Portable Generators and Ground Rods

[websparky]

Re: Portable Generators and Ground Rods

iwire wrote;

Also it seems most agree that the ground rod may aid in the dissipation of a lightning strike from the utility system.

Now I install a generator to power an outdoor concert on temporary structures, stage, light towers, control risers (front of house) etc.

Can anyone tell me what the ground rod connected to the generator frame does for us in this situation?

Is it solely for lightning protection and if so how would it help and what is it protecting?

Bob, I am trying to address your questions above by supplying this information below.

2000 NFPA 780 Standard for the Installation of Lightning Protection Systems

Appendix L1. Fundamental Principles of Lightning Protection.

The fundamental principle in the protection of life and property against lightning is to provide a means by which a lightning discharge can enter or leave the earth without resulting damage or loss. A low impedance path that the discharge current will follow in preference to all alternative high impedance paths offered by building materials such as wood, brick, tile, stone, or concrete should be offered. When lightning follows the higher impedance paths, damage may be caused by the heat and mechanical forces generated during the passage of the discharge. Most metals, being good electrical conductors, are virtually unaffected by either the heat or the mechanical forces if they are of sufficient size to carry the current that can be expected. The metallic path must be continuous from the ground terminal to the strike termination device. Care should be exercised in the selection of metal conductors to ensure the integrity of the lightning conductor for an extended period. A nonferrous metal such as copper or aluminum will provide, in most atmospheres, a lasting conductor free of the effects of rust or corrosion.

By adding a ground rod to a generator that is connected to the wiring systems of temporary structures at an outdoor event such as described, it serves to help maintain and equal potential between all connected items in the event of a lightning strike. It does not however provide any additional protection for the actual separately derived electrical system that the generator provides.

Dave

[ August 23, 2003, 10:20 PM: Message edited by: websparky ]

 

[don_resqcapt19]

Re: Portable Generators and Ground Rods

It's always seemed to me that the ground rods would help dissipate a lightning strike on anything struck (rides and booths) that are bonded to the system.

Lightning current won't travel very far on any type of grounding conductor. This is because lightning has a high frequency and even very large conductors of any length have high impedance to high frequency currents. The addition of a grounding electrode at the generator will provide no protection from lightning at the rides.
Don

 

[hurk27]

Re: Portable Generators and Ground Rods

Since the ride it self is the tallest and most likely to be struck by the lightning, not the generator. I think if you would install a ground rod I would connect it to the ride as this would provide the shortest path for a strike. why try to get a lightning strike to fllow a wire to a generator inwhich it has the possability to jump off and damage or injur somthing or someone.

 

[russ]

Re: Portable Generators and Ground Rods

Don:
If this ground rod doesn't provide any lightning protection, then I guess I'm as confused as Bob when he started this thread. The rod(s) is required in the case I described, so I'm with Bob,
I will insist that it be installed.Just to understand what your saying, is there no logical purpose for the rod(s) at all? Do you think it will help if lightning struck right at the generator area, and maybe dissapate the current, rather than send it out towards the rides and booths.

Russ

 

[russ]

Re: Portable Generators and Ground Rods

hurk27:

Rods driven for the rides is a good idea, but in this case not too easy. If it's not required by the code, I'd have a hard time convincing the church and the carnival operators that they needed them driven, all over the paved parking lot.

Russ

 

[iwire]

Re: Portable Generators and Ground Rods

Russ, If all the equipment is cord and plug connected do you still ask for the ground rod?

IMO an up to date carnival operator will have all the wiring cord and plug connected. If not you will probably find other electrical violations. Portable power cable with cam locks from distribution panels mounted in the generator trailer out to portable distribution panels or straight to heavy draw rides.

No need for a ground rod here, right?

Bob

[ August 24, 2003, 10:34 AM: Message edited by: iwire ]

 

[russ]

Re: Portable Generators and Ground Rods

Bob:

I still think the rod is required. I don,t think 250 .34 had these systems included. These generators can't be thought of as portable, in the sense of can it be carried away. As for vehicle Mounted Generators, I think this would apply to things like service trucks.
I feel this is still under 250.30

Russ

 

[iwire]

Re: Portable Generators and Ground Rods

Russ first off I hope you know that I am just trying to understand this, and if you ask for and get a ground rod more power to you.

