Is it possible to use 40A cable with 30A breaker?

Question

I have a stove running off a 40A cable. This cable is going into a 30A breaker. Is this allowed?

My next question is: I want to replace the stove with a laundry machine and/or a dryer. The dryer is supposed to run off 30A. Am I allowed to connect this dryer, which apparently requires 30A, to the 40A cable?

Is this 30A requirement a MINIMUM power requirement or is it not negotiable?

In other words, do I have to replace the 40A cable with 30A, or can I leave it there and run the dryer or the washing machine off it?

I am in Ontario, if this is relevant at all.

Answer 1

No one will complain about the wire capacity being larger

than the breaker. - It's safe.

Answer 2

A wire that is rated for 40 amps means that it CAN handle that much current.  If it only has 30 amps running through it, fine.  If you try running 50 amps through it it could heat up, melt the wire, and cause a fire.  Not a problem in your case though, the breaker will trip at anything over 30 amp.

Answer 3

Both OK and legal.  It's overkill.

It's like buying new tires for your car rated for 150mph.  You don't have to go that fast, but they have the CAPACITY for it.  Go faster and they might/will have problems.  Same idea.

Answer 4

You may oversize a wire but never undersize. It will be OK to use your 40 amp wire with a 30 amp breaker.