I’m looking at the grounding system on my new house and it just does not look right to me.
320 Amp service. As I understand it, the meter base will be wired to a 200 amp panel in the garage, and a nearby 200 amp disconnect. The 200 amp disconnect is wired to a 200 amp panel in the “unfinished basement” – which is actually just a really tall crawl space with a concrete floor.
Three ground rods and a ufer ground. One ground rod connects to the 200 amp panel in the garage, one ground rod connects to the 200 amp disconnect, and the third ground rod attaches to the 200 amp panel in the crawl space. Both 200 amp panels have the ground connected to the neutral.
The meter base and the 200 amp disconnect are not in place yet, and the ufer ground isn’t wired yet.
My understanding is that all of the ground wires should connect to one panel, and that is the only panel that should have the ground and neutral connected. This obviously isn’t wired like that.
Replies
I'm no electrician but my recollection from conversation with my electrical inspector is that every panel should have it's own ground rod and that the ground and neutral should only be bonded at the main.
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"You cannot work hard enough to make up for a sloppy estimate."
The panel is the basement is definitly a NO-NO.
The neutral should not be bonded to the ground at that point. And you need a 4 wire connection between the disconnect and main panel.
And there is no need or advantage to ground rod at that point. Only EXTERNAL structures need additional ground electrode system.
You don't need all of the ground electrodes. By the code the ufer is enough. Don't need any ground rods.
But there appears to be lots of confusion or local amendments about this.
Now 400 amp service is a bit trickly.
The neutral can be bonded to ground electrode system anyplace between the disconnect and the weather heat for overhead service. That is what the picture shows in the NEC handbook. Basically that means at the at the meter or at the disconnect.
But in either case the disconnect and the meter need to be bonded together. I THINK that can be done with with wire or metallic conduit and using special bonding bushings and nuts.
And where you have more than one electrode I THINK that the it bonded at one place and the other(s) at other places in the ground electrode system. IE the disconnet, the meter, or the other electrodes.
Lot of special and detailed requirements on this and I probably have several wrong. But I know that what you describe is also wrong on several points.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
All your grounds must be bonded into one system; rods, pipes, ground busses, and ufer.
All your neutral returns must also be bonded into their panels' neutral busses, then all the neutral busses must be bonded together.
The neutral and ground systems must, and can only, be bonded together at or near your primary (main) "Hot" system disconnect. IOW, the ground system cannot touch the neutral system more than once.
SamT
That agrees exactly with my understanding - plus I thought that the three ground rods should be wired in series to the ground connection on the main panel with one contiguous wire.
I asked the electricians and they were certain that it was wired correctly.
I mentioned it to the state licensed inspector. He said that since the crawl space panel was NOT a subpanel of the garage panel, that both should have the ground tied to the neutral.
Oh well, if the city inspector says it passes inspection, I can always fix it after they are all gone.
Paul, having more than one ground rod in a system is a big no-no from a lightning protection standpoint (and hence the requirements in the NEC). Granted there can be multiple grounds rods if they are connected together properly into a grounding ring, and I am NOT referring to the ground wires within your electrical wiring, but a separate ground ring. I manage 9-1-1 centers and this is a huge issue for us -- we are like a lightning magnet with all of our electronic equipment. The NEC allows the grounding and grounded legs to be bonded together only at the main service entrance, not at any of the subpanels. Bonding at subpanels, and having multiple ground sources, allows lightning to flow "backwards" through these wires in its efforts to equalize the potential throughout the building and blows the electronic equipment as it does so. One point of ground per structure, and only bonded at the service entrance. Very important.Woody
For a detailed and interesting discussion of grounding electrode systems and lightening, check out the following:http://www.iccsafe.org/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=11;t=000932;p=2
I had a long detailed reply with copies of the code, but my system locked up and it took too long to do it again."Paul, having more than one ground rod in a system is a big no-no from a lightning protection standpoint (and hence the requirements in the NEC)."That is not correct.In fact is a ground rod is used as a ground electrode it either has to be tested to be less than 25 ohms or a single ground rod needs to be installed at least 6 ft way.I also list a series of different types of things that can be used as electrodes and any of them that exist MUST BE USED.The key is tht they are treated as a Ground Electrode SYSTEM and only bonded to the neutral at one place in the system, the service entrance."Bonding at subpanels, and having multiple ground sources, allows lightning to flow "backwards" through these wires in its efforts to equalize the potential throughout the building and blows the electronic equipment as it does so"Bonding at a sub-panel also can lead to electrical danagers other than lightining damage.The code also allows a SUPPLIMENTRY ground electrode to be connected to the EGC at equipment. However, it can't replace the EGC..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
You don't specifically state -- is it an attached or unattached garage?
There is a breezeway between the house and garage, but a common foundation and roof, so it has to count as attached.
Hard to say if that counts or not.
If your view never changes you're following the wrong leader
The panel in the garage serves several circuits in the house, so I doubt that the inspector would consider them separate.