I think it can be argued that the type of generators used at fairs and carnivals are Vehicle-Mounted Generators, I see no definition of vehicle and they are certainly portable.

If we accept that these are Vehicle-Mounted Generators, then 250.34(B)(2) would be relevant.

250.34(B)(2) The generator supplies only equipment located on the vehicle or cord-and-plug-connected equipment through receptacles mounted on the vehicle, or both equipment located on the vehicle and cord-and-plug-connected equipment through receptacles mounted on the vehicle or on the generator, and

I find it interesting they use the word equipment "cord-and-plug-connected equipment" not the term Utilization equipment.

This to me says you could have any cord-and-plug-connected equipment (Panels, Disconnects, etc.) connected and still not be required to have a ground rod.

For yourself when does a portable generator become an SDS that would fall under 250.30?

I always took portable generator to mean any generator that was not permanent, meaning wired with temporary methods like flexible cords.

If we accept that the carnival can use temporary wiring methods, how can we say the generator is not temporary (portable).

One of the carnivals that I worked with kept a electric Demo hammer in the generator trailer to drive ground rods and had a winch mounted on the trailer to drag them back out.

Bob

[ August 24, 2003, 12:48 PM: Message edited by: iwire ]

 

[russ]

Re: Portable Generators and Ground Rods

Bob I understand where your coming from. I have to inforcing the code as I see it, and so far nothing we have discussed has changed my way of thinking. I don't mined change, as long as I can understand, it's within code, and safe.

Russ

 

[iwire]

Re: Portable Generators and Ground Rods

Originally posted by russ:
I have to inforcing the code as I see it,

Russ I would not suggest you do it any other way, thanks for your responses to this, take care.

Bob

 

[don_resqcapt19]

Re: Portable Generators and Ground Rods

russ,
For any cord and plug installation from any type of protable generator, I see no requirement in the code, for a grounding electrode system. In my opinion a truck or trailer mounted generator is covered by 250.34 and not by 250.30.
As far as lightning protection for the rides if the strike was at the generator, the addition of a grounding electrode may provide some protection over not having the grounding electrode for rides or equipment within 20' or 30' from the generator. The impedance of the EGCs between the rides and the generator is just too high for lighting to travel on.
Don

 

[gwz2]

Re: Portable Generators and Ground Rods

Does Article 525 address a carnival where all the electrical power is supplied by a truck mounted 3? 4W 208/120V 400A CB OCPD generator with two remote cord and plug connected 100A panelboards?

If 'Yes', which Section(s) so address ?

It seems that 525.10(A) would not apply.

525.10(A) and 525.31 is the only places I see 'generator' noted.

Glenn

 

[websparky]

Re: Portable Generators and Ground Rods

NEC 2002

525.31 Equipment Grounding.
All equipment requiring grounding shall be grounded by an equipment grounding conductor of a type and size recognized by 250.118 and installed in accordance with Article 250.

250.4(A) Grounded Systems.
(1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

250.4(B) Ungrounded Systems.
(1) Grounding Electrical Equipment. Non?current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth in a manner that will limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials.

 

[websparky]

Re: Portable Generators and Ground Rods

Portable and Vehicle-Mounted Generators are a horse of a different color!

NEC 2002
250.34(B) Vehicle-Mounted Generators. The frame of a vehicle shall be permitted to serve as the grounding electrode for a system supplied by a generator located on the vehicle under the following conditions:
(1) The frame of the generator is bonded to the vehicle frame, and
(2) The generator supplies only equipment located on the vehicle or cord-and-plug-connected equipment through receptacles mounted on the vehicle, or both equipment located on the vehicle and cord-and-plug-connected equipment through receptacles mounted on the vehicle or on the generator, and
(3) The non?current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame, and
(4) The system complies with all other provisions of this article.

