Required number of ground rods

[tom baker]

Probably 250.4(A)(1)

View attachment 2563387

Be careful saying it is for lightning protection though, that isn't exactly what it says there.

Subtle distinction, but important, limit voltage imposed vs protect from

 

[jaggedben]

What is example of unwise manner?

Too small a conductor and/or a conductor run high above the ground or through areas where flashover could damage sensitive or expensive stuff.

I also consider auxiliary electrodes (permitted but not required by the NEC) to be 'unwise' in general, unless proven otherwise in the specific case.

The case in point which brought this to my attention was the (stupid, since removed) 2014 NEC requirement for an auxiliary electrode for rooftop solar arrays. This essentially required that a combination of EGC and GEC be run over the roof and through equipment and ultimately connect two remote electrodes, where the EGC could also be as small as 14awg. Mike Holt explained at length in this video why that is a bad idea, see illustration around 10:20 in particular.

My belief is that if you have two widely separated electrodes that the NEC requires be bonded, the best practice would be to bury the bonding jumper in the ground outside the house, or at least run it through non sensitive crawlspace or basement area underneath the house. 'Unwise' in lightning prone areas would be through the middle of the house or over the roof. Or like, through the server room of a commercial building.

 

[kwired]

Too small a conductor and/or a conductor run high above the ground or through areas where flashover could damage sensitive or expensive stuff.

I also consider auxiliary electrodes (permitted but not required by the NEC) to be 'unwise' in general, unless proven otherwise in the specific case.

The case in point which brought this to my attention was the (stupid, since removed) 2014 NEC requirement for an auxiliary electrode for rooftop solar arrays. This essentially required that a combination of EGC and GEC be run over the roof and through equipment and ultimately connect two remote electrodes, where the EGC could also be as small as 14awg. Mike Holt explained at length in this video why that is a bad idea, see illustration around 10:20 in particular.

My belief is that if you have two widely separated electrodes that the NEC requires be bonded, the best practice would be to bury the bonding jumper in the ground outside the house, or at least run it through non sensitive crawlspace or basement area underneath the house. 'Unwise' in lightning prone areas would be through the middle of the house or over the roof. Or like, through the server room of a commercial building.

Not bonding the shield of communications cables and such to the GES also can present some issues. Don't seem to see it as much anymore but some those used to go to their own rod and not bond the the GES

 

[jaggedben]

Not bonding the shield of communications cables and such to the GES also can present some issues. Don't seem to see it as much anymore but some those used to go to their own rod and not bond the the GES

Yes, or their rod might be bonded in reality by tiny communication wires that run through the house to equipment that is in turn connected through the house to the electrical system.
I believe this is why the NEC now requires the Intersystem Bonding Bridge, so that comms technicians will (hopefully) bond there, and not (intentionally or unintentionally) create their own electrodes and undersized bonding jumpers through equipment.
Not sure how much of a real issue it has been, but still seems smarter.

 

[Jpflex]

You can debate the purpose and need but the bottom line is if you want the installation to be Code compliant then 250.32:
(A) Grounding Electrode. Building(s) or structure(s) supplied by feeder(s) or branch circuit(s) shall have a ground ing electrode or grounding electrode system installed in accordance with Part III of Article 250.

This is the code I was looking for. Reading people’s post is not hearing it from the horses mouth as it is with having the code

 

[Jpflex]

Several SCs are joined to make one residence with the one sub you mentioned? If so, one additional GES as kwire outlined.

Yes

 

[kwired]

Yes, or their rod might be bonded in reality by tiny communication wires that run through the house to equipment that is in turn connected through the house to the electrical system.
I believe this is why the NEC now requires the Intersystem Bonding Bridge, so that comms technicians will (hopefully) bond there, and not (intentionally or unintentionally) create their own electrodes and undersized bonding jumpers through equipment.
Not sure how much of a real issue it has been, but still seems smarter.

I have yet to see a communications, satellite TV installer, etc. land anything on a IBB since I began installing them. Have had them put a enclosure clamp on meter sockets or load centers when the IBB was right there and waiting for use though.

 

[Little Bill]

I have yet to see a communications, satellite TV installer, etc. land anything on a IBB since I began installing them. Have had them put a enclosure clamp on meter sockets or load centers when the IBB was right there and waiting for use though.

I was working at a house and had installed an IBB. There was a cable/satellite guy there doing an install. He came and asked me if I had a split bolt. I asked what size and why he needed it. He said to ground his system to the house grounding. I showed and explained to him about the IBB and that he didn't need to split bolt it. It was lunch time so I left to go eat. When I got back, I looked and saw that he had come up with a split bolt and used it instead of the IBB. He was gone so I couldn't question him about it!

 

[jaggedben]

You'd think NFPA would reach out to the major comms utilities with training materials. Actually on second thought, I have no real reason to think that.