Power requirements for an electric range

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scrypps

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Something has always confused me. When you look at the nameplate of a range, it gives a kilowatt rating for 208v and a kilowatt rating for 240v. Like almost any other appliance in existence, it might be tempting to figure out how much power is required by looking at the nameplate. In this case, take 9100 watts and divide by 208v and you get 43, which I would figure means the thing uses about 43A max, so I would run a 50a circuit. Take 12100 watts and divide by 240 and you get a different figure, just over 50. That alone has confused me already, there is no three-phase connection so why would 240v draw a larger amperage? At any rate, this is a low-cost GE range and it says in the instructions to put it on a 40a breaker. Fine.

Here's the thing though, not all range instructions tell you what size breaker to put it on. You can pour through the installation instructions and won't be able to find it. Today I looked at another GE range with an induction cooktop. It never says anywhere what breaker to protect it at or to supply the range with, (we looked hard), it only says "use a 40a rated cord". Well, I guess if the cord is rated at 40a, then you can put it on a 40a breaker. GE is a nice brand though, they tell you what to use, some brands don't. At any rate, I don't know why they put a name plate on that always is larger than 40A.

In the end, I don't care, no one is going to put all their burners on high and turn the oven on to 500 degrees. Still, it would be nice to know what to install it at. Frankly you can't go wrong with 50a in this case, but some ranges have higher nameplate ratings, what then?

Range-nameplate.jpg
 
An electric range is generally made with resistance heating elements. Basic Ohms Law: voltage = current * resistance. Increase voltage and current goes up, and power goes up as the square of the applied voltage.

Regarding circuit sizing for cooking appliances, code recognizes a number of demand factors for things such as ovens and ranges, letting you 'get away' with a circuit and OCPD lower than what you would expect from the KW rating, and also limits you to a maximum current that is rather larger than the name plate rating. I would not be surprised to see the above range on anything from a 40A to a 60A circuit.

-Jon
 
scrypps said:
That alone has confused me already, there is no three-phase connection so why would 240v draw a larger amperage?
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Because heating elements are resistive loads, whose currents vary proportionately with applied voltage.

Don't confuse this with motor loads, whose currents vary inversely with applied voltage.

Also, two lines of 208v are considered single phase.
 
With heating elements the resistance does not really change so a higher voltage applied to the same element will result in higher current.
The wattage of a fixed resistance changes with he square of the voltage change.
(240/208)² x 9.1 = 12.1 or (208/240)² x 12.1 = 9.1
 
don_resqcapt19 said:
With heating elements the resistance does not really change so a higher voltage applied to the same element will result in higher current.
The wattage of a fixed resistance changes with he square of the voltage change.
(240/208)² x 9.1 = 12.1 or (208/240)² x 12.1 = 9.1
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Thanks that is what I was missing when looking at the OP, knew the reason was missing the math.
 
Electric ranges, burners and ovens cycle. They are almost never always on solid. You would have to turn all four burners on High, and the broil (higher wattage in most ranges of the oven elements) on high. You do pull just above 40 amps when this happens. No one boils 4 pots of water while broiling their steak. Hence why the name plate rating is allowed to be lower. Breakers are sized for continuous amperage. Range loads aren't typically continuous.
 
micabay said:
Electric ranges, burners and ovens cycle. They are almost never always on solid. You would have to turn all four burners on High, and the broil (higher wattage in most ranges of the oven elements) on high. You do pull just above 40 amps when this happens. No one boils 4 pots of water while broiling their steak. Hence why the name plate rating is allowed to be lower. Breakers are sized for continuous amperage. Range loads aren't typically continuous.
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But the name plate IS lower. 9.1kW or 12.1kW. Why?
 
Besoeker3 said:
But the name plate IS lower. 9.1kW or 12.1kW. Why?
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The nameplate is the full power that the range can draw worst case scenario.

The installed circuit is permitted to be for somewhat lower power because of element cycling and actual expected use.

The two values on the nameplate are for two different supply voltages.

Jon
 
winnie said:
The nameplate is the full power that the range can draw worst case scenario.
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But it isn't the full power range it can draw if it can only 40kW. Makes no sense to me. But then I'm just a Brit with simple electrics.................:)
 
Besoeker3 said:
But it isn't the full power range it can draw if it can only 40kW. Makes no sense to me. But then I'm just a Brit with simple electrics.................:)
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I'm curious how would the Brits size the branch circuit for an electric range? Here a 12,000 watt range at its rated voltage would use a branch circuit sized for 8,000 watts. Do you guys have something similar?
 
infinity said:
I'm curious how would the Brits size the branch circuit for an electric range? Here a 12,000 watt range at its rated voltage would use a branch circuit sized for 8,000 watts. Do you guys have something similar?
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UK.
Most of the domestic lighting is single phase 230V, 13A receptacles. The receptacles are sometimes lower than 13A plugs.
The exception is a 30A electric cooker. This is typically four hobs, a double oven, and an eye level toaster gadget (I forget what it's called.)
This is the sort of arrangement we have with the electric hobs enclosed and gas hobs next to the work top.
 

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augie47 said:
Is the wine glass mandatory

Is the wine glass mandatory in all British pictures ?? (somewhat like a beer can in all Southern US pictures) :)
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That was my wife - and she is a Southern Belle.....................)
My usual is Scrumpy Jack. Or a Lagavulin on occasion me being a Scotsman.
 
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