# #8 for 50 amps. 310.16



## pimpin electrician

I've been taught a few different things about this topic. When using 310.16 which column do "YOU" use to decide what size conductor for your circuit?

I always install #6 for my hot tubs, ranges/ovens, and anything else that requires 50 amps.

I was taught in my apprenticeship to always use the 60 degree column to size your wire. Except when you need to derate your wire, then you use the 90 degree column before you make derating adjustments.

Then when working on a new 8 story apartment building, we ran #8 to all ovens. I'm not exactly sure if the breaker was sized at 40 or 50 amps though. My foreman on that job told me that he always uses the 90 degree to size his wire.

I remember when studying this topic that the degree columns have to do with all the termination points of the conductor being used. So i imagine if you are working on an old system then you should probably use the 60 degree column to be safe in that sense. If you are doing new construction i believe it is safe to use the 90 degree column, because i think that all lugs and terminations are rated 90 degrees now a days.

The reason i'm writing about this is because i have a customer that just purchased a new high end cooktop/range. He says that it requires 50 amps. He has a 40 amp breaker that was powering up his old unit. He wants to put a 50 amp breaker in so it doesn't void his warranty. I haven't been there yet, but i'm almost positive that it has #8 wire existing.

The conductors in this situation is a romex cable.

What would "YOU" do? Is it safe to have 50 amps running through #8 copper?
Just curious, i like to get reassurance from time to time on things.


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## MDShunk

We doing conductors in conduit here or NM/SER?


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## pimpin electrician

oh yeah... sorry... Romex


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## Rudeboy

Alameda? Yeah, my neighbor.

Welcome to the forum.
:thumbsup:


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## pimpin electrician

wassup rudeboy! you stayin busy these days?


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## Rudeboy

I've always run 6-3 for 50a oven circuit.


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## micromind

For conduit wire, check out 110.14, especially (C) (1) (a) and (b).

For type NM (Romex), look at 334.80

Rob


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## pimpin electrician

micromind said:


> For conduit wire, check out 110.14, especially (C) (1) (a) and (b).
> 
> For type NM (Romex), look at 334.80
> 
> Rob


Thanks, that helps alot! That say's it all right there.


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## pimpin electrician

Rudeboy said:


> I've always run #6 for 50a oven circuit.


That's how i work as well, but that is not the case with the situation that i am speaking of. i'm dealing with existing wiring.


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## Rudeboy

pimpin electrician said:


> wassup rudeboy! you stayin busy these days?


Yeah busy. Getting my forty. It's busier now. A few months ago was a little slower.
How about you?


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## Rudeboy

pimpin electrician said:


> That's how i work as well, but that is not the case with the situation that i am speaking of. i'm dealing with existing wiring.


Earlier this week I replaced an existing 10-3 with an 8-3 for a new oven rated at 40a.
Pretty easy crawl but the cat piss smell in the house was awful.


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## pimpin electrician

Rudeboy said:


> Yeah busy. Getting my forty. It's busier now. A few months ago was a little slower.
> How about you?


yeah, got a few good ones in the works right now. busy as i want to be right now. Good to hear your working! Take care bro.


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## macmikeman

The installation book might say the oven requires 50 amps but I bet it never sees that much load. I would keep the 40 amp breaker on the existing #8, run it, test it, test it more, and if it does indeed draw more than the 40 amps when running, show the owners and explain what you need to do to fix the situation. I would not put a 50 amp breaker on it. Circuit breaker terminations when less than 100 amps will most likely be rated at 75 deg sometimes but usually 60 deg. Above 100 amps you might run into 90 deg terminations.


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## Magnettica

If the oven is less than 12kw, #8 and 40 amp overcurrent protection is fine.

NEC 220.56


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## electricmanscott

macmikeman said:


> The installation book might say the oven requires 50 amps but I bet it never sees that much load. I would keep the 40 amp breaker on the existing #8, run it, test it, test it more, and if it does indeed draw more than the 40 amps when running, show the owners and explain what you need to do to fix the situation. I would not put a 50 amp breaker on it. Circuit breaker terminations when less than 100 amps will most likely be rated at 75 deg sometimes but usually 60 deg. Above 100 amps you might run into 90 deg terminations.


That's the route I'd take too.

Side note, here in MA you only have to go with the 60 deg rating if the NM is installed in thermal insulation.


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## 220/221

> Is it safe to have 50 amps running through #8 copper?


Yes, but the infinite wisdom of the NEC says the #8 in romex is special and is only capable of carrying 40 amps.

Also, I can't see how a smaller OCPD would logically void a warranty.


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## Toronto Sparky

Do they even make 60 degree or even 75 degree wire these days? I have not seen anything less than 90 degrees in years (unless it's used or existing)

I seem to remember 8/3 romex being rated @ 45 amps.


