The circuit breaker size for any appliance, including electric ovens, cook-tops, and ranges, depends on two things: How much current the device draws and the size wire required to provide that current. The circuit breaker is chosen to protect the wires from carrying more current than they are rated for. The amount of current a wire can carry depends on its insulation type and the diameter or gauge of the wire.
If a new circuit breaker is to be installed for a range on an existing circuit, the size of the new circuit breaker will depend on the size of the wire and the type of insulation on that wire. The range circuits in many older homes were wired with 8-gauge wire.
Older wiring including sheathed cable wiring was rated at 60 degrees Celsius. According to National Electrical Code (NEC) table 310-16, 8-gauge wiring rated at 60 C may carry up to 40 amperes of current. The circuit breaker for that type of wiring must not be greater than 40 amperes.
Modern ranges are capable of using more than 40 amperes of current, which was the older standard for electric ovens and ranges. Most new residential house wiring uses sheathed cable with insulation rated at 90 degrees Celsius. The NEC also specifies that sheathed cable must use the 60-degree rating for wire ampacity, regardless of of the insulation rating.
Since modern electric ovens and ranges can use more than 40 amperes, the next size wire must be used, which is 6-gauge wire. Six-gauge sheathed cable may carry up to 55 amperes, which dictates the maximum circuit breaker size. Since the electric oven and range don't require that much current, 50-ampere breakers are the norm.
Determining Current Requirements
Most appliance manufacturers will specify the wiring requirements in their documentation for the appliance. Another source of this information is right on the appliance. The National Electrical Code requires that appliances have a nameplate that specifies their electrical requirements. The nameplate specifies the voltage the appliance requires and the amount of power it consumes, in watts or kilowatts. Sometimes the amperes required are also given.
Amperes may be directly calculated from voltage and watts or kilowatts. Divide watts by voltage to find amperes. Divide kilowatts by 1,000, then by the voltage to find the amperes. Select a wire gauge that will safely carry the current and a circuit breaker that will not allow the current to exceed the wire ampacity.
Circuit Breakers for Electric Ovens
The NEC specifies the safe wiring codes and practices for residential wiring. Electric oven, range, and cook-top wiring is 240-volt wiring, which requires a double-pole circuit breaker. You can identify double-pole breakers by the two switches that are connected together -- you can't move one switch on or off independent of the other.
A new electric range requires 50-ampere breakers and wiring to meet NEC code. Electric cook-tops and built-in ovens may have other requirements. Base the circuit breaker size on amount of current they will draw and the wiring in place for connecting them.