It's important to be certain glass-lined devices is electrically grounded. In the case of AC spark testers This is often preferable for safety factors, but for DC testers it is actually essential. The voltage opportunity is used throughout the clean, dry glass surface area by an insulated, hand-held fault probe. https://www.quora.com/profile/Jacques-Donaldson-2/Heating-and-cooling-system-design-of-glass-lined-reactors-Glass-lined-reactors-are-crucial-components-in-various-indust