Imagine a welding process that requires no electricity, no heavy machines, and completes in split seconds, yet creates a bond stronger than the wire itself.
It is Cadwelding, also known technically as exothermic welding.
If you come from a background of MIG or Stick welding, this process will feel completely alien. You aren't using an electric arc to melt metal. Instead, you are acting like a chemist. You are using a precise mixture of powders to trigger a reaction that produces molten copper in the blink of an eye.
While "Cadweld" is actually a brand name (like Kleenex is for tissues), it has become the universal term for this specific type of bonding. It is the gold standard for electrical grounding. If you are building a cell tower, a data center, or a substation, you are going to be doing this.
In this guide, we will break down exactly how this "thermite" process works, why it is safer and better than mechanical clamps, and the critical safety steps you need to know before you light the fuse.
Key Takeaways:
- Definition: Cadwelding (a common name for exothermic welding) is a process that uses molten copper to permanently join electrical conductors without using electricity.
- The Reaction: It relies on a chemical reaction between aluminum powder and metal oxide to generate intense heat.
- Why Use It? Unlike mechanical clamps, a Cadweld connection fuses the metals into one solid piece. It will never loosen, corrode, or increase in electrical resistance.
- Primary Use: It is the industry standard for grounding systems, lightning protection, and bonding railroad tracks.
- Safety Alert: Water is the enemy. Even a drop of moisture in the mold can cause a dangerous steam explosion. You must pre-heat the mold every single time.
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What Is Cadwelding (Exothermic Welding)?
At its core, Cadwelding is a method of making electrical connections.
When you need to join two big copper cables together for a ground grid, you have two choices. You can use a mechanical clamp (a bolt and a nut), or you can weld them.
Mechanical clamps have a problem. Over time, the ground shifts. The temperature changes from winter to summer. The metal expands and contracts. Eventually, the nut loosens. Air gets in, corrosion starts, and the electrical connection fails.
Cadwelding solves this by melting the two wires together.
The Aluminothermic Reaction
You don't need a chemistry degree to understand this, but it is cool to know what is happening inside the mold.
The process uses a mixture of aluminum powder and copper oxide. When you ignite this mixture, the aluminum "steals" the oxygen from the copper. This reaction releases a massive amount of energy.
- The Reaction: Aluminum + Copper Oxide = Aluminum Oxide + Molten Copper + Heat.
- The Heat: It gets hot. We are talking over 4000°F (2200°C) in a fraction of a second.
- The Result: The molten copper flows down over your wires, melting them instantly and fusing everything into one solid nugget of copper. The aluminum oxide floats to the top as slag, which you chip away later.
How Does the Process Work?
Unlike arc welding, where you have a torch and a ground clamp, exothermic welding uses a specific set of tools. You cannot just "wing it" with this equipment. Everything must match.
1. The Graphite Mold
This is the heart of the system. It is a block of machined graphite (a type of carbon) that holds the wires in place and contains the liquid metal.
- These molds are fragile. If you drop one, it breaks.
- They are specific. You cannot use a mold designed for 4/0 wire on a 2/0 wire. The liquid copper will leak out the gaps and run all over your boots.
- Tip: Always check your cable size before you start. You can reference a Wire Gauge & Amp Chart to make sure your wire matches the mold capacity.
2. The Weld Metal (The "Shot")
The powder comes in tubes or cartridges. These are measured exactly for the specific mold you are using. If you have a large mold, you need a large shot (like a #150 or #200 cartridge). If you use a small cartridge in a big mold, the weld will fail.
3. The Handle Clamp and Disk
You need a special handle to hold the mold closed tight. Inside the mold, you place a small steel disk. This disk acts like a trap door. It holds the powder in the top chamber until the reaction happens. When the powder melts, it melts through the disk and lets the liquid copper drop down onto the wires.
Step-by-Step Cadwelding Procedure
This is a precision process. If you follow the steps, it works every time. If you skip a step, specifically cleaning or heating, it will explode or fail.
