mian grounding electrode

[george blanchet]

dear friends, i have a commercial customer (motel) who is experiencing pin holes in the domestic water line 90% hot/10%cold. the main grounding electrode is carrying 3.50amps from the mdp to building steel.
several equipment grounds have amperage across them from the mdp to the transformers,sub panel and equipment ranging from 3.5amps to 7amps.
no voltage readings have been taken at this moment. please advise on what would cause the problem on the domestic waterline holes?

 

[charlie b]

The grounding electrode system should never carry current, except when serving to clear a fault. If there is current, then there is a high resistance connection between a conductor (or other current carrying metal part) and the external (i.e., not normally current-carrying) metal part of some component, somewhere in the system. If the current is 3.5 amps on a 120 volt system, that means the resistance to ground, at the fault point, is no more than about 34 ohms. A conductor with some of its insulation partially rubbed off could account for this type of high-resistance fault.

My first suggested step in troubleshooting is to make sure the current really is there. What type of meter did you use (analog or digital), and how did you set it up to read current in these ground paths.

If the current really is there, then my next step would be to try and isolate the faulty component. Turn things off one at a time, and see if the current in the grounding system disappears. If that fails to isolate the problem, then turn off everything except the main breaker. See if there is current now. If not, then turn things on one at a time, and see if the current comes back.

Once you have isolated the fault to a single (or perhaps more than one) circuit, then start opening its outlets one by one, looking for worn insulation, or insulation rubbing against metal, or some other obvious signs of damaged insulation.

 

[wbalsam1]

Hi: Could it be grounded conductor return current from an earlier installer leaving a bonding screw in within a disconnect for the dryer or similar application sending the neutral current to the equipment ground at a location downstream from the main service equipment and grounding electrode system? I've seen this many times over the years.

 

[ghostbuster]

As Charlie says, make sure this is real ground current. A quick way to determine the source, is to perform "net current measurements" on the individual feeders. The feeder and the actual piece of equipment will then be quickly identified(for excessive ground current leakage).

 

[LarryFine]

George, it's entirely possible that the erosion has nothing to do with the electrical system.

 

[brian john]

It is my understanding, that most corrision related to electrical current is DC related and AC has not been proven to be a source of pin holes.

But as noted any grouind current issues should be resolved, for many reasons, besides pin holes.

http://strathmore-belpre.org/Pinhole leaks.htm

http://www.washingtonareapinholes.com/

thewre arew several ways to isolate neutral grond issues (the main source of ground current) I have posted this before.

There are several ways to locate this problem.

1. Perform zero sequence readings on each branch circuit (if possible) use a True RMS amp clamp and measure the phase/phase and grounded/neutral coonductors at the same time the circuits with any amperage are the culprits.

2. Measure grounded/neutral conductor voltage at the panel (should be close to ?0? millivolts) circuits with any loads should have an increase in measured voltage (between the grounded/neutral conductor and the Equipment grounding conductor (copper conductor or conduit makes no difference). If the voltage is low, similar to the reading in the PDU, that is a suspect circuit.

3. During a schedule outage turn off all the branch circuit breakers, unplug loads if possible and remove the grounded/neutral conductors from the neutral termination bar. Utilizing a low voltage megger 50VDC 0r 100 VDC (I use a low voltage megger to avoid damaging equipment with 500 or 1000 VDC meggers we normally use. The neutrals that megger bad, ?0? megohms, need to be traced out and the ?SHORTED? grounded/neutral conductor will need to be replaced, repaired, lifted depending on the exact nature of the problem.

 

[don_resqcapt19]

Charlie,

The grounding electrode system should never carry current, except when serving to clear a fault. If there is current, then there is a high resistance connection between a conductor (or other current carrying metal part) and the external (i.e., not normally current-carrying) metal part of some component, somewhere in the system. If the current is 3.5 amps on a 120 volt system, that means the resistance to ground, at the fault point, is no more than about 34 ohms. A conductor with some of its insulation partially rubbed off could account for this type of high-resistance fault.

The grounding electrode system will always carry some current as it is in parallel with the grounded conductor. In most cases this current will be much less than the 3.5 amps in application, but in the case where there is a common underground metal water piping system the current on that grounding electrode system will often be 25% or more of the total grounded conductor current. Also the grounding electrode system should not play a big part in clearing faults that originate on the load side of the service disconnet. That is the jog of the EGC(s) and the main bonding jumper or system bonding jumper in the case of SDS.
Don

 

[mdshunk]

I seem to remember a thread about high water PH (purposely, due to increased water treatment chemical post 9-11 in certain major cities) causing some pipe erosion. Can't put my finger on that thread now.

