I have a portable air compressor (Master Airbrush MAS TC-40T) I use frequently, usually for airbrush painting. Normally the compressor sits on a counter, and I do not touch it while it's running because I have no need to. However, yesterday when I touched the compressor while it was running, it shocked me several times.
When I got shocked, I was using the compressor to blow dust out of a ventilation fan in the bathroom ceiling. The compressor (which has a three-prong grounded power cord) was plugged into the bathroom's GFCI grounded outlet. I had the compressor balanced on top of a ladder and was leaning past it to point the spray nozzle at the ventilation fan.
Every few seconds I'd accidentally brush against the compressor's casing and get a shock. The first few shocks were very brief and I chalked them up to static electricity. However, one time when my finger touched the casing, I received a sustained shock that lasted a half-second or so until I pulled my finger away. At this point I disconnected the compressor and stopped using it.
Now I've done everything I know of to try to diagnose the problem and haven't found anything wrong:
- The Test/Reset buttons on the GFCI outlet are working correctly
- When I put the multimeter into AC Volts mode, insert the black probe into the outlet's ground slot and the red probe into the outlet's hot slot, the multimeter shows a reading of ~118V, which I think means the outlet is grounded correctly (I'm in the US with 120V power).
- When I put the multimeter into Resistance mode and touch one probe to the casing and the other to the ground prong on the power cable, the multimeter shows a very low resistance reading, which I think means that the compressor is internally grounded correctly. I've tried this with the compressor in several orientations in case the internal grounding wire is loose, but the readings are always about the same.
I can't think of anything else that could be wrong that I should be testing for. Have I tested everything that I should test correctly? Should I chalk the shocks up to static electricity?