Grounding 12 volt system

[Peppyy]

I know that vehicles have the negative terminal of the battery hooked to the body and frame, (or at least most new vehicles). Should a 12 volt battery bank in a house or garage be grounded to the earth?

In my 12 volt distribution panel I made, I included a seperate buss-bar for "Equiptment ground" which is earth ground. I have an 8' ground rod I was planning to attach the bar which is directly attached to the steel cabinet.

The negitive buss-bar is isolated from this at the moment which makes sense to me.

The bar on the right is the ground and the one on the left is the negitive. I am planning on using standard 12/2 romex for my 12v lighting and 12v outlets in the garage and thought it would be a good idea to ground the fluorescent fixtures, cabinet, etc.

These are the lights I plan to use. This one is running on 8 AA batteries in this photo.

I would also like to know if I can use the same ground rod for my inverter ground?

[georgeodjungle]

with my trace inverter directions said to only have one common ground.

[joelhacker]

Without giving a definite Yes or No answer, just a little advice

that I ususally use when working with grounding problems before

connecting them into a "solid" connection.

1. Take a voltmeter and measure the potential between the

two points.

2. If you see significant voltage potential between the two

points, grab a 12 or 120 volt light bulb and see how much

current (power) is between the two points.

3. If the light bulb lights, even dimnly, that is a significant

warning to me and requires some more investigation as to why

there is so much current/energy/power that is trying to "escape"

towards the ground potential...

Normally, that is how I've saved my rear a few times in these

type of situations.

Also, Just because a car uses common ground, doesn't mean that

you have to have an earth ground.  Just be careful before you

try hooking all your grounds together...A ground does not

necessarily mean "negative" or "Neutral".

Mabye someone else here will know what "one ground" means in

Trace Lingo...

[Tom in NH]

Someone correct me if I'm wrong, but somewhere I remember reading that electrical codes state that anything over 40 volts should have an earth ground.

I had a Xantrex inverter that blew up in a glorious display of smoke. I always blamed it on the fact that I had wrongly connected the negative battery terminal and the AC ground terminal to a common earth ground. I have a new inverter that runs fine, but the DC is not connected to the AC. I wouldn't recommend grounding the 12v. If you must, ground the ac.

--Tom

[drdongle]

I think it safe to say there is no simple answer to this question. The purpose of a ground is to shunt hazardous currents to ground rather than through a persons body. Now 12 volt systems are very safe in that regard, even though it is the current rather than the voltage that injurers and kills, you need enought potential

(voltage) to establish a current flow, and 12 volts just won't do it.

However lightning is an ever present problem and if there is any possibility of lightning striking the system and introducing dangerous voltages/currents grounding is a very good idea to be grounded. As your house also has grid power if there is the remotest possibility that there could be a cross between systems grounding is a good idea. That being said if you do ground the system the usual convention is to ground the negative side. Unless your in the Telecom business in which case you ground the positive side.

If in doubt, ground it.

[wpowokal]

OK with regard to DC grounding, this is how I have configured my sytem, one must accept here that different countries have different rules.

I run a 24V DC system, now ground is supposed to be zero potential, and here in Australia there are rules on the effectiveness of a mains (240V AC) ground.

I have a earth rod that the battery negatives are connected to, also there is a connection from the inverter to this ground, a light (small) wire for hum protection.

The mains from the inverter (240v here), is fed to a distribution board that has earth leakage protection. At this point the neutral and earth are tied to a ground rod, this is the only connection to ground for the high voltage side. This is necessary for correct operation of the earth leakage protection.

Earth leakage protection detects any short circuiting of current to ground, ie not returning via the neutral connection.

This is a very effective safety facility that protects people and equipment.

Unless I have totally miss-understand the rules, the same ground rod can be used for both battery earth and mains earth/ground.

In theory the ground rod in both cases should be sufficiently effective that both are at the same potential (ground or zero volts). That is if you connected a metre betwen both ground rods ( if you have two) then there should be very little potential (voltage) between each, which means there is an effective earth.

If you are in an area that has poor ground moisture then an effective ground rod can be obtained by creating a hole larger than the ground rod ie at least 6'(1.8m) deep, then filling it with bentinie clay, place the ground rod into this clay. Bentinite clay attacts and holds moisture, this helps create an effective earth.

Ok just my opinion, because an effective ground can never be over stated.

allan down under

[ghurd]

Not sure how this relates, but yesterday I was called to look a solar panel hit by lightning.

The lightning actually went for the 1000 gallon air tank, about 5 feet out from the building and 12 feet below the PV. The air tank is in a damp area on 6"x6" treated lumber.

The lightning hit the 1.5" iron pipe where it entered the building, knocked a 3"x10" hole in the wood siding, ran 10" up to the solar panel wire and blew off 3" of the outside insulation but not the individual wire insulation, 3 feet up the wire to a staple, and into the metal facia, 50' across the metal roof to the telephone box, and melted all the buried phone wires to the pole, about 150'.

At the same time, part of it went out the rubber air line about a foot inside the building, burning 6" of the low side, and 30 feet down the air hose at the first coupling, that was on the ground outside, the ends of the rubber are a little chared.  It still holds 100 PSI.

The charge controller is shot, but does not look physically damaged.

The caps blew off the battery and shot a lot of acid out around the room, no visable damage and it still tests full voltage.

Strange.

I did NOT install this system.

G-

[Peppyy]

It looks indeed as if this is a matter of opinion. My copy of the NEC is from 12 years ago and since code changes every 3 years I can't go by that.

The inverter warns only that it needs to be grounded to the chassis ground in a vehicle. This would indicate that there is no connection to earth ground in this type of instalation and that both the ground and the vehicle negitive are therefore the same potential.

My system is located where the grid is only available by way of an extention cord at the present time and I do not forsee using the equiptment I have in any way that the inverter could be connected to the grid.

It makes the most sense to me that the steel equiptment boxes and fixtures including the inverter should have an earth ground which is seperate from the 12 volt system however this would then be concidered an isolated ground system. No common connection between the neutral conductor on the inverter and earth ground.

Now I am getting even more confised.

[drdongle]

I have one more conformation that lighting is WEIRD, and appears to follow it's own rules.

[drdongle]

As you have two segrigated systems seperate grounding is OK but not necessary. If the run is not to far go ahead and use the same ground rod ( saves you the cost and labor for a second rod). Also if there happens to be an unknown path between the two systems, ( say a water pipe running close by, RE the lighting post on this thread) this elininates any differance in potentual between the two systems.

[OPEC BUSTER]

I think Allan was right on the grounding system./ I would like to add that grounding is a very tricky thing. what works in one place may not in another.I TRUST in COPPER TUBING burried under ground. The advantage is it contacts more earth to disipate any faulty current. I also have a grounding rod BUT it IS VERY important that ALL GROUNDING BE TIED TOGETHER AS ONE GROUND! EVEN THE TELEPHONE GROUND SHOULD BE TIED TO THE SAME GROUNDING SYSTEM, this way they all work together to disipate the unwanted dangerous currents.

Otis