I recently went out to a customer and the call was that they lost power to the building. Before I arrived, they already found the problem breaker, turned it off, and reset the 1200A GFCI main. The problem was a 70A RTU branch ckt. A compressor had a ground fault that caused the main to trip. There is a breaker at the panel and in the RTU, and the RTU has 70A fuses in series with the breaker in the unit, of which A phase was blown. I'm assuming it was the GF sensor that tripped the main, and this is not the first time they have had this problem at the semi-upscale restaurant. The adjustment dials for the ground fault sensor are set at max sensitivity as far as I can tell. I've always heard that an engineer is the only person qualified to adjust these dials. Seems to me that they should be adjusted to avoid this nuisance tripping that has happened at least twice now. Any thoughts?