Hazard of potential electrical current on water-main 2

[goulaigan]

Most utilities control the hazard of potential electrical current on conductive water services by installing temporary jumpers around the water service before the service is severed or replaced. What about the potential electrical current on the water-main? Is there a best practice to bond a conductive (cast or duct tile) water main before it is cut out?

 

[bimr]

NEC 250.68B requires that the "bonding jumper" be of sufficient length to permit removal of the water meter without losing the integrity of the bonding path. The bonding jumper is not a temporary jumper, it is permanent.

The NEC defines "bonding" as the permanent joining of metallic parts to form an electrical conductive path that will ensure electrical continuity and the capacity to conduct safely any current likely to be imposed.

Bonding equipment together does not necessarily mean that the equipment is properly grounded.

Each building is supposed to have a grounding electrode systems that ties everything together. The service entrance neutral conductor is grounded, this neutral is bonded to the main panel, a grounding electrode and all metal water piping systems installed in or attached to a building are bonded together.

In a building, the purpose of bonding is to prevent potential differences ( or shock ) between non-current-carrying metal parts.

If someone is getting shocked from voltage on a water main, the problem is that the metal piping is energized and it’s not bonded to the source. It’s just that simple.

 

[bimr]

http://ecmweb.com/grounding/electric_shocking_truth_grounding/index.html

 

[goulaigan]

Thanks! That link describes the hazard very well. During routine maintenance or water service replacement the hazard is easily controlled with the installation of a temporary jumper, use of amp meters etc. My question however remains. Is there a best practice for controlling the hazard of current in conductive water-main? We had an incident of arcing in the middle of an intersection through 4" cast pipe! The problem was traced back to a neutral problem in the area. As the article suggests, there had been no previous indication of a problem.
We are considering implementing a practice where bonding jumpers are installed around any section of conductive water-main that is to be cut out. Is this an over reaction?

 

[stanier]

The ductile iron and steel main suppliers would have you believe that it is unnecessary as the rubber ring provides an effective insulator in a pipeline.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[rconner]

stanier,
I believe AWWA has had for a great many years a policy statement relating to grounding of electrical circuits on water pipes. This statement is available on the AWWA website at

http://www.awwa.org/about/oandc/officialdocs/AWWASTAT.cfm.

I also believe there were probably multiple reasons including safety involved in the issuance of this statement.
Note per the AWWA policy statement, "AWWA does not object, however, to the connection of all interior piping of a building to the electrical service neutral and to a separate grounding electrode, provided that such interior pipe systems and grounding connections are electrically insulated from the water utility's pipe system."
At least in the USA as far as I know DIPRA (including members of AWWA as are their member companies), are quite clear in their endorsement of this AWWA policy e.g. as shown on the first page of the document at

http://www.dipra.org/pdf/directTappingPoly.pdf

. You are perhaps confusing the corrosion resistance advantages relating to the break up of e.g. of currents from any source that can be provided by some common ductile iron push-on joints, employing purposeful contact of only the rubber gasket (this is as explained in the document at

http://www.dipra.org/pdf/strayCurrent.pdf

), with this issue.
Of course, if a corrosion engineer or Owner etc. requires on the other hand e.g. a very low resistance jumper be welded across e.g. steel or rubber-gasketed ductile iron joints e.g. for monitoring or potential future installation of long-line cathodic protection, it should be understood in all regards that obviously even a ductile iron pipeline becomes a quite dependable conductor. I noticed where the original poster had posted this on another forum at

http://www.waterandwastewater.com/cgi-bin/yabb/YaBB.pl?board=general;action=display;num=1180722162

, one responder did note that he felt some currents (I guess he was talking about the common coatings on common iron water pipe e.g. not necessarily being the equivalent of heavy insulation on electrical wire), might however be rather quickly “discharged to ground”. This would appear to me to be dependent on the coating system, soils, and other factors.

 

[BigInch]

If current is discharged into the ground, I think that would indicate you've going to have cathodic metal loss troubles, no?

http://virtualpipeline.spaces.msn.com

 

[rconner]

BigInch,
I believe you are correct. As has been explained by DIPRA on the first page of the second/link reference I cited, "Grounding household electrical services to the copper water service line can result in stray current corrosion of the copper service and/or the Ductile or Cast Iron main."