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Discussion Starter · #1 ·
Hi,

I'm looking to replace my current oven with a new oven which calls for a 30amp circuit. My current oven circuit is 40amps (8-3 wire w/ground). Are there any issues connecting the oven's 10 gauge wire to my supply's 8 gauge wire?

The only way I can see this being a problem is if the oven pulled more than 30amps at some point. While I know that's possible with some 30amp rated condensers, can an oven do that?

Thanks!
 

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Scared Electrician
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swap out the 40a breaker for a 30a
 

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Semi-Pro Electro-Geek
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swap out the 40a breaker for a 30a
Does it call for a 30A circuit, or is it rated for 30A? Those are not the same thing. If it calls for a 30A circuit (saying something like, "maximum circuit breaker rating: 30A") then replace the 40A breaker with a 30A. If the oven is rated for 30A (saying something like, "240V 30A") then keep the 40A breaker - you need at least 25% extra circuit capacity above the actual load.
 

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Master Electrician
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Does it call for a 30A circuit, or is it rated for 30A? Those are not the same thing. If it calls for a 30A circuit (saying something like, "maximum circuit breaker rating: 30A") then replace the 40A breaker with a 30A. If the oven is rated for 30A (saying something like, "240V 30A") then keep the 40A breaker - you need at least 25% extra circuit capacity above the actual load.
On what basis do you make this statement?
 

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Lic Elect/Inspector/CPO
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MFG when the do the data plate and it says 240v/30amp, thney have already taken into account any variables.
That means use a 30 amp breaker.
 

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If the oven has a 30 amp plwer plug then it can be on a maximum 30 amp circuit.
 

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Master Electrician
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I suspect this might be a direct-wired wall oven?? Have you gotten the oven yet?
 

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Just as an example I looked at a GE wall oven manual which states

This appliance must be supplied with the proper voltage
and frequency, and connected to an individual, properly
grounded branch circuit, protected by a circuit breaker
or fuse having amperage as noted on rating plate.​
(Rating plate is located on front frame.)

In the case of the one I looked at, the product specs called out a specification of "BREAKER SIZE" so it's pretty explicit.
http://products.geappliances.com/Ma...er?RequestType=PDF&Name=320300_jrs06bj_r2.pdf

It really should be something that any confusion can be cleared up with the installation manual, which is usually available online for most new and even a lot of not new models.
 

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Civil Engineer
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This discussion seems to be inconsistent with a long history of posts on this forum by licensed electricians. In these posts, the electricians have pointed out that the purpose of a breaker is to protect the wiring, NOT the device, from overcurrent situations. Therefore, the maximum breaker size is driven by the wiring, NOT by the nameplate amperage on the device.

Previous posts have stated explicitly that the manufacturer of the device is required to install protection within the device to handle electrical issues such as overcurrent situations, faults, low voltage etc. For example, my GE wall oven uses 16 gage wire for a 30A circuit within the oven. I found this curious, as 16 gage wire would never be used in your house, and if it were it would be rated for perhaps 10 amps. On this forum, several electricians explained that within the stove, the manufacturer is free to use any type of wire they choose, so long as the device is rated appropriately by whomever rates the product, which is not NEC. So in my case, I have 10 gage wire connected to 16 gage wire, which is perfectly OK apparently, so long as the appropriate connector is used (the connector is listed in the installation manual, happens to be a split ring type of copper connector).

So my take is that based on past posts, you need a circuit with a minimum rated ampacity of 30A, and a breaker with a minimum rating of 30A, unless your manual specifically states that the breaker shall be exactly 30A. In that case, the manufacturer would be relying on the breaker as an overcurrent device to protect their oven, which I suppose they can do, but would be inconsistent with previous posts regarding the obligation of the manufacturer to protect their device independently of the breaker.

If the breaker is required to be exactly 30A, you could simply replace the 40A breaker with a 30A, as previously noted.
 

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Semi-Pro Electro-Geek
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On what basis do you make this statement?
Which part of my statement, the continuous load thing? An oven could operate for more than 3 hours continuously, as when broiling, so I would say it's subject to the OCPD and conductor derating rules (210-20(a) etc.). Perhaps not?
 

