Question

If the subcontractor on your job is installing #0000 (4/0) wiring, is he likely working on the security system wiring, main feed, telephone system, or on the building's data system?

Answer

#0000 or 4/0 (four aught) wiring is a large, half-inch- (1.3-centimeter-) diameter wiring that you would expect to see as part of the main electrical feed.