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Grounding is one of the most critical elements of any solar panel installation. Not doing so can lead to static discharge and lighting strikes that destroy the solar panel, inverter, battery and charge controller. Solar power systems that are not grounded can also damage any appliances or devices connected to the system. Therefore, you must ground solar with the right wire sizes.
Article 690 of the NEC mandates that #8 AWG or #6 AWG are the smallest wires that can be used with grid tied solar panels and inverter systems, and for solar panel output circuits, #10 or #12 AWG are allowed. A ground rod is also recommended if the installation area is prone to lightning strikes.
What Ground Wire Size is Needed For Solar?
The following table shows the NEC grounding wire size recommendation. The higher the AWG number, the smaller the wire. Note also that these are the minimum wire sizes you can use. These are the smallest allowable for safe grounding, but if you can get a large wire, use it.
|Circuit Amp Size
|AWG Copper Wire Size
If you are going to install a solar panel in your house or RV, make sure you use the right wire for grounding. Some suggestions.
Look up the instructions of your solar panel. It should have information on grounding and what wire size to use. It will either be the same as the NEC recommendation or maybe even larger. This applies for both home or RV solar panel installation.
You may use the table above as a guide. Check your service amps and pick the appropriate wire size. If your service is 300 amps, use #4 AWG, if it is 150 amps, the WindyNation #6 AWG solar wire kit is our recommendation, and so on. Never use a smaller wire than what is ideal because it might fail an inspection.
But electricians asking questions will be the least of your worries. Solar systems that are not grounded could be a disaster in the making. If you think solar arc is bad, not grounding is even worse.
Why Ground Solar Panels?
Grounding solar panels is necessary because:
- It reduces built up charge, making your system less attractive to lightning.
- If a charge builds or lightning hits, the discharge will go into the earth instead of your cable. Without grounding this will not happen.
- Grounding minimizes power shock from high voltage components.
- The NEC requires grounding. Article 690 includes solar panels, whether it is high or low voltage. Not grounding your system is not only risky but also illegal.
- A grounded connection minimizes the hum produced by some solar inverters, lights and other electronic devices.
The most common mistake solar panel owners make is assuming that lightning must strike directly to cause damage. In fact, lightning can hit miles away but still generate high voltage in your solar panel cable. Solar panels with long wires are particularly susceptible to this.
When the voltage surges it can destroy your appliances and entire solar power system. This can be prevented by grounding solar panels. Grounding means electrically wiring parts of the solar system to the earth (earthling).
How to Ground Solar Panels
Drive an 8 foot long copper plated rod into the ground at least 8 feet deep. The dryer the land, the more ground rods you should use. Space the rods 10 feet apart. Use clamps and #6 AWG bare copper wire to secure the rods together. The last step is burying the wire.
Before proceeding, check the plan that came with your permit. Instructions for grounding will be included. Follow them and you should pass the inspection easily. The #6 AWG is the smallest wire you should use. You can opt for larger wires, and you will probably pass inspection faster too. Only clamps for grounding should be used.
If your solar panel is at a distance from your house, place several rods close by. The wires should be buried at the trench along the power lines. You can also ground the wiring to metal water pipes as long as it is cold water. Avoid gas and hot water pipes.
Some more tips:
- The more grounded objects you connect, the less chance of lightning induced damage.
- Use copper or bronze connectors to avoid corrosion.
- Make sure the electrical connections are stable, durable and not corroded.
- If you cannot dig through the rocky ground deep enough, bury as much copper wire as you can. How many? At least 150 feet, multiple pieces that radiate out. Bury the copper wires in moist locations. The more prone to lightning the area, the more copper wire you have to bury.
- You can use secondhand copper wire. You can get these for cheap in any scrap metal shop.
- If the wiring is 30 feet or longer, get a metal conduit and put the wires there. By connecting this to your grounding, it won’t attract lightning as much.
Which Solar System Parts Have to be Grounded?
The solar panel metal frame, inverter frame, AC generator and the negative side of your solar system must all be grounded. If a wind generator is connected to your solar panel, it must be grounded too. The ground wires and the metal frame have to be bolted tightly.
Test your power system for leaks before grounding. Use a multimeter like the WeePro Vpro850L and set it to milliamp. Place the positive probe on your grounding configuration and the negative on the battery negative. The reading has to be zero.
Set the multitester to the lowest microamp setting and repeat the process above. If it is also zero, you can ground the power. If the tester picks up something up, inspect the positive as it might be touching the earth. The negatives should be grounded near the disconnect switch or the negative battery connection.
AC wiring and inverter frames should be grounded in the same way you ground other AC systems. Make sure the wires and cables are not corroded or worn out. Many inverters have grounding protection built in, but it is better to be safe.
Use the shortest wires possible for solar wiring. Set the wires in the frame and course them through a metal conduit. Run the negative and positive wires together as much as you can. Whenever possible, bury the wires to make it less susceptible to lightning.
Solar Panel Grounding FAQ
Does the Ground Wire Size Matter?
The ground wires have to be at least the size recommended by the NEC (see table). The wire can be larger than the recommended, but not smaller. If the ground is not the correct size the grounding system will not work and your solar panel will be exposed to lightning and other hazards.
What Happens if the Wire Gauge is Too Big?
Using a larger wire will not cause any harm to your system. The only drawback is large wires are more expensive and require bigger clamps. But it will not cause any damage to your solar panels or appliances. Some would recommend using a larger wire than the minimum specified by the NEC as it is safer and more durable.
What Wire Size Should Be Used on an Off Grid Solar System?
The same wire sizes used for a grid tied system, at least #8 or #6 AWG. And just like grid tied homes, you should use more copper rods if the location is prone to lightning strikes. Most off grid setups have a backup power source like a gas or large battery bank, and they need to be wired properly as well.
Do Ground Wires Have to be the Same Size?
For convenience they should be the same, but you can use different wire sizes as long as it is not smaller than #6 AWG. However there should be no effect on the grounding system as long as the minimum size specs are met.
What if the Ground Wire is Too Small?
The wiring will not be able to provide the protection needed by your solar panel against static discharges and lightning. If a lightning strikes, even far away, it could send out a high voltage surge that destroys your solar panel and everything connected to it.
Can a Ground Wire Cause a Fire?
Ground wiring can trigger a fire if is loose, worn out or gets eaten by an animal. That is why you have to bury the wires deep and if there is a problem with the system, have the wires checked and replaced. These problems can be avoided by burying the copper wires deep.
Does Ground Wire Have Current?
There should be no current in ground wiring. if there is, it is probably due to s short circuit. This is an unstable current, but the ground wire will transmit this to the earth and away from your electrical system.
How Far Should Ground Rods Be From Each Other?
The NEC states the rods have to be at least 6 feet apart and each rod at least eight fee deep. You can space the rods much further as long as they are connected with clamps.
In summary, grounding solar panels is necessary to prevent static discharge and lightning induced damage. The NEC also requires it so make sure your solar panel is grounded. By using the recommended AWG wire sizes given here, you can be assured your system and appliances are protected even during a thunderstorm.
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