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#196391 - 09/29/10 04:51 PM Clamp-on Ground System Testers
InspectorE Offline
Member
Registered: 10/08/04
Posts: 51
Loc: Hudson WI USA
Any comments on how well these work and what brands to get/stay away from? Seems like not having to install test rods or break the ground connection is a big plus.

Thanks for any comments!
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#196392 - 09/29/10 05:17 PM Re: Clamp-on Ground System Testers [Re: InspectorE]
HotLine1 Offline


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Registered: 04/03/02
Posts: 6776
Loc: Brick, NJ USA
I've heard nothing 'bad' about any of these tools, but I want to add I have not used any.

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#196400 - 09/30/10 08:55 AM Re: Clamp-on Ground System Testers [Re: HotLine1]
renosteinke Offline
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Registered: 01/22/05
Posts: 5316
Loc: Blue Collar Country
Call this post a 'warning shot' across every electricians' bow.

The NEC just says you need a ground rod ... that's ONE ground rod ... unless the resistance is greater than 25 ohms, in which case a second rod is needed.

The first aspect is that some have turned this requirement inside-out, saying that YOU have to 'prove' that your rod has the required low resistance - or, you MUST drive a second rod.

Next, every HI wants one of these gizmos so they can discover new 'defects.'

Together, these create a bias that we've been doing it all wrong for the past century, and that a single rod in never enough.
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#196401 - 09/30/10 10:13 AM Re: Clamp-on Ground System Testers [Re: renosteinke]
gfretwell Offline


Member
Registered: 07/20/04
Posts: 9038
Loc: Estero,Fl,usa
I think that is the perception. I usually hear the defacto answer is drive two rods if that is your only electrode. Florida pretty much makes the Ufer mandatory in new construction since the Ufer inspection is part of the footer inspection so it will always be "available". If you lose that connection you will be chipping concrete in most jurisdictions. That is why the "7 iron" is so popular. There is no exposed copper to be broken off and/or stolen.
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#196402 - 09/30/10 11:05 AM Re: Clamp-on Ground System Testers [Re: gfretwell]
mikesh Offline
Member
Registered: 06/07/06
Posts: 613
Loc: Victoria, BC, Canada
We don't see many rods any more in my area but the rules here are 2 - 10 foot rods 3 meters apart. There is so much rock and hardpan clay that ground plates are the rule except for a counterpoise ground for a HV service.
We dropped the resistance requirement from our code a long time ago.
Given the role a Ground wire serves I think it is mostly all overkill. It is rare that high voltages including lightning ever get on the low voltage wires, the neutral is the real fault current path to the source anyway.
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#196404 - 09/30/10 01:02 PM Re: Clamp-on Ground System Testers [Re: mikesh]
gfretwell Offline


Member
Registered: 07/20/04
Posts: 9038
Loc: Estero,Fl,usa
The function of the ground is not to clear faults, it is to create a local ground reference so the case of your drill is at the same potential as the concrete slab you are sitting on. In that regard, the ufer is your best bet. Earth ends up being a significant return path for neutral current tho, in spite of the theory and 250.6. Wye distribution pretty much assures it. Even with delta distribution, you will still be sharing the earth with the neutral. You want a local ground reference.
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Greg Fretwell
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#196405 - 09/30/10 02:49 PM Re: Clamp-on Ground System Testers [Re: gfretwell]
renosteinke Offline
Cat Servant
Member
Registered: 01/22/05
Posts: 5316
Loc: Blue Collar Country
I'm not sure what you mean by "the 7 iron," Greg. A picture. perhaps?
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#196406 - 09/30/10 03:53 PM Re: Clamp-on Ground System Testers [Re: renosteinke]
gfretwell Offline


Member
Registered: 07/20/04
Posts: 9038
Loc: Estero,Fl,usa
That term came from here. It is when you turn up a piece of rebar, built into the wall and make the Ufer connection there.
That is very popular here in SW Florida but right across the swamp on the East Coast, AHJs don't like it.

http://gfretwell.com/electrical/ufer.jpg
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Greg Fretwell
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#196407 - 09/30/10 05:38 PM Re: Clamp-on Ground System Testers [Re: gfretwell]
HotLine1 Offline


Member
Registered: 04/03/02
Posts: 6776
Loc: Brick, NJ USA
Reno:

As to the '2 rods'...basically most ECs I know 'just do it', as if it's looked at in a dollars and sense standpoint. Taking into account the $$$ of testing equipment, driving the reference rods & performing the test, economical sense is to drive the second rod & the job is done.

For some time, quite a few guys still installed rods with Ufers, and I still find the occasional 'water ground' with a jumper on the 2" plastic main, and PEX piped resi.

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John
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#196408 - 09/30/10 05:55 PM Re: Clamp-on Ground System Testers [Re: HotLine1]
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
I can't say I've ever used one of these clamp-on type testers.
I've always used the one with the two test rods, I suppose it's what you're bought up with I guess.
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