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I know I'm missing something but....


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Apparently my brain is having a case of the "Mondays"

Here's the situation: In the kitchen I typically turn on the stove/oven and also run the microwave and exhaust fan at the same time. Today, the stove/oven breaker tripped when I turned the exhaust fan on the microwave on with all the stove burners on as well as the oven. The stove/oven were without power but the microwave still was powered. It did this 3 times but only when the stove and oven were both on and either the microwave or exhaust were then turned on.

The panel is the original 25 year GE old panel. No double lugs or anything really noted at the panel except for the crappy grounding connections and nothing was labeled. The microwave was powered by the typical receptacle in the cabinet above the microwave.

I know the answer has to be obvious so can someone slap me upside the head and explain what the issue is?

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The range breaker is probably right at its limit with all the range elements turned on. Maybe the microwave fan motor is causing a slight voltage drop at the panel bus bar. In turn, that creates a slight amperage spike at the bus, just that tad more that trips the range breake which is operating at the edge of its limits.

What size was the range breaker? Maybe it's one size too small.

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The range is on a 30 amp breaker. I haven't had a chance to verify the info for the model yet but I believe it's properly sized.

Most electric ranges I see are on 40 or 50amp breakers.

Yes, it should be 40 amp for a modern electric range.

If it's an older house with a 30 amp breaker, the range outlet might be only 3-wire cable, missing the neutral. An electrician needs to repair that and it will probably involve installing a 4-wire #8 cable.

John I get your reasoning but would that same imbalance not happen when someone flips on a light or a bath fan elsewhere in the house? I suspect some foul play in the wiring behind the stove, a jumper from the microwave to allow the stove gauges to work maybe?

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50 amp is the usual spec, even 30 years ago. An amp meter check might be needed to discern between appliance defect, installed loads in excess of 80% of breaker and fatiqued breaker.

My money is on 'installed loads in excess of 80%...

Marc

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The range is on a 30 amp breaker. I haven't had a chance to verify the info for the model yet but I believe it's properly sized.

Most electric ranges I see are on 40 or 50amp breakers.

Yes, it should be 40 amp for a modern electric range.

If it's an older house with a 30 amp breaker, the range outlet might be only 3-wire cable, missing the neutral. An electrician needs to repair that and it will probably involve installing a 4-wire #8 cable.

John I get your reasoning but would that same imbalance not happen when someone flips on a light or a bath fan elsewhere in the house? I suspect some foul play in the wiring behind the stove, a jumper from the microwave to allow the stove gauges to work maybe?

Sure, something in another part of the house might cause it too. In this case, the inspector was operating things in the kitchen.

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The range is on a 30 amp breaker. I haven't had a chance to verify the info for the model yet but I believe it's properly sized.

Most electric ranges I see are on 40 or 50amp breakers.

Most of the electric ranges I see are on 30 or 40 amp breakers. I see 50's occasionally. I believe that the range should have been on a 40 amp and like what was suggested above someone ran the microwave receptacle off the range feed. Now that I've slept a little bit that's what my money is on.

Thank you gentleman!

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. . . Most of the electric ranges I see are on 30 or 40 amp breakers. I see 50's occasionally. I believe that the range should have been on a 40 amp and like what was suggested above someone ran the microwave receptacle off the range feed. Now that I've slept a little bit that's what my money is on.

Thank you gentleman!

The next time you see a normal-size range installed with a 30-amp breaker, check the kw rating on the range nameplate. I suspect that the breaker (and maybe the wires) will be undersized. Most ranges need 40-amp circuits. Many of them, with warming zones, warming drawers, and convection fans draw well above 40 amps and should be on 50-amp circuits.

As for your theory, if the microwave were tapped off the range feed, why didn't it die when the breaker tripped?

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For the electric ranges I run all elements simultaneously and leave them on for 2-3 minutes. This will often throw a 40 amp breaker. If the breaker is also taking out the microwave and fan then the 220 circuit is not dedicated. If it's a 30 amp breaker I won't even bother to turn the range on.

