Dielectric Strength
Dielectric strength is the maximum electric field an insulating material can withstand before it electrically breaks down and starts conducting, commonly reported in V/mil or kV/mm. In CNC manufacturing, this property determines whether machined insulation parts like G-10 spacers or fixture plates survive applied voltage without arcing through their thickness.
On the shop floor, dielectric strength is a specification limit, not just a material-sheet curiosity. When a G-10 spacer, barrier, or mounting plate is machined for electrical isolation, the machinist must confirm that the finished minimum wall thickness can handle the working voltage with margin. Typical perpendicular values of 500–750 V/mil mean a 0.060-inch wall can theoretically stand off tens of thousands of volts, but real-world service, humidity, and machining damage reduce that. Cutting G-10 is abrasive: carbide or diamond tooling, rigid workholding, moderate feeds, and good dust extraction are essential. Clean, resin-sealed edges preserve insulation; ragged edges expose glass fibers and create moisture ingress paths. In EDM, dielectric strength also governs the fluid’s behavior: it must hold off until the spark initiates, then recover rapidly. Therefore, understanding the reported test conditions and how machining changes the part is central to reliable insulation performance.
- Underspecified thickness versus voltage: A design may list a good insulating material but ignore the actual field strength across minimum wall thickness, so breakdown occurs through spacers or barriers in service.
- Machining damage that defeats insulation: Aggressive feeds, dull tools, or poor dust extraction tear the glass-resin matrix of G-10, leaving frayed edges and microcracks that absorb moisture and create leakage paths in humid service.
- Assuming all dielectric strength numbers are comparable: Values depend on test method, thickness, orientation, temperature, and medium, so comparing a supplier's kV/mm figure against a design requirement from other conditions leads to failures after thermal cycling or contamination.
Is dielectric strength the same as resistivity?
No. Dielectric strength is the breakdown threshold under an electric field, while resistivity describes how strongly a material resists current flow under non-breakdown conditions.
Why is G-10 common in CNC electrical fixtures?
G-10 combines electrical insulation with machinability and dimensional stability, making it suitable for machined insulating parts; however, its glass reinforcement makes tool wear and edge quality critical.
What does 500–750 V/mil mean in shop terms?
It means one mil of that material can withstand roughly 500 to 750 volts under the stated test orientation before breakdown, so actual allowable voltage depends on the real thickness and safety factor used in the design.