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Thursday, October 22, 2009

Electrical Enigma Exposed

What's up Doc? I'm redoing some electrical items in my '94 motorhome. I checked for continuity between the neutral and ground in the alternating current system (power off and unplugged) and got nothing. Should my coach’s frame and 120-volt AC system's ground and neutral be tied together? Would the generator and inverter be safe in this configuration as well?
Dave, (Overland Park, KS)

Dave, a very good observation on your part. Indeed, the motorhome AC electrical system is not like in a conventional home. In the motorhome, the neutral conductors are not grounded; the neutral and ground must be kept separate. In the panelboard distribution box the neutral buss bar is isolated and separate from the ground buss. The reason for keeping the ground wires separated from the neutral wires is to prevent the “skin” and chassis of the coach from becoming “hot” if the power supply cord (or campground pedestal) has reversed polarity. Only the ground circuit is connected to the frame of the motorhome. If, for example, you did measure continuity or resistance between the neutral and ground prongs on the shoreline cord, you’d need to dig further to find that interconnectivity.

Another thing altogether is electrical “bonding.” Bonding is not the same as “grounding” however. Bonding is required for those metal parts not part of the electrical system, but those that could become energized such as the chassis, a metal roof, aluminum siding, the metal casings of the inverter, converter and furnace, metallic water piping and LP tubing.

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