Oven

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John Wayne

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Hello -

A customer is thinking about replacing his wall oven. The wire going to the oven is 6-2 with ground on a 50 amp breaker. The new unit requires 40 amps. Would you leave everything as is or would you run an 8 gauge and 40 amp breaker? Thanks
 
If the wire is 6/2 with ground then that may be an issue as most ovens need a neutral...You need 3 wires and an equipment grounding conductor
 
If the 6/2 is not se cable then it was never code compliant. If it is se cable and comes from the service panel then you technically can leave it if you are just replacing the unit.
 
There is no reason to reduce the wire size when you reduce a breaker size; that would be a huge waste.

As an existing installation, you can keep the 3-conductor cable as long as it was compliant when installed.
 
Agreed. Verify the existing installation. You might have 6/3 and no ground, instead of 6/2 with bare ground. Transfer the 3-wire cord from the old appliance to the new one, using the bonding jumper for the chassis ground.

When you say: "The new unit requires 40 amps," are you referring to its actual load amperage or its maximum OCPD?
 
John Wayne said:
Hello -

A customer is thinking about replacing his wall oven. The wire going to the oven is 6-2 with ground on a 50 amp breaker. The new unit requires 40 amps. Would you leave everything as is or would you run an 8 gauge and 40 amp breaker? Thanks
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Does this guy drive a new Cadillac or Mercedes ? Does he wear expensive suits ? Sub Zero appliances in the kitchen?


Sorry I got carried away there.
 
If it doesn't need a neutral 6-2 with ground is fine. Many will need a neutral.

SE cable (two hots one bare) once was fine and still is if was compliant when initially installed, has to be coming from service panel and not a feeder supplied panel though.

Presuming ground/neutral issues are ok, I probably wouldn't even change the 50 amp breaker. You are allowed to put multiple cooking appliances on a 50 amp circuit. (210.23(C))
 
I just finished lunch and am feeling groggy from the carbs. So I need to stir up a bit of trouble, just to wake myself up. :happyyes:
ptonsparky said:
Change the breaker to a 40, collect money, go home and sleep well.
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If you do that, wouldn't you have to make sure the EGC is at least a #8? With a 40 amp breaker, a #8 phase conductor with a #10 EGC would normally be a match. But this would increase the phase conductor above the required ampacity. My quick calculation tells me that the proportional upsize for the EGC would be from #10 to #8.

Maybe I should just take a nap.:sleep:
 
charlie b said:
I just finished lunch and am feeling groggy from the carbs. So I need to stir up a bit of trouble, just to wake myself up. :happyyes:

If you do that, wouldn't you have to make sure the EGC is at least a #8? With a 40 amp breaker, a #8 phase conductor with a #10 EGC would normally be a match. But this would increase the phase conductor above the required ampacity. My quick calculation tells me that the proportional upsize for the EGC would be from #10 to #8.

Maybe I should just take a nap.:sleep:
Click to expand...

I was actually going to ignore that bit of twisted logic the code has going for it. Someday someone will figure out how to correct what nonsense it is.
 
Dennis Alwon said:
Tap a nap - the change is from #6 to #8 both of which require a #10 equipment grounding conductor.
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True, but irrelevant. :happyno: You would still need to upsize the EGC. The rule says that if you increase the size of the ungrounded conductors (with "increased" having been explained in the 2017 edition as meaning beyond the minimum ampacity requirements), then you increase the EGC proportionally.
 
charlie b said:
True, but irrelevant. :happyno: You would still need to upsize the EGC. The rule says that if you increase the size of the ungrounded conductors (with "increased" having been explained in the 2017 edition as meaning beyond the minimum ampacity requirements), then you increase the EGC proportionally.
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Dumber than dumb but you're correct that's what the book says. :huh:
 
I always assumed if the egc I used with the appropriate breaker was the same for the next wire size and breaker then what difference would it make. I believe In this case the equipment grounding conductor would have to be #6.
 
So if I increase the size of #12 to #6 then the equipment grounding conductor would have to be #6 however if I increase the wire from #8 to #6 the equipment grounding conductor still has to be #6-- what gives....
 
If you do that, wouldn't you have to make sure the EGC is at least a #8? With a 40 amp breaker, a #8 phase conductor with a #10 EGC would normally be a match. But this would increase the phase conductor above the required ampacity. My quick calculation tells me that the proportional upsize for the EGC would be from #10 to #8.

Maybe I should just take a nap.:sleep:[/FONT][/SIZE]
[/QUOTE]

Please help me out understanding this.
I'm not trying to put words in your mouth.
Are you saying that the GEC on #8/2 or #8/3 is not code compliant?
 
Knuckle Dragger said:
If you do that, wouldn't you have to make sure the EGC is at least a #8? With a 40 amp breaker, a #8 phase conductor with a #10 EGC would normally be a match. But this would increase the phase conductor above the required ampacity. My quick calculation tells me that the proportional upsize for the EGC would be from #10 to #8.

Maybe I should just take a nap.:sleep:[/FONT][/SIZE]
Click to expand...

Please help me out understanding this.
I'm not trying to put words in your mouth.
Are you saying that the GEC on #8/2 or #8/3 is not code compliant?[/QUOTE]

It is if that is what the load requires, 8s and a 40 amp breaker, for simplicity, with 10 EG.
Upsize an original 20 amp circuit of #12s to 8s because that is what you have on the truck would require all #8.
 
I think what he is saying is the next size up rule you would also have to next size up the ground..... splice 8's to the 6's and keep the 10 ground..
(Note: I don't have a 2017 book but I'm guessing there's a new definition)
 
Dennis Alwon said:
So if I increase the size of #12 to #6 then the equipment grounding conductor would have to be #6 however if I increase the wire from #8 to #6 the equipment grounding conductor still has to be #6-- what gives....
Click to expand...

The #12 part is correct but the #8 to #6 is not for a 40 amp circuit. Since you start with a 40 amp circuit and a #8 phase conductor by using a #6 for the same 40 amp circuit you have increased the size of the phase conductor therefore you must also proportionately increase the size of the EGC. So if the #8 AWG cable has a #10 EGC and the #6 AWG cable has the same #10 EGC you cannot use the #6 cable for the 40 amp circuit because you have not increased the size of the EGC (both cables have a #10 EGC). The proportionate increase in the EGC would be the same ratio as the increase from #8 to #6.

As I said previously DUMB...
 
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