Cable trays and busways at floor level or at slab penetrations shall have a waterstop no less than 50 mm in height. Sealing shall be tight and reliable, without visible cracks or. Scope: Firestopping for busway, cable trays, cables, and trunking passing through walls in enclosed electrical installations. Electrical fires can spread rapidly through the cables within a tray system, which is why choosing the right material for your cable tray is paramount in reducing the risk. Materials like steel. 3M Fire Barrier Moldable Putty+ is a one-part, halogen-free product designed to firestop electrical outlet boxes and a wide variety of through-penetrations including cable, conduit, insulated pipe and metal pipe, which penetrate fire-rated construction. But they're also vulnerable to overheating, electrical faults, and fire hazards.