grounding at transfer switch

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apj

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My question is:

The utility transformer feeds a 600 amp service to a building. We are installing a automatic transfer switch with a solid neutral bus between the transformer and the main disconnect. Do I need to drive a ground rod at the transfer switch, and should I bond my neutral and ground at the switch? The main disconnect is inside the building and the transfer switch is outside the building approx. 70 feet away.
 
Re: grounding at transfer switch

The general rule is to bond the ground and neutral at one and only one place. That prevents the ground and neutral from becoming parallel conductors. (If that happened, some of the neutral current would flow on the ground).

This is slightly different than your previous question regarding the utility. They will usually only run one conductor (for the neutral/ground) from their transformer to the main disconnect. Then it gets split into your neutral and ground wires at the main bonding point.

I would suggest you bond the ground and neutral at the utility service location only. Then you have to make sure there is no bond between the neutral and ground at the generator. If your transfer switch didn't have the solid neutral, you would bond at the service and at the generator. That way there would be one bond for each position of the transfer switch.

Steve
 
Re: grounding at transfer switch

Another point: unless the ATS is rated for use as service equipment (meaning it contains a service disconnect), there needs to be a utility disconnect ahead of it. Wherever the first disconnect is determines where the neutral, GEC's, etc., all connect together.
 
Re: grounding at transfer switch

Hey I would like more information on what grounding electrodes is present at the building?
250.50 then we know how many rods and where to put them. Neal
 
Re: grounding at transfer switch

Sorry Neal. The current grounding situation at the existing building is unknown, since this was installed 50-60 years ago. :(
 
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