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## danickstr

Just remember most ranges max out under 50 amps. and that is ONLY if they run both the top broiler and bottom baking elements, and ALL 4 top burners. 96% of the time, 40 amps will handle the load. If they are actually running all six elements at once and at full amperage, they are probably burning something :laughing:

THHN (THWN) is rated for 90 degrees C. Most terminations are rated at 75 degrees c. Therefore the wire chart is typically used at 75. As mentioned earlier, de-rating is at 90, because it is just wire to wire at the "hot spots". When the wires come into the boxes to the terminations, they spread out and the de-rating is no longer an issue.

But if is wasn't against code, I would be fine with #8 Cu on a 50 amp range breaker. I see no worries there, if everything is installed properly. But don't do it, it isn't code, unless you have a 90 degree breaker and receptacle, which I think do not exist.


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## smkie

I've always been taught 60 degree columb for anything under a 100 a, 75 degree for anything over 100 a, 90 degree for derating


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## NY ELECTRIC

We were talking about this a while ago I always run 6 to the high end ranges double oven etc. however after the discussion here I looked at the specs for some wolf and viking double ovens that call for a 50amp ocpd and none of them with doubble oven bread warmer whatever exceeded 12000kva so 8 would be ok.


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## Victory Pete

Magnettica said:


> If the oven is less than 12kw, #8 and 40 amp overcurrent protection is fine.
> 
> NEC 220.56


I am upgrading 10-3 romex to 8-3 for a new 8500W Cooktop. The existing breaker is a 40 amp. I am confused by the 75 and 90 degree rating for the breakers and outlets. So if I have 8-3 romex which is 90 degree rated, I need to have a breaker and outlet rated at 90 degrees also to fuse it at 50 amps? I don't get it, the rating is just the breaker and the outlet that restricts the current in the wire? The breaker and the outlet are already rated for 50 amps. I don't see the logic in this.


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## Black Dog

Victory Pete said:


> I am upgrading 10-3 romex to 8-3 for a new 8500W Cooktop. The existing breaker is a 40 amp. I am confused by the 75 and 90 degree rating for the breakers and outlets. So if I have 8-3 romex which is 90 degree rated, I need to have a breaker and outlet rated at 90 degrees also to fuse it at 50 amps? I don't get it, the rating is just the breaker and the outlet that restricts the current in the wire? The breaker and the outlet are already rated for 50 amps. I don't see the logic in this.


334.80 Ampacity. The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The allowable ampacity shall not exceed that of a 60°C (140°F) rated conductor. The 90°C (194°F) rating shall be permitted to be used for ampacity adjustment and correction calculations, provided the final derated ampacity does not exceed that of a 60°C (140°F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.80(A).
Where more than two NM cables containing two or more current-carrying conductors are installed, without maintaining spacing between the cables, through the same opening in wood framing that is to be sealed with thermal insulation, caulk, or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a) and the provisions of 310.15(A)(2), Exception, shall not apply.
Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a).


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## Victory Pete

Black Dog said:


> 334.80 Ampacity. The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The allowable ampacity shall not exceed that of a 60°C (140°F) rated conductor. The 90°C (194°F) rating shall be permitted to be used for ampacity adjustment and correction calculations, provided the final derated ampacity does not exceed that of a 60°C (140°F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.80(A).
> Where more than two NM cables containing two or more current-carrying conductors are installed, without maintaining spacing between the cables, through the same opening in wood framing that is to be sealed with thermal insulation, caulk, or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a) and the provisions of 310.15(A)(2), Exception, shall not apply.
> Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a).


Thanks for the post but this doesn't help. So when can I fuse 8-3 "NMB" with a 50 amp breaker?


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## Dennis Alwon

smkie said:


> I've always been taught 60 degree columb for anything under a 100 a, 75 degree for anything over 100 a, 90 degree for derating


This is somewhat true but there is more to it than that. BTW- look at art 110.14(C)

First off if the installation is new then you will see that all terminations are rated 75C so if your wire is rated 75C or higher then you can use the 75C column to size your wire, however if you are using NM or seu in some case, then you have to use 60C (art 334.80 and 338.10(B)(4)) for the sizing of the final ocpd.

If it is an old installation and there is no way to know what the temperature rating of the terminations are then you have to assume 60C for 100 amps or less and 75C for over 100 amps.

Not sure when that changed but it has been quite a while that the 75C terminals have been around.


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## lannjenks

Victory Pete said:


> I am upgrading 10-3 romex to 8-3 for a new 8500W Cooktop. The existing breaker is a 40 amp. I am confused by the 75 and 90 degree rating for the breakers and outlets. So if I have 8-3 romex which is 90 degree rated, I need to have a breaker and outlet rated at 90 degrees also to fuse it at 50 amps? I don't get it, the rating is just the breaker and the outlet that restricts the current in the wire? The breaker and the outlet are already rated for 50 amps. I don't see the logic in this.


