importance of earthing a rack battery and its cabinet ??

[Urge38]

Just wanted to ask if people earth their rack batteries and the cabinet??

my rack batteries have a earth threaded hole, with the earth logo on the front face of the batteries, and the rack has a earth block,
only on all the you tube videos, I don't see no one earthing there's


I was thinking to connect each battery (ie its metal body) via the screw on the front face showing the earth logo, all to the rack cabinet earth bus and then one earth to a ground spike.

is this needed???

 

[stienman]

Earth grounding is intended for safety from electrocution. It keeps human accessible metal parts electrically connected to ground so someone standing and touching the metal would never feel a shock, even if a failure occurred.

Failure modes of battery racks include not just the battery positive or negative shorting to the metal enclosure. They also include the charge controllers shorting the solar panel voltage to the battery positive or negative, or the inverter shorting AC input or another higher voltage to the battery positive of negative. If only one of the above happened, the enclosure would never reach above the battery voltage, but if the battery positive or negative shorted to the enclosure, and a solar charge or inverter failure put a high voltage onto the battery connections, then the enclosure could achieve a high voltage if it wasn't properly grounded.

It's not likely, but in general all power metal enclosures should have one or more earth ground connection point, and they should all be connected to a nearby grounding rod. This way any number of failures could occur, but electrocution by touching the outside of an enclosure is prevented.

So whether your local codes require it or not, it's safer to ground it than it is to leave it floating.

As a side note, different equipment may ground one or the other side of its supply and/or output. Don't assume that the negative of the batteries and the negative of the solar panels are grounded, and don't connect them to ground. Some individuals, thinking that since cars and RVs are wired this way do the same in fixed power applications, but it's not necessary, and it can lead to unsafe situations when equipment is mixed with positive grounding equipment.

 

[Urge38]

from the size of the m4 screw that in the front panel face, I was thinking it was more off a earth for static etc

I was going to use a heavy earth from the cabinet to the earth spike.

my battery manufacture makes no mention of using a earth, even though their equipment has one!!!

 

[timselectric]

No spike
Connect to your existing grounding system.
This grounding is for personal protection against shock.

 

[timselectric]

Just from the rack to the grounding system.
Each battery is bonded to the rack through the mounting screws.

 

[Urge38]

Just from the rack to the grounding system.
Each battery is bonded to the rack through the mounting screws.

to be fair, most rack batteries and cabinets are painted, you could not be sure all battery mounting bolts are going to get a good earth.

my grounding system is a earth spike

 

[timselectric]

my grounding system is a earth spike

The earth is a terrible conductor.
Doubtful it will keep you from getting shocked.
You are counting on a short to travel to your extra ground rod. Then through the earth. Then to find its way to your electrical grounding system.
Hopefully the earth is wet, when a short happens. Maybe it will save you.

 

[rmharrington]

Newbi here trying to make certain I make the safe moves in grounding my eg4-ll batteries and rack. So, here's the case:

1) I have the Signature Solar Preassembled battery rack capable of holding six batteries.
2) I have installed two eg4-ll 48-volt batteries.
3) Each battery has a bolt marked with the grounding symbol.
4) Front and read of the cabinet is pre-wired with a green ground between the door and the frame.

Questions:

1) Am I supposed to daisy chain a ground wire between the two bolts marked with the grounding symbol?
2) Should wiring then extend from one of the two bolts to connect with my current house grounding system?
3) Should I make the ground connection inside of my main panel, or can I just run direct to the external home grounding rod?
4) Should the grounding wire be bare solid copper or can it be stranded? Should it be open or bare?
5) Finally, please recommend correct sizing for said wires?

All help is appreciated. Finding answers to these questions is difficult. Three electricians have been to my house, but none seem to understand solar.

Thanks one and all.

 

[timselectric]

The batteries are bolted to the rack, with 4 bolts each.
This should be good enough for bonding everything together (you can verify this with a meter).
The bond wire going from the cabinet door to the cabinet, takes care the door. You can run a ground wire from the cabinet side connection of this wire, to your grounding system.
Wire size should be the same as for the inverter.
You can connect it to any part of the grounding system, as long as the path back to the N/G bond is the same size or larger.

Edit for clarity:
Once something is connected to the grounding system, it becomes part of the grounding system. Which allows it to be a connection point for other equipment grounding.

 

[pvgirl]

A star washer on one the rack screws will cut thru paint on the battery and make a better ground to the rack.

