Dry wood dust moving through flexible PVC vacuum hoses at 25 meters per second is an industrial static electricity generator. The triboelectric effect—friction between non-conductive wood chips and the plastic hose wall—routinely generates electrostatic potential differences exceeding **30,000 Volts**.
### The Combustible Dust Hazard
When fine MDF dust (
lt; 400\mu\text{m}$) reaches an airborne concentration between $30\text{ g/m}^3$ and $60\text{ g/m}^3$ inside an extraction duct, it forms an explosive fuel-air mixture. A single electrostatic spark jumping from the hose to a grounded machine frame can trigger a violent deflagration.
### The Proper Grounding Protocol
1. **Bare Copper Ground Wire:** Thread an uninsulated $1.5\text{ mm}^2$ solid copper wire through the entire interior length of the flexible spiral ducting.
2. **Terminal Bonding:** Securely clamp both ends of the internal copper wire to the steel frame of the CNC gantry and the grounded steel chassis of the cyclone dust collector.
3. **Verify Resistance:** Use an insulation multimeter to verify total loop resistance from the spindle dust hood to the main workshop earth ground is **under $5\,\Omega$**.
Static buildup is eliminated, protecting sensitive computer electronics from electrostatic discharge (ESD) crashes.