Is there any way to test a breaker?

AJ/FormS said
746watts =1hp IIRC,so 2hp is about 1500,and 1500/120=12.5Amps
The motor plate says 15, so that is a 20% safety, or My memory is poorer than I thought.
If it draws double to start, when the unloader is properly adjusted,then you would need 20/25 common breaker.

They probably calculated in the power factor which takes the product of the volts times the amps and then multiples it by the P.F. (usually 75% to 85% depending on the motor). This calculates in any and all other losses the motor is subjected to. It's actually pretty honest practice on behalf of the compressor company. Most of them were measuring peak to peak current on initial inrush, thus producing a higher number. They were then marketing the compressor as something that it wasn't. There was a class action suit and everyone that bought a compressor in a certain time frame was awarded $1.53 for thei grief and misery the compressor shysters caused them.

cosgig said
12 guage wire is only rated for 110 at 20a!!

20 amps is 20 amps regardless of voltage. Most wire you buy has a 600v rating but that's only for the insulation properties.

Moving right along, there's a couple issues that could be going on here. One is the breaker. Breakers do wear out over time depending on usage. They shouldn't, but they do. To answer your question directly, there is ways to test breakers. Nobody does this, but there is ways to test them. The reason they don't is because they're only about fifteen bucks, so they just replace them.

Second is the temperature in the garage or shop. If it's cold your oil or the grease inside your sealed bearings is going to thicken up and create more resistance than normal. This will increase the current drawn.

Third is your electrical connections. Check them all inside and outside the panel and make sure they're tight.