Ground Rod or Not? - Page 4 - Electrician Talk - Professional Electrical Contractors Forum

amptech · 11-20-2009, 08:30 PM

Bump

Where did everyone go? I am interested in rewire's rationale for not installing a grounding electrode at a RV campsite pedestal.

user5941 · 11-20-2009, 08:45 PM

Quote:

Originally Posted by amptech

Bump

Where did everyone go? I am interested in rewire's rationale for not installing a grounding electrode at a RV campsite pedestal.

I'm going to get a ruling on this monday , I may have to change my thinking and I may not. currently I do not view a pedestral as a structure as defined in art 100 I think a grounding conductor and bonding would be all that is required I will note I have never done a metered campround but have connected power outlets to sites. I am basing this on the definition as I see it but I am not an AHJ so I am going to talk to one from Saint Louis City .I am not saying i can't be wrong on this.

amptech · 11-20-2009, 10:25 PM

Rewire,
I am curious to know if you have read Soares Book on Grounding that I mentioned in earlier posts. If not, you should check it out. I think you would find it interesting.

user5941 · 11-20-2009, 10:40 PM

Quote:

Originally Posted by amptech

Rewire,
I am curious to know if you have read Soares Book on Grounding that I mentioned in earlier posts. If not, you should check it out. I think you would find it interesting.

no I haven't still reading MH book

Benaround · 11-21-2009, 05:36 AM

Quote:

Originally Posted by Lenny

In my case, we have bonded all the pedistals with a #2 alum. conductor and connected that to the ground-rods at the disconnects, which are also tied to the neutral. All disconnects are bonded also.

Lenny,

That would amount to an EGC connecting to a ground rod, the EGC

terminates on or after the N/Grd connection.

JohnJ0906 · 11-21-2009, 09:54 AM

Quote:

Originally Posted by amptech

That is a mostly true statement but incomplete. The purpose of a grounding electrode is to maintain earth potential(zero) at electrical equipment. Does each pedestal require a grounding electrode? I suggest you read 250.50 carefully then also read 551.74. If you have not read Soares Book on Grounding, I would highly recommend it. Soares explains grounding and bonding very well and clears up a lot of misconceptions and misinformation about grounding and bonding.

Also, I think a good look at 250.4(A)(1 through 5) is in order as well.

"The following general requirements identify what grounding and bonding of electrical systems are required to accomplish......."

AllStar · 11-23-2009, 08:25 PM

Quote:

Originally Posted by amptech

Maintain potential.

A ground rod is not to maintain potential, but solely to give lightning a direct path to earth. When you say equal potential, it usually refers to the bonding ring around swimming pools, which gives you the equi potential to all metal parts surounding the pool. ie.. pool light, ladder, dive platform.

JayH · 11-23-2009, 08:38 PM

Quote:

Originally Posted by AllStar

A ground rod is not to maintain potential, but solely to give lightning a direct path to earth.

Are you serious?

brian john · 11-23-2009, 09:06 PM

Quote:

Originally Posted by JayH

Are you serious?

He is.

What do you think the purpose of an electrode is?

NolaTigaBait · 11-23-2009, 09:10 PM

Quote:

Originally Posted by JayH

Are you serious?

are you?

JayH · 11-23-2009, 09:14 PM

Quote:

Originally Posted by brian john

He is.

What do you think the purpose of an electrode is?

A grounding electrode is not solely for lightning protection.

Rather than spend my time typing out all of the needs for ground I have copied and pasted for you:

The purpose of grounding is three-fold. First, grounding provides a low-impedance path for fault current to flow back to the source. In accordance with Ohm’s Law (V = I x R), a low-impedance path for fault current results in high levels of current to flow for a given voltage. For inverse-time overcurrent protective devices, such as circuit breakers and fuses, higher levels of fault current cause faster device operation to clear the fault. Grounding provides a low-impedance path for fault current to ensure that circuit breakers and fuses operated quickly to clear ground-faults from the system.

Second, the low-impedance path for fault current provided by grounding ensures that voltage drop is limited from the point of the ground-fault back to the source. Ground-fault current is safely shunted to ground through a low-impedance path to ground before voltage can rise to lethal levels on any electrical component, protecting personnel from shock hazards during ground-fault conditions.

Third, grounding provides an electrical reference to stabilize the voltage to earth on conductors and equipment to the system phase-to-ground voltage during normal operation. An ungrounded system permits the voltage to earth on conductors and equipment to rise to levels as high as the phase-to-phase voltage during ground-fault conditions. Grounding provides an electrical reference for equipment operation that limits the voltage stress on conductor and equipment insulation throughout the system, and also limits the voltage imposed by lightning, switching surges, or unintentional contact with higher-voltage lines.

sparks134 · 11-23-2009, 09:38 PM

yes, for lightning!!!

bthesparky · 11-23-2009, 09:58 PM

Ok heres the situation, did a 200 amp resy service today drove my 8ft. ground rod 3ft. off the foundation and at a more then adequate depth. The inspector comes out, looks everything over likes the work and is very happy and then proceeds to ask me where my second ground rod is. The utility company's service guidelines show nothing about having to have the second rod and he's trying to tell me that a second rod is a code requirement. I dont claim to be the sharpest guy but i do know how to read a code book and i see nothing about this second ground rod. I did find out by talking to the utility guy that they are now requiring it which is fine but i would like to know if its a code requirement that im missing. Thanks for any answers you guys can offer.

