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Anonymous
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# Posted: 22 Jan 2013 20:53
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I have a EU2000i which powers ( via 10g wire ) a freedom marine 3000 inverter charger. This charges 4 6V golf cart batteries with a big 12v fuse between the batteries and the inverter. I also have a couple of 40w solar panels to maintain batteries while I am away.
My problem is trying to ground the system... My cabin is built on a mostly rock island with a few not a lot of dirt. I bought a ground "spade" to attach with copper wire and bury but am worried it would not be deep enough. Other option was to drill into the sandstone rock ( not sure how deep ) and pound some rebar into it and attach copper there...
Questions are:
- which method should I use ?
- what gauge of copper wire to use?
Thanks.
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bldginsp
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# Posted: 22 Jan 2013 22:29
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There are two main aspects to grounding. The first is a connection to earth which you are talking about here. A connection to earth gives a path for lightning to get to earth, and so not to you hopefully, and not to destroy equipment hopefully. A connection to earth also goes a long way to prevent there being a difference of potential between any metal stuff you have and the earth. If there is such a difference of potential, and you are standing on the earth when you touch the metal, you become the path for the current to get from the metal to the earth. But if the metal is connected to earth that difference of potential cannot exist.
The other aspect of grounding has nothing to do with the earth. It has everything to do with causing your circuit breakers to trip or fuses to burn in the event of a ground fault- when insulation on wires wears through and the metal frame or other conductive material on your equipment gets electrically charged, then you touch it and get a shock. For the breaker or fuse to work, there has to be a low impedance path for fault current back to the source of power, to complete a circuit. Then the circuit amperage spikes in the event of ground fault, and the spiking current trips the breaker or burns the fuse, opening the circuit and relieving the danger.
This is the task of the equipment grounding conductor (EGC), the bare or green wire run with circuits usually called the 'ground' wire. All your circuits should have these, and they must be bonded to the neutral at the source- in your case the generator itself.
Many countries do not require the connection to earth, since power systems do not require this to operate and it's extra work. But the EGC is essential for the breakers or fuses to work, and must be there as a basic safety feature. But it must be connected to the neutral, at the source, and not elsewhere. Sometimes people connect their EGCs to the earth only, with a ground rod, thinking they have 'grounded' the system so it's now safe. It is safe against lightning, (or, safer) but not safe against ground fault unless the grounds are bonded to the neutral at the source. Most generators have this done in the factory wiring, so when you plug in it's done already. If your generator has a breaker box and you wire it yourself, beware.
The size of wire you use to connect to earth in a small system is probably not very important. A #6 or #8 bare copper is probably fine. But, if it does not have a low impedance connection to earth it won't work well for lightning or relieving differences of potential. Get as deep as you can to soil that stays moist all the time. I think drilling and getting an 8 foot ground rod in place is a good idea.
If you really want to study grounding, get Soare's Book on Grounding published by the IAEI. Not really well written but the info is all there. If you understand conceptually what electricians are trying to acheive with 'grounding' and 'bonding' you'll always know what the right thing to do is.
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bldginsp
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# Posted: 22 Jan 2013 22:34
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Follow the inverter manufacturer's instructions for grounding and bonding on that piece of equipment.
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Rifraf
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# Posted: 23 Jan 2013 03:59 - Edited by: Rifraf
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To ground my 200 amp service I just bought a grounding rod from home depot ( 10ft long i think) and used a post ponder and a little water to force it down 7 or so feet, I would of went 9 or more but I think I hit a very large rock formation.
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sparky1
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# Posted: 23 Jan 2013 12:40
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Rebar is Never acceptacle as a Grounding means.
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Anonymous
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# Posted: 23 Jan 2013 13:37
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bldginsp: Thanks for the insight... I am on west coast so little lightnig. I am mainly concerned about people safety. I should have mentionned I am adding a breaker panel so that power from inverter will run into a main. I am guessing that this is where my main ground needs to be with a copper wire grounding the box to ?? ). Any options for this given my lack of soil to bury a metal in depth ? I will also look at the reference you provided..
why is rebar no good ? do you need a specific metal ?
