Grounding a parking lot light

[Alwayslearningelec]

Just read this on EC&M website.

Grounding a parking lot light

I keep hearing that you shouldn’t use a ground rod at a standard metal parking lot light and that you should use an equipment-grounding conductor run with the circuits. The specifications for the project I’m working on now require both grounding methods. Is there a problem with this, and will I have to install two rods if I don’t have 25 ohms to ground?
The NEC requires the equipment-grounding conductor to be run with the circuit conductors, but it does not prohibit the use of auxiliary grounding electrodes, such as the ground rods. Section 250.54 repeats the requirement shown in 250.4(A)(5), where it states that the earth shall not be used as the sole equipment-grounding conductor. These auxiliary grounding electrodes do not have to be bonded to the grounding-electrode system as shown in 250.50 and do not have to meet the resistance requirements of 250.56. There are many pros and cons concerning the value of the auxiliary grounding-electrode ground rods for metal poles. They are of no value in providing a low-impedance ground-fault path to de-energize the circuit, but they may be of some value in providing a path for lightning strikes. Apparently, the specifiers think so.



So reading this article and the NEC a separate ground always have to be run with conduits for light poles. I am reading definitions in section 100 of the NEC. If a circuit has 1 phase wire, 1 neutral and a ground that may not necessarily be the EGC? That could just be considered the ground. What differentiates a regular ground from a EGC?

 

[infinity]

Just read this on EC&M website.

Grounding a parking lot light

I keep hearing that you shouldn?t use a ground rod at a standard metal parking lot light and that you should use an equipment-grounding conductor run with the circuits. The specifications for the project I?m working on now require both grounding methods. Is there a problem with this, and will I have to install two rods if I don?t have 25 ohms to ground?
The NEC requires the equipment-grounding conductor to be run with the circuit conductors, but it does not prohibit the use of auxiliary grounding electrodes, such as the ground rods. Section 250.54 repeats the requirement shown in 250.4(A)(5), where it states that the earth shall not be used as the sole equipment-grounding conductor. These auxiliary grounding electrodes do not have to be bonded to the grounding-electrode system as shown in 250.50 and do not have to meet the resistance requirements of 250.56. There are many pros and cons concerning the value of the auxiliary grounding-electrode ground rods for metal poles. They are of no value in providing a low-impedance ground-fault path to de-energize the circuit, but they may be of some value in providing a path for lightning strikes. Apparently, the specifiers think so.



So reading this article and the NEC a separate ground always have to be run with conduits for light poles.

An EGC is required to be run with the circuit. It can be a metallic raceway covered in 250.188.

 

[haskindm]

An equipment grounding conductor is always needed. An auxiliary grounding electrode at the pole is NOT required by the NEC but it is not prohibited. The resistance requirements do NOT apply (see 250.54). This electrode accomplishes nothing so the NEC does not specify how it is installed.

 

[Joethemechanic]

I kinda like to add a ground rod at each pole, I feel like it can help limit the damage caused by a lightening strike.

When I was a kid and playing with radios my dad got me a tower that was about 80 feet and we set it up in the yard for an antenna tower. Even without a dirrect strike I can tell you that antenna could pick up some large charges up there. Sometimes I could get an arc about an inch long from the antenna wire. (for some reason snow storms seemed to carry the largest charges)


I just never liked the idea of a static charge like that being carried back to the service ground by way of the EGC


Not to mention, on long EGC runs, I worry about the voltage drop in the case of a partial fault to ground (like in a ballast) that may not be enough to trip the breaker. The most important thing to consider is the difference in potential of the ground near the pole, and anything a person or animal might touch on the pole. An extra ground rod helps lessen the difference in potential.

 

[Alwayslearningelec]

An EGC is required to be run with the circuit. It can be a metallic raceway covered in 250.188.

So when using EMT or RGS why ever run a ground wire? If that spec calls for a separate ground?

 

[iMuse97]

So when using EMT or RGS why ever run a ground wire? If that spec calls for a separate ground?

If you run EMT or RMC underground, they won't last too long in most environments. I'd use PVC schedule 80 and run that equipment ground. Around here, most jobs also spec a ground rod at each pole. Most of the time our equipment ground is only one wire gauge smaller than the ungrounded conductor, so as to provide a good path back to the source.

 

[Alwayslearningelec]

If you run EMT or RMC underground, they won't last too long in most environments. I'd use PVC schedule 80 and run that equipment ground. Around here, most jobs also spec a ground rod at each pole. Most of the time our equipment ground is only one wire gauge smaller than the ungrounded conductor, so as to provide a good path back to the source.

Thanks IMUSE.....I cant believe how much I'm on this site.... Not to long ago I'd go out for beers on Fridays now I'm here on MH forum.....

 

[Alwayslearningelec]

If you run EMT or RMC underground, they won't last too long in most environments. I'd use PVC schedule 80 and run that equipment ground. Around here, most jobs also spec a ground rod at each pole. Most of the time our equipment ground is only one wire gauge smaller than the ungrounded conductor, so as to provide a good path back to the source.

Se I get confused..when you say RMC do you mean galvanized?

 

[jumper]

Se I get confused..when you say RMC do you mean galvanized?

RMC may be galvanized (GRS) but could be other. Usually the same.

 

[Alwayslearningelec]

RMC may be galvanized (GRS) but could be other. Usually the same.

