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Old 12-14-2012, 09:51 AM   #16
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Proper Grounding


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Originally Posted by westom View Post
I may have described same using different terms. Two ground systems are described by code in two completely different articles. Because each is so different.
It is all in the same National Electrical Code article - 250.

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That is completley different from another ground described as earth ground. Ten foot copper clad steel rods, Ufer ground, steel plates, etc are examples.
The NEC only requires 8 foot ground rods.

Another earthing electrode that is required, when present, is the water service pipe where there is 10 foot in contact with the earth (which is not present here).

Where there is not a metal water service pipe, the NEC wants interior water pipe bonded to the service by methods that are similar to what is required if it is used as an earthing electrode. For a 200A service a #4 wire would connect (250.104-A). (This is larger than the #6 wire required for ground rods - in Alan's post.)

Other pipes, like gas, are grounded by the ground wire in the branch circuit that supplies them (as in another post by Alan).

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Originally Posted by westom View Post
But wall receptacle safety ground is not part of an earth ground.
"Ground" wires have both an "earthing" and "bonding" function. Where equipment has a ground wire, it keeps exposed metal parts at approximately 'earth' potential. The bonding function carries 'fault' currents to trip a breaker.

The "bonding" function, incidentally does not depend on the earth connection. It depends on a connection between neutral and ground at the service disconnect. The high fault current to trip a breaker is carried by ground wires back to the service panel, through the N-G bond, and back to the utility transformer on the service neutral.

The necessary N-G bond at the service often looks like a mounting screw for the neutral bar - often colored green.

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Originally Posted by westom View Post
Bonding and earthing are different as even described by code. And then other electrical reasons make that difference greater. Makes a wall receptacle safety ground virutally useless for earthing a surge current.
Protectors that plug-in do not work primarily by earthing surges. The work by limiting the voltage from each wire to the ground at the protector. The voltage between wires going to the protected equipment is safe for the protected equipment.

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Old 12-14-2012, 10:03 AM   #17
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Proper Grounding


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Ok so here is the plan...I need to run #4 bare copper wire from the ground buss in the breaker panel directly to two 5/8" ground rods a minimum of 6' apart. Can the wire terminate at the second rod or should it loop back to the breaker panel?
It can end at the second rod. Ground rods are a really crappy earthing electrode. But they are easy to install.

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The breaker panel is on an outside wall so the distance to the first ground rod will be around 3'. Can I run the ground wire down from the panel inside the wall next to the insulation then out through the siding just above the foundation or do I need to put this in conduit...plastic or metal?
It does not have to be in conduit, but keep it protected from damage.

If it is in ferrous metal conduit it has to be bonded to the metal conduit at both ends - the conduit becomes part of the conductor.

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This morning I also found a green #10 ground wire in the attic and traced it to the other side of the house where it ran down through the soffit and along the trim on the door to two 1/2" ground rods that were buried about 8" apart. It is hooked to the ground buss in a large junction box in the attic where all the old wires and new wires from the service update were joined (the service panel was moved from a side room to the garage when the update was done). All the wires that have grounds that come into this junction box are hooked into the buss with it.

Should I leave this ground hooked up as it is or could this cause a problem??? The wire distance is around 20 feet.
Nice find.

The j-box ground should be connected back to the new service panel.

Disconnect the other ground rods. You do NOT want multiple separate earthing systems. In the event of strong surge currents to the earthing system, or a near lighting strike, the separate earthing systems may be thousands of volts different. That can show up at equipment.

Excellent information on surges and surge protection is at:
http://www.lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf
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Old 12-14-2012, 04:32 PM   #18
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Proper Grounding


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Originally Posted by wewiserangers View Post
Ok so here is the plan...I need to run #4 bare copper wire from the ground buss in the breaker panel directly to two 5/8" ground rods a minimum of 6' apart. ...
Should I leave this ground hooked up as it is or could this cause a problem??? The wire distance is around 20 feet.
I can only speculate why that #10 AWG ground wire exists. Sounds like it even violates code requirements for human safety. Also sounds like, if earthing a surge, then it may induce a surge on other wires. To conduct a surge inside the house. Undesireable.

Should it be removed? I cannot say because important details may be missing. But as described, it even violates code. Best have a professional inspect it.

Rods separated by 8 inches are only one rod. Driving two 8 foot rods only 8 inches apart implies someone with insufficient knolwledge was doing the work.

Again, only implies. I cannot make a recommendation. Can only define what should exist.

The bus bar should connect short to earth as described so that protectors are actually part of a protection system. Routing that #4 ground wire is best when routed to ground rods while separated from other non-grounding wires. With no sharp bends. It could be routed inside plastic conduit. But unnecessary.

Best is to route one uncut wire from the bus bar, through a clamp on the first rod, and terminated to a clamp on the second. One solid copper wire is best.

Some drive those rods into a hole. Then line that hole maybe with a 6" PVC pipe and a cap. So that the bare copper wire clamped to both rods is buried. And so both junctions are easily inspected and protected. Not necesssary, but a better installation.

Also required for human safety is a bare copper ground wire from that breaker box bus bar to where any copper water pipe enters the building. Not sufficient for earthing. Essential for human safety as required by code.

