Bluedog225
Texas
Solar charge controller. We love our acronyms.
Ground mount panels grounding questions.
- Thread starter doox00
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I love this thread. It's got a lot of good info.
There is "earth ground" and "equipment ground"
For equipment ground there is AC ground and DC ground.
If there is a grid connection at the property, then the utility provides at the service entrance for normal 240V residencies (in USA) an L1 black hot 120 volts, an L2 red hot 120 volts which are out of phase with each other (ie split phase), a neutral (white which completes the circuit) and a bare copper or insulated green copper wire which is the AC ground. There is a required BOND at only one point in the main panel between the neutral wire and the utility ground wire. This is the only place anywhere on the AC side that a neutral to ground connection should exist. Arising from this BOND is the ground buss bar and neutral buss bar. The purpose of the neutral wire is to complete the circuits to operate equipment such as a blender. The purpose of the ground wire is to connect to equipment chassis such as a microwave oven exterior, an electric fan case, a metal mounting box, etc. By grounding these metallic equipment fixtures, there is a route for current to flow if the neutral is interrupted (rather than only through a body) and this helps prevent shocks and electrocution.
On the DC side, earth ground is accomplished by either making certain a bonded connection of a copper wire to a solar panel frame and any metallic parts of the PV mount are connected to a ground rod locally or carried back via a bare copper wire or insulated copper wire to an accessible AC grounding buss bar point or grounding rod. The solar array carries current under normal conditions by means of two conductors, PV+ and PV- to make a DC circuit that lands on a PV charge controller or other DC capable appliance. Without any grounding of the array, panels or the landing equipment, a person could be electrocuted by DC current passing through their body if they come in contact with a live DC circuit.
If a PV array has a locally installed (at the array) combiner box and DC disconnect, and if they are metallic, they must be grounded via a wire connection. Use of PVC boxes and conduits outdoor carrying DC circuits should also carry a grounding wire inside them unless the PV array is earth grounded at the array. If the PV array is earth grounded at the array, and no ground wire travels to the landing equipment of the DC circuit, then that landing equipment must be grounded locally by either a grounding rod or to the AC ground buss point.
If off grid, this can be by a grounding rod and ground buss bar and wires between batteries, inverter, charge controllers, sub panels, conduits (metallic indoors) and any other electrical equipment and metallic boxes. In an off grid case, with an inverter and AC power, a ground to neutral BOND is created in only one location, usually at the inverter. If you are off grid and using a portable generator tied into your off grid inverter, the neutral to ground BOND is again, only in the inverter, not at the generator. If using a portable generator in a free standing condition not connected to an inverter, then that generator should have an internal neutral to ground bond and even a grounding rod connection.
Now, if the DC circuit is brought to a landing where there is a utility grid tie, then the grid tie will supply an AC side ground that originated in the main panel service entrance. In this case, your DC ground from the array carried by the ground wire can land on the AC buss bar to establish equipment ground and earth ground. There would be no neutral to ground bond at the inverter or a generator. And there would be no grounding rod at the array.
There is "earth ground" and "equipment ground"
For equipment ground there is AC ground and DC ground.
If there is a grid connection at the property, then the utility provides at the service entrance for normal 240V residencies (in USA) an L1 black hot 120 volts, an L2 red hot 120 volts which are out of phase with each other (ie split phase), a neutral (white which completes the circuit) and a bare copper or insulated green copper wire which is the AC ground. There is a required BOND at only one point in the main panel between the neutral wire and the utility ground wire. This is the only place anywhere on the AC side that a neutral to ground connection should exist. Arising from this BOND is the ground buss bar and neutral buss bar. The purpose of the neutral wire is to complete the circuits to operate equipment such as a blender. The purpose of the ground wire is to connect to equipment chassis such as a microwave oven exterior, an electric fan case, a metal mounting box, etc. By grounding these metallic equipment fixtures, there is a route for current to flow if the neutral is interrupted (rather than only through a body) and this helps prevent shocks and electrocution.
On the DC side, earth ground is accomplished by either making certain a bonded connection of a copper wire to a solar panel frame and any metallic parts of the PV mount are connected to a ground rod locally or carried back via a bare copper wire or insulated copper wire to an accessible AC grounding buss bar point or grounding rod. The solar array carries current under normal conditions by means of two conductors, PV+ and PV- to make a DC circuit that lands on a PV charge controller or other DC capable appliance. Without any grounding of the array, panels or the landing equipment, a person could be electrocuted by DC current passing through their body if they come in contact with a live DC circuit.
If a PV array has a locally installed (at the array) combiner box and DC disconnect, and if they are metallic, they must be grounded via a wire connection. Use of PVC boxes and conduits outdoor carrying DC circuits should also carry a grounding wire inside them unless the PV array is earth grounded at the array. If the PV array is earth grounded at the array, and no ground wire travels to the landing equipment of the DC circuit, then that landing equipment must be grounded locally by either a grounding rod or to the AC ground buss point.
