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Joined: Jan 2005
Posts: 5,445 Likes: 2
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"Saving money" often turns out to be an expensive choice.
Compared to the costs of digging the ditch, running your circuits, etc., the cost of feeder wire is quite small. At least run your wire in pipe- pipe at least one size larger than you need- so you can replace it easily if you ever need to. If you fail to run in pipe, or fail to bury it two feet down (minimum), my experience tells me you will be replacing it after a few years. Why dig twice?
Two ground rods? Why? One is plenty- though it would have been better to have placed a "UFER" in the slab. Oh, well, hindsight and all that!
My practice -and please note that there is room in the code for a few different approaches here- is to: -Run a ground wire from the "main" panel to this "sub" panel, landing it on a ground buss (separate from the neutral buss); and, -Plant the rod, and connect the wire from it to this same ground buss. Of course, I make sure the neutral buss is NOT bonded to the case.
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Joined: Jan 2004
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Two ground rods? Why? One is plenty Hey Reno, what about 250.56?
George Little
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Joined: Mar 2005
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i am in washington and two ground rods are required by WAC (washington administative code) unless you pay to get an engineering report testing the ohms to PROVE you have 25ohms or less and even then the AHJ's dont like it and you have to go to their supervisor to get a blessing...not worth the hastle.
george the garage will have little load on it lights (some flourescent mostly incandescent) few plugs for power tools 120 volt(drill,saw ect...)garage door opener. and a small office in it more plugs a 2000 Watt heater and a computer in it. maybe a future rv plug down the road. are harmonics going to come into play here?
the gec will goto the ground bar(floating neut) in the panel with the rods and building bond, is this what they mean single point grounding?
if buss is rated at 75 degrees then its ok, how/where is that listing?
thanks again guys, h20
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Joined: Dec 2003
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The 75 degree reference may be refering to 110.14(C) for termination temperature ratings.
Earl
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Joined: Dec 2003
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What do you mean by "floating neutral"?
Earl
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Joined: Jan 2004
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If your panel buss and breakers are rated for 75 degree C and the grounding buss is bonded to the metal enclousure and the neutral buss is "floating" (not bonded to the enclosure then it sounds like you are going to be code compliant. The grounding electrode needs to go to the grounding buss and the panel must have a main and the neutral must be full size based on what you said about the load. The grounding electrode conductor minimum #8 but most installers will run #6 because it can be installed without being in conduit. No concern about harmonics. Single point grounding is another topic all together and what you are doing is just plain old grounding.
George Little
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Joined: Jan 2005
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250.56...the "25 ohm or less" requirement....good point, George! And Irrellevant.
I sat "irrellevant" because this part of the code addresses the "grounding system." As the garage being discussed is a separate structure, and not a separate service....any ground rod driver would technically be supplimental to whatever there is at the main service.
Now, some may say 'but the garage is so far away.' In this case, "far" is a good thing. As documented in the American Electricians' handbook, as well as implied by the NEC requirement that supplimental electrodes be at least six feet away, the farther apart the ground rods are, the more evvective they are. Seems backwards, but there it is!
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Joined: Jan 2004
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Reno- Read 250.32(A). Each separate Building or Structure fed from a common Service needs it's own Grounding system as discribed in Part III. I understanding your reasoning but every inspector I know asks for a Grounding Electrode system at each building where there are more than one circuit.
George Little
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so george "the neutral must be full size" then #8 would be full size since it doestn't have an * and is rated at 50 amps. correct?
h20
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Joined: Apr 2004
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Look for a label in the panel that says something like "Neutral terminations rated 60/75C". If you have that, then you can use the 75C rating of your wire.
Mark Kent, WA
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