NEC Multiple electrodes

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lrgallan

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I am in an argument with an Engineer who is stating that in a multiple grounding electrode (cold water pipe and ground rod) where the ground rod does not have a reading of less than 25ohms that an additional (third) grounding electrode is required. The ground system read 2.8 ohms at the box but the ground rod was 280ohms.

Is there any formal documentation out there that describes the intent of the Code so I can get his Engineer off my back.

Allan
 
Re: NEC Multiple electrodes

I think you need to go back one step further, to 250.53(D). The path of the engineer?s reasoning might have gone along the following lines:
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">250.53(D): If I use a pipe, then I must supplement it with another electrode.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">I choose to use a rod as the other (supplemental) electrode.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">250.53(D)(2): Since I chose a rod, it must comply with 250.56.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Although 250.56 starts out by talking about a single electrode, I was sent to this section by the earlier statement that says that the ground rod has to comply with 250.56. That tells me that it has to meet the 25 ohm rule, without regard to the fact that is only a supplemental to the pipe. If it fails to make 25 ohms, then I need to ?augment? it with still another electrode.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">I choose to use a second rod as the other (augmented) electrode.</font>
<font size="2" face="Verdana, Helvetica, sans-serif">I agree with the engineer.
 
Re: NEC Multiple electrodes

These replies are not in line with the language in the NEC Code. Section 250.50 states that you use only those items in 250.52 (A)1 through (A)6 which includes rods. PER the NEC Section 250.56 is only applicable to cases where you have a single electrode. If a rod is used as part of 250.52 then it is not a single electrode. So why would you have to supplement.

Following the reasoning of the enginneer every rod in florida would have unlimited rods in series as no rod will register less than 25 ohms so every rod would have to be augmented.

Where would you draw the line when no more augmetation is required?
 
Re: NEC Multiple electrodes

Originally posted by lrgallan:
These replies are not in line with the language in the NEC Code.
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In my opinion the replies are exactly correct.


Originally posted by lrgallan:
Where would you draw the line when no more augmetation is required?
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You draw the line with one additional Rod, Pipe, or Plate Electrode.

250.56 Resistance of Rod, Pipe, and Plate Electrodes.
A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified by 250.52(A)(2) through (A)(7). Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1.8 m (6 ft) apart.
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[ March 23, 2005, 03:16 PM: Message edited by: iwire ]
 
Re: NEC Multiple electrodes

250.53(2)Supplemental Electrode Required:
metal underground water pipe shall be supplemented by additional electrode.

Pick up at second sentence,

It shall comply with 250.56
I can't see anyway of getting around
250.56 Allan

[ March 23, 2005, 03:04 PM: Message edited by: dillon3c ]
 
Re: NEC Multiple electrodes

Irgallan,

Maybe this will help, Some day that copper water pipe [GEC] will get replaced with PVC ,by suppementing with only one ground you lose your GEC entirely,but with 2 rods you still have a GEC.

frank
 
Re: NEC Multiple electrodes

I have a customer who lives in a sandy area who has lost several electronic items after a thunderstorm. There is only 1 ground rod and it does not look like an approved rod. The house is an old house with 2 wire system. Would driving 1 or more new rods help her? Also wonder if re-wiring with 3 wire system would be beneficial. Any suggestions will be appreciated.
 
Re: NEC Multiple electrodes

Thanks for the advice georgestolz. I have checked into the tvss's and found one that will work I believe.
 
Re: NEC Multiple electrodes

I was going to let others follow along behind me and say it, looks like it didn't happen. Getting some more grounding happening would probably aid that TVSS a bunch.

I'm going out on a limb here, but I'd imagine since it diverts power to ground, if the potential on the neutral were to rise with the ungrounded conductors, the TVSS's operation would be impaired. Try to get some grounding electrodes in place. :)

(I imagine that explanation is a little off key, which was why I didn't offer it in the first place. :D )
 
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