8ga CU wire - Ampacity

[Spudland_Dave]

So I'm reading some conflicting info on the Ampacity of 8ga CU wire...

Long story short...I need 5' of wire to wire in a 50A Range Plug....8-3 wire gonna be fine?

 

[madosta]

All of my 50amp welded plugs are 6ga cu. Why not just use #6?

 

[rlitman]

It depends on what you're doing with said plug. If this is a dedicated circuit for a welder, it will probably be fine. If it is a circuit for a range, that's a no-go.

 

[Spudland_Dave]

All of my 50amp welded plugs are 6ga cu. Why not just use #6?

No reason not to use #6...

As for its use. I wired up my existing garage with a 14-50R...made myself a converter to go from 14-50 to 6-50 when I weld (Refused to pay 70 bucks for the Genuine Miller one)... I also can hook my Generator up to it, and my compressor, etc.. (Along the way I've made a few convertor/extension cords) even to the point of being able to hook up my 20a 220v Pressure Washer up to it.
This weekend I'm gonna want to use my compressor IN the garage, so I'm gonna wire up an outlet under my panel...down the road I dont even expect using this outlet, but it will be nice to have just in case.

I could easily use #6, I've got all kinds of #6 CU wire at home.

Why did I go 14-50R in the first place? Because thats whats on the front of a Miller Trailblazer/Bobcat...so I've got plenty of experience with it and its cheap & easy to deal with and sorta industry standard...

 

[Jose G]

8ga will withstand about 40-45A without problem. easy to find wire that size (6ga isnt easy to find)...but its not rated to 50A in any way. if you plan of using a 180A welder... 8ga will be more than enough. but still... not 50A ready.

 

[Spudland_Dave]

6ga it is then!
Biggest problem is wiring the 2 gang box...big stiff wire, normal box..working it all in isnt fun. I know I used choice words on my last one....

 

[Jose G]

you could try a 4x4 box to help you get more space.

 

[wyliesdiesels]

Dave-

The reason ur getting conflicting specs is because there is different insulation temperature grades of wire. For example, while the conductors in Romex/NM has 90C deg rated insulation, it is limited to a 60C deg ampacity by NEC code. Also, because of 240.4d, anything #1 and smaller(if I remember right- don't have my book in front of me) is sized based on 60C deg rating.

If you are talking about #8 Romex, it is limited to 40a, #6 Romex is 50a. Now, if u were to use #8 THHN wire, it has a higher ampacity(I believe 55a @ 75C deg- again don't have my book in front of me). So if u wanna use #8 wire for 50 amps, use individual THHN wire and u will be fine!

 

[Spudland_Dave]

Dave-

The reason ur getting conflicting specs is because there is different insulation temperature grades of wire. For example, while the conductors in Romex/NM has 90C deg rated insulation, it is limited to a 60C deg ampacity by NEC code. Also, because of 240.4d, anything #1 and smaller(if I remember right- don't have my book in front of me) is sized based on 60C deg rating.

If you are talking about #8 Romex, it is limited to 40a, #6 Romex is 50a. Now, if u were to use #8 THHN wire, it has a higher ampacity(I believe 55a @ 75C deg- again don't have my book in front of me). So if u wanna use #8 wire for 50 amps, use individual THHN wire and u will be fine!

Gotcha..so that means I could do #8 THHN, inside a conduit with a ground and voila. IF I go this way, what ground wire should i use..I assume Bare #10 is adequate? Because this is literally straight 18" below the breaker box, conduit is doable easily.

Of course i went thru my scrap pile, and I've got a 3' piece of 6ga Romex...not enough. unless a take a piece off my 30' section...just gotta debate the $$ side of buying some #8 vs using what I got.

Thanks!

 

[Speedy Petey]

8ga will withstand about 40-45A without problem. easy to find wire that size (6ga isnt easy to find)...but its not rated to 50A in any way. if you plan of using a 180A welder... 8ga will be more than enough. but still... not 50A ready.

WHAT are you talking about??? You are guessing at all of this.
And #6 is SUPER easy to find everywhere.

 

[Speedy Petey]

Dave-

The reason ur getting conflicting specs is because there is different insulation temperature grades of wire. For example, while the conductors in Romex/NM has 90C deg rated insulation, it is limited to a 60C deg ampacity by NEC code. Also, because of 240.4d, anything #1 and smaller(if I remember right- don't have my book in front of me) is sized based on 60C deg rating.

If you are talking about #8 Romex, it is limited to 40a, #6 Romex is 50a. Now, if u were to use #8 THHN wire, it has a higher ampacity(I believe 55a @ 75C deg- again don't have my book in front of me). So if u wanna use #8 wire for 50 amps, use individual THHN wire and u will be fine!

THIS is the correct answer.

Bottom line:
#8NM cable = 40A
#8THHN in conduit = 50A

 

[wyliesdiesels]

WHAT are you talking about??? You are guessing at all of this.
And #6 is SUPER easy to find everywhere.

I was gonna correct him, but I'm too tired to bicker! And yeah, just saw all different forms of #6 @ Homo depot the other day- #6NM, #6 THHN, #6 bare, etc. etc.!

 

[pattenp]

Dave-

The reason ur getting conflicting specs is because there is different insulation temperature grades of wire. For example, while the conductors in Romex/NM has 90C deg rated insulation, it is limited to a 60C deg ampacity by NEC code. Also, because of 240.4d, anything #1 and smaller(if I remember right- don't have my book in front of me) is sized based on 60C deg rating.

If you are talking about #8 Romex, it is limited to 40a, #6 Romex is 50a. Now, if u were to use #8 THHN wire, it has a higher ampacity(I believe 55a @ 75C deg- again don't have my book in front of me). So if u wanna use #8 wire for 50 amps, use individual THHN wire and u will be fine!

Wrong NEC section. It's 110.14(c). 240.4(d) is overcurrent protection of small conductors. Also the 60C requirement on conductors #1 and smaller is somewhat meaningless because of the "Unless clause" in 110.14(c)(1) where if the device is marked otherwise. Since most devices are are marked 75C.

Here's a good Mike Holt video about 110.14.

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