Portable Generators and Ground Rods

[hickman]

Re: Portable Generators and Ground Rods

In the four pages of rebutals I have only heard the reason for ground rods twice. It is to give electricty a path back to the source.Which is the same reason that we have ufer grounds, building steel grounds, ect. Sure you can touch the hot wire of an ungrounded gfi to earth and not have it trip. But touch it to earth and then grab hold of the frame and see who becomes the path back to the source. Ground rods are driven for personal safety. Now they may help in a lightning strike but the primary purpose is safety. thanks for hearing my two cents worth.

 

[Ed MacLaren]

Re: Portable Generators and Ground Rods

In the four pages of rebutals I have only heard the reason for ground rods twice. It is to give electricty a path back to the source.

Really??
I hope you don't mind if I ask what kind of contracting you do?

Ed

 

[pierre]

Re: Portable Generators and Ground Rods

Earlier, (page 4) there is mention in the posts of equipment grounding conductors (as was referenced to 525.31). I thought this thread was dealing with Grounding Electrode Conductors and grounding electrodes (aka ground rod). Was/is this a slip or do you actually mean an equipment grounding conductor?

Unless I am way off the mark here, it would seem that 250.34(A)(1) & (2) should not be too hard to decifer. I am not trying to offend anybody, does the above code section read that difficult? What am I missing?

My read is that for most 'portable generators', a ground rod is not necessary. End of story - No?

 

[pierre]

Re: Portable Generators and Ground Rods

Bob
If I may answer the three scenarios you have stated? This is my interpretation of 250.34.
All three of the situations would require a ground rod.
They do not meet the requirements of 250.34(A)(1).
I am guessing (I am not using the ^$$uming word) that this equipment you are discribing is not cord and plug connected, but is hardwired.

Pierre

 

[hurk27]

Re: Portable Generators and Ground Rods

Hickman:

touch the hot wire of an ungrounded gfi to earth and not have it trip.

First this is not to down you as I like to teach.
A GFCI does not have to be grounded to function as it does not reference the ground wire to determine when there is a ground fault. this is why Replacement receptacles as permitted by 406.3(D). Do not have to have a ground wire. The GFCI works by monitoring the current between the hot and neutral conductors (ungrounded and grounded conductors). if there is 5 amps on the hot then there will be 5 amps on the neutral. if there is only 4.94 amps on the neutral then the circuitry in the GFCI will trip and shut off the receptacle. when the feed (hot) does not equal the return wire then it must be returning on another conductor,earth,you,ground,Etc...

The other thing is figure using Ohm's law on how much current a ground rod will fault to the source through the earth at 25 Ohm's and at 120 volts and you will see why a ground rod will never be a fault path of normal house current. It is only for higher voltages. Bonding is for the providing a path for fault current
250.4 (5) Explains this to a tee

here it is in case you don't have a code book:

(5) Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a permanent, low-impedance circuit capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be used as the sole equipment grounding conductor or effective ground-fault current path.

(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.

[ September 05, 2003, 01:27 AM: Message edited by: hurk27 ]

 

[hurk27]

Re: Portable Generators and Ground Rods

P.S.

I like to teach.

Hickman
This is when I find something I can relate to but there is still much for me to learn and I couldn't be at a better place than this forum as you will find out we will argue disagree and the like but no one gets upset as we all are here to learn even when I post an answer to someone's question if I have it wrong someone will let me know and I have learned something new. there are some great and knowledgeable electrician's here and will steer you in the right direction.

 

[pierre]

Re: Portable Generators and Ground Rods

Hickman
Not to beat a dead horse, but to reiterate what Wayne has said to help drive a point across. The grounding electrode conductor and the grounding electrode, are not in place to facilitate the opening of a circuit breaker or a fuse or an overcurrent protective (OCPD) device of any kind in premise wiring.

If you were to remove the grounding electrode conductor from the panel, a ground fault will still open the OCPD if the EQUIPMENT GROUNDING CONDUCTOR IS CONNECTED PROPERLY.
All electrons (current) that leave a source (battery, generator, fuel cell, etc...) want to go back to the source and will use any and all routes to get there. Hence they will travel on metal surfaces such as a raceway. There will be current traveling on the grounding electrode, but because of the higher impedance, not enough will travel on it to open the OCPD.
That is one of the reasons we want an 'EFFECTIVE GROUND FAULT CURRENT PATH', to open the circuit as fast as possible reducing the likely hood of an injury and/or damage to equipment, a fire you know all the things an electrician doesn't want to think about .

