[joe-nwt]

As part of my job I do grounding investigations, so yes

So would you agree that a ground electrode serves purposes other than to dissipate lightning? I mean, if that current wasn't on that electrode it might be going through a person....

 

[pietnel007]

Yep, we had a site that was impedance grounded and the UPS's worked but would not parallel.

Impedance grounded is still grounded. The neutral from the star point still feeds the circuit from the top of the impedance and at the bottom of the impedance it goes to ground where al your other grounded components are bonded to.

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[pietnel007]

Yep, we had a site that was impedance grounded and the UPS's worked but would not parallel.

The impedance just limits the amount of earth fault current when an earth fault arises.

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[brian john]

Impedance grounded is still grounded. The neutral from the star point still feeds the circuit from the top of the impedance and at the bottom of the impedance it goes to ground where al your other grounded components are bonded to.

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Yes I know what an Impedance grounded system is, BUT UPS's did not like it and would not work, did you not see that in my post?

 

[pietnel007]

Yes I know what an Impedance grounded system is, BUT UPS's did not like it and would not work, did you not see that in my post?

Wonder why it would not work.

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[splatz]

I am not super solid on this but I think that the grounding system and a low-impedance ground are important for operation of MOV type surge protection that shunts surges to ground.

I did not think that's what they're talking about in 250.4, I think the idea is, when one of the current carrying conductors on the system is at ground potential, the phase-to-ground potential is limited, so in the event of a strike to ground or a utility high voltage fault to ground, less damage occurs to the system and to the building and the people in it.

True or false?

 

[joe-nwt]

True.

 

[460 Delta]

I did not think that's what they're talking about in 250.4, I think the idea is, when one of the current carrying conductors on the system is at ground potential, the phase-to-ground potential is limited, so in the event of a strike to ground or a utility high voltage fault to ground, less damage occurs to the system and to the building and the people in it.

True or false?

At the previous r-mix company I worked at, they have 3 floating 480 Deltas. A year and a half ago one control trailer burned up at night, after what I finally found out to be a primary to secondary short. It was a sub metering setup from a primary metered mine power. When I got there the mine superintendent was flipping out because we were on the same bank as his test lab and it was winter. I thought the fire shorted the secondary drop and blew the cutouts.
Uhh no, I fused the cutouts and closed them then shut the knives at the road. All was great for about 5 seconds then the RR RRR RRRR RRRRR RRRRRR!!!!! The circulating current was taking off like mad! I barely opened the knives in time to keep the xformer from completely blowing.
I tried every way possible to explain to the owners what happened, but I couldn’t get through to them about the hazards of a floating Delta and why a corner ground is important.

 

[Bird dog]

At the previous r-mix company I worked at, they have 3 floating 480 Deltas. A year and a half ago one control trailer burned up at night, after what I finally found out to be a primary to secondary short. It was a sub metering setup from a primary metered mine power. When I got there the mine superintendent was flipping out because we were on the same bank as his test lab and it was winter. I thought the fire shorted the primary drop and blew the cutouts.
Uhh no, I fused the cutouts and closed them then shut the knives at the road. All was great for about 5 seconds then the RR RRR RRRR RRRRR RRRRRR!!!!! The circulating current was taking off like mad! I barely opened the knives in time to keep the xformer from completely blowing.
I tried every way possible to explain to the owners what happened, but I couldn’t get through to them about the hazards of a floating Delta and why a corner ground is important.

To these owners, maintenance is a necessary evil.

 

[460 Delta]

To these owners, maintenance is a necessary evil.

And I was some sort of practitioner of a dark art. Ultimately their view became, if I don’t understand it, it’s unimportant. If you want some real hair raising stories, send me a PM. That one is really tame by contrast.

 

[Bird dog]

And I was some sort of practitioner of a dark art. Ultimately their view became, if I don’t understand it, it’s unimportant. If you want some real hair raising stories, send me a PM. That one is really tame by contrast.

One story I heard was about a jbox cover blowing off in a break room (maybe a 3x3?). smh

And I was some sort of practitioner of a dark art.

Great line. Maybe make that your signature.
Old ship maps...past here there be sea monsters...

 

[460 Delta]

One story I heard was about a jbox cover blowing off in a break room (maybe a 3x3?). smh


Great line. Maybe make that your signature.
Old ship maps...past here there be sea monsters...

