Light Pole grounding

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ashtrak

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I know this is a subject that Mike Holt is really hot on from some of the things I've read on his site i.e. parking lot pole grounding.. Question is-- we are mounting new light poles on a passenger platform at one of our rail stations. The drawings show a ground rod driven under the platform at each pole location,#4 ground to 10' rod. We have one lug in the pole. Should the circuit ground from the panel and the internal light pole ground all be under one lug with the ground rod, or will we create ground loops doing it this way? Also it's important to know that this is an electrified railroad running at 25 cycle (light poles are 277v at 60 cycle). We do a lot of bonding at the passenger locations i.e. railings and metal structures but we try not to bond the 60cycle to the 25cycle. I probably over complicated the picture with the 25 cycle story but even disregarding that should we bond under a seperate lug at the light pole. I'd like to hear your opinion... Thanks
 
the incoming EGC needs to be connected to the metal pole structure in some convenient way. otherwise if you get a loose wire, it won't short out and trip the OCPD, which is a real good idea to keep from killing someone.

there is no ground loop issue. the rod serves no real purpose, unless I suppose to provide a path to ground in the event of a driect lightning strike. but the concrete base is probably a better grounding electrode then the ground rod (but not a NEC legal one).
 
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Okay then what about an industrial machine, say an injection molding machine? I work at a place that has these machines that inject hot plastic into a mold. The manufacturer reccommends that you drive a ground rod for each machine and I tried to ask them what the purpose was for and the manufactures rep said it is to take any stray voltages to ground. This one confused me because I see an EGC all ready ran to the service sized IAW the OCP. Doesn't this present a alternate path for a fault to go? The ground rod is driven well inside a building so the amount of moisture in the ground is minimal and the only connection to the EGC is at the terminal where the EGC is connected. Can someone explain this one to me or link me to a place where it is explained? I have reservations about this practice. I post this question to all the guru's of electron manipulation in hopes that they can help me out on this one because I am perplexed.
 
The additional ground rod is not a danger and is not a code violation assuming the required EGC is in place.

That said the additional ground rod will do absolutely nothing.
 
I agree with Bob. See 250.54.

Don't be surprised next cycle ( 2008 ), when this may be called an "auxilliary grounding electrode." ;)

Drive all the ground rods they want, but always ensure that a proper Equipment Grounding Conductor is installed to the equipment.
 
I get machinery suppliers asking me to do this all the time. I think they are just trying to pass the buck when their machines don't work right and, to the average Joe it sounds like a good idea. First I tell the customer that it's a waste of time and then I install the rod and bill them for it. It gets a bit stickier when I'm asked to disconnect the eq grd to prevent stray voltage, I always refuse but I've seen a few maintenance workers do it anyway.
 
These additional ground rods are called supplementary grounding electrodes. They are installed because someone does not understand the purpose of grounding per the NEC. There are no NEC requirements that need to be met for supplementary grounding electrodes, they may be installed however the person requesting them would like for them to be installed se 250.54 in the 2005 code. The DO NOT replace the required equipment grounding conductor. Ground the pole or equipment as required by the NEC and then install as many suplementary grounds as the designer requires. They will do little or no good, but with a proper equipment grounding conductor installed, they will do no harm.
 
The only time I've seen individual rods for machinery was for dissipation of static charges, typically from friction and such forces.
 
I'm beginning to wonder if the ground rods at machinery, for instance, don't do a lot of good when you are looking at frequencies greater than 60 hz. I wonder if all these fancy grounding schemes, including burying them in charcoal, don't actually help in other instances than our 60 hz scenarios.

I thing there is a consensus that they don't do much for ground fault assistance, and are suspect for touch potential protection, but I am beginning to wonder about noise reduction.

Jim T
 
"I suppose to provide a path to ground in the event of a driect lightning strike."


The reason for the driven rod, is to drain static from the pole, not to conduct a direct lightning strike, the theory is, if you bleed the static to a near plane, it will reduce the build up, and hopefully avoid a strike, the same applies to communications antennas, the ground wire is not to conduct a strike, but rather bleed the static build up.

On industrial equipment, they install the rod, to bleed to the nearest plane.
 
How would a rod be better for this purpose then the EGC?


If you noticed in the communications section, they now have a limit of 20ft of discharge ground wire, from protector to ground unity, the idea is the shortest distance possible.

The same applies to discharge of static, the rod creates a near plane where the equipment is located.
 
satcom said:
The same applies to discharge of static,
Click to expand...

I have to disagree here, static is easily bled off.

As far as a light pole goes just the fact is has a concrete base in the earth is enough or the EGC alone would be enough.
 
Bob,

I wish that was the case, we would have saved a fortune, on some antenna farms, if the base of the tower did not require rods.

Static discharge systems, should not be confused with other grounding methods.
 
satcom said:
Bob,

I wish that was the case, we would have saved a fortune, on some antenna farms, if the base of the tower did not require rods.

Static discharge systems, should not be confused with other grounding methods.
Click to expand...

IMO the grounding electrodes you are talking about at antennas are not for 'static' electricity. I don't know what those electrodes do but they are not to control the static under discussion here.

Static electricity will not build up on light poles in contact with the earth or connected to an EGC.
 
The build up from a near storm can easly overcome the ability of the electrical system ground path to discharge fast eniough, so we install a near point ground.

Bob is correct when he says it serves no purpose, the grounded conductor is the protection, i think some pole manufactures, ask for it only to attempt to discharge build up, to a near point.
 
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In a situation such as where these ground rods are placed (adjacent to railroad) it is quite possible for the rods to have a reverse effect, as far as draining static.The engines operate from a 25 cycle 12kv catenary system (one wire) where the power for the traction motors is transfered through a pantograph on top of the engine. The traction motors are constantly looking for a return path to the substations as they travel,as the wheels (trucks) are the return path. Anyway, the light pole ground rods (if the engine is in the right place at right time) can become the return path and the amperage measured at the rod can become substantial. Thats the reason I was questioning the ground rod return being connected to the EGC, Iwas curious to see what the opinions of others was about this. On a run of the mill parking lot( no electrified railrod close by) would standard practice be to put the EGC and rod wire under the same lug? I see a lot of poles with the ground wire from the rod on an ouside lug or around a hut and washerand the EGC made up on a seperate lug,mabe this is done just to accomadate the wire size?
 
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