Auxillary Grounding Electrode Required?
Auxillary Grounding Electrode Required?
(OP)
I have a NEC question. We are installing a new electrical service and panel (outdoors) for a lighting project. The service is single-120/240V and is grounding at the service entrance (outdoor cabinet, panelboard, utility meter) via 2 ground rods. A grounding conductor is run with each branch feeder circuit to each light pole and the metal pole is bonded to the grounding conductor.
The local inspector says a auxilliary grounding electrode is required at each pole location. Is this correct? Section 250.54 in the 2008 NEC tells me if i install an auxilliary electrode to connect it to my system ground conductor, but not that is required. Does anyone know where this is required?
The local inspector says a auxilliary grounding electrode is required at each pole location. Is this correct? Section 250.54 in the 2008 NEC tells me if i install an auxilliary electrode to connect it to my system ground conductor, but not that is required. Does anyone know where this is required?






RE: Auxillary Grounding Electrode Required?
Rafiq Bulsara
http://www.srengineersct.com
RE: Auxillary Grounding Electrode Required?
I agree with Rafiq, it's probably not worth a battle with the inspector. It could be a local requirements and/or custom.
David Castor
www.cvoes.com
RE: Auxillary Grounding Electrode Required?
RE: Auxillary Grounding Electrode Required?
Rafiq Bulsara
http://www.srengineersct.com
RE: Auxillary Grounding Electrode Required?
Maybe the local inspector is requiring the ground for lightning protection.
RE: Auxillary Grounding Electrode Required?
We measured two structures and in both cases the foundation had lower resistance than the rod, as expected. I've seen other articles and blog comments that say the same thing.
I believe that that if the anchor bolts are connected the the rebar in the conrete foundation, that the resistance to earth is better than a single ground rod. I would think that the impedance to lightning strike current is also less.
One concern is that the lightning current will blow the foundation apart by overheating the rebar and vaporizing mositure in the conrete. (I saw remnants of a windmill foundation where this occured.) I don't know of any actual lightning stike on a street light pedastal where the foundation failed. Maybe it has happened.
If the inspector wants a ground rod, put one in. It probalby won't help much but it will make him feel better,
RE: Auxillary Grounding Electrode Required?
If you have a ground fault and the ground wire is the same size as the phase wire, the light pole will be at 1/2 the phase voltage until the circuit breaker operates. With long circuits, that could be enough time to injure someone leaning against the pole. Better to add a ground rod to make the pole and surrounding earth closer to the same voltage.
Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.
RE: Auxillary Grounding Electrode Required?
We really have this same issue anytime there is a ground fault to any electrical equipment. That equipment will be energized with a voltage that is equal to the voltage drop on the EGC, and like you said this voltage will be there until the fault is cleared.
RE: Auxillary Grounding Electrode Required?
I agree with that.
I think you have disputed me previously on this topic. If you want to recommend against grounding electrodes at the poles and are willing to put your stamp on it, that's fine with me, but I won't.
I think a concrete pole base itself may be the best electrode for this purpose, but it has be constructed with the necessary reinforcing steel for a proper Ufer system. I'm not sure that I would trust it would be installed correctly since it cannot be inspected after the fact. Therefore I'll stick with ground rods.
Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.
RE: Auxillary Grounding Electrode Required?
I won't recommend against it, but I see no real use for it. It is my opinion that the perceived safety benefit of installing the grounding electrode for light pole bases is far greater than the real one.
As a contractor, it is rare for me to find a set of stamped drawings that call for the installation of a ground rod or other grounding electrode for a light pole base. I have no issue with installing one when the drawings call for it as I get paid by the hour and that increases the labor hours.
25 years ago, it was common to find a grounding electrode requirement on the drawings, but those drawings often left out the required EGC.
RE: Auxillary Grounding Electrode Required?
Rafiq Bulsara
http://www.srengineersct.com
RE: Auxillary Grounding Electrode Required?
You could reasonably argue that lightning protection is not required, but if the inspector or contract requires the ground rod, then you would lose the reasonable argument most of the time.
RE: Auxillary Grounding Electrode Required?
It's not required by the NEC, and certainly cannot substitute for an equipment grounding conductor.
Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.