Pierre

 

[don_resqcapt19]

Re: Portable Generators and Ground Rods

hickman,

Ground rods are driven for personal safety.

Ground rods provide almost no increase in safety for people. They do not provide equal potential nor do they clear faults. In the case of vehicle mounted generators, you can actually make the case that the installation of a ground rod decreases safety. With out the rod, there is no potential to the earth, but as soon as you bond the system to the earth there is potential to earth.
Don

 

[hickman]

Re: Portable Generators and Ground Rods

I am a generator contractor. Just driving a ground rod doesn't mean that you have satisfied the code. You still have to have less than 25 ohm's for it to be effective. depending on soil conditions this can be a real task at times. Mike Holt has a video on it. on a building in Seattle I had to imbed 185 feet of 4/0 copper after first driving 16-10 ft ground rods and not meeting the requirements. Keep in mind here we are talking ground rods and not lightning protection.

 

[roger]

Re: Portable Generators and Ground Rods

Hickman, to satisfy the code all you have to do is drive two rods and go home.

Please take note of the text in the drawing below and the fact that these rods are connected to an MGN, they ultimately have the MGN backing them up which a generator wouldn't have.

Roger

[ September 05, 2003, 11:20 AM: Message edited by: roger ]

 

[charlie b]

Re: Portable Generators and Ground Rods

Originally posted by hickman: Just driving a ground rod doesn't mean that you have satisfied the code. You still have to have less than 25 ohm's for it to be effective.

Nothing in the code requires a grounding electrode system to be less than 25 ohms. What the code says is that if the first rod doesn?t give you 25 ohms (let us say, for instance, it is 100 ohms), then you must drive a second rod. You don?t have to measure again. The combined resistance to ground of the pair of rods might still be over 25, and the code would still consider it ?effective.?

 

[bennie]

Re: Portable Generators and Ground Rods

A ground rod on metal objects is the same as my old invention of installing a ground electrode conductor between the clouds and the earth, to prevent lightning strikes.

There appears to be no logical explanation for the phenomenon of clouds achieving a different potential than the earth.

The Marine Corp blimp hanger at El Toro LTA Base in California, often has clouds form inside the structure. These clouds cause small scale lightning strikes on the interior, when it is dry, and hot outside.

Above ground metal tanks and towers, if not effectively grounded, can and will attain a high potential difference to earth, by electrostatic charging. A person making contact will create a mini-lightning discharge.

An electrostatic discharge, across a PC board, can destroy the solid state components.

 

[hickman]

Re: Portable Generators and Ground Rods

Try doing that an a federal project or one that requires that you prove that 25 ohm's and see how far your arguments take you. Also what about the Gensets that we install indoors? Still need a ground rod and I don't see any Lightning strikes on them in the near future. There is also the topic if manufactures recomendations. I have seen small portables with a ground lug. If it is recomended by the manufacture it is as good as code no matter who mounted it on the truck.

 

[karl riley]

Re: Portable Generators and Ground Rods

Hickman, you mention Mike Holt's grounding video. For the sake of your own safety and that of your customers, please look at it again. If you still think the ground rod provides personal safety look at it again, and again.

In the U.K., at remote farm locations they allow a ground rod for clearing faults, but since they know the impedance it too high to clear a fuse or breaker, they install a relay coil around the GEC which will trip a breaker at 30 milliamps.

Karl

 

[hickman]

Re: Portable Generators and Ground Rods

I never said that ground rods were the answer to tripping circuit breakers. However if I am standing next to a generator that has a fault that is looking for a path back to the source that ground rod as poor as it is will still be a better path back than my human body. whether that circuit breaker trips or not. I notice that you did not comment on the manufactures recomendations. I would just bet that many of the manufactures that I deal with would not agree with most of the large generator installations that are on some of the portable equipment mentioned in this forum. I would bet that they would want to see some specific grounding requirements like ground rods.

 

[roger]

Re: Portable Generators and Ground Rods

Substitute a genset for the transformer below and see how a ground rod can actually be more dangerous in some cases.

thanks to www.codecheck.com

As far as manufactures info, it can be wrong and misunderstood.

Roger

[ September 05, 2003, 11:46 AM: Message edited by: roger ]

 

[charlie b]

Re: Portable Generators and Ground Rods

Originally posted by hickman: Try doing that an a federal project or one that requires that you prove that 25 ohm's and see how far your arguments take you.

