Consistent and reliable current and voltage make welding far easier. However, there is more to delivering the right amount of current and voltage to your material than just turning the dials on the welder. The welder dials control what voltage and current your welder puts into the lead wire, however you still need to ensure that the current and voltage is delivered smoothly to the part your welding.

What Makes a Quality Ground Clamp?

A lot goes into providing a strong electrical ground connection. Ground clamp material, cross-sectional area, contact geometry, contact pressure, and travel distance all matter when it comes to delivering quality welds.

Material Characteristics

Quality material delivers quality tools. With a ground clamp the material affects a few critical characteristics including conductivity, corrosion resistance, hardness, and strength.

Conductivity

Conductivity measures how easily electrons flow within a material. The higher the conductivity the less resistance electrons face. Materials with greater conductivity need less cross-sectional area because they provide less resistance to flow. As resistance builds up the material begins to heat up and can even burn through. As heat increases resistance also increases leading to a run-away effect that can quickly destroy your conductor.

Conductivity works similarly to a road speed limit, the greater the conductivity the more electricity can flow, just as higher road speed limits allow for more traffic to flow. Similar to electricity, if you just to push too many vehicles onto a road traffic flow begins to decline regardless of the speed limit which typically only gets worse until you reduce the number of vehicles.

Corrosion Resistance

Materials can tarnish. Tarnish is a thin layer of corrosion that forms on the surface of material. Tarnishing occurs when the surface layer of material undergoes a chemical reaction, typically with oxygen. This tarnished layer substantially increases the contact resistance of a ground clamp making it far less effective at transferring current.

• There are a few ways of preventing tarnish from ruining your ground clamps.
• You can polish the clamping surface with steel wool or another abrasive.
• You can clean off the surface with baking soda, or even coca cola which is a common trick for auto mechanics to clean car battery terminals.
• Alternatively you can use nickel or gold plating to provide a tarnish free surface. Benzotriazole can also work as a temporary corrosion inhibitor, but it will wear off far faster than gold or nickel plating.
• You can also use aluminum or a copper chromium or other alloy that provides superior corrosion resistance with a slight decrease in conductivity compared to pure copper.

Hardness

At the microscopic level surface contacts look far different than they do at the macroscopic level. At the microscopic level, what would seem to be a smooth surface is actually filled with ridges and uneven terrain. As a result of these ridges and uneven terrain, there is far less microscopic contact area on a smooth surface than we would expect. Unfortunately for us, electrons only care about what occurs at the microscopic level. Having a clamp with increased hardness compared to the material being clamped allows for greater pressure to be used so that these ridges can be shoved together tighter which increases the real contact area and therefore increases the total amount of current that can flow freely.

Hardness also prevents a clamp surface from wearing down and becoming smooth. When an electrical contact smooths it's contact area where electricity is transferred actually decreases due to the pressure decreasing.

Strength

Clamps need strength to apply adequate pressure to transfer electricity. The more pressure that a clamp can apply, the greater the contact conductivity. Many materials that offer substantial conductivity do not have adequate strength to also apply enough force to transfer electricity through a contact point. Alloys are great at combining conductivity with strength.

Materials

Copper

Copper has the best conductivity properties of any non-precious metal thanks to it being the only non-precious metal that only has one valance electron which is free to move with little resistance.

Unfortunately Copper, unlike Gold is prone to tarnishing when exposed to air which reduces contact conductivity. This requires polishing copper contact points to maintain high conductivity. Fortunately the standard use of a copper clamp where rubbing occurs assists to polish the surface without additional work.

Copper is a malleable and mid-strength material which prevents it from applying significant pressure without deforming. While this makes copper non-marring it also means that clamps with copper jaws wear quickly. As the contact surface smooths, the contact area that actually transfers electricity reduces as the pressure declines. This is why quality clamp jaws have toothed contact points instead of smooth contact points to increase the contact pressure.

Aluminum

Aluminum has about 67% less conductivity compared copper. However, aluminum is cheaper than copper and does not tarnish which makes it a low maintenance contact for when you don't need the conductivity of copper to transfer current.

Aluminum is softer than steel which makes it non-marring for most welding projects but also makes it prone to wearing with time. Similar to copper, this wearing reduces the peak pressure which reduces the real electrical contact area.

Aluminum does provide significantly more strength compared to copper which makes it great for carrying more clamping force.

Zinc/Brass

Zinc and Brass are far less conductive than other mentioned materials. However, their reduced cost makes using increased cross-sectional areas to reduce resistance more economical.

Copper is around 3.6X more conductivity than Zinc or Brass. However, higher strength brass can have substantially more strength compared to copper, around similar strength to aluminum.

Brass is around 2.6X cheaper than Copper for the same volume. This means that if you have strength concerns and don't need to transfer massive amounts of current, then Brass will offer a more economic solution.

Gold

Gold is a precious material and we all know that it's not cheap. However, Gold is also a great conductor thanks to only have one valance electron similarly to copper. What makes Gold an even better electrical contact compared to Copper is it has a strong resistance to corrosion and therefore doesn't tarnish. This is why many high-quality electric contacts on computers, headphones, and other electronics use gold plating.

While a gold platted ground clamp may be one of the coolest looking welding tools out there, it isn't really economical or needed for most applications and therefore isn't used.

