Bonding Ground & Neutral @ Outdoor Generator Docking Station

[Sparky2791]

I am working on a project with an electrical contractor to install an outdoor generator docking station. Plans are to intercept the incoming underground feeders from the utility transformer and reroute them into the docking station which will be service entrance rated and have both a service entrance circuit breaker and a generator circuit breaker with a kirk key lock between them. Since the service entrance circuit breaker will now be located outside in the docking station remote from where the current grounding electrode system is located (inside the building) and because you should only bond the neutral to ground once in the system I have a few questions;

• Should the neutral to ground bonding jumper be removed from the existing grounding electrode system (GES) inside the building currently?

• What should the ground wire from the docking station to the existing GES in the building be sized on (250.66 or 250.122). This seems to be a bonding jumper so 250.122 however it is after the neutral to ground bond was made so is it an equipment ground now and 250.66 rules?

• Is it necessary to drive a ground rod @ the docking station?

I am having confirmed if a ground wire is currently installed in the existing service entrance feeders and what size it is.


Thank you for your time.

 

[iceworm]

I am working on a project with an electrical contractor to install an outdoor generator docking station. ...

I have not heard the term docking station used in conjunction with a generator. Does one roll up with a transportable gen, plug in the power conductors, no auto controls?

... Plans are to intercept the incoming underground feeders from the utility transformer and reroute them into the docking station which will be service entrance rated and have both a service entrance circuit breaker and a generator circuit breaker with a kirk key lock between them. Since the service entrance circuit breaker will now be located outside in the docking station remote from where the current grounding electrode system is located (inside the building) and because you should only bond the neutral to ground once in the system ....

Perhaps could post a one-line - three phase, singlephase, 208/120, 480V. 240/120, 120/240. A pencil sketch will do fine. It would make it easier to see

... Plans are to intercept the incoming underground feeders from the utility transformer and reroute them into the docking station which will be service entrance rated and have both a service entrance circuit breaker and a generator circuit breaker with a kirk key lock between them. ...

The gen CB is 3 pole, the service and gen neutrals are tied together? The gen is not an SDS?

• Should the neutral to ground bonding jumper be removed from the existing grounding electrode system (GES) inside the building currently?

...

Provided the picture I have is the same as you are installing:
Yes
And you may wish to look into removing the gen N-G bond. Do you have a place picked for the N-G bond that covers both the gen and the service?

...

• What should the ground wire from the docking station to the existing GES in the building be sized on (250.66 or 250.122). This seems to be a bonding jumper so 250.122 however it is after the neutral to ground bond was made so is it an equipment ground now and 250.66 rules?

....

I am not following your reasoning

The conductors from the docking station are a feeder - correct? If so I would think 250.122 governs

• Is it necessary to drive a ground rod @ the docking station?

....

It is a service. Do what you would do for a service. There is a list.

... I am having confirmed if a ground wire is currently installed in the existing service entrance feeders and what size it is. ...

This piece is now a feeder. I suspect it should be 5 wire

ice

 

[Sparky2791]

I have not heard the term docking station used in conjunction with a generator. Does one roll up with a transportable gen, plug in the power conductors, no auto controls?

Docking station is permanently installed to accept cam lock cable feed from roll up generator. Docking station has 2 breakers with kirk key locks to prevent both from being closed on same bus.

Perhaps could post a one-line - three phase, singlephase, 208/120, 480V. 240/120, 120/240. A pencil sketch will do fine. It would make it easier to see

Attached for reference with main question I am asking regarding equipment bonding jumper.

The gen CB is 3 pole, the service and gen neutrals are tied together? The gen is not an SDS?

Yes. No. No.

Provided the picture I have is the same as you are installing:
Yes
And you may wish to look into removing the gen N-G bond. Do you have a place picked for the N-G bond that covers both the gen and the service?

See single line for my revised thoughts on this.

I am not following your reasoning

The conductors from the docking station are a feeder - correct? If so I would think 250.122 governs

Yes, a feeder but a service entrance feeder. See single line for my revised thought on this

It is a service. Do what you would do for a service. There is a list.

See single line for my revised thoughts on this

This piece is now a feeder. I suspect it should be 5 wire

Confirmed that it is. Although I have see it where they did not install the ground wire (not sure why):dunce:

ice

Ultimately the question is relating to 250.30 (A) (2). It states that the EBJ is sized based on derived phase conductors to the first disconnect switch, which currently is the buildings SDS. Now that we are looking to add the docking station in between the derived system (Utility Transformer) and this SDS the new 'first disconnect' will now be in the docking station. So will the ground wire from the docking station to the SDS be still be sized based on derived phase conductors?

 

[augie47]

A couple of side notes prior to your specific question:
Your "docking station" will need to be Service Entrance Rated since it serves as your service (first means) of disconnect.
Since your docking station does not switch the neutral, your generator should not be a SDS and there should be no neutral ground bond at the generator, rather a equipment grounding conductor installed from the docking station to the generator
As far as your questions:
With the docking station you have effectively relocated your service entrance to that point. A neutral to ground connection should be established there (at the docking station) and all grounding electrode connections routed to that point.
An equipment grounding conductor sized per 250.122 (or another effective means such as the conduit) should be routed to the existing equipment to connect all grounding conductors and enclosures.
There should no neutral to ground connections beyond the docking station.

 

[Sparky2791]

A couple of side notes prior to your specific question:
Your "docking station" will need to be Service Entrance Rated since it serves as your service (first means) of disconnect.
Since your docking station does not switch the neutral, your generator should not be a SDS and there should be no neutral ground bond at the generator, rather a equipment grounding conductor installed from the docking station to the generator
As far as your questions:
With the docking station you have effectively relocated your service entrance to that point. A neutral to ground connection should be established there (at the docking station) and all grounding electrode connections routed to that point.

What about the grounding electrode system established in the existing building? How does this connect to the new GES established at the docking station since it is remote from the building? Ultimately the only part of the GES I can create at the docking station is to drive a ground rod. None of the other means of a GES per NEC 250.50 are available in this remote location.

 

[augie47]

Sorry. I did not pick-up that the docking station was remote from the building... as the younger set states "my bad".
Somewhat a fine line depending on your docking station being treated as a "seperate structure".
If that be the case, it would need it's own Grounding electrode system,
still need to be service rated and have neutral to ground bonding.
An GEC sized per 250.122, would be run to the existing gear for grounding purposes and the existing grounding electrodes would be connected to that point with no neutral to ground connection.