- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Current flow on the water line is commonplace where there is a municipal water system in place. That is a commonplace occurrence in my book.
250.6 Objectionable Current
- Thread starter jxofaltrds
- Start date
- Status
Current flow on the water line is commonplace where there is a municipal water system in place. That is a commonplace occurrence in my book.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Why?
Do you consider such current to be inherently "objectionable"?
I am by no means an expert on such things but based on what people here have said previously it seems to me that it is all but impossible to avoid some current on the water pipe unless it is plastic.
- Location
- Massachusetts
Pretty much every service in North America that has grounded conductor and is in an area with a metal pipe water distribution system will have grounded conductor current on those metal water lines.
It is not simply common it is normal.
If you have objectionable current 250.6 applies.
I don't see this current on the water line as objectionable I see it as normal due to the electrical distribution system we use here.
Can you please elaborate on why you see this as objectionable or unsafe?
Do you have statistics to show us the number of house fires, injuries to occupants or others caused by this current?
False, even with intact neutral you will have current flow as the water line is electrically in parallel with the grounded conductor.
Are you sure the result will not be less safe than leaving it in place?
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Bob, I am curious why you are comfortable with amps of current flowing on metallic water piping (an incidental parallel path which is capable of carrying current but not _intended_ to carry current), but adamant that milliamps of current should not be permitted on an EGC (a path which is not intended to carry current on a regular basis, but which is carefully installed to be capable of carrying hundreds or thousands of amps for a short duration)?
http://forums.mikeholt.com/showthread.php?t=166318&page=4
It is pretty clear that Inspector Mike is concerned about EMFs caused by unbalanced currents; and the health effects of these fields are 1) far from proven and 2) if they exist very low order for most people (if they caused lots of obvious harm then there would be no controversy!)
But honestly, is there any reason that we _shouldn't_ consider current flow on metallic water piping 'objectionable', in the same way we object to unintended current flow on any other bonded metal that isn't an intentional circuit conductor? There are plenty of reports of plumbers being electrocuted by this sort of unintentional current flow.
-Jon
http://forums.mikeholt.com/showthread.php?t=166318&page=4
It is pretty clear that Inspector Mike is concerned about EMFs caused by unbalanced currents; and the health effects of these fields are 1) far from proven and 2) if they exist very low order for most people (if they caused lots of obvious harm then there would be no controversy!)
But honestly, is there any reason that we _shouldn't_ consider current flow on metallic water piping 'objectionable', in the same way we object to unintended current flow on any other bonded metal that isn't an intentional circuit conductor? There are plenty of reports of plumbers being electrocuted by this sort of unintentional current flow.
-Jon
- Location
- Illinois
- Occupation
- retired electrician
But that is really what we have where there is a common metal underground water piping system that serves the area. The GECs and main bonding jumpers at multiple buildings result in multiple connections between the grounded conductor(s) and the water pipe. We have the same thing with the shield of cable TV systems that are bonded to the electrical grounding system at each building.
It is not uncommon to find 20% or more of the grounded conductor current on the water pipe. I am not sure how much of a hazard that really it, but it is a big hazard to people working on the water line when you have an open service neutral conductor.
I am just not sure that 250.6 lets us eliminate the use of a required grounding electrode. I thought that CMP5 addressed this issue and said no, a number of code cycles ago, but I did not find anything in the ROPs.
jxofaltrds
Inspector Mike®
- Location
- Mike P. Columbus Ohio
- Occupation
- ESI, PI, RBO
http://www.ecs.csun.edu/~bruno/MultiGroundedNeutralFinal_4-17-7.pdf
?NESC Rule 092 - 1997
?D. Current in Grounding Conductor
?Ground connection points shall be so arranged that under
normal circumstances there will be no objectionable flow of
current over the grounding conductor. If an objectionable flow
of current occurs over a grounding conductor due to the use
of multi-grounds, one or more of the following should be used:
1. Abandon one or more grounds.
2. Change location of grounds.
3. Interrupt the continuity of the conductor between ground
connections.
XIV. LEGISLATION AND REGULATION
It is interesting to note the courts thinking on code and
legislature enactments. Wisconsin legislation states:
?Sec. 288C. Compliance With Legislation or
Regulation.
