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Kitchen subpanel questions


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A 1975 house I visited over the holidays has had some renos done.

In the bedroom wall behind the kitchen, a 40 amp subpanel has been installed. The subpanel has a 40 amp breaker for the kitchen range and a 20 amp breaker for two counter top receptacles.

At the breaker panel, the label that originally said 'Range' now says 'Sub'. So we can assume that the original 8/3 cable to the range outlet now feeds that subpanel. I pulled covers and found no incorrect wiring, no sign of a problem, grounding is correct, all copper wiring.

Is there anything unacceptable about what was done here, assuming all grounding and polarities are correct?

Could the homeowner install another breaker in this 40 amp subpanel, 15 amp for a microwave outlet? I recommended not adding another circuit.

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I would add up the loads and see if the total exceeds 80% of the volt-ampere capacity of the sub (9,600 VA). That includes the range, any other appliances like dishwasher, disposer, as well as all countertop appliances.

This method probably doesn't mesh with what the codes require on new construction but it's what I do. It's simple enough to explain to the client.

Marc

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I don't see how I can predict the loads with any accuracy without hiring an electrician to do a megger test.

Will the range ever draw 80% of 40 amps? Maybe not. What if they swap this stove out for a different model?

My question is whether a 40 amp subpanel can be permitted to supply the 40 amp range outlet and the 20 amp counter outlets.

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I think they're pushing their luck with it as it is. Most basic ranges pull about 30 amps with everything on. That doesn't leave much for the countertop receptacles. A 1,500w toaster oven (12.5 amps) could push it over the edge.

If they want another circuit, run it from the service panel.

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Well that's right. A basic electric range might only need a max of 30 amps, but a KitchenAid glasstop convection oven for example can draw 45.4 amps per the data plate.

Since we can't restrict what the future loads will be, that subpanel should have been upsized to 50 or 60 amps, IMO.

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As long as ALL wires (especially the feeder) are correctly sized for the breaker feeding them, then there is no safety issue. For example, some 100 amp panels have space for 24 @ 2 pole 40 amp breakers. The panel will be overloaded and the main for the panel will trip, but it will not be unsafe.

Accurate panel loading should be made doing normal NEC calcs and using the correct diversity factor.

Or you could WAG it using something like this

http://wireyourownhouse.com/tools/housecalc.html

If all wire is correctly sized, I would say that it is all ok. I would tell, not write, the owner that he could add it himself but it will probably trip the breaker from time to time & if that is a problem, he should definitely upsize - and he should really have an electrician recheck.

I like to look at different scenarios because sometimes I am looking at a ritzy establishment and sometimes... not.

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As long as ALL wires (especially the feeder) are correctly sized for the breaker feeding them, then there is no safety issue. For example, some 100 amp panels have space for 24 @ 2 pole 40 amp breakers. The panel will be overloaded and the main for the panel will trip, but it will not be unsafe.

Accurate panel loading should be made doing normal NEC calcs and using the correct diversity factor.

Or you could WAG it using something like this

http://wireyourownhouse.com/tools/housecalc.html

If all wire is correctly sized, I would say that it is all ok. I would tell, not write, the owner that he could add it himself but it will probably trip the breaker from time to time & if that is a problem, he should definitely upsize - and he should really have an electrician recheck.

I like to look at different scenarios because sometimes I am looking at a ritzy establishment and sometimes... not.

A conductor adequate to the breaker but not adequate to the connected load is not something I'd ignore.

Conductors should be sized to carry the connected load. Breakers should sized to the conductor except for multi-motor appliances that are labeled with conductor and breaker specs.

Marc

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