JayH · 11-23-2009, 10:14 PM

There is not a NEC code requirement as long as you have not exceeded 25 ohms resistance and you have driven an 8' rod.

If there is a local code then you need to tell the inspector "show it to me."

wareagle · 11-23-2009, 10:25 PM

Unless you can show that the ground rod resistance is 25 ohms or lower you have to drive a second rod. Most electricians do not bother to test the resistance. They just drive the second rod.

JohnJ0906 · 11-23-2009, 10:42 PM

Quote:

Originally Posted by JayH

A grounding electrode is not solely for lightning protection.

Rather than spend my time typing out all of the needs for ground I have copied and pasted for you:

The purpose of grounding is three-fold. First, grounding provides a low-impedance path for fault current to flow back to the source. In accordance with Ohm’s Law (V = I x R), a low-impedance path for fault current results in high levels of current to flow for a given voltage. For inverse-time overcurrent protective devices, such as circuit breakers and fuses, higher levels of fault current cause faster device operation to clear the fault. Grounding provides a low-impedance path for fault current to ensure that circuit breakers and fuses operated quickly to clear ground-faults from the system.

Second, the low-impedance path for fault current provided by grounding ensures that voltage drop is limited from the point of the ground-fault back to the source. Ground-fault current is safely shunted to ground through a low-impedance path to ground before voltage can rise to lethal levels on any electrical component, protecting personnel from shock hazards during ground-fault conditions.

Third, grounding provides an electrical reference to stabilize the voltage to earth on conductors and equipment to the system phase-to-ground voltage during normal operation. An ungrounded system permits the voltage to earth on conductors and equipment to rise to levels as high as the phase-to-phase voltage during ground-fault conditions. Grounding provides an electrical reference for equipment operation that limits the voltage stress on conductor and equipment insulation throughout the system, and also limits the voltage imposed by lightning, switching surges, or unintentional contact with higher-voltage lines.

The grounding electrode, and the planet earth has nothing to do with what I highlighted in red.

Take a look at 250.4(A)(1 through 5) - especially (5)

surfbh · 11-23-2009, 10:57 PM

Quote:

Originally Posted by cdnelectrician

Resistance is the opposition of current flow, Impedance is the oppostion of current flow at a given frequency (lightning for example)

Lots of bad info in this post, but this definition of impedance is totally wrong! Impedance is the total opposition to current flow. It is the algebraic sum of resistance, capacitive reactance and inductive reactance.

brian john · 11-23-2009, 11:02 PM

Quote:

The purpose of grounding is three-fold. First, grounding provides a low-impedance path for fault current to flow back to the source. In accordance with Ohm’s Law (V = I x R), a low-impedance path for fault current results in high levels of current to flow for a given voltage. For inverse-time overcurrent protective devices, such as circuit breakers and fuses, higher levels of fault current cause faster device operation to clear the fault. Grounding provides a low-impedance path for fault current to ensure that circuit breakers and fuses operated quickly to clear ground-faults from the system.

NOT THE PURPOSE OF A GROUND ELECTRODE Grounding/bonding yes Ground Electrode NO, NO, NO.

Quote:

Second, the low-impedance path for fault current provided by grounding ensures that voltage drop is limited from the point of the ground-fault back to the source. Ground-fault current is safely shunted to ground through a low-impedance path to ground before voltage can rise to lethal levels on any electrical component, protecting personnel from shock hazards during ground-fault conditions.

NOT THE PURPOSE OF A GROUND ELECTRODE Grounding/bonding yes; Ground Electrode NO, NO, NO.

Quote:

Third, grounding provides an electrical reference to stabilize the voltage to earth on conductors and equipment to the system phase-to-ground voltage during normal operation. An ungrounded system permits the voltage to earth on conductors and equipment to rise to levels as high as the phase-to-phase voltage during ground-fault conditions. Grounding provides an electrical reference for equipment operation that limits the voltage stress on conductor and equipment insulation throughout the system,

NOT THE PURPOSE OF A GROUND ELECTRODE Grounding/bonding yes Ground Electrode; NO, NO, NO.

Quote:

and also limits the voltage imposed by lightning, switching surges, or unintentional contact with higher-voltage lines.

You finally hit on something.

amptech · 11-23-2009, 11:26 PM

Brian,
I guess someone should have corrected Soares before they started publishing and distributing his book.
In the situation described in the original post there is a good possibility of a difference in potential between the metallic enclosure of the pedestal and the surrounding earth if no electrode is present. Lightning protection is a big part of the reasoning for grounding electrodes but touch potential is as well. Touch potential can be deadly in a situation as described in the OP. Wet ground, bare feet and a lot of physical contact likely with the pedestal. A human body touching the enclosure will be a shorter path than the lengthy #2 AL EGC and will likely conduct a good portion of stray current.
If you would indulge me, I'd like to hear your reasoning for disagreement with Soares on this point. Maybe I need to be corrected in my understanding.

JayH · 11-23-2009, 11:48 PM

Quote:

Originally Posted by brian john

NOT THE PURPOSE OF A GROUND ELECTRODE Grounding/bonding yes Ground Electrode NO, NO, NO.

NOT THE PURPOSE OF A GROUND ELECTRODE Grounding/bonding yes Ground Electrode NO, NO, NO.

NOT THE PURPOSE OF A GROUND ELECTRODE Grounding/bonding yes Ground Electrode NO, NO, NO.

You finally hit on something.

Can you have grounding without a grounding electrode?