Very few cheap factory compressors (yes, your is indeed a cheap factory compressor, more on that later) can start against pressure. The purpose of the unloader is to relieve pressure at the pump when it shuts off. Every air compressor has to have some type of unloader. There are two possibilities here, electrical or mechanical.įirst, mechanical. So the compressor must be hard-wired, and it must be the only thing on the circuit. Therefore, you could use a larger breaker than the wire is normally rated for, but in no case can you use a larger breaker than the receptacle is rated for. The minimum wire size is 125% of the full-load current. HP, but I bet this motor doesn't list a HP on the nameplate. Usually, we use a table in the codebook that gives amps vs. If the compressor is hard-wired (not cord-and-plug connected), according to article 430 (motors) in the code, the maximum breaker size is 250% of the full-load current. Look on the motor nameplate, I bet is says for amps (FLA) something around 20. The actual running HP is more like 2 HP or so. It would produce 5.5HP for less than 2 minutes before it burns up. ![]() The 5.5HP rating is not the actual running HP, it's the maximum HP the motor will produce before it stalls. One solution, if your panel is Square D QO (not homeline) is to get a high-magnetic 20 amp breaker. These compressors are notorious for extremely high starting current. Basically, the breaker is seeing the motor starting current as a fault. The reason the breaker trips occasionally is because the starting current of the motor is very close to the magnetic tripping current of the breaker. What else can I do other than running another line? If I do this I'm gonna run a 50 amp breaker. It ran for several cycles without blowing but I'm just waiting for the next time. I went downstairs and put in a new 20 amp breaker and started it again. I put it all back together and started it up with the drain valve open and it immediately blew the breaker. I had a friend check out the capacitor and he said it was good. I can spin the motor easily by hand, so nothing is wrong there. I also checked the check valve to make sure it was working and it was fine. I ordered a whole new pressure switch assembly from Craftsman and put it on last night. They got really corroded from sparking during on/off cycles. I started having trouble with the contacts in the pressure switch of the compressor. The compressor now works better but it still blows 50 percent of the time. The air compressor is the only thing on this circuit. I used 12-2 wire in a PVC conduit with a 20 amp Square D breaker and a 20 amp outlet. So, I ran the line out the basement wall in the ground along the front of the house and into the garage. The house has two different level roofs with no easy way to go between them either. The basement is finished, so I can't run wire there, plus the living room between the garage and basement is on a slab. The reason it took so long is because there was noway to run it thru the house. ![]() I ran a new line from the main breaker box. I put up with this for years until last year I decided to fix the situation. The manual calls for a minimum 15 amp dedicated circuit. This didn't surprise me because it was a 15 amp circuit that had other things on it. ![]() I put it in my garage on the original circuit and blew once in awhile. I have had it for years and have always had trouble with it blowing breakers. I have a Craftsman air compressor (model 919.165190). It seems like there are a bunch of knowledgeable people here, so here goes my question. I'm new to this forum but have been reading some of the posts.
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