How to Properly Ground Powder Coated Parts with a Dedicated Ground Rod

Improve the attraction of powder to your parts while powder coating.

If you are powder coating a metal part, it must be grounded. The ground is what attracts the powder to the part. The better the ground, the more efficient your powder coating gun can work, especially when spraying multiple coats or intricate parts. Often a powder coating gun or the guns control box will come with a small 18-gauge ground wire and a mini alligator clip that you can connect to your part to ground it. I will call this the "stock" ground. The stock ground continues through the control box, through the small gauge wire to plug into a wall outlet, and then finally reaches ground after it travels through your buildings electrical. This is not a sufficient ground for proper powder coating. No matter how good of gun you have, you need to install a DEDICATED GROUNDING ROD.

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What are the advantages of using a grounding rod when powder coating?

Faraday Cage Areas:

Using a ground rod helps reduce the issues associated with Faraday cage areas. Faraday cage areas are areas of a part that are electrically shielded due to the geometry of the part. These areas are usually located in recesses or tight corners. You will notice as you powder coat, especially a more intricate part, that no matter how much powder you spray, some areas of the part remain uncoated. All of the powder is instead being attracted to the larger, more open surfaces adjacent to these areas. This results in an uneven coating with too much powder on the large areas, and bare spots in the tight areas, as you can see on the wheel below. Having a proper ground like the grounding rod will significantly reduce these problem areas and allow these areas to attract the powder more easily.

The grounding rod will help significantly, but if you are using a hobbyist-level powder coating gun, it will not cure it 100%. There are tricks that you can do to further reduce the impact of Faraday cage areas, but the most reliable method is using a professional-level powder coating gun.

Multiple Coats:

After spraying the first coat of powder and partially-curing it, you may want to apply another coat after this, whether it be clear, a translucent, or any other subsequent coat. This is another situation where a grounding rod will help. That first coat of powder acts as an electrical insulator covering the entire part. It is insulating the ground which is responsible for dissipating the charge of the powder. When spraying the next coat, if the charge is not being dissipated to ground, a buildup of charge will occur on the part, which will actually repel the powder. Without a sufficient ground, it will seem like nearly your entire part is behaving like a Faraday cage.

The proper ground that is provided by the grounding rod will allow more charge to dissipate through previous coats, making subsequent coats easier to apply. This will not be adequately accomplished by the small ground wire that is packaged with many powder coating guns. Mutli-coats are much easier after a properly installed grounding rod is connected to your part.

However, just as with the Faraday cage areas, a grounding rod can only improve multi-coats so much. With most hobbyist guns (less than $200) and a properly installed grounding rod, you will be able to apply two or three coats with somewhat minimal issues. Applying more coats than this will require a more expensive powder coating gun.

Reduced Powder Waste:

With a correctly installed grounding rod, more powder from your gun will be attracted to your part instead of ending up on the floor. This increased transfer efficiency results in less money spent on powder and a cleaner and safer shop/garage.

What is a Grounding Rod?

A ground rod is a long copper coated rod that gets driven into the ground. The sizes vary, but for the powder coating application, I recommend the length of the ground rod be at least 8 feet (10 feet would be better) and 3/4 inch diameter. If you live in a warmer area, your local hardware stores may only carry 5/8 inch x 8 feet ground rods, in which case you may have to spend a little more and buy it at Grainger. If you live in a colder area, they can be purchased at your local Home Depot or Lowe's for about $35: 3/4 in. x 10 ft. Ground Rod at Home Depot.

Ground Rod Installation

The ground rod gets hammered into the ground almost entirely. This can either be done on a ladder with a sledge hammer and a bit of effort, or if you already have or want an SDS rotary hammer, you can make quick work of it with a ground rod driver bit. You want to leave about 6 inches of the rod protruding above the ground so you can clamp the wire to it. The other end of the ground wire will connect to your parts while they are being coated, either directly or through the use of racks and hooks. For the least amount of resistance to ground, and therefore the best powder coating transfer efficiency, install the ground rod as close as you possibly can to your powder coating area.

If you plan on powder coating in your garage or shop, you can install the grounding rod right through your floor for the shortest possible distance to your powder coating area. Simply drill a hole in your garage floor with a masonry bit and a SDS+ rotary hammer, and install the grounding rod through the garage floor down into the ground below. Be mindful of any plumbing or electrical lines that may run underneath the floor before doing so. Also make sure to size your masonry bit a little larger than the ground rod so that you don't scrape all the copper coating off as you drive it down through the concrete. If you are moving and need to get rid of the grounding rod sticking through the floor, simply pound it the rest of the way down and fill the hole up with some concrete patch. Here are a couple of examples of this:

A ground rod clamp like either of the ones shown below allow you to secure the ground wire to the grounding rod. You will also need a length of wire to connect your grounding rod to where you hang your parts.  US electrical codes specify that the wire connecting a ground rod is 6-gauge or 8-gauge solid or stranded copper wire. You can use larger diameter copper wire if you prefer, but don't go smaller than 8-gauge The choice between solid or stranded won't make that much of a difference as long as the remainder of the ground rod system is setup correctly. Stranded wire is more flexible than solid, and it is capable of carrying higher current. Solid wire has less resistance than stranded wire, and less resistance is more important than current-carrying ability when it comes to dissipating the charge from powder coated parts. However, many people swear by solid and just as many swear by stranded, so I would suggest using whatever your personal preference is, or whatever is most readily available to you at the best price.