 

[hurk27]

Re: Portable Generators and Ground Rods

The only requirement is that the equipment grounding conductor is to be installed per: article 250! This means that any equipment grounding conductor installed between the source and the load outlet must be installed in accordance of article 250 If you look at article 250 it requires the equipment grounding conductor to be bonded at the first mean's of disconnect to the grounded circuit conductor and there is no requirement for it to be connected to a ground rod, That is the job of the grounded circuit conductor. with a vehicle mounted generator the grounded circuit conductor is only required to be bonded to the vehicle for a GE, which is only a requirement of a separately derived system such as a generator.
Grounded circuit conductor is only a wire that provides the path for fault current and thats it. The bonding to the neutral is for the fault current's return path back to the source, the rest of 525.31 spell's this out the article must be read in the whole context not just the first half.

The equipment grounding conductor shall be bonded to the system grounded conductor at the service disconnecting means or, in the case of a separately derived system such as a generator, at the generator or first disconnecting means supplied by the generator. The grounded circuit conductor shall not be connected to the equipment grounding conductor on the load side of the service disconnecting means or on the load side of a separately derived system disconnecting means.

 

[charlie b]

Re: Portable Generators and Ground Rods

I go away for a weekend and three pages of comments show up! Next time, I should bring a lap-top on a vacation. - - - - - - NOT!

Originally posted by don_resqcapt19: Charlie, If the lightning jumped across miles of sky to get to the generator, why wouldn't it jump a few more inches to earth?

Because of Newton?s First Law of Motion, the applicable part of which is as follows: An object at rest (such as an electron) will remain at rest, unless acted upon by an external force. The massive difference in charge between the cloud and the planet establishes a massive force (an electrostatic force). This is the force that causes the electrons to move (i.e., from the cloud to the planet).

Originally posted by don_resqcapt19: I can't imagine the generator, acting as a capacitor, holding all, or even a small portion, of the energy of a lightning strike.

I can. The electrostatic force will impel the electrons in the direction of planet Earth. If during their trip to the planet, a vehicle?s frame gets in their way, the electrons could hit, and be imparted onto, the frame. Some might pass through or around the tires (especially if they are wet), thus making their way into dirt. But there is no physical law that prevents some of the charge from being left behind on the frame. As to the ones that remain, an electrostatic force similar to the one that first set them in motion still exists, but the force is not as strong as the original. It might not be strong enough to push them through the insulated tires. But due to a human body?s having much lower resistance than tires, the force could be strong enough to push the electrons through a person who touches the frame.

Originally posted by websparky: Hi Charlie, Sorry to disagree with ya! But when this event we call "lightning" occurs, all of the electrical charge is dissipated and spent. There is no residual charge left in the object that served as a conductor. Dave

Don?t be sorry to disagree. It?s what makes our country great. I?m not sorry to disagree right back at ya! First of all, if all of the electrical charge is spent, then there would never be a second lightning strike. And lightning strikes Mother Earth thousands of times each hour. Secondly, the charge carried in a single lightning strike will not stay in the air. It will be dissipated. I agree with you there. But people have been injured, and even killed, by a lightning strike on the car in which they were riding. But it was not the lightning event itself that caused the injury. It was their attempting to leave the vehicle afterwards, and receiving a shock when their foot touched the ground.

 

[tom baker]

Re: Portable Generators and Ground Rods

There is a proposal for the 2005 NEC to clarify that portable generators at carvinals (Art 527) will require "ground rods".

 

[bennie]

Re: Portable Generators and Ground Rods

A portable generator is one that can be carried. A trailer mounted generator is one that can be transported.
Portable generators are small, and don't need any method for relaxing possible electrostatic charges.

Trailer mounted units can build up a static charge.

A slab mounted generator is a slab mounted generator. Needs a connection to the dirt.

 

[bennie]

Re: Portable Generators and Ground Rods

A generator, when it is the only power source, is a component of a separately derived system. Earth connection is required, as stated in 250.30.

 

[iwire]

Re: Portable Generators and Ground Rods

Bennie welcome back, this topic was screaming for your input.

[ August 25, 2003, 04:10 PM: Message edited by: iwire ]