Attach a ground wire from one of the threaded studs (A) at the bottom of the housing, to the mounting plate (B). The ground resistance between all system parts shall be < 0. Power from factory ground must be installed by a qualified electrician. Each DISTRIBUTION BOX and controller must be grounded. In factories, construction sites, and even commercial buildings, this question pops up all the time. Your boss might insist on it, while your. Zone Classification: Explosive atmospheres are categorized into zones according to how often and for how long explosive gasses or particles are present. Zones 0, 1, and 2 handle gases and vapors, while Zones 20, 21, and 22 handle dust. These. Internal Arrangement: Electrical components and wiring within the box must be neatly organized, clearly labeled, and aesthetically arranged for ease of maintenance.