I had an argument with someone at m job about this many months ago. If you saw a spec say RMC would you automatically say it's galvanized? No, right? But what kind of conduit id RMC then? Thick wall without the galvanized? Does anyone really used RMC(non gal)???

 

[jumper]

I had an argument with someone at m job about this many months ago. If you saw a spec say RMC would you automatically say it's galvanized? No, right? But what kind of conduit id RMC then? Thick wall without the galvanized? Does anyone really used RMC(non gal)???

As I said, RMC is usually RGS, but not always.

344.2 Definition
Rigid Metal Conduit (RMC). A threadable raceway of
circular cross section designed for the physical protection
and routing of conductors and cables and for use as an
equipment grounding conductor when installed with its integral
or associated coupling and appropriate fittings. RMC
is generally made of steel (ferrous) with protective coatings
or aluminum (nonferrous). Special use types are red brass
and stainless steel.

Remember Rob Roy and O-cal also, PVC coated steel.

 

[kwired]

I had an argument with someone at m job about this many months ago. If you saw a spec say RMC would you automatically say it's galvanized? No, right? But what kind of conduit id RMC then? Thick wall without the galvanized? Does anyone really used RMC(non gal)???

Supply house probably stocks both aluminum and galvanized steel. Stainless maybe they have, brass will likely be special order at a lot of places.


Reading through your posts I want to point out that using a ground rod is an option you can have at the light post. It is not an substitute to running an equipment grounding conductor with the circuit conductors. A ground rod only is almost always too high of a resistance for enough current to flow to trip an overcurrent device should there be a fault to the metal pole. The only purpose for the ground rod would be for lightning dissipation.

A metal raceway is a suitable equipment grounding conductor, whether or not it is suitable for conditions where it is installed is an entirely different issue.

Going back to the OP:

What differentiates a regular ground from a EGC?

Equipment grounding conductor is the regular ground. It is 'earthed' back at the service equipment via the grounding electrode system. It is permitted to have supplemental grounding electrodes connected to it but not required to. This is entirely design decisions. The ground rod has nothing to do with equipment grounding, it is nothing more than an attempt to equalize the potential between the equipment grounding conductor and earth.

 

[iwire]

I kinda like to add a ground rod at each pole, I feel like it can help limit the damage caused by a lightening strike.

There is no way a rod adds anything that the large block of concrete has not already provided.

 

[Joethemechanic]

There is no way a rod adds anything that the large block of concrete has not already provided.

How do you know they aren't wooden poles? And if they are wooden, I'm fine with a plate or a coil of wire stapled to the bottom

 

[Alwayslearningelec]

Supply house probably stocks both aluminum and galvanized steel. Stainless maybe they have, brass will likely be special order at a lot of places.


Reading through your posts I want to point out that using a ground rod is an option you can have at the light post. It is not an substitute to running an equipment grounding conductor with the circuit conductors. A ground rod only is almost always too high of a resistance for enough current to flow to trip an overcurrent device should there be a fault to the metal pole. The only purpose for the ground rod would be for lightning dissipation.

A metal raceway is a suitable equipment grounding conductor, whether or not it is suitable for conditions where it is installed is an entirely different issue.

Going back to the OP:

Equipment grounding conductor is the regular ground. It is 'earthed' back at the service equipment via the grounding electrode system. It is permitted to have supplemental grounding electrodes connected to it but not required to. This is entirely design decisions. The ground rod has nothing to do with equipment grounding, it is nothing more than an attempt to equalize the potential between the equipment grounding conductor and earth.

Thanks a lot or that explanation .

 

[ptonsparky]

If you run EMT or RMC underground, they won't last too long in most environments. I'd use PVC schedule 80 and run that equipment ground. Around here, most jobs also spec a ground rod at each pole. Most of the time our equipment ground is only one wire gauge smaller than the ungrounded conductor, so as to provide a good path back to the source.

I'd use 40. A bit cheaper with larger ID.

 

[Alwayslearningelec]

If you run EMT or RMC underground, they won't last too long in most environments. I'd use PVC schedule 80 and run that equipment ground. Around here, most jobs also spec a ground rod at each pole. Most of the time our equipment ground is only one wire gauge smaller than the ungrounded conductor, so as to provide a good path back to the source.

Imuse when you say RMC do you mean gal? If so ow would galvanized to last LNG? Isn't it ment to be in that type of environment ? Thanks

 

[ptonsparky]

Length of time is subjective. GRS, RMC, IMC are allowed to be used underground in this area. Some places it is still good after 20 years, others have sections rusted away completely. I quit thinking GRS etc was the best after remodel on a few gas stations. Often enough the conductors were in the sand fill with nothing but a bit of rust here and there indicating conduit had been there at one time.

 

[iwire]

I kinda like to add a ground rod at each pole, I feel like it can help limit the damage caused by a lightening strike.

There is no way a rod adds anything that the large block of concrete has not already provided.

How do you know they aren't wooden poles? And if they are wooden, I'm fine with a plate or a coil of wire stapled to the bottom

OK, lets say wood poles buried in earth with some lighting fixtures at the top.

A lightning bolt travels miles through the sky and nails the fixtures at the top of the pole.

Additional electrodes will do what?

 

[kwired]

I had customer with a wood pole with 2 flood lights lighting an outdoor horse arena get struck by lightning last summer. Pole had top 6-8 feet literally split and one light fell to the ground with the chunk of pole still attached. This was not the highest object in the area so don't believe that myth. It was just lucky enough to be the right potential at the right time.

I don't think any grounding electrode was going to make any difference.