Should the transformer or the disconnect go to the ground rod?

[Cjmccarthy]

When grounding a service point, do you ground the disconnect and bond the transformer, ground the transformer and bond the disconnect, ground both the disconnect and transformer or , does it matter? bellow is a picture of a site and the plans we want to make sure complies to NEC.

 

[infinity]

Both the service disconnect and the transformer are required to be connected to the GES. The service neutral and the secondary neutral would also be bonded at their respective locations.

 

[Cjmccarthy]

Both the service disconnect and the transformer are required to be connected to the GES. The service neutral and the secondary neutral would also be bonded at their respective locations.

So both the disconnect and transformer should go to the ground rod utilizing separate wires?

 

[kwired]

GEC to the transformer secondary should land wherever you have the main bonding jumper. It is usually allowed to be either at the transformer or at the first secondary disconnecting means.

 

[kwired]

So both the disconnect and transformer should go to the ground rod utilizing separate wires?

That is acceptable, a bonding jumper to the service GEC or any other electrode (when present) is also acceptable

 

[infinity]

So both the disconnect and transformer should go to the ground rod utilizing separate wires?

If the ground rod is the GES then both the transformer and the service disconnect must connect to it. As kwired stated there are several ways to do it.

 

[Cjmccarthy]

If the ground rod is the GES then both the transformer and the service disconnect must connect to it. As kwired stated there are several ways to do it.

Several ways??? Can we go from the disconnect to the ground rod and then bound the disconnect to the transformer? would that adhere to NEC?

 

[jaggedben]

I don't follow how the picture matches up to the plans. What kind of transformer is involved and what is the primary and secondary voltage? I don't see a transformer in the picture. Is it at the same structure as the service disconnect, or a separate structure?

Grounding a service and a separately derived system are separate issues. Everything at the same structure that needs to be grounded gets grounded to the same electrode system. Separate structures get separate electrode systems.

Bonding is also separate from grounding.

 

[Cjmccarthy]

I don't follow how the picture matches up to the plans. What kind of transformer is involved and what is the primary and secondary voltage? I don't see a transformer in the picture. Is it at the same structure as the service disconnect, or a separate structure?

Grounding a service and a separately derived system are separate issues. Everything at the same structure that needs to be grounded gets grounded to the same electrode system. Separate structures get separate electrode systems.

Bonding is also separate from grounding.

on that pole there is a disconnect and behind it there is a transformer. sometimes the transformer could be a stepdown (from 600v to 240/480) sometimes is could be a step up. each location is a separately derived system for that location. So if I am understanding you correctly, the disconnect and the transformer needs to have a dedicated wire to ground rod, is that correct?

 

[augie47]

on that pole there is a disconnect and behind it there is a transformer. sometimes the transformer could be a stepdown (from 600v to 240/480) sometimes is could be a step up. each location is a separately derived system for that location. So if I am understanding you correctly, the disconnect and the transformer needs to have a dedicated wire to ground rod, is that correct?
View attachment 2573069

You can run a dedicated grounding electrode conductor from each OR you can run one from the disconnect and split bolt the one from the transformer to that one. (there are other options but that seems to be common here)

 

[Cjmccarthy]

You can run a dedicated grounding electrode conductor from each OR you can run one from the disconnect and split bolt the one from the transformer to that one. (there are other options but that seems to be common here)

Thank you, So if I go from the disconnect to the ground rod with say a #6 wire, then I can use a #6 wire from the disconnect buss bar to the transformer? I just want to make sure we adhere to NEC.

 

[jaggedben]

That transformer looked like the back of a panelboard to me.

Thank you, So if I go from the disconnect to the ground rod with say a #6 wire, then I can use a #6 wire from the disconnect buss bar to the transformer? I just want to make sure we adhere to NEC.

No, you would go from the transformer to a split bolt in the GEC outside of the enclosures.

Think of it as...
You have a point on the service that you will ground. You have a point on the separately derived system that you will ground. These are both wires going to ground(ing electrodes), not to each other. They are allowed to join paths on the way to the ground,.i.e. tap to a common grounding electrode conductor. But they can also stay separate.

 

[Cjmccarthy]

That transformer looked like the back of a panelboard to me.


No, you would go from the transformer to a split bolt in the GEC outside of the enclosures.

Think of it as...
You have a point on the service that you will ground. You have a point on the separately derived system that you will ground. These are both wires going to ground(ing electrodes), not to each other. They are allowed to join paths on the way to the ground,.i.e. tap to a common grounding electrode conductor. But they can also stay separate.

wouldn't it just be easier to have 2 wires, one from the disconnect and one from the transformer to the ground rod? The FDOT does not allow splits bolts, it would have to be CAD welded (Exothermic welding), that is what is acceptable to the Department.

 

[augie47]

2 separate wires is fine. Normally you would use a separate acorn clamp for each

 

[Cjmccarthy]

What NEC code do I reference?

 

[kwired]

wouldn't it just be easier to have 2 wires, one from the disconnect and one from the transformer to the ground rod? The FDOT does not allow splits bolts, it would have to be CAD welded (Exothermic welding), that is what is acceptable to the Department.

Do they also require exothermic weld connection to the rod?

I know sometimes certain authorities like to make these kind of rules but often with no real justification. IMO if the tap to the main GEC must be exothermic weld then it only makes sense to require the connection to the electrode itself to be exothermic weld. The current path is never better than it's weakest point.

 

[Cjmccarthy]

Do they also require exothermic weld connection to the rod?

I know sometimes certain authorities like to make these kind of rules but often with no real justification. IMO if the tap to the main GEC must be exothermic weld then it only makes sense to require the connection to the electrode itself to be exothermic weld. The current path is never better than it's weakest point.

Yes they do, per spec 620-2.5

620-2.5 Exothermic Grounding Bond: Make all connections to the ground rod assemblies using exothermic welds.

620-3 Installation.
620-3.1 General: Construct a single-point grounding system. Install the primary ground rod assembly in an electrical pull box so that the top four inches are accessible for inspection, resistance testing, and maintenance. The primary ground rod assembly and electrical pull box shall be installed between 12 inches to 36 inches from the element being grounded. The top of all other ground rod assemblies connected to the primary ground rod assembly in an array must be buried a minimum of 18 inches below grade. Direct bury grounding conductors used to connect ground rod assemblies a minimum of 18 inches below finished grade. Bond all ground rod assemblies and ground rod arrays together with solid bare
tinned copper wire unless otherwise shown in the Plans. Install grounding conductors in a straight path.
Make all bonds between ground wires and ground rod assemblies and ground rod arrays with an exothermic bond with the following exception: do not exothermically bond sections of ground rods to create the ground rod assembly and do not exothermically bond
connections within a cabinet. Apply an anti-oxidant compound to all mechanical connections. Connect primary surge protection for power at the service entrance or main disconnect. Connect secondary surge protection at point of use, unless otherwise shown in the Plans. Ensure that lightning protection systems conform to the requirements of the National Fire Protection Association (NFPA) Code NFPA 780, Standard for the Installation of Lightning Protection Systems. Install SPDs that have an operating voltage appropriate for the characteristics of the circuits they protect. The NFPA requirements do not apply to lighting systems.

 

[Isaiah]

When grounding a service point, do you ground the disconnect and bond the transformer, ground the transformer and bond the disconnect, ground both the disconnect and transformer or , does it matter? bellow is a picture of a site and the plans we want to make sure complies to NEC.


View attachment 2573068 View attachment 2573067
View attachment 2573067

One thing you don’t want to do is to create a parallel neutral path between the service disconnect and the upstream transformer


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