Help on finding the right size ground bar?

[JonL]

I just realized that I hadn’t paid enough attention to the grounding of all my solar gear. My bus bars are rated at 500 A and I will be pushing around 350 A through my whole system.
So what size ground bar or type do I need for all my gounding connections? I need at least 12 grounding connections. Thanks

 

[Jim Burrow]

With respect to grounding, there should be no current flowing through it unless you develop a short somewhere. Whatever size you use for your return (white wire) common bar is good enough for the grounding wires. But I'm no licensed Electrician and one of those guys may tell you differently.

But in my house sub-panel circuit breakers. The ground bar is the same size and the common return bar for the white wire.

 

[JonL]

I guess what I’m worried about, is whether my cheap $10 bar that has holes in it that you just screw in the wires, can handle a huge charge short through the system. it seems like I should have something better!

 

[Jim Burrow]

It's supposed to have holes. Take a moment and look inside your circuit breaker sub-panel on your house. You will sever several bars. One bar for the white wires on the left side of the panel and one bar for the white wires on the right side of the panel. You should see a third bar for the bare and or green (sometimes gray) wires. Notice that the all are long and full of holes with screws that hold the wires in place.

However, your average house has a main breaker for 100 Amps. I can't imagine having 500 amps running through your house. Plus I have never seen a common bar at the hardware stores bigger than what you see in your house sub-panel.

It will be interesting to hear what others in the group that are experienced with this solar stuff to chime in.

Notice the white looking common bars two are for the white return to source wires and the two on the sides are the grounding bars

 

[Dzl]

I guess what I’m worried about, is whether my cheap $10 bar that has holes in it that you just screw in the wires, can handle a huge charge short through the system. it seems like I should have something better!

I would think (I am also not an electrician or qualified to have an opinion worth listening to on safety matters) that using components of the same or greater rating and quality as your current carrying conductors (and components) would be a sufficiently safe approach. As I understand it, one purpose of equipment grounding is to allow your OCP devices (fuses/breakers) to trip if a fault develops. Since OCP devices are sized to protect the current carrying conductors, sizing the equipment grounding conductors, greater than or equal to the current carrying conductors seems like it would ensure that they are also protected by the OCP.

Of course, for more specific and legitimate guidelines, you could consult either a qualified electrician or a relevant electrical code (ABYC, Coast Guard and portions of the NEC code are in the resources section of this forum).

 

[Supervstech]

Keep in mind a fault will spike current for less than a second.
#16 wire will handle 150A for a short time.

 

[Dzl]

Keep in mind a fault will spike current for less than a second.
#16 wire will handle 150A for a short time.

Does the NEC provide a rule of thumb or general guidance on OP's question or is it all contextual?

 

[HRTKD]

What fastener does your equipment provide to attach the ground wire? On my Victron solar charge controllers it's small. Nowhere near the size of the solar panel input ports (which max out at ~6 gauge). Given how dinky the fastener is, there is no way that Victron is expecting me to connect a 6 gauge wire to the ground screw.

I used 10 gauge wire between components and the ground bus bar. From the ground bus bar to the chassis of my trailer, I used a thicker wire. I don't recall what it is. It was something laying around. It's thicker than 10 gauge for sure.

 

[JonL]

Just so everybody’s on the same page, this is not for a house – it’s for an off grid solar system.
in the photo you can see what I’m using. All my equipment is running through this tiny ground bar. I’m using eight gauge wire.

 

[Jim Burrow]

current flows on the outside of the wire and not through it. With respect to a bar, the current is not flowing through it. The current will take the shortest less resistance both between two wires. So just because you have a large long bar, the current will only travel between the two wires that are in the same hole and screwed down. I see nothing wrong with that bar. But again, I'm not a licensed Electrician, but an old retired Electronic Engineer that has most of the time dealing with low 9v DC current designs.

 

[JonL]

current flows on the outside of the wire and not through it. With respect to a bar, the current is not flowing through it. The current will take the shortest less resistance both between two wires. So just because you have a large long bar, the current will only travel between the two wires that are in the same hole and screwed down. I see nothing wrong with that bar. But again, I'm not a licensed Electrician, but an old retired Electronic Engineer that has most of the time dealing with low 9v DC current designs.

