Normal drop and a 4 meter box on the exterior. 4 SEs (NMT) going to the 4 panels under the back porch basement walkin.
Ground was taken from a water pipe that was on the downstream side of one of the 4 water heaters. Suretest had the ground impedance at the best recepticle at 7.3 ohms. The main water line was at the front of the building, some 45 feet away.
This “ground electrode condutor” entered the first panel and was connected to the neutral bus (Challanger, 100 amp panels).
The neutral bus was bonded to the panel enclosure with one of those little clips.
The three remaining panels had the neutral bus bonded to the panel boxes.
All the panels were connected with EMT, that was properly bonded to the panel boxes.
Was ground continuity proper? Where all the panels “service equipment”? Is the bonding of the panels, only through the EMT enough?
Sorry, no pictures. (Hey! Learn to be verbally decriptive.) :mrgreen:
If the EMT came through a concentric knock-out, then there should be a grounding bushing attached to one. If it is not concentric, then I believe the connector (with the EMT pushed all the way, so that the hub is in contact) should be adequate.
If you really have 7.3 ohms of ground impedence you should defer. This won’t clear a fault on a 20 a breaker and will take quite a while to trip a 15. Ground impedence anything above 1 ohm is a potential problem.
BTW this has nothing to do with the ground electrode. It is only testing the neutral to equipment grounding conductor, back through the main bonding jumper. In your case I would look for a loose EMT connector if they don’t pull a hard wire ground.
The ground isn’t really “taken” from anywhere. What you observed was either the metallic water piping being bonded, as required, or it was the grounding electrode conductor connection. If this was the grounding electrode conductor connection, it was in a not very desirable location in terms of functionality. If this was simply bonding for the metallic pipework, it’s fine. In any case, the location or the quality of the connection to the metallic pipework has absolutely nothing to do with your measured high ground impedance on any given branch circuit. I would also rather suspect a loose EMT joint, but it could also be a loose/marginal main bonding jumper in the serving panel.
To be clear, the water pipe, on the hot side of one of the water heaters, was the “grounding electrode conductor connection”.
I understand that the high ground impedance can have many causes (you would vomit if you saw this place, BTW: All “Chicago Code” approved with regards to the electric, or maybe it was just that the owner was a big wig in the local plumber’s union).
my point, and question, was about the bonding of the ground to neutral an only the first panel, with neutral bonded to metal on the subsequesnt panes (that little clip) and the EMT bonded between the metals of the subsequent panels.
You should only have the neutral bonded in the service disconnect enclosure. I am betting when you lift the bond in the other panels your 7 ohms will get worse.
The big problem with EMT is when you have a sloppy installation and they use the raceway for bonding. (no ground wire)
That was part of my point, Greg. All four panels had disconnects and all four were, for your purposes, were being treated and service equipment. i would have thought that, in such a case, they would have run the GEC into each panel and bonded it directly.
You only need to ground a service once but when you have the ground occuring in the service disconnect they will usually bring one to each enclosure. That still has nothing to do with the impedence you see with your sure test. It is only looking at the continuity between the neutral conductor and the grounding conductors in the feeder and branch circuits via the bonding jumper.
If your voltage drop number is reasonable the problem is in the EGC or the bonding jumper. You could disconnect the ground electrode entirely and the sure test should still show good ground impedence