If off grid, this can be by a grounding rod and ground buss bar and wires between batteries, inverter, charge controllers, sub panels, conduits (metallic indoors) and any other electrical equipment and metallic boxes. In an off grid case, with an inverter and AC power, a ground to neutral BOND is created in only one location, usually at the inverter. If you are off grid and using a portable generator tied into your off grid inverter, the neutral to ground BOND is again, only in the inverter, not at the generator. If using a portable generator in a free standing condition not connected to an inverter, then that generator should have an internal neutral to ground bond and even a grounding rod connection.
Now, if the DC circuit is brought to a landing where there is a utility grid tie, then the grid tie will supply an AC side ground that originated in the main panel service entrance. In this case, your DC ground from the array carried by the ground wire can land on the AC buss bar to establish equipment ground and earth ground. There would be no neutral to ground bond at the inverter or a generator. And there would be no grounding rod at the array.
cs1234
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What counts as not in conduit? If you had conduit behind your ground mounted solar panels, right up against the frame of the panel, to keep critters and such from having as much cable to chew on, and had your EGC in there, and it was only 10awg..
Could you expose it briefly, say a few inches, to connect to a ground lug on the panel / racking?
Or is that too much distance not in conduit and you need to use 6awg and then downgrade it back to 10awg for the run in conduit?
timselectric
If I can do it, you can do it.
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Usually the easiest solution is to run the appropriate size in conduit to a box (combiner, junction, or pull box). Then connect it to a #6 , that runs exposed behind the panels.
This box is also where you would switch from standard conductors to PV wire for the positive and negative.
Hedges
I See Electromagnetic Fields!
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That would be the case if they could trip a breaker, which is the case for AC circuits and battery circuits.
I say that EGCs for PV DC are current-carrying conductors.
PV circuits have various forms of bonding, or are isolated.
Some are grounded through a 1A "GFCI" fuse, in which case that would blow.
For an old-time PV system having PV- hard-grounded, a short of PV+ after combiner box (let's assume that is at the PV array) would result in ground wire carrying ISC continuously. Not for a second.
Transformerless GT PV inverters have (or had) the potential to pump DC into the electric grid. And they do superimpose AC on PV wires (at least 208V and 480V applications, not always split-phase.) So other interesting "grounded" or referenced to ground through AC, and backfed issues.
The only time PV breakers trip is if one string has fault to frame, and 2, or probably requires 3, other strings dump current into it. In that case breaker per string trips for that one string.
My old system had one ground wire sized to one PV string, going to a box with a couple strings attached. Doing it differently on future system for a couple of reasons.
Solar Charge Controller, for DC coupled PV.
We alternatively have grid tied GT PV inverters (also AC coupled to battery inverters),
And AIO or Hybrid, with PV inputs and battery inputs.
In all cases, PV circuit terminates at some MPPT (or PWM) charge controller, so that's where PV array frame bond wire should go.
Couple other NEC rules.
6 awg is allowed to be routed exposed. I think that is also minimum the size allowed to run across joists/rafters not run along a board for support.
4 awg allowed to be unprotected. Not sure how that differs from wires across joists. (Of course ground in a PV array is jumping across frames and rails by itself, while in house wiring you've got 6 awg 3 + ground in a jacket.)
So I'll be running 4 awg insulated in conduit with wires for 4x PV+/PV-, transition to 4 awg solid bare across the array. I'll lay that in tinned lugs, might need to do something to avoid bare copper to aluminum contact so it isn't inclined to corrode.
I think I'll run lengths of EMT with plastic nuts on the end between 4x sections of rooftop array, feed PV wires through them. But the bare ground I'd rather avoid copper to conduit contact.
Tim - what dissimilar contact should I avoid? Just bare copper to aluminum? How about bare copper to galvanized steel? How about bare copper to bare steel? I've made holes in electrical boxes and run bare ground wire out through it.
ScrotpusGobbleBottom
Corn Pop was a bad dude.
Scc solar charge controller
timselectric
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EGC is for protection against shock from the AC power.
DC ground fault protection (when it exists) is built into the DC equipment.
Which also uses the grounding system. And follows the same instantaneous trip protocol.
The Grounding system is not intended or designed to carry any current, other than fault current.
The DC system is isolated (ungrounded) from everything else. (With the exception of fault detection or protection)
There is no hazard, until a person can become part of a circuit.
The grounding system makes sure that this can't happen, by keeping everything that can be touched, safe to touch.
timselectric
If I can do it, you can do it.
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I have never seen issues with copper to steel (it's usually coated or painted) , but aluminum, and tin should be avoided. Galvanized coating should provide a good barrier.
Thank you for your patience, learning something new today. So I run a wire through an EGC lug on each of the panel frames, all the way back to my N+G bonded busbar at service entry in the same conduit as my PV wires? It's over 100ft away so not sure if that's an issue.
