I had an engineer tell me today that a tankless hot water heater with sensitive electronic controls was not operating properly because a 'second ground' run thru a correctly installed emt was connected directly to the neutral bus in the service panel and not to a separate ground bus. He understands the two busses connect directly to one another in the panel, but he says it makes a difference and can create a ground loop which affects the point of reference of the electronic controls at the unit.

Could a foot and a half of #4 really make a difference? Maybe this should be in the technical area, but I was having trouble getting that one up.