I read an old forum on installing ground rods at light poles. From what I understand, this is not necessary or useful. Can someone please further explain this? Also, is there anything in the NEC that would dictate using a wire size larger than #6 for a grounding electrode conductor connected directly to a ground rod?
Ground rods at light poles
- Thread starter lizzie14
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charlie
Senior Member
- Location
- Indianapolis
Re: Ground rods at light poles
Second question first. Larger than #6 is never required for service grounding to a ground rod.
First question, if columns are anchored to a concrete base, the rebar in the base and anchor rods act as a grounding electrode. IMO, if the column is a direct imbedded fiberglass type, it does need a grounding electrode. Keep in mind that the Code doesn't require one and the unqualified persons who may work on the system may think that the ground rod is all that is needed for grounding the column and/or fixture. In other words, the ground rod may provide a false sense of security and may do nothing to protect the lighting system.
Second question first. Larger than #6 is never required for service grounding to a ground rod.
First question, if columns are anchored to a concrete base, the rebar in the base and anchor rods act as a grounding electrode. IMO, if the column is a direct imbedded fiberglass type, it does need a grounding electrode. Keep in mind that the Code doesn't require one and the unqualified persons who may work on the system may think that the ground rod is all that is needed for grounding the column and/or fixture. In other words, the ground rod may provide a false sense of security and may do nothing to protect the lighting system.
russ
Senior Member
- Location
- Burbank IL
Re: Ground rods at light poles
I have no real hard evidence to back up the following claim. An engineer I know told me I-DOT (Illinois Department of Transportation), requires ground rods at light poles, to keep the concrete bases from blowing apart during lightning strikes
[ May 20, 2005, 11:03 PM: Message edited by: russ ]
I have no real hard evidence to back up the following claim. An engineer I know told me I-DOT (Illinois Department of Transportation), requires ground rods at light poles, to keep the concrete bases from blowing apart during lightning strikes
[ May 20, 2005, 11:03 PM: Message edited by: russ ]
bphgravity
Senior Member
- Location
- Florida
Re: Ground rods at light poles
Actually, ground rods act as an anchor for when hurricanes try to blow over the light poles.
There is some truth to the lightning issue. I have read that if lightning strikes a system utilizing a concrete-encased electrode, the heat from the lighting stroke will turn the moisture in the concrete and below the concrete into steam which expands and cracks the foundation. To deter this from happening, concrete encased electrodes can be supplemented with grounds or plates to help limit the full stroke going into the slab.
It sounds good in theory, but I have never really seen or read any proof of this happening.
Actually, ground rods act as an anchor for when hurricanes try to blow over the light poles.
There is some truth to the lightning issue. I have read that if lightning strikes a system utilizing a concrete-encased electrode, the heat from the lighting stroke will turn the moisture in the concrete and below the concrete into steam which expands and cracks the foundation. To deter this from happening, concrete encased electrodes can be supplemented with grounds or plates to help limit the full stroke going into the slab.
It sounds good in theory, but I have never really seen or read any proof of this happening.
Re: Ground rods at light poles
In Akron, Ohio the minimum GEC is #4 solid copper or #2 stranded copper. This has to do with interpreting the machanical damage protection requirements.
The mechanical requirement for #4 copper can be interpreted as requiring #4 copper for a ground rod in some situations.
The #6 copper wire rule for rods and plates is a throwback to the wiring rules for telegraph systems.
In New York State, if you are using any ground rods you must use at least 2 rods. The GEC must be #4 solid running unbroken from the service switch, loop wired through the first rod clamp, loop wired through the second rod clamp. then must return to the service via a different path and protective conduit. This way, if somebody should cut the wire while gardening you still have 2 ground rods.
In Akron, Ohio the minimum GEC is #4 solid copper or #2 stranded copper. This has to do with interpreting the machanical damage protection requirements.
The mechanical requirement for #4 copper can be interpreted as requiring #4 copper for a ground rod in some situations.
The #6 copper wire rule for rods and plates is a throwback to the wiring rules for telegraph systems.
In New York State, if you are using any ground rods you must use at least 2 rods. The GEC must be #4 solid running unbroken from the service switch, loop wired through the first rod clamp, loop wired through the second rod clamp. then must return to the service via a different path and protective conduit. This way, if somebody should cut the wire while gardening you still have 2 ground rods.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Re: Ground rods at light poles
I'm curious, doesn't the state of New York have a different code/licensing for each county? Under what authority are they requiring the scenario you've mentioned?
hmspe
Senior Member
- Location
- Temple, TX
- Occupation
- PE
Re: Ground rods at light poles
Consider this "thinking out loud"....
From what I remember, Ufer found that a concrete encased electrode was 3 ohms or less. In this area, even two ground rods seldom get as low as 25 ohms.
Lightning strikes a pole. The paths are steel pole / j bolts / rebar (Ufer) and steel pole / #6 copper / ground rod. Power splits in inverse proportion to the impedance, so probably 90% of the lightning takes the Ufer path. 100% of the power blows up the base, but 90% doesn't....
At a seminar I attended Mike Holt talked about driving a ground rod in the back yard, applying 120v, and measuring the current. I think he measured 2 amps, in Florida. Arizona has to be worse than that. On my list of things to try.
Martin
Consider this "thinking out loud"....
From what I remember, Ufer found that a concrete encased electrode was 3 ohms or less. In this area, even two ground rods seldom get as low as 25 ohms.
Lightning strikes a pole. The paths are steel pole / j bolts / rebar (Ufer) and steel pole / #6 copper / ground rod. Power splits in inverse proportion to the impedance, so probably 90% of the lightning takes the Ufer path. 100% of the power blows up the base, but 90% doesn't....
At a seminar I attended Mike Holt talked about driving a ground rod in the back yard, applying 120v, and measuring the current. I think he measured 2 amps, in Florida. Arizona has to be worse than that. On my list of things to try.
Martin
ryan_618
Senior Member
- Location
- Salt Lake City, Utah
Re: Ground rods at light poles
250.54 says you can use cat 5 to go from the ground rod to the light pole, since it is a supplementary electrode.
250.54 says you can use cat 5 to go from the ground rod to the light pole, since it is a supplementary electrode.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: Ground rods at light poles
I think it would still be subject to the requirements of 310.5.
I think it would still be subject to the requirements of 310.5.
charlie
Senior Member
- Location
- Indianapolis
Re: Ground rods at light poles
George, if you are adding a rod that is not required, why do you need to do anything with it at all? Actually, you can drive it and not hook it up at all.
250.54 Supplementary Grounding Electrodes Supplementary 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 250.56, but . . .
George, if you are adding a rod that is not required, why do you need to do anything with it at all? Actually, you can drive it and not hook it up at all.
250.54 Supplementary Grounding Electrodes Supplementary 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 250.56, but . . .
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: Ground rods at light poles
That's wierd.
That's wierd.
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