I reaffirm my statement that the code does not require 25 ohms. I am fully aware that many owners include requirements in their projects for far lower values for resistance to ground. As an engineer, my designs conform both to codes and to owner requirements. The engineering company for which I work has frequently written specifications for values of 5 ohms or even lower. But these facts do not alter the fact that the NEC does not require 25 ohms.

However if I am standing next to a generator that has a fault that is looking for a path back to the source that ground rod as poor as it is will still be a better path back than my human body.

True. And therefore the path that includes the ground rod will get the lion?s share of the current. That notwithstanding, a human body can still get enough current to create a new set of grieving family members. It only takes 1/10th of an amp. I would like to echo the views of several other forum members: a ground rod does not serve the function of providing personnel protection for anything short of medium voltage systems.

 

[hickman]

Re: Portable Generators and Ground Rods

Lets take another look. You are on a jobsite which requires the use of a generator. an accident severs the grounded conductor of the service entrance conductors leaving the ungrounded conductors intact. You in your hast never installed a ground rod to the frame. You go over to the genset and grab the frame of the generator. What do you think will happen?
As for myself I do not care to be the path of any electrical current, Nor will I allow my clients. So I drive the ground rods and if possable tie them into building steel and ufer grounds. Bottom line I believe in grounding. even if it is poor at times it is better than nothing. And I would hope that you would feel the same.

 

[don_resqcapt19]

Re: Portable Generators and Ground Rods

hickman,

However if I am standing next to a generator that has a fault that is looking for a path back to the source that ground rod as poor as it is will still be a better path back than my human body.

Can you explain how the above is possible? The grounding electrode system should have nothing to do with power finding its way back to the source. If the fault is at the generator, why would the grounding system even be involved in the circuit?
If the fault it remote from the generator the path back to the generator (source) should be the equipment bonding (grounding) conductor.
Don

 

[Guest]

Re: Portable Generators and Ground Rods

Here is the text of the codecheck.com link regarding the illustration above:

Ground Fault Shock Hazard::

Ben is in danger . As usual, his experiments are extremely dangerous.

Since the 19th century, most electrical distribution systems are deliberately connected to earth.

Franklin's lightning rods, in no small way kicked off the convention.

Ironically, this connection to earth creates a new hazard, voltage potential to earth. If the electrical system could be isolated from earth, there would be less shock hazard.

A toaster is an example of an appliance that does not have its metal enclosure connected to an earth reference.

When the fraid (sic) "hot" wire comes in contact with the metal case, the case immediately presents a potential of 120 volts to anything connected to earth. Here it is the plumbing system, deliberately connected to earth.

Unfortunately for our pretend Ben, human beings can pass electrical current easily. Ben is in the loop of an electrical circuit.

Small amounts of current through the heart can be lethal.

Bold added by me for emphasis. Ben may in danger. The modern residential chef is not. An earthen ground may be a hazard in the kitchen. Insulated ground (double-insulated) devices may be a better solution. However, in the case of a kitchen and a toaster the modern kitchen will be safe because the toaster will be plugged into a
GFCI circuit or receptacle.

Why don't we require more GFI protection in a residence? Why not GFI everything that is physically possible? If GFI was the standard, and not the exception the price of GFI protection would go down. Yes, I understand that there may be some devices that are not reliable with a standard GFI fault threshold. Maybe there should be two levels of protection? One for the "regular" stuff, and another level for say refrigerators? Nobody wants to have a minor ground fault spoil their food. Maybe appliances like refrigerators should not be ground-fault protected, but instead should have ground-fault indicators . When a fault is detected a light and/or buzzer could go off. There could also be a shut-down mechanism if the fault were not corrected within a "reasonable" time. It would be a GFI with a delay, like a "slow-blow" fuse.

QUESTION: In your residential experience what devices should never go on a GFI?

QUESTION: Would ground-fault indicators on appliances be worth the price of admission?

QUESTION: Would the price of GFI protection devices go down significantly if they were the standard and not the exception?

Thank you for this discussion. It is very compelling and it really resonates with me. I am glad to be able to share all your knowledge, and experience. This is quite a think tank! Please take my comments above as simple brainstorming and not as fact or the final word. This post is warranted to be 94.6% accurate. This post is presented for informational and discussion purposes only and is never intended to be disrespectful or confrontational. If you find a factual error in my post or you find my grammar confusing, please notify me offline so I can edit my post to your benefit.

../Wayne

PS: Is it "fraid" or "frayed"? I'll ask ieSpell. Nope ieSpell did not recognize fraid, but I will let it stand.