Went on service call Friday. Found compressor contactor welded shut. This was compressor #3. This is a four circuit 3 phase 460v Rheem. Ohmed out everything, checked voltage, checked wiring. Everything looked good so I replaced contactor. Compressor ran good. Checked voltage, amps, and pressures-all ok. The weekend on call tech called me and said he went there (less than 24 hrs later) and its welded again. Also tripped ground fault in mcc room. Plant electrician assured him ground fault will only trip when 277v or greater is detected to ground. Our on call tech said he wanted to replace compressor. Any thoughts?