?Compliance with a legislative enactment or an
administrative regulation does not prevent a finding of
negligence where a reasonable man would take additional
precautions.?
To bad the Main is not a GFCI. If it tripped all day long bet some would want to fix it then!
?NESC Rule 092 - 1997
?D. Current in Grounding Conductor
?Ground connection points shall be so arranged that under
normal circumstances there will be no objectionable flow of
current over the grounding conductor. If an objectionable flow
of current occurs over a grounding conductor due to the use
of multi-grounds, one or more of the following should be used:
1. Abandon one or more grounds.
2. Change location of grounds.
3. Interrupt the continuity of the conductor between ground
connections.
XIV. LEGISLATION AND REGULATION
It is interesting to note the courts thinking on code and
legislature enactments. Wisconsin legislation states:
?Sec. 288C. Compliance With Legislation or
Regulation.
?Compliance with a legislative enactment or an
administrative regulation does not prevent a finding of
negligence where a reasonable man would take additional
precautions.?
To bad the Main is not a GFCI. If it tripped all day long bet some would want to fix it then!
- Location
- Massachusetts
A reasonable question.
As long as our distribution system uses a MGN I expect current on a GEC, I don't expect current on an EGC.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
The debated hazard of magnetic fields aside, if you lost the neutral then a very real risk exists.
Iwire will call me crazy, and I am, but I am in the school of thought where I firmly believe ground and neutral should be kept separate all the way back the utility transformer X0 bushing.
- Location
- Illinois
- Occupation
- retired electrician
Would that really change anything as far as "objectionable current? You would have a bonding connection to the water piping system at each building and you will still have the parallel paths for the grounded conductor current via the water piping system.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
If electrical distribution was done with EGC and neutral attached only at the transformer X0 bushing, then the water pipe connection would be to the _EGC_, not to the neutral. The objectionable current from the local supply neutral would disappear.
However, I am not sure if article 250 would even permit this installation! If the 'service' from the utility were to include separate grounded conductor and EGC, does article 250 permit an installation without a 'main bonding jumper'???
-Jon
- Occupation
- Licensed Electrician
How so? There would still be neutral current through the earth and the buried water pipes all the way back to the power plant, no?
You must have a MBJ. However with current codes, when the "service conductors" are underground you have to float the neutral at the house, pull an EGC from the house out to a meter pedestal and bond the ground to the neutral there. In practical terms that moves the MBJ out to the POCO xo.
jxofaltrds
Inspector Mike®
- Location
- Mike P. Columbus Ohio
- Occupation
- ESI, PI, RBO
Let's assume for a second that an electrode did cause a hazard. Does the code 'allow' us to remove that hazard?
Better yet does the code allow us to remove any hazard? Or is that assumed?
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Because the utility uses a 'Multi Earth Neutral' primary distribution neutral current will still have a parallel path through the soil, and some portion of this would flow though the various neutral connections and ground electrodes.
Moving the neutral to GEC bond to the transformer secondary, and then bringing an EGC to the home with no bonding jumpers in the home would eliminate neutral currents from the secondary on the common underground piping.
I _think_ but do not know that the currents on the GEC to the pipe caused by the secondary would likely be much larger than currents from the primary. I'd love to find out more.
Interesting. I guess this depends on where the meter itself is located. Since the main bond can be anywhere between the meter and the main disconnect, there is likely quite a bit of design choice about the location.
-Jon
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
Yes, because the neutral wont have a bonding jumper at the service, only the EGC.
mopowr steve
Senior Member
- Location
- NW Ohio
- Occupation
- Electrical contractor
I am with you 100%
Dont like the extra work but your right. I've seen a number of open neutral cases on utility side where considerable "objectionable current" sourced back to the transformer via shielding of cable and phone system wires to the extent of causing and near causing fires.
Im beginning to believe that this whole grounding/bonding of other systems together needs a referendum as to many parallel paths are being created.
I think Mike Holt even eluded to this that there should be only one point at which you provide a grounding electrode system which brings me to think also the XO bushing at transformer.
Unless as stated before discontinue the use of neutral systems all together and go to a phase to phase system. Maybe a long road but we've changed the light bulb.
- Occupation
- Licensed Electrician
It is becoming standard to put a meter pedestal with a main breaker at the property line and that becomes your first disconnect.
- Status