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Old 05-23-2011, 11:45 PM   #1
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30amp oven on 40amp breaker


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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Old 05-23-2011, 11:57 PM   #2
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30amp oven on 40amp breaker


swap out the 40a breaker for a 30a

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Old 05-24-2011, 01:39 AM   #3
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30amp oven on 40amp breaker


Quote:
Originally Posted by Saturday Cowboy View Post
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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Old 05-24-2011, 06:34 AM   #4
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30amp oven on 40amp breaker


Quote:
Originally Posted by mpoulton View Post
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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Old 05-24-2011, 06:45 AM   #5
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30amp oven on 40amp breaker


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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Old 05-24-2011, 07:16 AM   #6
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30amp oven on 40amp breaker


If the oven has a 30 amp plwer plug then it can be on a maximum 30 amp circuit.
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Old 05-24-2011, 08:04 AM   #7
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30amp oven on 40amp breaker


I suspect this might be a direct-wired wall oven?? Have you gotten the oven yet?
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Old 05-24-2011, 09:52 AM   #8
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30amp oven on 40amp breaker


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/Mar...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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Old 05-24-2011, 10:07 AM   #9
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30amp oven on 40amp breaker


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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Old 05-24-2011, 06:01 PM   #10
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30amp oven on 40amp breaker


Quote:
Originally Posted by brric View Post
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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Old 05-24-2011, 06:39 PM   #11
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30amp oven on 40amp breaker


Quote:
Originally Posted by mpoulton View Post
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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Old 05-24-2011, 07:00 PM   #12
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30amp oven on 40amp breaker


Quote:
Originally Posted by Daniel Holzman View Post
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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Old 05-24-2011, 08:53 PM   #13
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30amp oven on 40amp breaker


Quote:
Originally Posted by Saturday Cowboy View Post
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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Old 05-24-2011, 08:56 PM   #14
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30amp oven on 40amp breaker


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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Old 05-24-2011, 09:03 PM   #15
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30amp oven on 40amp breaker


Quote:
Originally Posted by mpoulton View Post
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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