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The stove should be on its own dedicated circuit,I normally run a 30a circuit for them unless its some special set up they want to install.

The microwave should be on a 20a small appliance circuit,which is unaffected by the oven circuit.

Unless of course somebody bootlegged power someplace between the panel and oven to get power for it.

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The stove should be on its own dedicated circuit,I normally run a 30a circuit for them unless its some special set up they want to install.

The microwave should be on a 20a small appliance circuit,which is unaffected by the oven circuit.

Unless of course somebody bootlegged power someplace between the panel and oven to get power for it.

I assume you are talking about a circuit for only a wall oven (or only a range). I see these on 30 amp circuits, but a combination range/oven typically requires 40 amps or larger.

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. . . Most of the electric ranges I see are on 30 or 40 amp breakers. I see 50's occasionally. I believe that the range should have been on a 40 amp and like what was suggested above someone ran the microwave receptacle off the range feed. Now that I've slept a little bit that's what my money is on.

Thank you gentleman!

The next time you see a normal-size range installed with a 30-amp breaker, check the kw rating on the range nameplate. I suspect that the breaker (and maybe the wires) will be undersized. Most ranges need 40-amp circuits. Many of them, with warming zones, warming drawers, and convection fans draw well above 40 amps and should be on 50-amp circuits.

As for your theory, if the microwave were tapped off the range feed, why didn't it die when the breaker tripped?

Electric ranges are the minority here but I will def. check the nameplate for the kw rating.

As for my theory it's a quandary and therein lies my confusion.

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. . . Most of the electric ranges I see are on 30 or 40 amp breakers. I see 50's occasionally. I believe that the range should have been on a 40 amp and like what was suggested above someone ran the microwave receptacle off the range feed. Now that I've slept a little bit that's what my money is on.

Thank you gentleman!

The next time you see a normal-size range installed with a 30-amp breaker, check the kw rating on the range nameplate. I suspect that the breaker (and maybe the wires) will be undersized. Most ranges need 40-amp circuits. Many of them, with warming zones, warming drawers, and convection fans draw well above 40 amps and should be on 50-amp circuits.

As for your theory, if the microwave were tapped off the range feed, why didn't it die when the breaker tripped?

Electric ranges are the minority here but I will def. check the nameplate for the kw rating.

As for my theory it's a quandary and therein lies my confusion.

We don't see many built in ovens around these parts,normally the plain old slide in ovens normally.

Those are the ones Im referring to.

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. . . Most of the electric ranges I see are on 30 or 40 amp breakers. I see 50's occasionally. I believe that the range should have been on a 40 amp and like what was suggested above someone ran the microwave receptacle off the range feed. Now that I've slept a little bit that's what my money is on.

Thank you gentleman!

The next time you see a normal-size range installed with a 30-amp breaker, check the kw rating on the range nameplate. I suspect that the breaker (and maybe the wires) will be undersized.

As for your theory, if the microwave were tapped off the range feed, why didn't it die when the breaker tripped?

I am picturing a 4-slot outlet on a 30 amp 3-wire feeder.

Maybe now he needs a neutral for 120 volt gauges, dashboard computer, etc so he adds a neutral jumper from the 120 v range hood circuit.

Maybe that's a bit far-fetched, too.

Maybe there are rats chewing on insulation and the two circuits are shorting together.

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It can get scary. I once found a #12 cable serving a cook range fed by a 50 amp breaker. There were no visible signs of cable overheating but nonetheless, a disaster waiting to happen.

John, there are situations where it is OK to have a cooktop served by a tap of 12 gauge wire protected only by a 50-amp breaker. NEC 210.19(A)(3) Exception 1 allows this when you have a large conductor (usually 6 AWG) from the breaker to a junction box under the range, and smaller tap conductors going to a range and a wall mounted oven. The tap conductors need only match the nameplate rating of the appliance, be rated at least 20 amps, and be as short as practical.

The 50-amp breaker will still protect the conductors in a short circuit, and they are protected against overload by being capable of supplying the rating of the range.

Of course, if you saw 12 gauge wires directly connected to the 50-amp breaker, that would indeed be scary.

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