Thanks again.
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Rifraf
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# Posted: 24 Jan 2013 12:58 - Edited by: Rifraf
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The grounding rods they sell are a polished type copper , I think rebar would rust and loose good contact with the points you connect to it. as well as rust in ground and get a poor ground connection in general that's my guess.
On a side note, the grounding rods I found at home depot were about 10 - 12 dollars.. not too pricey
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bldginsp
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# Posted: 24 Jan 2013 14:59
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If you have a main panel from which you will distribute all your power, and it is fed by an inverter, I think the thing to do is bring all your grounds to that panel, and land them all on a bar that is electrically connected to the panel. This means bring in the grounds with the circuits, and the ground from the ground rod, and a ground attached to any metal water piping, and a ground attached to any other metal piping (gas) and attach them all to the bar. Then, most important, bond the bar to the neutral. Do this only at this main distribution panel, not at any other panels down the line (if you ever have them). This main panel is your service, receiving power from your utility- the inverter, and you only bond grounds and neutrals at your primary service. You don't bond them elsewhere to avoid the possibility of return current passing through your grounds.
Rebar can make an excellent grounding rod, particularly if embedded in concrete. One 8 or ten foot length of rebar is probably not going to be as effective as a copper coated ground rod. A ground rod is the least effective of most electrodes just because it is so small and has limited contact with the earth. Rebar in a footing has much more contact. If you trench for piping or whatever, put in a #2 solid copper in the bottom of the trench for 20 feet at least, that's a good electrode. You are trying to get the best contact with earth that you can to reduce the impedance on the electrode. Typical ground rods work ok so long as you can get them down there and the soil they are in stays moist.
If you can't drive a ground rod 10 feet deep, you can dig a trench and bury it. Get it as deep as you can, again, trying to keep it in moist soil. If you are on such rocky soil you can't dig at all, run one or more #6 or #4 solid copper wires on the ground, or as deep as you can, for as far as you can- like 50-60 feet. That's going to cost a lot in copper, but a basic connection to earth is an important safety feature both for lightning and other imposed voltages.
I once saw a fire lookout building on top of a rock mountain with little soil where they ran solid copper wires from the building down the mountain side on several sides for hundreds of feet, on top of the rocky soil. Serious lightning threat there, so they took extreme measures.
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Anonymous
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# Posted: 18 Feb 2013 20:19
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Thanks very much for the thorough response bldginsp.. It sounds like the best bet would be to dig that deep trench ( as deep as I can anyway ) in as shady as spot as I can that gets wet and maybe attached the panel to a ground rod ( and then pour some concrete on it to broaden the contact ). Cabin is totally off grid so no steel water lines or gas lines to add to grounding. Maybe in summer I can water area while at the cabin and will be fine balance of year ( given I can't get very deep ). I get your point about bringing everything to the panel so will go this route. Thanks again.
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bldginsp
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# Posted: 20 Feb 2013 08:04
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You're welcome. Pouring concrete won't help with the ground connection, it's all about water content. Wet concrete and wet dirt do the same thing. The only reason rebar in concrete is a good ground is just because there is so much of it in any typical foundation, and more contact with earth is always better.
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toyota_mdt_tech
Member
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# Posted: 20 Feb 2013 10:28 - Edited by: toyota_mdt_tech
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Quoting: Rifraf On a side note, the grounding rods I found at home depot were about 10 - 12 dollars.. not too pricey
It will be from about $8 to $25 depending in type and diameter. I seen they have a small diameter and a larger one, plus they have copper clad steel or galvanized steel. The copper clad was the most expensive. Especially if you went with the larger diameter.
In my area, they are requiring 2 ground rods, so many feet apart tied into the panel ground. They can be sunk below grade to prevent a trip hazard or being impaled. This is for the main panel, not sure if its required for a sub panel.
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