meaning the wire won't be carrying more than 50A. The 90C rating lets you know the wire supports up to 55A before hitting that 90C melting point. As long as breaker max amps is less than wire max amps you're fine.
    – Machavity
    Oct 16, 2021 at 14:12

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