Grounding of PEMB

[dvcraven0522!]

The question come up at recent meeting relative to grounding requirements of a pre-engineered metal building. The suggestion to provide a ground rod at each column location as marked was discussed. I can see making connection to building steel but not sure a ground rod is necessary. I do not have info on what type of slab will be provided. This building is 80'x168'.

Dan Craven

 

[kwired]

Find out what is there for footings for those main truss members. Might be good chance they are qualifying electrodes.

Might also be chance of qualifying CEE in any other footings they may have.

No ground rods are required by NEC if you have either of what I mentioned.

 

[don_resqcapt19]

A lot of those don't have much for footings...just localized at the columns and not likely enough rebar to be a CCE and you can't use a floor slab as a CCE.
I would just put two rods near the service equipment, and a single bond to the steel, assuming it is all tied together as a structure. If the steel is not interconnected to form a metal building frame, I don't see 250.104(C) even requiring the steel to be bonded.

 

[petersonra]

The question come up at recent meeting relative to grounding requirements of a pre-engineered metal building. The suggestion to provide a ground rod at each column location as marked was discussed. I can see making connection to building steel but not sure a ground rod is necessary. I do not have info on what type of slab will be provided. This building is 80'x168'.

Dan Craven

The type of slab does not matter, nor does the building size.

There is nothing in the code that ever requires more than two rods for a structure if grounding rods are used.

A bond to the steel structure might or might not be required by code. Putting one in up front to eliminate inspection hassles might be worthwhile even if not required. I don't recall offhand exactly what the requirements are around a bonding to the steel structure but I think there's a good chance that if a bond to the steel structure is required, ground rods would not be necessary.

Who is making these suggestions?

 

[dvcraven0522!]

Thank you all for your responses.

I have attached a detail of the connection to the slab per PEMB details PDF. As you can see there is not much in the way of footings and for a CCE. I am thinking if I provide the proper grounding at the service entrance per the attached grounding detail PDF and provide a green grounding equipment conductor in all conduit along with proper bonding I would not require any additional grounding for the building.

 

[brantmacga]

Currently working on an industrial plant expansion. The wall we are extending the slab from is about 200’ long with a dozen or so steel columns, and every one of them is bonded to a ground rod driven right outside that wall. Our new slab was poured right up to the existing and around the GEC’s. I’ve never seen this sort of install and thought it peculiar. I don’t know what their existing footings are like, but our slab has another dozen piers and 36” deep footings that are full of steel.

 

[don_resqcapt19]

Thank you all for your responses.

I have attached a detail of the connection to the slab per PEMB details PDF. As you can see there is not much in the way of footings and for a CCE. I am thinking if I provide the proper grounding at the service entrance per the attached grounding detail PDF and provide a green grounding equipment conductor in all conduit along with proper bonding I would not require any additional grounding for the building.

Are the building columns connected to each other by metal structural members? If so 250.104(C) requires a bonding connection to the steel.

 

[kwired]

Thank you all for your responses.

I have attached a detail of the connection to the slab per PEMB details PDF. As you can see there is not much in the way of footings and for a CCE. I am thinking if I provide the proper grounding at the service entrance per the attached grounding detail PDF and provide a green grounding equipment conductor in all conduit along with proper bonding I would not require any additional grounding for the building.

In the grounding details document it shows connection to a "UFER". So apparently there is something there that qualifies as a CEE.

If you have a CEE or qualifying structural steel electrode, NEC does not require use of rod(s). Apparently whoever designed this thinks they are needed for whatever reason anyway.