 

[ImAnIdiotPleaseBePatient]

The earth is a terrible conductor.
Doubtful it will keep you from getting shocked.
You are counting on a short to travel to your extra ground rod. Then through the earth. Then to find its way to your electrical grounding system.
Hopefully the earth is wet, when a short happens. Maybe it will save you.

I understand how the ground/fault system works with a ac circuit on an ac breaker, but how does attaching the cabinet of dc batteries with no breaker help prevent you from getting shocked if there was a short and the case became “hot.”

i believe you but i dont understand. in an AC circuit, the fault was cause high amperage to travel through the breaker and flip the breaker, which prevents the electrocution. but in the case of a battery case becoming hot, i dont really even understand what would happen. can you explain it please?

 

[timselectric]

I understand how the ground/fault system works with a ac circuit on an ac breaker, but how does attaching the cabinet of dc batteries with no breaker help prevent you from getting shocked if there was a short and the case became “hot.”

i believe you but i dont understand. in an AC circuit, the fault was cause high amperage to travel through the breaker and flip the breaker, which prevents the electrocution. but in the case of a battery case becoming hot, i dont really even understand what would happen. can you explain it please?

Any exposed metal parts can become energized.
More so, if part of the electrical system.
It's not to protect you from the DC voltage in the batteries. It's to protect you from the possibility of AC voltage on the metal parts.
It's mainly to cover a combination of what ifs.
If the inverter malfunctions and puts AC voltage on the battery side. And finds its way to the case.

 

[webbbn]

As a side note, different equipment may ground one or the other side of its supply and/or output. Don't assume that the negative of the batteries and the negative of the solar panels are grounded, and don't connect them to ground. Some individuals, thinking that since cars and RVs are wired this way do the same in fixed power applications, but it's not necessary, and it can lead to unsafe situations when equipment is mixed with positive grounding equipment.

Some of this doesn't make sense.

First, I find it hard to believe that anyone would ground the positive lead of the battery. It's very common for the negative terminal of DC powered devices to be connected to ground, which is going to be a problem.

Just to give an example, if you powered a Pi from a buck converter connected to your batteries, and positive is connected to ground, then the "ground" on the pi would actually be -5V WRT ground. That's not going to go well if you connect a USB port to something that has the negative voltage terminal connected to ground.

Second, I don't think the batteries should be connected to the metal case, so there should be no chance of the case getting energized by the batteries or inverter. The case should be electrically isolated from the rest of the system.

If you do connect, say the negative terminal of the battery to the case, and ground the case, you've now made a second electrical connection between your battery and the inverter, which could bypass your fuses/breakers. That's not a major problem if all your fuses, switches, breakers, and relays are on the positive side, but are you sure that's the case in the inverter? Low-side MOSFET switches are very common, especially in high current circuits.

 

[timselectric]

First, I find it hard to believe that anyone would ground the positive lead of the battery.

Remote telecom systems are positive grounded battery systems.

 

[webbbn]

Remote telecom systems are positive grounded battery systems.

I'm not sure what you're referring to, but I was specifically referring to the solar batteries. I'm sure there are positive grounded systems out there, especially in telecoms, but it's not common practice, especially in modern electronics.

 

[timselectric]

I'm not sure what you're referring to, but I was specifically referring to the solar batteries. I'm sure there are positive grounded systems out there, especially in telecoms, but it's not common practice, especially in modern electronics.

If someone's only experience with DC systems. Was in the telecom industry. They might think that positive grounding is the norm.

 

[Quattrohead]

It helps with static electricity too, imagine you walked out of your warm cosy house into the garage and touched the battery, because you like to see the display, but you are carrying 1000's of volts because of your nylon slippers. That zap you give the battery front could cause a problem to the delicate circuitry in the BMS.

 

[Quattrohead]

It's very common for the negative terminal of DC powered devices to be connected to ground

Only in cars, nothing else ever.
And now newer GM trucks in the rust belt are crapping out with weird electrical problems because those "ground straps" are corroding.

 

[timselectric]

Jeeps and Ram trucks, too.

 

[webbbn]

Only in cars, nothing else ever.
And now newer GM trucks in the rust belt are crapping out with weird electrical problems because those "ground straps" are corroding.

Maybe I worded that improperly, but it's exactly the same as the situation in cars, where the negative battery terminal is connected to the frame. I think you'd be hard pressed to find a AC-DC power supply that has a ground pin, that doesn't tie the negative terminal to ground. Probably (I would hope) bench supplies, but pretty much all other electronics that will be the case. The case is grounded, the PCBs are grounded, the cables connecting them are grounded, and all the voltages are positive with respect to ground (other than possibly PC supplies that might have some old remnants of negative voltages).