Welding is a process that involves the use of electricity and usually a metal arc in order to join two pieces typically made of metal. Welding is what allows both small and large joints to be made be it for the construction of cargo ships or a bird cage. But since you're working with electricity, you need to keep yourself and your workspace safe. While not the only solution, using earth clamps is one of the most important things you can do. An earth clamp is able to ground your workpieces and thus keep you safe from an electric shock. This same surge of electricity can also damage equipment.
What to Look for in Earth Clamps
Conductivity
Probably the most important factor of earth clamps is their level of conductivity. The higher the level of conductivity of a welding ground clamp the more electricity can flow. Welding earth clamps with greater conductivity don't need a large cross-sectional area and thus are far smaller and more portable. A highly conductive clamp won't heat up as quickly too and thus the risk of it burning through is far less.
Hardness
With a clamp that has increased hardness, you can have a better clamping force. Why is this important? Because on a microscopic level the surface of a welding earth clamp is not smooth and thus it doesn't come in perfect contact with the workpiece. This unfortunately makes for a smaller contact area and lower conductivity. But with a greater clamping force, you can have a high conductivity clamp with less pressure being put on it.
Corrosion Resistance
Since welding earth clamps are made of metal, corrosion is quite a familiar sight. Metal can tarnish mainly because of exposure to oxygen and water. This causes a chemical reaction that creates a thin layer of corrosion on the surface of a welding ground clamp. To avoid this from happening you should go for clamps that have been gold-plated or nickel-plated. You can also get clamps that have been combined with copper chromium or aluminium alloy.
Surface Area
As you already know a greater surface area makes for better conductivity but it also provides something else - grip. A greater surface area combined with a strong clamping power means you're getting a secure welding earth clamp. This way your grounding is going to improve overall. When working with curved materials, make sure to use a welding ground clamp with a curved clamping surface.
Clamping Power
Although clamping power affects quite a lot of factors it is reliant on only one. That's the spring. The spring of an earth welding clamp determines the clamping power and thus the surface area and conductivity of a clamp. The tougher the spring is the higher the clamping power and the better the grip you will have on your workpiece.
You'll be able to tell a more affordable clamp from a high-quality one if you test out their spring. If the spring is not that tough it's usually a lower-quality clamp you have in your hand. But keep in mind stronger springs will require a lot of strength from you to open and close the clamp.
Materials of Earth Clamps
Copper
If you want your earth welding clamp to have the best conductivity possible at any form factor then you should go for one made of copper. Although copper is prone to tarnishing the effect is not as detrimental to it as to other materials. Copper is quite malleable though but it's still a mid-strength material that won't deform under light pressure.
Gold
As precious as it is, gold is actually quite good at conducting electricity. Although it doesn't come cheap, it makes for a great alternative to copper. Especially when you want a clamp that won't tarnish. But although gold has its pros, it also comes with downsides and one of them is its extremely high price.
Silver
Silver earth clamps are even better than ones made of copper as they are more conductive than copper. But this is only the case at room temperature. Just like gold, silver is an expensive material that unfortunately does tarnish.
Zinc/ Brass
The cost of both zinc and brass-made clamps is quite low but the reason why that's the case is exactly their low conductivity. Zinc and brass are 3.6X less conductive than copper but they are stronger.
Aluminium
What comes with a similar strength level as zinc and brass and is also less conductive than copper is aluminium. Although aluminium makes for a low-maintenance clamp it does wear out the same way as one made of copper. Keep in mind though that aluminium clamps have a higher clamping power than copper clamps.
Conclusion
Safety should be your number one priority when working high currents nearby. When welding, a helmet and welding gloves are not the only equipment that matters. Without the proper grounding clamps, you wouldn't stand a chance against the power of an electrical shock.