Silver

Silver is the best conducting material at room temperature that know of today thanks to also only have one valance electron. Silver however being a precious metal and only having 1.06X more conductivity than Copper makes it far less frequently used. Unlike Gold, Silver also does tarnish which is why owners of real silverware find themselves needing to polish it.

DIMIDE's Preferred Ground Clamp Material

When you add in all the different alloys, there are a lot of materials out there. However, one outperforms all the others. C18200 Chromium Copper has amazing properties for a ground clamp. C18200 Chromium Copper is 99.1% copper and 0.9% Chromium. Thanks to the high level of copper it maintains 80% of the conductivity of pure Copper which is far better than even Aluminum.

C18200 Chromium Copper also offers excellent heat treating capabilities thanks to chromium. This allows for superior structural performance with both wear resistance under high pressure and the capability to deliver substantial clamping force.

C18200 Chromium Copper also has increased corrosion resistance to prevent tarnishing thanks to the chromium.

C18200 Chromium Copper maintains strength at high heat making it great for maintaining strength while welding.

Cross-Sectional Area

Cross-sectional area is a critical component to the transferring current. The larger the cross-sectional area is, the more current can flow. This is similar to a road with more lanes. A 60 mph road with 3 lanes allows for more traffic to flow through than a 60 mph road with 1 lane. This is why you need to use a larger diameter wire for more current.

Switching between a pure copper jaw and a chromium copper jaw with 80% of the conductivity of copper just means you need 1.25X the cross section area to transfer the same amount of current.

Contact Geometry & Pressure

When it comes to transferring current through a contact, the contact geometry matters. It's critical to maximize the contact area at the microscopic level at which electrons can flow between the ground clamp and the grounded material. To maximize contact area you need to increase the applied pressure.

There are two ways to increase applied pressure. 

1. One way is to increase the force being delivered
2. The other way is to reduce the contact area

This may be counter-intuitive, but decreasing the macroscopic contact area increases the contact pressure which in turn actually increases the microscopic  contact area in which electrons can flow. This is because what appears to be a smooth surface at the macroscopic level is actually a rigid and uneven surface at the microscopic level.

If you have ever looked at a machined surface through a powerful microscope you will see that it's actually a rigid and uneven surface. Unfortunately electrons can't jump the microscopic gaps from ridge to ridge between contact surfaces, and therefore need actual contact on the microscopic level. Increasing the contact pressure pushes these ridges tighter together which increases the total contact area.

This is why a ground clamp with sharper teeth experiences less resistance than a ground clamp with a smooth surface in spite of the later appearing to have greater contact area to the naked eye.

Travel Distance

The distance that current has to travel matters a lot. a 10 ft wire can carry substantially more current than a 200 ft wire. Unfortunately for welders, you need high amounts of current which means that you're in a constant fight with resistance. Most welders include information on what wire gauge you need to use for different current outputs at different travel distances and duty cycles.

For instance, a 1 gauge wire can carry 300 Amps of current up to 150 ft while you will need to use a larger 1/0 gauge wire to carry 300 Amps of current up to 250 ft.

Fun fact, this issue is why we use Tesla invented AC (Alternating Current) to power our grid, as it allows for current and voltage to be interchanged. We dramatically increase the voltage and reduce the current to be able to transfer electrical energy over far greater distances with far less loss due to resistance thanks to Energy = Current * Voltage and Resistance = Current / Voltage. This allowed us to transport electrical energy from power plants to houses far away. AC also had the massive added benefit of being able to transform electricity from current to voltage and back so that you didn't need a unique line for every different voltage requirement, you could just add a transformer to the device.

Making a Better Ground Clamp

DIMIDE is working on making the coming soon DIMIDE 1/4 Series Clamp modular. Part of this modularity will be to transform it into a top-quality ground clamp.

• To deliver top-quality you need top materials which is why we have a bias towards using hardened C18200 Chromium Copper.
• Our clamps are designed to deliver substantial force especially compared to competitive ground clamps. This increased clamping force delivers increased pressure and therefore increased contact area.
• Our modular ground clamp jaws will have plenty of cross sectional area to easily transfer the current you need.
• To reduce the current travel length, the lead wire will connect directly into the modular clamp jaw.
• This clamp will also have all the added benefits of our standard DIMIDE 1/4 Series Clamp including increased opening capacity, and the ability to use a pipe jaw to ground different shapes.

Measuring Ground Clamp Quality | Voltage Drop

Now that you know what makes a quality ground clamp, you may want to determine if your ground clamp is adequate. The process to do this is similar as the process to testing a car battery. Measure the voltage drop between welding lead wire and the grounded part next to the clamp. This voltage drop affects how much voltage and current actually reaches your part. By minimizing the voltage drop you gain increased control over your welding settings and are therefore able to deliver higher quality welds. As current increases, so does the voltage drop for the same clamp making you need a much higher-quality clamp for higher Amperage welds. One rule of thumb is to try to maintain a voltage drop of 62.5 mV or less.

Sources:

https://www.thoughtco.com/electrical-conductivity-in-metals-2340117

https://www.researchgate.net/figure/Electric-conductivity-versus-Rockwell-C-hardness-in-precipitation-hardened-IN718_fig4_245413418

https://www.lincolnelectric.com/en-us/support/welding-solutions/Pages/selecting-proper-size-welding-cables.aspx