 

[mdshunk]

3. During a schedule outage turn off all the branch circuit breakers, unplug loads if possible and remove the grounded/neutral conductors from the neutral termination bar. Utilizing a low voltage megger 50VDC 0r 100 VDC (I use a low voltage megger to avoid damaging equipment with 500 or 1000 VDC meggers we normally use. The neutrals that megger bad, ?0? megohms, need to be traced out and the ?SHORTED? grounded/neutral conductor will need to be replaced, repaired, lifted depending on the exact nature of the problem.

Now that's an awesome tip! Do you happen to have a link to the low voltage megger that you like to use for that? Would an ordinary ohm meter suffice, or do you believe that you need the 50 or 100 volts of 'umph' of the low voltage megger for finding certain N-G faults?

 

[ptonsparky]

We often, every day, use a Greenlee DVC6 tester for these types of ground faults and have never been disappointed. It acts much like an old Simpson meter. Placing one lead on the conductor and another to ground or EG, a good conductor chirps as it charges. Just like a capacitor. Once it stops remove one lead and wait a few seconds. If it chirps again, maybe you have a problem.

Really interested in knowing if we should be using 50 to 100 volts. I would think the neutral to ground fault would almost have to be bolted, not high resistance, to add significant current to a water line. Not arguing just really curious.

 

[NoVA Comms Power]

I also use Brian's posted procedure (Step #3) in my quest to "seek-out and destroy" improper (load-side) Neutral-to-Ground bonds ("shorts") ...

... although I've always used a "standard" continuity test instrument. (Fluke 87)

I too am interested in other's opinions re: the use of meggers for this task.

 

[brian john]

Pton/MD the reason I use a 50-100 VDC megger is to minimize damaging any sensitive electronic equipment plugged into the branch circuits and shorting a plug strip TVSS (giving a false reading) with 500 VDC or 1000 VDC. On a branch circuit I would prefer the higher voltage, but opt for the lower voltage for reasons stated.


I carry 5 meggers for a variety of reasons and test one 1000-5000 VDC, one small 500-1000 VDC compact light weight, one 50-1000 VDC, one analog battery hand crank (it is embarassing to have a dead battery this one over comes that issue) this megger also has an analog volt meter and in conjunction with my analog Simpson I use for phasing ATS's utility to generator, I prefer the analog as the response is easier to watch and one 10-100 VDC for ESD floor testing.

http://www.avobiddle.com/bmm80.htmTHIS BMM80 is only 50-500 VDC mine same number is 50-1000VDC But the spec sheet states 50-1000 VDC

 

[mdshunk]

Pton/MD the reason I use a 50-100 VDC megger is to minimize damaging any sensitive electronic equipment plugged into the branch circuits and shorting a plug strip TVSS (giving a false reading) with 500 VDC or 1000 VDC.

Understood, but is there any benefit from using 50-100 volts, as opposed to the volt or two from a DMM?

 

[brian john]

For this particular issue most likely the answer would be no. I just prefer meggers *1, but when you get into distribution equipment, the 1000 VDC is a must. A continuity tester will not show up on insulation breakdown.

*1 Often when we are tracing down grounded neutrals the cost runs into 5 figures for a day ($20,000.00+) I think my customers feel better seeing the techs utilizing a megger (test equipment) in lieu of a simple flashlight with lead.

 

[mdshunk]

*1 Often when we are tracing down grounded neutrals the cost runs into 5 figures for a day ($20,000.00+) I think my customers feel better seeing the techs utilizing a megger (test equipment) in lieu of a simple flashlight with lead.

Obviously I'm in the wrong end of the business. :grin:

 

[brian john]

Obviously I'm in the wrong end of the business. :grin:

MD: 2 men 8 hours during the week to look for obvious problems, 10 men (with meggers) 150.00 an hour (Doubletime, on a Sunday) for 12 hours, plus one hour travel and equipment rental (equipment calibration once a year), report time on Monday, meeting with customer and it gets to be like any other job.

Oh and 36 years of working weekends, week nights and at one time every holiday (I gotten away from the holidays for me and my employees).