The electrical code does not allow wires smaller that #2 to be paralleled to a connected load.
You should not use any wire smaller than 8 AWG COPPER in a 40 amp breaker. If you have any questions about your application, you should contact a local electrical contractor for your own safety.
If you have 100 amp wire, you can use it for a 60 amp circuit, or for any circuit of 100 amps or less. But if you have a 60 amp circuit, 60 amp wire is thinner and cheaper than 100 amp wire.
40 amp
No a #12 wire is only rated for 20 amps. The 40 amp breaker will not protect the #12 wire. A 40 amp breaker should have a #8 wire connected to it which is rated at 45 amps. The only time that a breaker is allowed to be bigger that the wire size rating according to the electrical code is when a motor is connected to the breaker. This is to stop the 300 percent inrush of the motor full load amps from nuisance tripping a smaller sized breaker.
The electrical code does not allow wires smaller that #2 to be paralleled to a connected load.
12 AWG.
A 25mm sq electrical cable is equal to a #4 AWG conductor. A #4 copper conductor with an insulation factor of 75 and 90 degrees C is rated at 85 and 95 amps respectively.
Electrical wire size is directly dependant on the load amperage that is connected to it. The higher the load amperage, the larger the cross sectional area of the wire needs to be. The connected amperage to a conductor is determined by a group of electrical experts and their results are then written into the latest addition of the electrical code book of the country in which you live.
25mm cable
Yes, at any electrical supply store.
You should not use any wire smaller than 8 AWG COPPER in a 40 amp breaker. If you have any questions about your application, you should contact a local electrical contractor for your own safety.
You should be concerned. It is only legal if the wire that was feeding the load from the 15 amp breaker was a # 10 copper wire. Any wire size smaller is against the electrical code rules. Make sure about the wire size. If he was a licenced electrician or not he should be reported to the local electrical inspector. If he is a certified electrician, and he says it is ok then it is ok. He knows what he is doing and will not do anything to put his certificate in any harm for something that little.
If you have 100 amp wire, you can use it for a 60 amp circuit, or for any circuit of 100 amps or less. But if you have a 60 amp circuit, 60 amp wire is thinner and cheaper than 100 amp wire.
40 amp
what kind of power wire?(a power wire for an amp maybe) what kind of power wire?(a power wire for an amp maybe)
No a #12 wire is only rated for 20 amps. The 40 amp breaker will not protect the #12 wire. A 40 amp breaker should have a #8 wire connected to it which is rated at 45 amps. The only time that a breaker is allowed to be bigger that the wire size rating according to the electrical code is when a motor is connected to the breaker. This is to stop the 300 percent inrush of the motor full load amps from nuisance tripping a smaller sized breaker.