First thought is loose connections. Especially if someone of dubious qualifications has been inside the panels. Have there been any other electrical problems or modifications? Verify that all neutral and ground connections are solid.
The next thought is spikes and surges. Have you tried a good surge suppressor for this unit? Is this lightning country? Does the building have any equi-potential grids? Are they bonded to the service? You mentioned there is some questionable DIY work. I would check for grounds being used as neutrals and vice-versa. Are there any common systems between buildings? Such as metal piped water or gas lines, metal fences, video systems, computer networks, telephones, etc. Electric fences develop some nasty voltages. How about some miswired equipment? What are the other loads in the building or any large loads on the property?
The last thought is poor power coming from the utility. Is the property at the end of a very long run? Is it near some switched PF capacitor bank? Is there a very large load near the property like a mine or a sawmill?
Larry C
Editted because I forgot the first line.
[This message has been edited by LarryC (edited 04-26-2006).]