Then after that, I don't need to ground the rack itself?
cs1234
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If that is where your Solar Charge Controller is as well. Ground it to your buildings grounding system near the location your PV wires were going to go into your SCC.
It is not.
If you aren't sure your rack is grounded by touching the panels (which you are grounding), then ground the rack as well. It can use the same wire as the panels are using.
All metal attached to your system, ground it.
Yes, it's an MPP Solar LV6548 inverter, the AC output ground is attached there as well, it's the point of ground for everything both on grid and off grid.
Thank you, might as well just get the rack while I'm at it then on that same ground string.
timselectric
If I can do it, you can do it.
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Back to any part of the grounding system.
This can be at the AIO. Since you already have the grounding system there.
The rack also needs to be grounded.
If the rack is rated for grounding, you can connect to it, and it can provide the panels ground through the rated attachment points.
JungleTim
New Member
EXACTLY. Maybe timselectric can read this and comprehend it.
I think you need to read this again.
There are several inaccuracies in the post...
The utility does NOT provide a ground curcuit... the connecting electrician bonds the local ground point to the utility neutral at the first disconnecting means...
NEC does allow for a ground rod at a PV array, but it REQUIRES that and any metallic components exposed to be tied to the home main grounding conductor...
cs1234
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Why put in an ancillary grounding rod? It just seems like extra work for nothing to me.
Are there certain extreme distances where it makes sense?
What is the potential benefit?
JungleTim
New Member
Sure, ignore me. I only have 44 years in the industry engineering large diesel generators and 50 mw battery systems at over 6,000 sites across the US. I also happen to hold an electrical contractor's license in two states. Have fun with your forum.
timselectric
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Hedges
I See Electromagnetic Fields!
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I think if your grounding system is hundreds of feet away at the house, a fault in something like a high voltage transmission line could pass current through the earth, so there is a large potential between earth at the PV array an earth at the house.
If you ran a wire from ground rod at the house to PV panel frames, and they were electrically isolated from the earth, then when you stand on the earth and touch the frame you experience that large potential.
Code requires grounding rod at second building if wires run to it and supply multiple circuits. But not if they just supply one circuit. I suppose the idea of ground rod in that case is to make sure earth around the building is at same potential as chassis of appliances and of tools you plug in and use outdoors.
Nothing is perfect. Seems like NEC was trying to address something there, but allowed an exception.
Your lug shown is to lay the copper ground wire in the inlay and tighten it down with the screw. HOWEVER, THAT PARTICUALR LUG IS CHEAP AND REQUIRES A SCREW AND NUT WHICH WILL MAKE THE BOND BETWEEN THE FRAME AND THE LUG. THIS IS USUALLY A GROUNDING NUT OR GROUNDING SCREW WITH I THINK AT LEAST THREE THREAD TURNS THROUGH THE PANEL FRAME.
Just tightening this lug to the frame will not bond the lug to the frame. the proper screw and screw/nut to make the bond must be used.
There are more expensive lugs that make the bond when tightened to the frame.
zanydroid
Solar Wizard
Ah good point that is the wrong lug. I don’t have the product names in front of me, but Weeb has lugs optimized for panel bonding and for rail bonding.
The Unirac SM Lite manual lists the Weeb part numbers. They have aluminum oxide insulation piercing, rated for the metal types typically encountered, and torque specs.
Does Brightmount manual not list the lugs? Lame
The Unirac SM Lite manual lists the Weeb part numbers. They have aluminum oxide insulation piercing, rated for the metal types typically encountered, and torque specs.
Does Brightmount manual not list the lugs? Lame
zanydroid
Solar Wizard
I think the issue is that you rubber stamped a pretty long post that was about 90% accurate but had some details that were off either due to fundamental inaccuracy or poor word choice (I read the grounding system and at least a skim could make it sound like a TN-S instead of TN-C-S. And that’s not good)
Do you have any examples of correct bonding screw to be used here, or a better alternative product?
IronRidge XR-LUG-03-A1 Grounding Lugs, Low Profile
Shop now for IronRidge XR-LUG-03-A1 Grounding Lugs Low Profile.
www.stellavolta.com
The ridges on the lug surface cut into the anodized aluminum panel frame to complete the bond.
Here is another one:
Aluminum Lay-In Grounding Lug – Solacity
Aluminum lay-in lug, tin-plated, 14 - 4 AWG, stainless set-screw & mounting hardware, cUL listed #aluminumlug #groundlug #layinlug
www.solacity.com
zanydroid
Solar Wizard
Note that weeb that goes into the top of the rail is customized for Unirac.
Are you sure EG4 manual does not recommend hardware?
General WEEB article
Using the WEEB solution for grounding in solar applications?
A brief introduction to the WEEB grounding and bonding products.
www.greentechrenewables.com
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