Seperate ground for each service into house??


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Old 09-08-14, 02:53 AM
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Seperate ground for each service into house??

A friend of mine asked me to come over and look at his electrical service. His house is a side-by-side attached. Two separate living areas, except the basement is common area; no wall divider. He has two individual electrical services (two meters) that each feed a breaker box (each main OCP 100A-each ground/neutral bars bonded together).

One breaker box has a solid copper ground wire (about a #6) going from the breaker box out side the window near it to a ground rod. From this breaker box he has a stranded copper wire going to the other breaker box (separate service) to the ground/neutral bar. This box has no other ground.

He has an incoming main water line (one for the entire house) on the opposite side of the basement. What I proposed to him is that both breaker boxes should be grounded separately independent of each other. Since there is a main water line coming into the house from the floor encased in cement that he should run at least a #6 solid bar ground wire continuously independent of each other over to where the main water line comes into the house (jumper over the shutoff valve). Remove the stranded copper ground wire that was connecting the two breaker boxes.

At this point the remaining ground in one box (the original going from the breaker box to the ground rod) he can leave as a supplemental ground and also add such the same to the other breaker box so each breaker box has it's own separate ground going to the income main water line and also a ground rod.

I believe it may not be necessary to have both going to a ground rod as a supplement but would not hurt as long as each are separately grounded both going continuously independently with min copper solid #6 (maybe #4) to the incoming main water line.

Do I have this correct??
 
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Old 09-08-14, 03:11 AM
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I am not an electrician however in my (previous) work I did have to be aware of electrical code requirements. I have also been retired for over nine years so my information may be severely out of date.

IF these two services to one building serve two independent housing units then each must have its own grounding system. Remember, a "service" is the point of connection of the utility's wires through the meter and to the first overcurrent protection device, either a fuse or circuit breaker. If there is only one utility connection or one meter then this is NOT two services but a single service with a "sub"-panel. (The term sub-panel does not exist in the NEC.)

I would agree with you that each "service" needs an independent Grounding Electrode Conductor (GEC) from the service panel to the water main. In addition each service would need a supplementary connection to a "made" electrode, commonly a driven ground rod. Each of these GEC needs to be a single piece or connected via non-reversible connectors. Whether or not individual ground rods for each service would be required is something that I do not know.

Remember also that the NEC is a "model code" and has no power of enforcement. It is ONLY when a state, county or municipal legislative body enacts the NEC into law that it becomes law. The legislative body has the power to add to, or delete from the model code as it sees fit. That means that the ONLY code that really matters is the code enforced in your particular area.
 
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Old 09-08-14, 04:33 AM
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I would expect two grounding systems for the two services.
 
 

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