Step 1: Preparation and Cleaning
This is where 90% of failures happen. The wire must be bright and shiny.
- Remove Insulation: Strip the wire back far enough so no insulation enters the mold. Burning insulation creates gas, and gas creates bubbles (holes) in your weld.
- Clean the Wire: Use a wire brush or a solvent cleaner. If the wire is covered in mud, oil, or oxidation, the weld will not stick.
- Dry the Wire: If the wire is wet from rain or morning dew, you must dry it with a torch.
- Note: As with standard welding, preparation is everything. You can read more about how dirty materials cause issues in our guide on Welding Machine Troubleshooting.
Step 2: Pre-heating the Mold
You must heat the graphite mold before you make the first weld.
- Why? Graphite absorbs moisture from the air. Even on a sunny day, there is water trapped in the pores of the mold.
- The Danger: If you pour 4000°F liquid copper onto water, that water instantly turns into steam. Steam expands to 1600 times its volume. This results in the molten metal exploding out of the top of the mold.
- The Fix: Use a propane torch to heat the mold until it is too hot to touch (about 250°F). You should do this before the first weld of the day and in between shots if the mold cools down.
Step 3: Assembly
- Insert Wires: Place your clean wires into the mold.
- Clamp: Close the handle clamp. It should snap shut with a bit of resistance. If it is too loose, liquid metal will leak out.
- The Disk: Drop the steel disk into the bottom of the reaction chamber (the funnel at the top). Ensure it is sitting flat.
- The Powder: Pour the weld metal powder into the chamber on top of the disk. Do not pack it down; leave it loose.
- Starting Powder: Depending on the brand, you will tap a little bit of "starting powder" (usually located in the bottom of the tube or lid) onto the lip of the mold. This is like the fuse. It ignites easier than the main powder.
Step 4: Execution
- Close the Lid: Close the graphite lid.
- Warn Everyone: Yell "Fire in the hole!" or "Firing!" so people don't look directly at it without glasses.
- Ignite: Use the flint gun (striker) to spark the starting powder.
- Wait: The reaction takes about 3 seconds. It will flash, smoke, and sizzle. Wait another 10 to 15 seconds for the metal to solidify.
- Open: Open the mold and remove the finished connection.
- Clean: Use a natural bristle brush or a mold scraper to clean out the slag before the next shot.
Cadwelding vs. Mechanical Connections (Clamps)
Why go through all this trouble with gunpowder and molds when you could just use a wrench and a clamp?
Conductivity
A mechanical connection is just two pieces of metal touching each other. On a microscopic level, they are only touching in a few spots. This creates resistance. A Cadweld fuses the wires into a single molecular mass. The connection actually conducts electricity better than the wire itself because the bond is pure copper.
Longevity and Maintenance
Mechanical clamps are "high maintenance."
- Thermal Cycling: As wires heat up (from current or sun) and cool down, they expand and contract. This naturally loosens screws and bolts over time.
- Corrosion: Moisture gets between the clamp and the wire. Rust forms. Rust does not conduct electricity.
- The Cadweld Advantage: Once an exothermic weld is made, it is permanent. You can bury it in the dirt, pour concrete over it, or hide it in a wall. It will never loosen. It will never corrode. You never have to check it again.
Fault Current Capacity
If lightning strikes a building or a massive short circuit happens, the ground wire has to carry a huge amount of energy for a split second. A mechanical clamp might melt or blow apart under that stress. A Cadweld connection can handle more current than the wire itself. The wire will melt before the weld does.
Safety Hazards and PPE
Cadwelding is safe if you respect it, but it is unforgiving if you are careless. You are creating a miniature volcano in your hands.
Managing Extreme Heat
The reaction produces heat that is significantly hotter than standard welding arcs. The slag that pops out is molten glass and aluminum oxide.
- Gloves: You need heavy-duty leather welding gloves. Thin mechanics gloves will melt to your skin if a spark hits them.
