Cadweld is a term you hear often, especially when working on equipment grounding designs. But what exactly is it, and how does it work? Sometimes, a short video offers the best form of explanation . . . .
A cadweld is a brand name of the generic process called exothermic welding. Exothermic welding is used to join copper conductors together to make low-impedance, durable electrical connections at physical joints. If exothermic welding weren’t used to reinforce the ground connection joints, then over time, due to corrosion and the effects of high currents at mechanically-weak connection points, the joint resistance would increase and threaten the effectiveness of the ground path.
That could result in a serious safety hazard.
The joints are formed when copper cables are brought together, or when a copper cable is joined to a ground rod, a piece of rebar, or a flat surface. A graphite mold is used to secure the joint together. The thermite powder and welding material is poured into the mold. Once lit, the powder burns to produce molten copper which flows down through the mold and around the joint. Afterwards, the mold is removed and the welded joint remains.
The exothermic welding process is used to produce white-hot molten metal in a fast-acting chemical process. The molten metal flows over the joint and bonds and binds the joint together. It is one of the methods allowed by the NEC in Article 250.8 to connect equipment grounding conductors, electrode conductors, and bonding jumpers.
Cadwelds are used when installing ground grids or connecting new equipment to existing ground grids. They can join copper to copper, copper to steel, or copper to cast iron. The joints can be welded and then buried in the ground or concrete with little fear that they will degrade over time.
Exothermic welding is also used to produce molten iron to weld railroad rails together.
You can quickly and easily flip through pictures of typical joints by reviewing the Cadweld Welded Connections Quick Reference Guide.
But best of all, you can see it in action by watching the short video below. It’s less than three minutes long. The narrator explains the process in the beginning, then takes the weld outside and shows it in action. He ramps up his video quality by using a good microphone; that makes all the difference in the world.