Generator SDS

Status
Not open for further replies.

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
2008 Cycle.

So I'm dealing with a 800A generator supplying an optional standby system at a data center. The neutral is switched at the ATS, making this a Separately Derived System. The generator is outside in a bricked-in enclosure alongside the RTUs. It is about 20' from the building it serves.

There is no structural steel within the building (the ceiling is held up by three isolated steel trusses), no metal water pipe.

There was a suggestion to route the generator's GEC to the 800A utility service disconnect, and another suggestion to drill a hole in the concrete pad at the generator and drive a ground rod.

How would you handle this?
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
The auxiliary building is twenty feet away and it doesn't have a grounding electrode system already??

At any rate I would drive a ground rod and wait until someone made me to add a second.

What is causing the need to drill through the slab rather than pounding a ground rod outside the building?
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
The generator is sitting on a slab.

There is a GEC, but we don't know for sure where it goes. There is also a ground rod under the service disconnect.

My thinking was that the generator is a structure and there's nothing there.
 

ceb58

Senior Member
Location
Raeford, NC
You want the Generator GEC to eventually be equipotential with the Service GEC. Are you running a EGC with your gen feeder?

Agreed, all of our gen. whether SDS or NSDS are tied into the grounding ring to form a single point system.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Unless you take some very extra ordinary steps there will be connections between the generator and utility grounded conductors even where the ATS switches the grounded conductor. The most common will be the fact that the ATS enclosure has to be connected to the EGC from both systems. The main and system bonding jumpers will provide the connection between the EGCs and their respective grounded conductors.
 

ceb58

Senior Member
Location
Raeford, NC
Sorry for not being clearer:dunce:

He is talking about shelters at communication sites like radio or cell towers. Everything gets bonded. If you stand still too long one of the guys on the grounding crew will stick a ground wire on you ankle.

Yes, this is what I am speaking of. And your ankle is'nt the only place:eek:

Unless you take some very extra ordinary steps there will be connections between the generator and utility grounded conductors even where the ATS switches the grounded conductor. The most common will be the fact that the ATS enclosure has to be connected to the EGC from both systems. The main and system bonding jumpers will provide the connection between the EGCs and their respective grounded conductors.

And that has been my argument for some of our sites. The powers to be are now requiring our gen. to be installed as SDS systems. They say it is better for the electronic equipment with nothing to back that statement up with. I cant tell any difference from a site that is non-SDS compared to a site that is. But when you bring up the fact that with a SDS on a single point grounding system you will never break the bond between the utility neutral and the EGC's they change the subject.:?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
There is only one way that I know of that you can make a SDS code compliant and have no electrical connection, other than the earth between the grounded conductors of the two systems. I can't think of any way that you can make that happen where you have an ATS and where the grounded conductor is used as a circuit conductor.
 
Status
Not open for further replies.
Top