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GFCI/ parellel ground


Chad Fabry
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I had my first mishap today on the inspection I did. I had to ask the ladu of the house if she would mind unplugging her curling iron while I tested the gfci. She did and I tested it..I was smart this time and knew that was protected by a breaker. The GFCI clicked off as it should and I raced down to the basement to click it back so she could do here hair. No clicky, nuthin. It gfci'd for the last time. I told her she looked great w/ the left side done and the right side still straight and found it odd that she saw no humor in that.

Now I have a question. The pool pump receptacle is outside near the pool, 4 prong plug, 220/240v. It has it's own ground rod with the ground wire I presume wired to the ground terminal. (Exterior power was off).I know I read somewhere that parellel ground paths aren't good...could someone take a moment and explain the concept?

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Originally posted by Chad Fabry

I had my first mishap today on the inspection I did. I had to ask the ladu of the house if she would mind unplugging her curling iron while I tested the gfci. She did and I tested it..I was smart this time and knew that was protected by a breaker. The GFCI clicked off as it should and I raced down to the basement to click it back so she could do here hair. No clicky, nuthin. It gfci'd for the last time. I told her she looked great w/ the left side done and the right side still straight and found it odd that she saw no humor in that.

Just quote Ecclesiastes 3: 1-8 (or the Byrds) and hand her an extension cord.

Now I have a question. The pool pump receptacle is outside near the pool, 4 prong plug, 220/240v. It has it's own ground rod with the ground wire I presume wired to the ground terminal. (Exterior power was off).I know I read somewhere that parellel ground paths aren't good...could someone take a moment and explain the concept?

I'm a tad weak in this area. You want to get Cramer to answer this one for sure. One thing I do know for sure, however, is that the receptacle's grounding terminal had better not *only* go to the ground rod. There *must* be a real, honest-to-goodness wire that, eventually, leads back to the neutral terminal bar at the service.

As for adding supplementary grounding rods near the pool, I don't see why that would be bad; current doesn't normally travel on those things, they're just there to dissipate surges from lightning & such.

- Jim Katen, Oregon

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  • 4 weeks later...

In NEC 2002 section 680.6, it says that

"The following equipment shall be grounded:

...

(3) All electrical eequipment associated with the recirculating system of the specified body of water."

Under the definition of grounded: "Connected to earth or to some conducting body that serves in place of the earth"

I for one, am not that conducting body.

Hope that helps.

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Originally posted by Chad Fabry

The pool pump receptacle is outside near the pool, 4 prong plug, 220/240v. It has it's own ground rod with the ground wire I presume wired to the ground terminal. (Exterior power was off).I know I read somewhere that parellel ground paths aren't good...could someone take a moment and explain the concept?

Are you sure about the plug? Why would it be 120/240V?

The plug and receptacle are required to be a locking type. (Curved blades and slots) to prevent someone from putting something else into it.

It should not be connected to a ground rod, but it probably wouldn't hurt if it was (assuming the equipment grounding conductor is connected to the pump.) A pool pump required bonding to the metal in the shell of the pool and other metal in and around the pool area. Are you sure this was not a bonding wire?

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Originally posted by kurt

I'm one of those that could use a nice *simple* explanation of why parallel grounding paths are bad; anyone got the time to explain it?

If I hear this stuff enough, sooner or later it will burn its way into my noggin.

That's what I was after too. I should have asked it that way.

The pump was a 20 amp 240v pump. There was 3wire, w/ground 10 gauge uf cable supplying juice to the receptacle. There was a bare ground coming from within the box attached to a driven ground rod. I didn't pull the cover so I'm not sure how everything was hooked up, but in my mind the receptacle was grounded to the panel and to the driven ground rod.

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Chad...

This is from Mike Holts newsletters. It's one of the best explanations I've seen of why a ground rod alone isn't safe.

"Danger: Because the resistance of the earth is so high, very little current will return to the power-supply neutral if the earth is the only ground-fault return path. If a ground rod is the only ground (bonding) connection, then the earth is being used as the sole ground-fault current path, in violation of 250.4(A)(5). The result is that the circuit overcurrent protection device will not open and metal parts will remain energized at a lethal level waiting for someone to make contact with them and the earth. Therefore, a ground rod cannot be used to lower touch voltage to a safe value for metal parts that aren't bonded to an effective ground-fault current path."

If the pool pump does have a EGC back to the panel, then I'm real fuzzy on the potential thing and whether the extra ground rod does any harm.

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The two ground rods at the service equipment are because some soil conditions make resistance too high with just one. Having one somewhere else would not be a substitute as a lightning strike on the service drop (etc) would have to travel along the EGCs to get to it. THAT may be the reason the pump ground rod is not a good idea.(?) I'm now officially over my head and pulling things out of my butt!

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My understanding is that you can have as many ground rods as you want as long as they are connected together within the same system-----where you get into trouble with parralell paths is when a ground rod(s) is added and they not are connected together in the system. Or a similiar situation would be if you grounded to a water pipe but the water pipe wasn't connected to the system ground.

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So, can anyone explain in clear & concise language (that I can plagiarize) explain why trouble ensues w/the parallel paths? I kinda get it, but I need the nailed down "if you have X, the result will be Y". I don't wanna attempt explanations in my reports that I can't explain.

Any takers this time?

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Originally posted by Richard Moore

Chad...

This is from Mike Holts newsletters. It's one of the best explanations I've seen of why a ground rod alone isn't safe.

"Danger: Because the resistance of the earth is so high, very little current will return to the power-supply neutral if the earth is the only ground-fault return path. If a ground rod is the only ground (bonding) connection, then the earth is being used as the sole ground-fault current path, in violation of 250.4(A)(5). The result is that the circuit overcurrent protection device will not open and metal parts will remain energized at a lethal level waiting for someone to make contact with them and the earth. Therefore, a ground rod cannot be used to lower touch voltage to a safe value for metal parts that aren't bonded to an effective ground-fault current path."

If the pool pump does have a EGC back to the panel, then I'm real fuzzy on the potential thing and whether the extra ground rod does any harm.

I guess I get that statement...does it mean if there's a short between hot and ground (not the neutral) that not enough current will pass to trip the breaker leaving all the stuff that's connected to the ground (not the neutral) hot?

Like the device boxes and junction boxes?

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Hi All,

Douglas has a lot to say about grounding and bonding in his book, but I think this is what Kurt is looking for.

From Electrical Inspections of Existing Dwellings - 2001 Edition:

[Chapter 3, page 3.8] If a second electrode is installed, it must be connected to the same grounding electrode system as the house electrical system. Failure to bond the two electrodes together actually introduces hazards to the system instead of reducing hazards. In a lightning storm, there can be a large voltage potential between nearby points of earth. Installing two electrodes to these different points, then bringing conductors from each electrode to an appliance, has the effect of bringing that voltage potential to the appliance.

For example, if the cable TV connection has its own ground rod, separate from the electrical system, one point on the earth (the CATV's ground rod) is being brought to the antenna hookup of the TV. A different point of the earth (where the house electrical system meets its ground rod) is being brought to the TV thorugh the grounded conductor. They may be very close together at the television, and thousands of volts apart at the earth. During a lightning storm, the added ground rod for the CATV greatly increases the likelihood the TV will be damaged. The damage potential is eliminated if the two grounding electrodes are bonded together outside the building. The basic rule is that ALL grounding electrodes, no matter what their purpose, must be bonded together.

ONE TEAM - ONE FIGHT!!!

Mike

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