No 15 amp circuits

70-year-old house, everything has been rewired. But there are no 15 amp circuits which I can’t recall ever having seen before. Is this a problem?

No, it is not a problem, Tim…if the wire are 12 gauge or equivalent to the breaker.


Ok thanks! All wiring was appropriate gauge.

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So lamps and what not won’t be over-amped?

No, not that I can see, Tim…you’re good.

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To calculate the amperage of a device, one must divide the number of watts by the volts powering the circuit. So a lamp with a 100 watt light bulb will use (100 w/120v) = .833 amps

Increasing the size of the breaker has no effect on the current drawn by the device.


For general purpose lighting and receptacle circuits 15 or 20 amp circuits are permitted with the appropriate size conductors.


What about a dedicated circuit such as a small furnace that only needs a 15. The size of the wire is fine, but would they either need a fuse at the furnace or change the breaker.

A 15 amp fuse is often at the service shut off.

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You’re correct, if a unit had a maximum overcurrent protection device size of 15 amps then a 20 amp circuit could not be used.


I hear ya on that. I was worried about overheating.

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