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Master Electrician
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Which part of my statement, the continuous load thing? An oven could operate for more than 3 hours continuously, as when broiling, so I would say it's subject to the OCPD and conductor derating rules (210-20(a) etc.). Perhaps not?
Not anywhere I would be working or broiling.
 

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Scared Electrician
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the purpose of a breaker is to protect the wiring, NOT the device, from overcurrent situations. Therefore, the maximum breaker size is driven by the wiring, NOT by the nameplate amperage on the device.
True the breaker does protect the wire and MUST be sized for the wire. But the appliance that it will be feeding is relevant. The branch circuit must be sized for the application. You can't just run anything as long as the breaker matched the wire-it MUST also match the load.





On another note I don't think kitchen stoves are subject to the continuous load requirements. Could somebody please check and provide reference?
 

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Discussion Starter · #13 ·
swap out the 40a breaker for a 30a
Thanks, it looks like I'll probably do that just to play it safe. This might sound like a dumb question, but is it okay to go "over-sized" on your wire? What I mean is, since the current wire is 8 AWG, it won't be an issue to throw a 30amp breaker on that line, right? I only bring this up because I had an HVAC contractor once tell me that the wire you run has to match-up with the breaker, both ways. Which makes since if you're trying to run a 20amp protected circuit with 14 AWG, but I'm not sure what the problem would be if you're running 15amp over 12 AWG.
 

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Electrical Contractor
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It's fine to be "oversized" on your wire.

I'm surprised that an HVAC contractor said such a thing. It's more common to have what appears to be an undersized wire on a breaker when dealing with HVAC units, than the other way around.
 

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Discussion Starter · #15 ·
Does it call for a 30A circuit, or is it rated for 30A?
That's a good question. The only thing the manual says is this: "Models rated at 5.1 kW and below at 240 volts (3.8 kW and
below at 208 volts) require a separate 30-amp circuit." As if it's an instillation manual for a few different ovens. I don't have the oven yet so I can't get more info than that. I just want to have the right line in place when I do get it. Though I can always swap breakers later if needed.
 

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Discussion Starter · #16 ·
It's fine to be "oversized" on your wire.

I'm surprised that an HVAC contractor said such a thing. It's more common to have what appears to be an undersized wire on a breaker when dealing with HVAC units, than the other way around.
Thanks, KB, that's what I thought. At least THAT HVAC contractor is not undersizing his wire, even if he never 'oversizes' it.
 

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Discussion Starter · #17 ·
...the purpose of a breaker is to protect the wiring, NOT the device, from overcurrent situations.
Daniel, I agree and that's why I didn't think it would be a problem connecting it to the existing 40amp line. My 1amp alarm clock is plugged into a 15amp receptacle and there are no issues there. Either way, I thought it might be different with high voltage appliances and that's why I'm asking everyone here.
 

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" Euro " electrician
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Kyle, yes, direct-wired wall oven. The existing was a plug-in range so I have to remove the old 40amp receptacle. I don't have the oven yet.
Ok the other issue which I know with older range receptale genrally have 3 conductor set up while the newer one are 4 so if you have three conductor set up then follow the owner manual for hook up in 3 conductor fashion there is a section to address on that.

Oh the other thing when you swap over from 40 to 30 amp breaker some breaker may have issue to get the #8 AWG conductor fit in the termation screw if that the case you may have to make a pigtail for it.

Merci,
Marc
 

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Discussion Starter · #20 ·
...to get the #8 AWG conductor fit in the termation screw if that the case you may have to make a pigtail for it.
I think you are correct. This might be throwing another log on the fire here, but I just realized the #8 AWG is actually #6 AWG aluminum wire. I know that I will also need to use a CU/AL split bolt connector to make the proper connection to the copper at the junction box. I actually plan to install a second box just so I can make an aluminum to copper connection and then run copper to the oven box. I really wish I could pull new wire and get rid of the aluminum, but it's next to impossible at this point :(
 
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