Thanks for your input. One thing about electricity I’ve learned, you need to look at every single element to make sure it’s done right! ?

 

[MadElectrician]

It's helpful to describe what you are doing in more detail. Grounding and bonding is the most confusing area of electrical and the largest section in the NEC. I can't tell you anything from the information you wrote. However, if I just look at your picture, what you have is simply a bunch of wires fastened together. There is no rating on something like that as it's simply a connection device. I'd probably twist those wires together for added strength. PS what am I looking at? Is this an equipment ground that goes to a ground rod or cold water pipe? You say "not a house, but off grid solar." I'm not sure what that means. Are you grounding the actual solar array?

 

[JonL]

It's helpful to describe what you are doing in more detail. Grounding and bonding is the most confusing area of electrical and the largest section in the NEC. I can't tell you anything from the information you wrote. However, if I just look at your picture, what you have is simply a bunch of wires fastened together. There is no rating on something like that as it's simply a connection device. I'd probably twist those wires together for added strength. PS what am I looking at? Is this an equipment ground that goes to a ground rod or cold water pipe? You say "not a house, but off grid solar." I'm not sure what that means. Are you grounding the actual solar array?

Thanks for clarifying things, a lot of the stuff I don’t think about. This is in the house, just not connected to the grid power. I have a copper rod used for lightning in the backyard and the solar panels have copper wire around their bases and going down to the copper rod.
Then below, you have the charge controllers, inverters and batteries grounded and going out to the same copper rod in the backyard.

 

[MadElectrician]

Thanks for clarifying things, a lot of the stuff I don’t think about. This is in the house, just not connected to the grid power. I have a copper rod used for lightning in the backyard and the solar panels have copper wire around their bases and going down to the copper rod.
Then below, you have the charge controllers, inverters and batteries grounded and going out to the same copper rod in the backyard.

Got it. This is just for safety so that nobody gets shocked. There should be no charge on those wires under normal circumstances. As long as your device is mechanically sound you have no issues. I'd grab it and twist up the wires though. Then the bar is moot.

 

[JonL]

Got it. This is just for safety so that nobody gets shocked. There should be no charge on those wires under normal circumstances. As long as your device is mechanically sound you have no issues. I'd grab it and twist up the wires though. Then the bar is moot.

Good insight, thanks! ??

 

[LB3]

current flows on the outside of the wire and not through it. With respect to a bar, the current is not flowing through it. The current will take the shortest less resistance both between two wires. So just because you have a large long bar, the current will only travel between the two wires that are in the same hole and screwed down. I see nothing wrong with that bar. But again, I'm not a licensed Electrician, but an old retired Electronic Engineer that has most of the time dealing with low 9v DC current designs.

current flows on the outside of the wire and not through it. With respect to a bar, the current is not flowing through it. The current will take the shortest less resistance both between two wires. So just because you have a large long bar, the current will only travel between the two wires that are in the same hole and screwed down. I see nothing wrong with that bar. But again, I'm not a licensed Electrician, but an old retired Electronic Engineer that has most of the time dealing with low 9v DC current designs.

This is incorrect. ‘Electricity’ travels through copper. DC experiences no skin effect at all and at 50-60 Hz the skin effect is 8-10 mm. Far deeper than the radius of any solid core wires or bars we use on the A/C side of our solar systems.

The skin effect is quite significant at really higher frequencies which is why most coax cables we run UHF and VHF signals over are copper plated steel rather than more expensive copper core wires.

 

[Supervstech]

This is incorrect. ‘Electricity’ travels through copper. DC experiences no skin effect at all and at 50-60 Hz the skin effect is 8-10 mm. Far deeper than the radius of any solid core wires or bars we use on the A/C side of our solar systems.

The skin effect is quite significant at really higher frequencies which is why most coax cables we run UHF and VHF signals over are copper plated steel rather than more expensive copper core wires.

I have given up trying to teach this.
Experts in their field know stuff, and will argue this ad nauseam...