By The joints in an earthing system are its weakest point. A loose or corroded clamp raises resistance, overheats under fault current, and slowly fails. Exothermic welding solves this by fusing conductors into a single permanent connection — and an exothermic welding kit is what makes it possible on site. This guide explains how it works, what’s in a kit, and when to use it.
What is exothermic welding?
Exothermic welding (also called thermit welding) joins two conductors by a controlled chemical reaction. A powder of copper oxide and aluminium is ignited inside a graphite mould placed over the conductors; the reaction produces molten copper that flows around and fuses them into one solid connection. There’s no external power or flame source needed — just the reaction itself.
The result is a joint that is permanent, corrosion-resistant, and has the same current-carrying capacity as the conductor itself — unlike a mechanical clamp, it won’t loosen or degrade over time.
What’s in an exothermic welding kit?
A typical kit has two main parts:
- Graphite mould — shaped for the specific connection (cable-to-cable, cable-to-rod, cable-to-plate, etc.) and conductor size.
- Weld powder (and igniter) — the exothermic charge, sized to the mould, that produces the molten copper.
Handling tools (clamp/handle, cleaning brush, flint igniter) complete the set. Moulds are reusable for many welds; the powder is consumed per joint.
See Ashlok’s exothermic welding kits → Exothermic Welding Kit
Where is it used?
Exothermic welding is the preferred connection method for:
- Earthing grids and mats in substations, plants and infrastructure.
- Bonding earthing electrodes, conductors and busbars where a maintenance-free joint matters.
- Lightning protection down-conductor and earth-termination connections.
Anywhere a joint must last the life of the installation without maintenance, exothermic welding is the standard.
Exothermic welding vs mechanical clamps
A mechanical clamp is quick and cheap but relies on contact pressure that relaxes over time, and the contact surfaces corrode — resistance rises and the joint can fail under a fault. An exothermic weld is a molecular bond: lower resistance, no corrosion at the joint, and no maintenance. For critical earthing, the weld is worth it.
Frequently asked questions
Is an exothermic weld better than a clamp? Yes for permanence — it fuses the conductors into one piece with full current capacity and no loosening or corrosion. Clamps suit temporary or accessible joints.
Do I need electricity to do exothermic welding? No — the reaction is self-sustaining once ignited. That’s why it’s ideal for remote sites.
Is the mould reusable? Yes — a graphite mould lasts many welds; you replace the weld powder per joint.
Which mould and powder size do I need? It depends on the conductor sizes and connection type — tell us your requirement and we’ll match the kit.
Can it join copper to steel/rod? Yes — there are mould/powder combinations for cable-to-rod, cable-to-plate and other configurations.
Ashlok manufactures exothermic welding kits along with its full earthing and lightning-protection range, since 1999. Explore exothermic welding kits → · New to earthing? Start with our earthing electrode guide.