ground rod for remote panel at swimming pool

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Re: ground rod for remote panel at swimming pool

A tip of the hat to Charlie, I've brough this up before and it hasn't really settled in yet. :)

It seems to me that all the fault current in a primary-secondary fault that wasn't faulting line to line, would be faulting to the POCO neutral, to complete a circuit back to it's source.

What would the neutral to the house be doing in this scenario? There isn't a path back to the source except through the grounding electrodes. If there were an open neutral, then those grounding electrodes would be lost to the transformer, so it wouldn't be able to use them anyway, right?

My head's starting to ache. :D
 
Re: ground rod for remote panel at swimming pool

What would the neutral to the house be doing in this scenario? There isn't a path back to the source except through the grounding electrodes. If there were an open neutral, then those grounding electrodes would be lost to the transformer, so it wouldn't be able to use them anyway, right?
Click to expand...
Right and there would also be no HV on the neutral, but thats not what we are protecting from.
What we are trying to protect from is:
1. Lost neutral
2. lost neutral makes contact with a primary line
3. it send the primary voltage to the house service equipment to get to a return path via the houses electrode system.
4. you have installed a post with 4 circuits on it.
5. you have another post with one circuit on it

The question is which one would be safer in this scenario, and why would a grounding electrode make one safer but not the other?
 
Re: ground rod for remote panel at swimming pool

It seems to me that all the fault current in a primary-secondary fault that wasn't faulting line to line, would be faulting to the POCO neutral, to complete a circuit back to it's source.
Click to expand...
George, our primary voltage will use all available paths back to the substation. Keep in mind that we are not talking about 120 volts to ground and/or neutral but normally in the 8.6kV class. :D
 
Re: ground rod for remote panel at swimming pool

The grounding electrode provides the essential function of connecting the electrical system (or electrical equipment) to the earth.

The earth is considered to be at zero potential.

A primary purpose of the grounding electrode is to maintain the electrical system and electrical equipment at the same potential present where the grounding electrode is located.

As discussed, it also serves to dissipate overvoltages into the earth.

I do agree that a grounding electrode system needs to be installed at this structure used to support the swimming pool sub-panel.

shortcircuit2
 
Re: ground rod for remote panel at swimming pool

Regarding the post and if it's a structure:
Heres what I heard from Mike Holt once....
Code is Code
We don't like the rules we don't agree with.
Its ok for someone else,
But not if its costs us time and money.
:cool:

[ May 27, 2005, 11:10 PM: Message edited by: tom baker ]
 
Re: ground rod for remote panel at swimming pool

The reason that the definition of structure was added to the NEC, was/is to help it conform to the building code (which has the same definition).
I also agree that for electrical purposes it is too broad in one sense and not specific enough in other senses.


Structure (as applied to building codes) That which is built.

Structure (as applied to electrical installations) A structure or building that encloses or houses electrical equipment.

Just a thought :)
 
Re: ground rod for remote panel at swimming pool

Originally posted by shortcircuit2:
The grounding electrode provides the essential function of connecting the electrical system (or electrical equipment) to the earth.

The earth is considered to be at zero potential.

A primary purpose of the grounding electrode is to maintain the electrical system and electrical equipment at the same potential present where the grounding electrode is located.
Click to expand...
This is a typical belief however a ground rod can not keep the equipment at the same potential as the earth.

If the equipment was to become energized from the circuit conductors the ground rod would do very little if anything.
 
Re: ground rod for remote panel at swimming pool

Originally posted by hurk27:
Hey Bob someone forgot to tighten the top clamp. :D
Click to expand...
:roll:

No they did not forget to tighten the the top clamp, they overtightened the bottom clamp with a cordless. :mad:

They also have the clamps facing opposite directions which is sloppy IMO.
 
Re: ground rod for remote panel at swimming pool

Morning Iwire...real early...2am?

A grounding electrode will not place the equipment at the same potential as the earth?

Please explain, I don't understand.

Although the electrode may not serve the same purpose at a pole structure as it would at a building, the code doesn't make exception to it. If it did, it would leave much argument in the field to what installations require it and which don't.

Remember my post about the requirement to bond the interior water piping system that is street fed with plastic with a full size 1/0 copper for a 400 amp service to a dwelling that only has a couple of ground rods as the electrode system with a #6 copper GEC...

Once again the code doesn't make exception to the bonding requirement because it would cause to much debate in the field.

shortcircuit2
 
Re: ground rod for remote panel at swimming pool

Originally posted by shortcircuit2:
A grounding electrode will not place the equipment at the same potential as the earth?

Please explain, I don't understand.
Click to expand...
I will try, hopefully Roger will post a picture that helps. :)

When a ground rod is driven into the earth it is not the same thing as terminating a EGC onto a steel cabinet.

The resistance at the connection between the EGC and the steel cabinet will be very, very low.

Now when we get back to a ground rod the earth does not have the low resistance of the steel.