- Clothing: Wear cotton or wool (natural fibers). Synthetic clothes like polyester or athletic wear will melt instantly if a hot spark lands on them. You can find more on proper gear in our Welding Safety and Maintenance guide.
Eye and Flash Protection
The reaction gives off a bright white flash. It isn't quite as dangerous as the UV radiation from TIG welding, but it is bright enough to cause spots in your vision.
- Glasses: Always wear safety glasses with side shields.
- Shades: It is recommended to use a light shade (Shade 3 or 5) or look away at the moment of ignition.
- The Real Danger: The real danger to your eyes isn't the light; it is the flying sparks. Never look down directly into the mold vent when firing. For more on protecting your vision, read our article on Welding Eye Injury Prevention.
The Moisture Danger (Steam Explosions)
We mentioned this in the steps, but it is worth repeating. Water is the enemy. If you are working early in the morning, the dew on the grass is a hazard. If you are sweating heavily and sweat drips into the mold, it is a hazard.
When water turns to steam inside the mold, it acts like a bomb. It sprays molten copper out of the mold openings at high speed. This is the most common cause of injury in exothermic welding. Always pre-heat your mold.
How It Differs from Arc Welding
If you are an experienced welder, you need to switch gears mentally when doing this.
No Power Source
You do not need a generator or an outlet. This makes Cadwelding perfect for remote sites. You can hike up a mountain to a cell tower or work in the middle of a field with just a small toolbox.
Different Skill Set
Arc welding (like Stick or TIG) requires "motor skills." You need a steady hand to manipulate the puddle. Cadwelding requires "procedural discipline." You don't need a steady hand; you need to be good at following instructions.
- Did you clean the wire?
- Did you insert the disk?
- Did you check the mold for gaps?
- Did you heat the mold?
If you want to compare the dexterity needed for arc welding versus the setup focus of Cadwelding, check out our TIG Welding Tips for Beginners. TIG is about art; Cadweld is about chemistry.
Conclusion
Cadwelding is the unsung hero of the electrical world. It sits quietly underground, buried in concrete, or hidden behind walls, keeping our buildings and towers safe from lightning and electrical faults.
While it lacks the artistic flair of TIG welding, it creates a connection that is mechanically and electrically superior to anything else. By using a chemical reaction to create molten copper, you ensure your electrical infrastructure is safe and reliable.
Remember the three pillars of a good Cadweld:
- Cleanliness: Shiny wire only.
- Dryness: No moisture in the mold.
- Correctness: Match the mold to the wire and the powder.
If you respect the heat and follow the steps, you will create a bond that will outlast the wire itself.
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FAQs About Cadwelding
Here are the questions we hear most often from guys in the field.
Can you Cadweld in the rain?
No, you should never Cadweld in the rain. The graphite mold must be completely dry, and rain makes that impossible. Any moisture can cause a violent reaction or explosion. If rain starts, stop work or use a fully waterproof tent designed for Cadwelding.
Is Cadwelding permanent?
Yes, a Cadweld connection is permanent. Once the weld is made, it becomes a solid molecular bond between the metals. You cannot loosen or remove it like a bolt. The only way to remove it is to physically cut the conductor.
Can I reuse the graphite mold?
Yes, graphite molds are reusable if they are handled carefully. A well-maintained mold can last around 50 to 100 welds. Graphite is soft, so scraping it with metal tools or dropping it can cause damage. If the mold starts leaking molten metal or loses its shape, it should be replaced.
Is this the same as stick welding copper?
No, Cadwelding is not the same as stick welding copper. Stick welding uses an electric arc and special rods, and copper is very hard to weld that way. It usually requires heavy pre-heating and advanced skill. Cadwelding is a chemical process and is much easier for bonding grounding and copper cables.
Can I use a different brand of powder in my mold?
It is not recommended to mix powder brands with molds. While the basic chemistry is similar, the powder amount and burn rate can vary by brand. Using the wrong size charge can cause poor welds or safety issues. For best results, always match the powder brand to the mold brand.