Tuesday, May 14, 2013

Generator Installation Problems


I have a 1960 PD4104 GMC bus.  It has been converted to a motor home.  The issue that I am dealing with is polarity.  Most vehicles today have negative grounds.  What this means is that the negative post of the vehicles battery is connected to the frame of the vehicle and the positive post is connected to all the components.  If you take a wire that is connected to the positive side of the battery and touch the frame, you get a short.  This is not good.  When this happens there can be sparks, melted wires and sometimes even fires. 

Back before the 1960’s some vehicles used positive grounds.  Again, this time the positive post was connected to the frame and the negative post to all of the components.  Electricity does not care which direction it travels.  All it needs is a complete circuit or circle to function.  Positive ground vehicles worked just fine.  Sometime in the 1960’s someone made a regulation or a law or something and all vehicles after that date were negative grounds.  Nowadays I suppose that a component could be polarity sensitive.  I have heard that a motor may run in different directions depending on the polarity.  But I don’t know for sure.

So here’s the problem.  My bus is positive ground and the generator is negative ground.  What happens if I bolt the generator to the frame of the bus?  Am I going to have a short circuit?  I did not know the answer. I was thinking that grounding two systems with different polarities to the same medium would cause me problems.  I called the generator maker and asked the question.  Naturally the maker wanted me to talk to a dealer and referred me to one.  I called and asked the question.  The dealer did not know the answer.  I guess part of the problem is that there have not been very many positive ground vehicles in the universe for a long time and everyone who dealt with the problem is retired or dead and no one knows for sure.
Undeterred I turned to my bulletin board service for the answer.  The first person to respond to my post said it was possible.  The second said it was not.  There was a lot of back and forth between both camps.  I still do not know the answer for sure.  I guess I will just install the generator and see if the bus burns down.  I’ll let you know.

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