Both bare copper and insulated THHN wire will work fine to connect your ground rod to your parts. 
It is really another personal preference based on what you would prefer to install, as both meet US electrical codes and are sufficient for powder coating. If you do decide to use an insulated wire, I would recommend using green to satisfy electrical codes (in the US). You can purchase this type of wire at your local hardware store, either by the roll or by-the-foot. Since you should have a very short run between the ground rod and powder coating area, by-the-foot will likely be the cheapest option.

 

 

Completing the Connection from Ground Rod to Part

You have the ground rod installed, and the ground wire clamped to it. Now you need to determine how you would like to complete connection to you parts. There are different methods for doing this depending on if you powder coat on a rolling rack, a stationary rack, in a spray booth, or another method.

Connecting a Powder Coating Rack to Ground Rod

If you have a large powder coating oven, you most likely will also have a rolling rack that you roll into the oven. If you powder coat your parts on the rack itself, whether its in a spray booth or not, the most common method of grounding is to connect the ground wire to the rack. The path to ground will travel from the part to a hook, then the hook to the rack, and from the rack to the ground wire. This means that the ground wire will need to be easily removable from the rack so that it can remain mobile. This can probably be accomplished many different ways but here are a couple of options.

You can use a spring loaded clamp such as a welding ground clamp or a battery jumper cable and clip it onto your rack before coating. Both of these options have been tested with good results. See the picture below for an example, just make sure to use a higher quality clamp.

If you would prefer a more solid connection, you can crimp a wire lug to the end of the ground wire connected to the grounding rod, and then fasten the lug to the rack using a bolt (or weld a stud to the rack) and wingnut. This crimp-on lug would require that you used stranded wire for the ground wire. While more secure, it is a little less convenient because you have to spin off the wing nut every time the rack needs moved.

Those are just a couple of options that you can do to connect the ground rod to the rack. The most important thing to keep in mind, whatever solution you decide on, is that there needs to be good contact between the ground wire, rack, and parts. Use as few connections to reduce resistance and failure points. Also, make sure that the contact points between every connection is clean bare metal each time you powder coat. Powder build up on the rack or part hanging hooks can reduce or completely block the path to ground.

Grounding Parts in a Spray Booth

If you hang your parts in a spray booth to powder coat or you just use a stationary rack, the tried-and-true method of connecting parts to the ground rod is by using another ground rod or even a copper pipe if you're not hanging anything too heavy. This would be done by mounting a shorter grounding rod horizontally near the top of the booth. You can use the same type of ground rod clamp on this that you used for the in-ground grounding rod to attach the ground wire. Then parts are simply hung on the ground rod inside the spray booth when powder coating. This is a very clean setup that has a minimal amount of connections. This method is shown in the two spray booths below.

Clamping ground wire from ground rod to spray booth hanging rod. This clamp can be installed on the outside of the spray booth wall to prevent powder build up.

A very helpful item to add to this type of setup is a swivel powder coating hook. This hooks onto the bar and has a swivel base that you would then hook your standard part hook from. This allows you to rotate the part while coating so you can spray all sides. It does add some extra connection points in the ground path, but these hooks are specifically made for powder coating so they are designed to maintain the ground path. It is still always smart to check the resistance with a meter to make sure.  These should stay in your spray booth and never be placed in the oven. You can clean uncured powder off of them very easily with a blast of compressed air.

Ground Parts on a Stationary Rack

Many new powder coaters and hobbyists will setup a make-shift rack to powder coat in the corner of the garage, or outside the garage door. This isn't ideal but because the part is open to contaminants and the powder is not contained, but its workable if you're just starting out. My first powder coating rack is shown below. It was setup as cheaply as possible and with as few connections as possible. I soldered the ground rod coming from the dedicated grounding rod directly to the hanging hook. This setup, while crude, was a noticeable improvement over the stock ground that came from the Craftsman powder coating gun I started out with. This setup would be easy to replicate with a swivel hook instead of a fixed hook so that you don't have to walk around the rack as you are coating.

Improving the Dedicated Grounding Rod Performance

Following the recommendations in this article will allow most people to setup a very reliable ground. However, there are some cases where more can be done to improve the dedicated ground rod system even more.

A ground rod is able to dissipate charge better when installed in moist ground. If your setup allows for it, you can possibly improve the ground more by placing the ground rod next to a rain gutter, the drip line from an AC condenser, or any area where the soil remains wet.

Some climates have very dry or sandy soils that will significantly increase the resistance between the ground rod and the ground and reduce its performance. Tests can be done to determine the resistivity of your soil so you can better determine how to overcome the issue. You can also determine what steps were taken when your building's electrical ground rods were installed so you can mimic the setup for your powder coating ground rod. You can also try contacting the relevant department in your city, or even your power company to see if they can give you advice on this issue.

A common first step to try to resolve this issue is by adding an additional ground rod to increase the available surface area to dissipate charge to the ground. Using the largest grounding rods available, they should be places at least 6 feet apart, but if you're using 10 ft ground rods, then 10 feet apart would be ideal. The two rods each need to have their own clamp, they need to be wired together, and then you would run your grounding wire to your coating area from one of them.

With the Dedicated Ground Rod Set Up, It is Time to Test

From a safety standpoint, the resistance from the ground rod to a grounded part should not exceed 1 Megaohm (10^6 Ω or 1,000,000 Ω). From a powder coating performance standpoint, you want the resistance to be as close as possible to 0 Ω. The correct tool to accurately measure the resistance from ground rod to part is a Megohmmeter.


Now that you know how to set up a proper dedicated grounding rod, its time to set one up yourself.  It is worth it! I noticed improvements immediately. Second coats sprayed like they were the first coat and Faraday cage areas were minimized to only the tightest areas.