Raceway Design

Cables are contained in some type of raceway, typically conduit, duct, or cable tray. The raceway protects the circuits from mechanical damage and influences the reactance and ampacity of the cables it contains. Conduit shall be sized properly so cables can be pulled without damaging the cable jacket or insulation and so adequate cooling exists when the cables are energized. When designing conduit and duct systems, sizing of the conduits and pull boxes are governed by the NEC. NEMA and CTI also provide publications useful for the design and construction of raceway systems. Pulling tension and sidewall pressure must be calculated to assure that the cables will not be damaged during installation. Pulling tension is often the controlling factor for control and instrumentation cable, while sidewall pressure typically controls for power cables. Cable tray provides more versatility than conduit or duct systems, but installation challenges can still be faced.