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Author Topic: BX cable ground loops  (Read 18264 times)

Kevin Graf

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Re: BX cable ground loops
« Reply #30 on: April 27, 2014, 06:38:36 pm »

While I'm not sure that it was ever in the NEC code book, using a internal metallic water pipe as a Safety Ground (EGC) to retrofit older two wire systems, was an accepted practice in many jurisdictions for a long time period.

One danger with metallic water pipes is that they may be carrying 'lost neutral' currents (yours or your neighbors). Plumbers have been killed.
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Jeff Bankston

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Re: BX cable ground loops
« Reply #31 on: April 27, 2014, 06:39:02 pm »

Well only one official connection! But the EGC may be bonded to the metal building framing any number of times and that framing can make easy contact to the Ufer or water pipe.
unless its a wood frame of concrete frame(skeleton) building. if its an old concrete building like a few i worked in we would have to bust concrete(not allowed) to find rebar so the 2 grounding points are the cold water pipe and a ground rod. on new buildings we cadweld a ground wire to the rebar right below the main disconnect.
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Jeff Bankston

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Re: BX cable ground loops
« Reply #32 on: April 27, 2014, 06:48:56 pm »

While I'm not sure that it was ever in the NEC code book, using a internal metallic water pipe as a Safety Ground (EGC) to retrofit older two wire systems, was an accepted practice in many jurisdictions for a long time period.

One danger with metallic water pipes is that they may be carrying 'lost neutral' currents (yours or your neighbors). Plumbers have been killed.
we are never allowed to use a branch water pipe as the main ground. the main ground must be connected to the main water pipe within 5 feet of where it enters the building. this is to prevent it from being disconnected at any time during normal operations. plumbers know this and if there is a problem on the other side of the water pipe the power for the building is shut down. the only ground we are allowed to connect to a branch copper water pipe is an I.G. ground. if its a steel frame building i usually put a clamp on a beam/collumn , crimp a connector on the wire and bolt it to the beam clamp.
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Kevin Graf

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Re: BX cable ground loops
« Reply #33 on: April 27, 2014, 07:33:59 pm »

My post was about the EGC Safety Ground system. The main external ground GEC is what is connected to the external water pipe.

Not just any rebar can be used as a Ufer ground system (GEC).
By the way Herbert G. Ufer was the consultant's name that developed the system.

http://en.wikipedia.org/wiki/Ufer_ground
« Last Edit: April 27, 2014, 07:39:11 pm by Kevin Graf »
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Jeff Bankston

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Re: BX cable ground loops
« Reply #34 on: April 27, 2014, 09:49:21 pm »

My post was about the EGC Safety Ground system. The main external ground GEC is what is connected to the external water pipe.

Not just any rebar can be used as a Ufer ground system (GEC).
By the way Herbert G. Ufer was the consultant's name that developed the system.

http://en.wikipedia.org/wiki/Ufer_ground
i know but i didnt use the name Ufer because i didnt know if anyone here would know what i was talking about. we have always called it "The Ufer". i rarely hear it called the "concrete encased electrode" even though thats whats printed on the blue prints. are you fur going to lunch now ?


p.s. for those that dont know concrete retains a lot of water.

 i also installed a lenght of bare 4/0 in a long trench(dont remeber the lenght) encased in concrete once per the blueprints. they filled the trench half way up with concrete and we placed the 4/0 on it and kept it in the center as they poured the rest. thats the only time i ever did one of those grounds.
« Last Edit: April 27, 2014, 10:00:30 pm by Jeff Harrell »
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Mike Sokol

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Re: BX cable ground loops
« Reply #35 on: April 27, 2014, 10:04:08 pm »

p.s. for those that dont know concrete retains a lot of water.

That's also why a lot of musicians have been shocked while standing on a concrete floor in their basement and playing an ungrounded electric guitar. Concrete can be VERY conductive.
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Mike Sokol
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Re: BX cable ground loops
« Reply #36 on: April 27, 2014, 10:35:38 pm »

That's also why a lot of musicians have been shocked while standing on a concrete floor in their basement and playing an ungrounded electric guitar. Concrete can be VERY conductive.

Lightning hit a church bell tower here a few years ago.  The moisture in the limestone flashed to steam and sent large chunks of stone flying all over the parking lot.
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Craig Hauber

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Re: BX cable ground loops
« Reply #37 on: April 28, 2014, 01:12:54 am »

we are never allowed to use a branch water pipe as the main ground. the main ground must be connected to the main water pipe within 5 feet of where it enters the building. this is to prevent it from being disconnected at any time during normal operations. plumbers know this and if there is a problem on the other side of the water pipe the power for the building is shut down. the only ground we are allowed to connect to a branch copper water pipe is an I.G. ground. if its a steel frame building i usually put a clamp on a beam/collumn , crimp a connector on the wire and bolt it to the beam clamp.
Found one of those water-pipe ground clamp setupsnear the service entrance on a small commercial-job where we were upgrading the panel.  It was a valiant attempt, but the clamp was fastened to 1" PEX  :-)
(wish I had snapped a pic)
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Craig Hauber
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Jeff Bankston

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Re: BX cable ground loops
« Reply #38 on: April 28, 2014, 01:34:49 am »

Found one of those water-pipe ground clamp setupsnear the service entrance on a small commercial-job where we were upgrading the panel.  It was a valiant attempt, but the clamp was fastened to 1" PEX  :-)
(wish I had snapped a pic)
some people are just .......... ! that reminds me of a guy srcewing a ground pigtail to plastic wiremold type stuff.
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Mike Sokol

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Re: BX cable ground loops
« Reply #39 on: April 28, 2014, 07:34:25 am »

some people are just .......... ! that reminds me of a guy screwing a ground pigtail to plastic wiremold type stuff.

I'm not sure I can say any more than this photo from RV.net showing a "dirt ground".
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Mike Sokol
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Re: BX cable ground loops
« Reply #39 on: April 28, 2014, 07:34:25 am »


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