Arrrrr. In your best Robert Newton pirate voice.

 

[brian john]

So would you agree that a ground electrode serves purposes other than to dissipate lightning? I mean, if that current wasn't on that electrode it might be going through a person....

NOPE, If it was not there it would be somewhere else, if the service is bonded to the H20 and there is sufficiently low resistance to allow current to flow all you have done is set up a current loop or this could be parallel current from the utility transformer to the main service. But what you are stating is seldom seen due to Earth resistance usually you will see the current on water pipes that are shared from places that have their own services.

 

[brian john]

I am not super solid on this but I think that the grounding system and a low-impedance ground are important for operation of MOV type surge protection that shunts surges to ground.

I did not think that's what they're talking about in 250.4, I think the idea is, when one of the current carrying conductors on the system is at ground potential, the phase-to-ground potential is limited, so in the event of a strike to ground or a utility high voltage fault to ground, less damage occurs to the system and to the building and the people in it.

True or false?

I was not asking this, though my question was a little open to interpterion.
In Theory true but what are the odds that a 8' rod driven in the ground connected to a #6 CU will dissipate the surge? Take a residential service Want about the 4/0 Aluminum neutral feeding back to the transformer all all the driven electrodes on the utility distribution, which one has lower impedance?

 

[VELOCI3]

I was not asking this, though my question was a little open to interpterion.
In Theory true but what are the odds that a 8' rod driven in the ground connected to a #6 CU will dissipate the surge? Take a residential service Want about the 4/0 Aluminum neutral feeding back to the transformer all all the driven electrodes on the utility distribution, which one has lower impedance?

It depends upon where the earth grounds fall within the gradient created by the strike.


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[joe-nwt]

NOPE, If it was not there it would be somewhere else, if the service is bonded to the H20 and there is sufficiently low resistance to allow current to flow all you have done is set up a current loop or this could be parallel current from the utility transformer to the main service. But what you are stating is seldom seen due to Earth resistance usually you will see the current on water pipes that are shared from places that have their own services.

In absence of metallic water piping or "some other place" an electrode is the place where an objectionable current should be.

So what were some of the circumstances that led to you measuring current on a GEC?

 

[brian john]

It depends upon where the earth grounds fall within the gradient created by the strike.


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It Depends on the duration and energy of the strike AND

Where the electrode is in relation to the structure is the area of influence cut in 1/2 because it is driven next to a building
Is the ground frozen? Dry, Sandy? Has the electrode been in the Earth for years? Is the soil corrosive to metal, have there been previous lighting hits that can affect the soils ability to conduct?.

If the driven electrode is so important to grounding for a safe electrical distribution system why the old drive one and test and less that 25 ohms you are OK, but if the test results 500 ohms drive a second one 6' away (which is not the best distance for two 8' electrodes to obtain maximum sphere of influence) and walk away and never worry again about the affects of age on the electrode.

 

[brian john]

In absence of metallic water piping or "some other place" an electrode is the place where an objectionable current should be.

So what were some of the circumstances that led to you measuring current on a GEC?

HOW? WHY?

In regards to your second inquiry.
As part of grounding surveys to ascertain why there is current on the neutral to ground bond and in the days of CRT monitors to find ground current source that resulted in screen shake, or in TV and recording studios for 60 hz hum, in control centers, I have been doing this for over 40 years.

I am struggling to remember finding any significant current on a driven grounding electrode, except where there was a loop set up where the installer brought two grounding electrode conductors from a ground grid to the Neutral/ground bar at the main service even then it was minimal current.. Grounding within a facility TO ME is where the emphasis should be not the ground rod. I see inspectors dwell on ground electrodes (rods and water pipes) and ignore real grounding issues.

 

[SparkyBB]

How many electricians feel grounding a service is necessary for operation, not bonding, but grounding to an electrode?

It seems that some electricians feel a connection to earth is a necessity for an AC power system to operate.

Works fine until a Squirrel eats through
The neutral on the Tri plex feeder from the Pole and then The occupant of the house gets a real nasty shock in the shower and they call me. The little guy was still nibbling on it when I finally traced it back, I've often wondered the hows and whys of him developing a taste for aluminium.

 

[weevilz]

Ask them where the ground rod is for their truck...

The ground rod on the truck is the frame. ; )