If utilities enter the building at different locations, then best is to reroute those utility wires (ie cable, telephone) to enter and be earthed at the service entrance. A utility also demonstrates a kludge (good, bad, and ugly) solution to defective installation of utliity wires. This outside and buried interconnection also improves earthing:
http://www.duke-energy.com/indiana-b...ech-tip-08.asp

While discussing this, appreciate that above is only a 'secondary' protection layer. Each protection layer is only defined by what actually does the protection. Also inspect your 'primary' protection layer. A picture demonstrates what to inspect:
http://www.tvtower.com/fpl.html

Last edited by westom; 12-14-2012 at 04:36 PM.
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Old 12-15-2012, 09:01 AM   #19
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Also required for human safety is a bare copper ground wire from that breaker box bus bar to where any copper water pipe enters the building. Not sufficient for earthing. Essential for human safety as required by code.
The wire is usually bare solid but can be stranded and insulated.

The OP does not have a metal water service pipe, so the connection to the interior water pipe is not as an earthing electrode but to bond the water pipe. Connection rules are similar, but the connection does not have to be where the water service enters the house.

A metal municipal water system is the lowest resistance to earth of any electrode that is available at a house. Ground rods are likely the highest resistance to earth electrodes. For new construction a "concrete encased electrode" (Ufer ground) is often required by the NEC - another good electrode.
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Old 12-15-2012, 09:42 AM   #20
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Proper Grounding


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Originally Posted by wewiserangers View Post
Ok so here is the plan...I need to run #4 bare copper wire from the ground buss in the breaker panel directly to two 5/8" ground rods a minimum of 6' apart. Can the wire terminate at the second rod or should it loop back to the breaker panel?

The breaker panel is on an outside wall so the distance to the first ground rod will be around 3'. Can I run the ground wire down from the panel inside the wall next to the insulation then out through the siding just above the foundation or do I need to put this in conduit...plastic or metal?


This morning I also found a green #10 ground wire in the attic and traced it to the other side of the house where it ran down through the soffit and along the trim on the door to two 1/2" ground rods that were buried about 8" apart. It is hooked to the ground buss in a large junction box in the attic where all the old wires and new wires from the service update were joined (the service panel was moved from a side room to the garage when the update was done). All the wires that have grounds that come into this junction box are hooked into the buss with it. .
Add a #6 copper wire as a grounding electrode conductor from the two ground rods 8 inches apart around the house to the GEC from the panel to the other ground rods. Now the green #10 equipment grounding conductor becomes legitimate in that it ends at a point on the grounding electrode system.

There is a table of sizes for GECs that is dependent on the amperage of the electrical system. The maximum GEC required going to ground rods is #6.
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Old 12-16-2012, 12:30 PM   #21
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Add a #6 copper wire as a grounding electrode conductor from the two ground rods 8 inches apart around the house to the GEC from the panel to the other ground rods. Now the green #10 equipment grounding conductor becomes legitimate in that it ends at a point on the grounding electrode system.
Ignoring the difficulty of running a #6 wire from the double ground rods to the panel....

Suppose there is a strong surge that results in 1000 surge amps to the ground rods at the panel. And suppose that the resistance to earth of those rods is a near miraculous 10 ohms. The potential of the "ground"; at the service panel is 10,000V above 'absolute' earth potential. In general the voltage drop away from a ground rod is in the first 3 feet of the rod [so the second rod spaced 8 inches from the other distant rod is useless]. The distant rods will be far more than 7000V from the "ground" at the service. The neutral at the service (if installed correctly) is connected to the "ground" at the panel. So the power wiring will be over 7000V from the distant rods - not what you want. (If the attic j-box is also connected to the new service panel the j-box ground will be a fraction of 7000V from the power wires.)

But you suggest a #6 wire connecting the distant ground rods to the new ground rods. A surge from lightning is a very short event. As a result it has relatively high frequency current components. As a result the inductance of the wire is more important than the resistance. The IEEE surge guide (link has been provided) has an example with a ground wire from a cable entry protector to the earthing system that is 30 feet long with 10,000V between ends. A larger diameter wire can greatly lower the resistance, but not so much the inductance.

A nearby lightning strike can also result in the 2 sets of ground rods being thousands of volts apart.

Separate earthing systems are a bad idea. You want to combine all the earthing systems into a single system then connect at a common point to that single system. The distant rods should be abandoned and the ground at the attic j-box connected to the new panel (if it is not already connected).

The distant ground rods increase the risk of damage.

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Originally Posted by AllanJ View Post
There is a table of sizes for GECs that is dependent on the amperage of the electrical system. The maximum GEC required going to ground rods is #6.
I agree. The connection to a ground rod only has to be #6 wire because a rod is a pretty crappy electrode. Ufer grounds only have to be #4. The wire size to connect a metal water service pipe goes up as the size of the electrical service increases.
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Old 12-17-2012, 07:55 AM   #22
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Proper Grounding


I have decided to cut and pull the wire out from the closely spaced ground rods as it will be difficult to run a wire from the new ground rods to the old due to a patio and landscaping in between. I did also consult a local electrician and he thought this was also a bad idea to use these. I traced the green wire back to one of the bedrooms where two of the outlets had been grounded off of it. This wire had been attached to the ground bar in the panel in the attic when the update was done, so this is now grounded in the new system. The remainder of the wire which I found went to the ground rods had been abandoned after the update.

I have everything I need to get this finished up now. I will be going with #6 solid copper instead of #4 with two 5/8" X 8' ground rods. The rods will be 8 feet apart which will put the second rod just in front of where my phone line comes in so I can ground this also. When I pulled on the ground wire for the phone service it pulled right out of the dirt. I never even found a rod after digging down there!

The distance to the first ground rod is right about 3-1/2'. It is a straight shot down from the breaker panel with only a very slight curve as it comes down to the ground rod. Hopefully I can get it all put in this morning.

Thanks everyone for the input. It has been a big help.

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