The earth is just like a big resister and depending on where along that resister you take your measurement of resistance from the ground rod to the rest of the earth it will show varying values.

Don't try this at home, but imagine if you drive a ground rod into the earth, now connect a 120 volt supply to the top of the rod.

Now standing with you feet firmly on the ground say 2' from the rod what will happen if you touch the rod with your hand?

You will get blasted. the rod will not be at the same potential as the earth due to the resistance / impedance of the 'rod to dirt' connection.

Trying to force electrical equipment to remain the same potential of the earth is like trying to get a firm footing on mud. ;)
 
Re: ground rod for remote panel at swimming pool

Okay, consider this picture:
Posts.jpg

Let's say that Wayne's post is fed from a three-wire, two hots and a neutral. Let's assume Bob's post is fed from five different circuits, with grounding conductors.

The transformer faults primary to secondary, causing the grounding electrodes to begin faulting current back to the source.

What makes Wayne's panel more desireable to touch than Bob's bell boxes?
 
Re: ground rod for remote panel at swimming pool

Cool picture, I can fit my pointy head into that house. :D

Originally posted by georgestolz:
What makes Wayne's panel more desireable to touch than Bob's bell boxes?
Click to expand...
Given the failure you describe I would not want to touch either Wayne's panel or my bell boxes.

IMO, To the delicate human body the small difference the ground rod will make will not be noticed.
 
Re: ground rod for remote panel at swimming pool

Do service OCPD's sometimes trip during surges?

If there is a high incidence of that occuring, wouldn't make it sense to the the OCPD disconnect the neutral at the same time, cutting all ties to the supply? The POCO wouldn't get use of the grounding electrodes to fault current, but the residents of the house would be safer, wouldn't they?

Edit:

I doubt regular circuit breakers trip during such an event. Wouldn't it make more sense for a device to be installed that would disconnect the premises wiring from the POCO during such an event, as opposed to the POCO using premises grounding electrodes as conductors for their 8600 volt fault? :confused:

[ May 28, 2005, 09:28 AM: Message edited by: georgestolz ]
 
Re: ground rod for remote panel at swimming pool

George, we protect ourselves but not the customers. What you are suggesting is the same as requiring extra air bags on my car so you don't have to have any on your car. :D
 
Re: ground rod for remote panel at swimming pool

Charlie, you think so? It seems to me the POCO is relying on the customer's equipment to operate POCO OCPD's. A device installed on the service to disconnect POCO conductors from premises current-carrying and grounding conductors seems like an airbag for the customer: that would leave it up to the POCO to provide their own seat belt to open their OCPD's. :)
 
Re: ground rod for remote panel at swimming pool

George, if the customers were disconnected from our power, our lines would still be protected. If you connect, you have to protect yourself as best as you can. For what it is worth, we do the best we can to protect our customers but we are a long way from perfect (even though I do work for an electric utility). :D
 
Re: ground rod for remote panel at swimming pool

Time for George's thirteenth grounding lesson:

250.4(A)(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.
(2) Grounding of Electrical Equipment. Non-current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials.
Click to expand...
How does grounding "limit the voltage imposed by line surges"? If grounding did this on it's own, we wouldn't need TVSS's, would we? :)

If the POCO's primary lines will clear their own faults without the assistance of the house's grounding electrodes, why do we expose the grounding system of the house to that potential hazard?

Honestly, would a shunting mechanism, perhaps triggered by a TVSS, be a safer option, or is there something I don't understand? (Believe me, I expect that there's something I don't understand. :D )

[ May 28, 2005, 06:10 PM: Message edited by: georgestolz ]
 
Re: ground rod for remote panel at swimming pool

George, if the customers were disconnected from our power, our lines would still be protected. Keep in mind that we are not protecting your wiring or equipment, just ours. We are normally trying to keep as many of our customers in service as we possibly can by protecting our lines, not our equipment and certainly not yours. If we can do both, we will make every effort to do so. :D
 
Re: ground rod for remote panel at swimming pool

George
The reason I question this requirement is because either way voltage is fed to the load (HV from primary, LV from secondary) It will be through a wiring method that almost always will have a much lower impedance then any ground rod can ever expect to over come. The only way I could see earth ever being used to protect from an electrical shock in either case would be from installing a equal potential grid under all places a person using power could possibly ever be.
This would bring the earth up to the same potential of the offending voltage.
A simple ground rod will not do this, as soon as the person leaves the influence of the rod the voltage between the equipment and Earth will be as high as the voltage faulting to the rod minus voltage drop of the feeding conductors.

It is simple to calculate to see what I mean.

R1= resistance of the feeding conductors
V1= supply voltage
R2= resistance of electrodes at the main service
V2= the voltage feeding from the main service to end load
R3= resistance of the conductor feeding the final load to the equipment
R4= Electrode at the load end
V3= the voltage drop across the human body holding the drill standing on earth 20' away from R4

Anyone want to take a stab at it?
 
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