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Author Topic: BX cable ground loops  (Read 18667 times)

Jeff Bankston

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Re: BX cable ground loops
« Reply #40 on: April 28, 2014, 07:52:31 am »

I'm not sure I can say any more than this photo from RV.net showing a "dirt ground".
yeah but you gotta admit , its dirt cheap !
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Cailen Waddell

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Re: BX cable ground loops
« Reply #41 on: April 28, 2014, 08:27:46 am »

So not to be a broken record here, but I am still having trouble understanding the cold water ground from an IG buss. Where is the ground neutral bond?  And where is the bond to the primary ground? 

It would seem to me, if you have an IG panel, it has to run to the regular ground buss bar in the main disconnect panel, at the same point of the ground neutral bond for the building.  In the case of system fed with an isolation transformer and having an isolated ground system, it would feed to the Xo on the transformer where the neutral originates. If at the point a cold water ground is appropriate, then fine, but an isolated ground is really an isolated ground path for fault current, and if you just tag your IG buss over to a cold water pipe, there is no guarantee a fault current would find that ground neutral bond and the breaker would trip?

That's not really a question I guess, but that's me explaining it the way in understand it.  Please correct me.

 
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Stephen Swaffer

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Re: BX cable ground loops
« Reply #42 on: April 28, 2014, 08:51:37 am »

I agree-there should be one point in the system that the neutral and any and all GEC are bonded together-and at that point the IG should also be connected.  Where this happens can vary-but the most convenient and common is in the panel or enclosure that contains the service disconnect.

I think code does allow bonding to a GEC in another location, however as I mentioned earlier simply meeting code is not always the best design.  Especially with an IG-consider why you are using it-I personally would want to see a good preferably copper path back to my main bonding point- jumping to another point on the GEC kind of defeats the purpose of an IG.
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Steve Swaffer

Kevin Graf

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Re: BX cable ground loops
« Reply #43 on: April 28, 2014, 09:03:37 am »

i know but i didn't use the name Ufer because i didn't 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 ?

It turns out that the NEC code book doesn't use the word 'Ufer' ether.
------------------------------------
A good article on the subject:

"What Is A 'Ufer' Ground?"
'Concrete-encased Grounding Electrodes
'

Published: April 2013
By Michael Johnston

- See more at: http://www.ecmag.com/section/codes-standards/what-ufer-ground#sthash.7jDp4WT9.dpuf
http://www.ecmag.com/section/codes-standards/what-ufer-ground
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Speedskater

Jonathan Johnson

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Re: BX cable ground loops
« Reply #44 on: April 28, 2014, 07:54:28 pm »

If I were to wire a building -- and I am NOT an electrician, inspector, or engineer, nor do I own a recent copy of the NEC -- I would have one common bonding point for all of these systems where available:
  • Equipment grounding conductor (the one that's bonded to every box and raceway)
  • Panels/conduits/raceway
  • Isolated ground EGC
  • GEC to building steel
  • separate GECs to separate utilites (gas, water, sewer, telco, CATV, coffee, beer, etc.) where they enter the building
  • GEC to Ufer/concrete-encased electrodes (rebar)
  • GEC to "ground rods"
  • Neutral conductor

Note that there may be non-metallic portions of utilities that interrupt electrical continuity between disparate metallic portions. (That's a fancy way of saying Joe the Plumber patched the copper pipe with a length of plastic.) In that event, there should be a jumper wire bypassing the insulative portion to electrically bond the two metal portions.

Because utility pipes and electrical raceways and boxes may be directly attached to building structure, as well as the primary EGC that bonds every box, this represents secondary bonding points that under certain circumstances can cause ground loop currents. (Except for EGC-to-box bonds, the secondary bonding points to structure and utilities can be interrupted by other trades so does not constitute a valid safety ground connection.) Therefore, for equipment that is sensitive to ground loops, the isolated ground system provides a safety ground that minimizes those ground loop currents.

Notes:
EGC = Equipment grounding conductor
GEC = Grounding electrode conductor
« Last Edit: April 28, 2014, 07:57:43 pm by Jonathan Johnson »
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Stop confusing the issue with facts and logic!

Mike Sokol

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Re: BX cable ground loops
« Reply #45 on: April 28, 2014, 09:15:21 pm »


  • separate GECs to separate utilites (gas, water, sewer, telco, CATV, coffee, beer, etc.) where they enter the building


How do you get utilities to run coffee and beer into your building? That sounds GREAT!  8)
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Mike Sokol
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Jeff Bankston

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Re: BX cable ground loops
« Reply #46 on: April 28, 2014, 09:56:54 pm »



Note that there may be non-metallic portions of utilities that interrupt electrical continuity between disparate metallic portions. (That's a fancy way of saying Joe the Plumber patched the copper pipe with a length of plastic.) In that event, there should be a jumper wire bypassing the insulative portion to electrically bond the two metal portions.

thats why the main service groung has to be connect to the first 5 feet of the main water pipe that enters the building. the water pipe that connects to the city water supply has to be either copper , cast iron , steel and thats the law , there are no exceptions. after the first 5 feet you can use whatever you like as long as it meets code.

you only want 2 grounding points unless the engineer has a reson for more. too many grounding points can cause hum in equipment.

the reason all gas lines are bounded together and grounded to the first 5 feet of the main water pipe is to try to prevent static buildup which could cause and explosion if theres a leak. it is also suppose to prevent a spark if an earthquake breaks a pipe. a steel frame building with metal studs also provides a "mechanical ground". concrete and wood frame building dont do anything to provide a mechanical ground.
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Stephen Swaffer

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Re: BX cable ground loops
« Reply #47 on: April 28, 2014, 10:42:22 pm »

the water pipe that connects to the city water supply has to be either copper , cast iron , steel and thats the law , there are no exceptions.

I do not doubt that that is the case in LA.  Where I live, only about half my customers-resi or commercial-have city water.  Those that have rural water receive water from a system of pvc piping, almost all if not all new wells use pvc or pex.  In the city, I have to be aware that the incoming line might be lead (yep-really) and since lead will melt too easily, it cannot be used as a ground.

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Steve Swaffer

Jeff Bankston

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Re: BX cable ground loops
« Reply #48 on: April 28, 2014, 11:03:43 pm »

I do not doubt that that is the case in LA.  Where I live, only about half my customers-resi or commercial-have city water.  Those that have rural water receive water from a system of pvc piping, almost all if not all new wells use pvc or pex.  In the city, I have to be aware that the incoming line might be lead (yep-really) and since lead will melt too easily, it cannot be used as a ground.
doesnt matter. an arc can blow a hole in copper , steel or cast iron.
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ProSoundWeb Community

Re: BX cable ground loops
« Reply #48 on: April 28, 2014, 11:03:43 pm »


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