Yes, a 30 amp breaker is a 30 amp breaker. It must however be able to fit the box it is installed in.
No tandem breakers are of the same value.
If it is a 30 amp breaker then it is a 240 volt outlet.
You have a double pole breaker for 240Volt supply. The maximum current is 15 amp.
No. The breaker must protect the circuit components such as wiring, outlets and switches that are connected to the breaker. Therefore if you have a 30 amp circuit as dictated by its components you need to protect it with a 30 amp or less breaker.
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.
50 amp breaker.
That's pushing it but it can work. It depends if you have central A/C, electric range, water heater, etc. Those are your amp suckers. You'll need to be mindful when operating the hot tub; not running the dryer, oven, or other large appliances.
If you are talking about a breaker in a house panel then a 15 amp breaker would be used. It is the smallest amperage breaker that you will find in a house panel.
Replace the 30 Amp Breaker with a 15 Amp breaker.
The breaker commonly used for ranges is a 40 amp. This size is used to cover the total wattage of the range. If for some reason all of the top elements and the oven were in use at the same time then the amperage drawn would be just under the trip setting of the breaker. If this same scenario were played out on the range with a 30 amp breaker supplying the power it would trip the breaker.
No, you should not install a 30 amp circuit breaker to a machine which normally requires a 20 amp supply. The circuit breaker is protecting the wire to the machine. That wire is likely only rated for 20 amps, (# 12 awg). Therefore, a 30 amp breaker could allow too much current to go through the wiring to the machine and cause the wire to burn down. Replace the 3 phase 20 amp breaker with the same amperage breaker.
A 50 amp breaker is an overcurent device.