In the facility that I work in there was an audit done for electrical safety(mainly to shut me up). One of the findings was a current of 11.4 amps on the wire that runs from 2 ground rods to the ground bus in the main service panel(2000 amps). Everything seems to be bonded (building steel, water lines before the meter, etc.) and I'm not worried about someone touching their tongue to building steel and exploding or anything like that, but my main concern is for fault detection and the safety of personnel and equipment in the event of an undetected fault. The folks I work under don't seem too concerned and I've been known to assume a situation to be worse than it actually is. But for my own peace of mind I would like to hear what some of you folks have to say about it.
You didn't say what type voltage system, grounded or ungrounded.
14 Amps may or may-not be a problem.
I would think if it is less than 1% to 3% of the systems unbalanced of the ungrounded conductors involved, it may not be a serious problem. Depends on the use of the system.
Had seen a system up-grade, for a dwelling, from a 2W 120V to 3W 120/240V system. Had been alerted by a contractor, other than the contractor doing the service change, that he had been called for a service call at the site. He told me that on the 2W 120v system that when the ungrounded conductor was carrying 27 amps, the grounded conductor was only carrying 9.5 amps.
When called to inspect the service change for release to the utility, I checked the 2W system and got the same type readings. The ungrounded conductor was carring about 65% more current than the grounded conductor and the GEC to the city water was carring the 65% current that the grounded conductor was not carrying.
Contacted the utility, the engineer asked me to OK the service and they would replace the triplex ( one conductor was not used since this was a 2W system) from their transformer pole to the dwelling.
After the utility changed their metering to the 3W system and a new triplex drop to the dwelling, The grounded conductor was still only carrying about 35% of the ungrounded conductors when turning "OFF" all CB's on one leg of the ungrounded system and the water GEC was carrying about 65%.
Apparently, the city water system had a better (lower resistance path) parallel path back to the utilities pole mounted transformer grounding system than the aluminum service drop triplex. There were 6 other services attached to the transformer, so there were many other parallel paths of the grounded conductor(s).
I could not justify the Water GEC carrying about 65% of the grounded conductor return path. I would liked to check all of the services water GEC for amps vs the ungrounded conductors.
I wanted to follow-up more than I did, but the city just let the situation pass.
Re: current on the ground wire#76348 01/19/0102:18 PM01/19/0102:18 PM
I hear that the current flowing on the (copper) water piping has a very detrimental effect on the pipes and adds minerals to the water. How serious a problem is this? I hear about it every once in a while, but never in depth.
My guess it that this sort of thing is quite common and that it is often overlooked because of the difficulty in tracing the source of the problems
Re: current on the ground wire#76349 01/20/0111:46 PM01/20/0111:46 PM
I would like to perform tests on the six neutrals, grounding electrode conductors, and the secondary ground conductor at the distribution transformer. Should all the service neutrals be grounded to a common metal water pipe, this would connect them in parallel, with each other, and with the earth path back to the transformer secondary ground. It would be interesting to see what the current distribution would be, with a controlled load applied to all six services. It would also be interesting to see what develops, should the piping be changed to plastic. Any broken service neutral connection would become immediately obvious. The first clue would be smoke from computers, tv's, and whatever.
Re: current on the ground wire#76350 01/22/0110:25 PM01/22/0110:25 PM
On a grounded system with XO grounded at the utility transformer and at the service, there will ALWAYS be current on the grounding electrode system. Current does not as many like to say "follow the path of least resistance", it follows all paths that are available. The current is divided among the parallel paths in relation to the resistance of the paths with the most current flowing on the path will the least resistance. In your system, you have the earth in parallel with the grounded conductor between the transformer and the service. The better your grounding electrode system, the more current will flow through it. Don(resqcapt19)
[This message has been edited by resqcapt19 (edited 01-23-2001).]
Re: current on the ground wire#76352 01/23/0105:38 PM01/23/0105:38 PM
Of my post of the 65 percent ( % ) of the grounded conductor current returning on the water GEC, I did not open the water GEC to check the voltage across the open connection for I did not want to take a chance on doing harm to some load equipment.
I suspect that the actual VD would not have be very high voltage because of the near-by ROD GE (Grounding Electrode).
But, I do wonder of the dangers of someone servicing the water piping.
The city's water piping had a 14" line about 8' from the utility transformer pole and ran by several utility primary lines' poles. There was/is also a 6" water line on the opposite side of the street which supplied water to at least three of the dwellings, maybe all of the dwellings, served by the transformer.
It just doesn't seem correct to have 65 % of the unbalanced current returning to the source on the water GEC. It certainly is not returning to the transformer with the "circuit conductors" as implied by 250-24(b)(1).
I wonder what would happen if a bolted ground fault would occur at the service panel.