When cable trays pass through walls or floors, seal openings using fire-rated penetration sealing materials. Do not modify or damage the tray coating or structure during use. The effective weatherproofing of cable trays helps to keep weather out, preventing damage to the building envelope, avoiding thermal breaks, maintaining the indoor environment and helping to keep the various cables and wires protected. Fire. FIRSTO firestops are designed to seal multi-cable and cable tray penetrations of fire-rated walls and floors. Working in inaccessible openings is often cumbersome. Cables, cable bundles, conduits, bundles of conduits, empty pipes, cable trays and cable ladders may also pass through penetration seals in walls and floors and should be taken into consideration during all phases of design and application. The last part of our penetration seal series of articles. Cable tray installation must comply with specific technical standards to ensure electrical safety, system reliability, and long-term maintainability. 15 is the right general reference, but 501. UL's standard on Type TC says it has a "gas/vaportight continuous sheath," but is silent on whether it can.