Battery Bank Grounding

Anawa · January 2015

A recent post made in December raised some questions for me concerning battery bank grounding.

As soon as my structure is completely dried-in and it warms a bit outside, I will be installing an Outback FP2 system. The general wiring diagram for the FP2 shows a ground from the battery box to the DC grounding buss.

http://www.solar-electric.com/lib/wind-sun/FP2_Quick_Start_Guide.pdf

Similar to the recent post on the other thread, there is not much connection information on this ground at the battery box. The assumption by the forum contributors was that the battery bank was installed in a metal enclosure that, most likely, had a grounding buss or some kind of lug.

I would like some thoughts on how to go about grounding my batteries: (a) Does the metal bins that the forklift batteries sit in suffice as a "battery box" that could be grounded?, (b) If so, what kind of connection is required between the grounding cable and the metal bin?, (c) How should the separate "boxes" be connected?, (d) Will #4 bare cable be okay?

PS: I intend fabricate a movable and vented battery box made from wood to "cover" and protect the batteries.

Thanks
Anawa

BB. · January 2015

Re: Battery Bank Grounding

Grounding large pieces of metal/metal around electrical/metal plumbing/etc. is intended to prevent the metal from reaching "dangerous voltage/levels of current" by shorting the offending cable to ground--Which should pop the fuse/breaker.

With batteries, typically the cables on/around the batteries are not fused at the battery terminal, but somewhere else (at the main box where the cables terminate, etc.). So, there is no fuse to pop. Letting the box "float" means that an unintended connection can "energize" the box relative to ground--You could get shorts (with hand tools, etc.) when working about the "floating metal box". In general, grounding the box would probably be safer.

I would probably use jacketed cable around the battery (grounding, cabling). There is sufficient electrolyte around (splashing, misting) and such that can get on the cable--And it is very difficult to clean/neutralize stranded cable. Plasic/Rubber Jacketing will keep the cable cleaner/help the copper to last longer (reduce corrosion).

-Bill "in my humble opinion" B.

Ethan Brush · January 2015

Re: Battery Bank Grounding

IMO bonding the battery box is a bad idea. I dont like the greatly increased chances of creating a short while working on or around the batteries, dropping a spanner, etc.... Remember, one of the big disadvantages of a grounded system is that it makes a line to ground short circuit possible.

Anawa · January 2015

Re: Battery Bank Grounding

Not sure, but it seems that there are opposing view points on this issue. Perhaps my convoluted questions immediately propelled the discussion into the mystic bowels of "grounding-dom". For that indiscretion, I humbly apologize. Maybe a better way to understand what needs to be done is to simplify my question as: Does the battery bank require grounding? We can go from there.

FWIW, The fork-lift battery bins will be sitting on a concrete slab that is "tied" to the Ufer grounding system by virtue of connecting rebar between the foundation, concrete walls, and then the slab. Don't know if this information is germane, but throwing it out there.

Thanks
Anawa

gww1 · January 2015

Re: Battery Bank Grounding

Anawa
I installed the same system you are about to install. I remember seeing what you referanced in the installation manual. I did not ground my battery bank and I did try to follow the instructions in outback manual. I may be dreaming this, but my vauge memory seems to recall a statement in the manual that said the ground from the negative battery lead was unneeded if you where using the outback mounting plate and ac/dc sub panels. One thing is for sure. If you study the manual, you will be able to see if my memory is valid or not, cause what was in the manual will not change just cause I remember it. It will be in it or it wont.
Cheers
gww

I will say that the wiring diagram you linked to shows one. The inverters have a big ground lug on them that the manual had a ground coming from the battery negative to. I believe the diagram you linked is covering something differrent. I still didn't do it but cant see where grounding the steel battery case would hurt.

Anawa · January 2015

Re: Battery Bank Grounding

Thanks, gww. I'll review the manual more closely. If I can pass muster according to Outback on this issue and not get tangled-up in the grounding debate, it will be a blessing.

Anawa

gww1 · January 2015

Re: Battery Bank Grounding

anawa
I am sorry. I added content after you read my post.
gww

Cariboocoot · January 2015

Re: Battery Bank Grounding

Ethan Brush wrote: »

IMO bonding the battery box is a bad idea. I dont like the greatly increased chances of creating a short while working on or around the batteries, dropping a spanner, etc.... Remember, one of the big disadvantages of a grounded system is that it makes a line to ground short circuit possible.

This doesn't make any sense.
Ground in itself has no inherent Voltage potential to either positive or negative so connecting the battery box to Earth ground does not increase the risk of shorts. The battery terminals are the biggest risk to dropped-tool shorting and that will not change just because the box around them is grounded.

I think you are referring to the combination of connecting negative to ground and then grounding the box, making it essentially one big negative terminal all around the batteries. There is not a significant increase in risk from doing this, but neither is it necessary to ground a battery box.

In fact DC grounding is largely unnecessary, but in some instances required and in others potentially helpful.

Regrettably it is not as simple as "you always do it like this".

Ethan Brush · January 2015

Re: Battery Bank Grounding

Cariboocoot wrote: »

This doesn't make any sense.
Ground in itself has no inherent Voltage potential to either positive or negative so connecting the battery box to Earth ground does not increase the risk of shorts. The battery terminals are the biggest risk to dropped-tool shorting and that will not change just because the box around them is grounded.

You are right, if the system is ungrounded. However If the system IS a grounded system, then earth, or anything connected to it, will have potential to the ungrounded conductor of the system.

I think you are referring to the combination of connecting negative to ground and then grounding the box, making it essentially one big negative terminal all around the batteries. There is not a significant increase in risk from doing this, but neither is it necessary to ground a battery box.

Yes that was the situation I was envisioning.

In fact DC grounding is largely unnecessary

I agree! But...there is that ugly word "grounding" again that means three different things. We should all (including me, I forget to practice what I preach often) be specific when we use the word "ground" and clarify if we mean A) providing a fault path back to the source

connected equipment to earth C) connect one conductor of an electrical system to earth. These are the three things "Grounding" generally refers to. Note that A has nothing to do with the earth/dirt at all. I am a fan of calling A "bonding"

Alaska Man · January 2015

Re: Battery Bank Grounding

My bank is not grounded, but everything else is.

BB. · January 2015

Re: Battery Bank Grounding

If you have lightning in the area--I believe that grounding the battery bank is a "Good Thing" to keep lightning energy from progressing beyond the battery bank.

Grounding to pop breakers in a short circuit--A good idea. But floating can work too (basically, if you short to a floating metal structure, then there is no short).

Of course, if there is a second short later--Then all bets are off.

In industry/marine usage--Floating power systems have manual or automatic checks to ensure that the system is "still floating". If there is a single short to "something else that is grounded"--Then the system posts a fault condition for somebody to repair.

-Bill

Battery Bank Grounding

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