I have an air compressor for running tools in my garage. I recently moved the compressor to the basement and put an accumulator tank in the garage ceiling. I did this to reduce noise in the garage and outside.
It works very well, but now I'd like to control power to the compressor from the garage via my insteon or zwave home automation system.
Years ago, I made the mistake of plugging a compressor into an outlet with its switch in the 'on' position. (The manual advises against this.) After a major arc flash, part of the plug was missing, and I replaced the outlet and plug. So, I suspect that the initial inrush current may be some hundreds of amps depending on where the piston last stopped, and I'm reluctant to trust a standard 20 amp relay to the job.
How many amps should I plan for?
The compressor is "rated" at 120v, 14.5A. My compressor manual does not mention how I would like to choose a relay or switch that will show no appreciable wear after 5000-10000 cycles.
What type of relay should I use?
Here's a picture of the compressor:
And one of the labels on the back
Best Answer
I would just use a standard air conditioning condenser relay rated for 30 amps or more to start with. Make sure it is rated for horsepower larger than your compressor. (To really calculate the inrush current you need the code letter from the motor nameplate under the LRA or locked rotor current. Then see Table 430.7(B) in the NEC. Multiply your horsepower by the number from the table and divide by one thousand. See this article here.)
Or just start with an A/C relay like I said above and if it wears out fairly quickly you could spend much more money for a higher rated motor contactor. An A/C relay probably costs $30 or less.
The other thing to consider is when you decide to upgrade your compressor, make sure it is a two-stage compressor. A two stage starts the motor unloaded and then engage the compressor after the motor is running. This significantly reduces the inrush current to the motor since it is starting unloaded. The single stage style is required to start with the compressor under pressure and consequently requires a large inrush current.
Good luck and stay safe!