Separate Ground Rod for Communications

[MrSparky1962]

I am on a project that is using the 2008 NEC. The communications riser diagram shows at least (3) locations where a pedestal mount cabinet will be set outside of the building. In each case the designer is indicating a separate ground rod at the pedestal that is not bonded back to anything. Also in all (3) cases, the only cabling going to and from these pedestals is non-conductive (dielectric) fiber. There will be at least (1) branch circuit feeding each cabinet and they will all have active communications equipment in them.

Per Section 770.100(D), I believe these ground rods must be bonded back to the electrical system ground, even though there is no electrical path back to the building via the communications cabling. AM I missing something?

 

[ActionDave]

Welcome to the forum.

I agree that the remote ground rod connection should be brought back to the main, or to a single point somewhere that is bonded to the main. There is an exception in the code that allows auxiliary ground rods to be left on their own, but I don't think it is a good idea.

What kind of project is this?

 

[Dennis Alwon]

I agree with you that the bonding for the communication should be connected back to the grounding electrode system. BTW. I corrected the article to 800 instead of 700

 

[MrSparky1962]

Welcome to the forum.

I agree that the remote ground rod connection should be brought back to the main, or to a single point somewhere that is bonded to the main. There is an exception in the code that allows auxiliary ground rods to be left on their own, but I don't think it is a good idea.

What kind of project is this?

Thanks Dave, I would be interested to review the exception. I agree that it wouldn't be a good idea, I would just like to review for future reference. The project is at the Orlando International Airport. We are beginning a new South Terminal expansion.

 

[MrSparky1962]

I agree with you that the bonding for the communication should be connected back to the grounding electrode system. BTW. I corrected the article to 800 instead of 700

Hi Dennis,

Actually, I should have said 770.100(D). :slaphead: It is a fiber system, not copper.

Thanks

 

[cpinetree]

What if the pedestals were considered separate structures?
Could you put in a GES and tie it to the single circuits ground conductor?

Please don't crucify me for asking this, just curious.

 

[Dennis Alwon]

Hi Dennis,

Actually, I should have said 770.100(D). :slaphead: It is a fiber system, not copper.

Thanks

I corrected it again....lol

 

[petersonra]

What if the pedestals were considered separate structures?
Could you put in a GES and tie it to the single circuits ground conductor?

Please don't crucify me for asking this, just curious.

A feeder to a separate structure requires an intersystem bonding doohickey. You would have to have a GES at the structure along with an EGC coming in with the feeder. The EGC, GES and the intersystem bonding doohickey would all be connected together at the disconnecting means for the structure.

If the single circuit is a branch circuit there is no requirement for a GES at the structure and I think (but am not 100% sure) no requirement for an intersystem bonding doohickey. Nothing prevents you from adding either or both though. You still have to bring in an EGC with the branch circuit.

 

[cpinetree]

A feeder to a separate structure requires an intersystem bonding doohickey. You would have to have a GES at the structure along with an EGC coming in with the feeder. The EGC, GES and the intersystem bonding doohickey would all be connected together at the disconnecting means for the structure.

If the single circuit is a branch circuit there is no requirement for a GES at the structure and I think (but am not 100% sure) no requirement for an intersystem bonding doohickey. Nothing prevents you from adding either or both though. You still have to bring in an EGC with the branch circuit.

So a grounded conductor and 2 grounding conductors (1 sized for the circuit and 1 a #6 for the GES?) fed from the main building?
Looks like when we do sheds they have been missing a grounding conductor for the GES. :ashamed1:

We have always tied the GES and intersystem bonding doohickey to the ground bar on the sub panel that is fed from the house with 2-#10 hot, 1-#10 neutral (Grounded conductor), and 1-#10 green (Grounding conductor)
Often the inspectors want to know why we installed the doohickey :lol: - because code says we need to:thumbsdown:

 

[don_resqcapt19]

Welcome to the forum.

I agree that the remote ground rod connection should be brought back to the main, or to a single point somewhere that is bonded to the main. There is an exception in the code that allows auxiliary ground rods to be left on their own, but I don't think it is a good idea.

What kind of project is this?

Not really...those rods or other auxiliary grounding electrodes are required to be connected to the circuit EGC.

250.54 Auxiliary Grounding Electrodes
One or more grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding requirements of 250.50 or 250.53(C) or the resistance requirements of 250.53(A)(2) Exception, but the earth shall not be used as an effective ground-fault current path as specified in 250.4(A)(5) and 250.4(B)(4).

 

[ActionDave]

Thanks Dave, I would be interested to review the exception. I agree that it wouldn't be a good idea, I would just like to review for future reference. The project is at the Orlando International Airport. We are beginning a new South Terminal expansion.

Wow. You are in for some fun. :roll:

Here is the exception.

250.54 Auxiliary Grounding Electrodes

One or more grounding electrodes shall be permitted to be
connected to the equipment grounding conductors specified
in 250.118 and shall not be required to comply with the elec-
trode bonding requirements of 250.50 or 250.53(C) or the
resistance requirements of 250.53(A)(2) Exception, but the
earth shall not be used as an effective ground-fault current
path as specified in 250.4(A)(5) and 250.4(B)(4).

 

[ActionDave]

Not really...those rods or other auxiliary grounding electrodes are required to be connected to the circuit EGC.

You are correct. I did not not word my reply well.

 

[petersonra]

So a grounded conductor and 2 grounding conductors (1 sized for the circuit and 1 a #6 for the GES?) fed from the main building?
Looks like when we do sheds they have been missing a grounding conductor for the GES. :ashamed1:

We have always tied the GES and intersystem bonding doohickey to the ground bar on the sub panel that is fed from the house with 2-#10 hot, 1-#10 neutral (Grounded conductor), and 1-#10 green (Grounding conductor)
Often the inspectors want to know why we installed the doohickey :lol: - because code says we need to:thumbsdown:

The GES is at the remote structure. If it is not required there is no GEC at the remote structure. the GES is always at the structure served.