The problem is not the current rating of the breaker, but the temperature rating of that breaker at the termination point. The wire acts as a heat sink for the termination, so if you have a 60C rated breaker, you are going to need a bigger wire to sink the heat away from the breaker, hence you are stuck with the 60C column regardless of the 90C rating of the wire.

There are no circuit breakers rated higher than 75C according to the UL White Book.


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## 220/221

pimpin electrician said:


> Thanks, that helps alot! That say's it all right there.


Yeah but it doesn't mean we are not goint to beat it to death with unnecessary comments :laughing:

I started resi wiring when SE was the common material for ranges and always used 50A breakers. 

When the 4 wire became the new method and romex was the new material, I had no idea that it was classified different and use 50A breakers for a decade.

A customer pointed it out to me :jester: so I looked it up :laughing:

90% of the inspectors here don't say anything though. It's a technical foul in my book. 8=8


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## Victory Pete

lannjenks said:


> The problem is not the current rating of the breaker, but the temperature rating of that breaker at the termination point. The wire acts as a heat sink for the termination, so if you have a 60C rated breaker, you are going to need a bigger wire to sink the heat away from the breaker, hence you are stuck with the 60C column regardless of the 90C rating of the wire.
> 
> There are no circuit breakers rated higher than 75C according to the UL White Book.


While I was driving back from the supply house with my 8-3 MC, I realized that the larger the size wire that is used, will heat up the least, so yes a 60C rated connection wants the bigger wire. Thanks for your help.

PS So when can you use 8-3 MC with a 50 amp outlet and breaker? An AHJ had me do this recently.


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## lannjenks

8-3 MC works fine for 50A as long as your breaker and load connections are rated at 75C. The problem with using #8 on a 50A breaker in residential is the 60C limitation of romex due to 334.80 as some previous posters have noted. That would limit #8 romex to a 40A breaker.


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## BababooeyHTJ

Why couldn't you use 8-3 mc on a 50a device?

With everything that you've learned in this thread you should be able to get that answer on your own.


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## Victory Pete

BababooeyHTJ said:


> Why couldn't you use 8-3 mc on a 50a device?
> 
> With everything that you've learned in this thread you should be able to get that answer on your own.


Thanks for your useless post!


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## lannjenks

I think sizing wire is one of the most misunderstood things in the codebook.


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## BababooeyHTJ

Victory Pete said:


> Thanks for your useless post!


Do you have 60c connections? Do you need to derate for any reason like temperature? No? Then you're good to go.

#8 is good for 50a at 75c.


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## Dennis Alwon

Victory Pete said:


> PS So when can you use 8-3 MC with a 50 amp outlet and breaker? An AHJ had me do this recently.


There is no limitation on MC as there is on NM however if the terminals are 75C as stated earlier then 8/3 MC can be used at 50 amps. If the terminals are not marked on the panel or if the panel states 60C then 8/3MC cannot be used at 50 amps but rather at 40 amps


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## Meadow

electricmanscott said:


> That's the route I'd take too.
> 
> Side note, here in MA you only have to go with the 60 deg rating if the NM is installed in thermal insulation.


Wait, NM is permitted to go higher?


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## Jakeleg600

pimpin electrician said:


> I've been taught a few different things about this topic. When using 310.16 which column do "YOU" use to decide what size conductor for your circuit?
> 
> I always install #6 for my hot tubs, ranges/ovens, and anything else that requires 50 amps.
> 
> I was taught in my apprenticeship to always use the 60 degree column to size your wire. Except when you need to derate your wire, then you use the 90 degree column before you make derating adjustments.
> 
> Then when working on a new 8 story apartment building, we ran #8 to all ovens. I'm not exactly sure if the breaker was sized at 40 or 50 amps though. My foreman on that job told me that he always uses the 90 degree to size his wire.
> 
> I remember when studying this topic that the degree columns have to do with all the termination points of the conductor being used. So i imagine if you are working on an old system then you should probably use the 60 degree column to be safe in that sense. If you are doing new construction i believe it is safe to use the 90 degree column, because i think that all lugs and terminations are rated 90 degrees now a days.
> 
> The reason i'm writing about this is because i have a customer that just purchased a new high end cooktop/range. He says that it requires 50 amps. He has a 40 amp breaker that was powering up his old unit. He wants to put a 50 amp breaker in so it doesn't void his warranty. I haven't been there yet, but i'm almost positive that it has #8 wire existing.
> 
> The conductors in this situation is a romex cable.
> 
> What would "YOU" do? Is it safe to have 50 amps running through #8 copper?
> Just curious, i like to get reassurance from time to time on things.


Well I would say that romex isn't 90degree wire,so would have to use 75degree column . So I would say no on 50amp breaker.


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## Wardenclyffe

IBTL


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## micromind

Jakeleg600 said:


> Well I would say that romex isn't 90degree wire,so would have to use 75degree column . So I would say no on 50amp breaker.


The code requires NM cable (Romex) to use the 60C column even though it's rated at 90C.


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## kb1jb1

Old thread caught in limbo.


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