Yes, provided that you don't really need 20 A on the circuit.
No tandem breakers are of the same value.
If the 12,000 BTU A/C only requires 20 amps to run then yes you can use the same 12 gauge wire but you cannot change it to a 15 amp breaker. You will need to install a 20 amp double pole breaker. If it requires more than 20 amps you will have to replace the wiring and breaker.
A 15 amp receptacle is protected by a 15 amp breaker. The 15 amp breaker will trip on any current over 15 amps. So if the 20 amp machine draws a full 20 amps, then the answer is no. Due to some operations of machines they will not draw the full nameplate amperage until they reach a certain point in there cycling. The machine may run at the start but when it reaches that point it could trip the breaker. If the machine is not hardwired but plugged in, you could not run a 20 amp machine on a 15 amp receptacle, due to the different pin configurations on the plug cap.
If the full load amps rating of the motor on the name plate is exactly 15 amps you need to use # 12 wire. If it is a longer run you may have to go up one more wire size. The breaker size you need is 30 amps.
A 15 Amp extension cord can be plugged into a 20 Amp circuit. It is important that what you're extending does not require more then 10-12 Amps.
For typical residential house wiring 12 AWG wire is required for a 20 Amp breaker. If you change out the breaker for a 25 A breaker you would have to rewire the circuit with 10 AWG. In that case you could up the breaker to 30 Amps. All outlets and switches should be rated at the same voltage and current as the breaker.
A minimum of 15-amp breaker is "needed", but a 20-amp is often required by electrical code for that situation.
14 gauge will handle it with a 15 amp breaker. If you use 12 gauge use a 20 amp breaker.
Look on the heater and see what amps it is pulling. That will determine the wire size and breaker size. It must be on a dedicated circuit. 15 amps = AWG # 14 wire with 15 amp breaker 20 amps = AWG # 12 wire with 20 amp breaker 30 amps = AWG # 10 wire with 30 amp breaker 40 amps = AWG # 8 wire with 40 amp breaker
no. the breaker is 40amps.fire hazard
A circuit breaker protects the wires that the devices are connected to. If the devices that are connected to the circuit are 20 amps the wire size should be #12 wire fed from a 20 amp breaker. This breaker should not trip unless the circuit is overloaded or a fault occurs on the circuit. If the devices that are connected to the circuit are15 amps the wire size should be #14 wire fed from a15 amp breaker. This breaker should not trip unless the circuit is overloaded or a fault occurs on the circuit. Putting 20 amp sockets on this 15 amp circuit will work but the circuit is limited to the amount of load that can be plugged in. You will not get the full capacity of the 20 socket because the breaker will trip at 15 amps.
No, the breaker is there to trip at 20 amps because the supply wiring can only supply 20 amps max at that point. So a larger breaker could give you a house fire.