To achieve maximum ampacity, cables in a tray must be installed with at least one cable diameter of spacing between them.

Underfloor raceways cannot be installed in areas subject to corrosive vapors or in hazardous (classified) locations unless allowed by specific NEC provisions, such as 504.20 and 501.10(B)(3).

Messenger-supported wiring in industrial establishments may use any conductor type listed in Table 310.4(1) or (2) or medium-voltage cables. Additional requirements apply for weather and sunlight exposure.

Surface metal raceways with metal less than 1.02 mm (0.040 in.) nominal thickness cannot be used where the voltage exceeds 300 volts between conductors.

Knob-and-tube wiring requires a minimum clearance of 25 mm (1 inch) between the conductor and the surface it passes over to ensure safe operation and proper heat dissipation.

Cable trays are prohibited in hoistways and areas subject to severe physical damage, ensuring safety and compliance.

When equipment grounding is required, a separate grounding conductor must be installed within the surface nonmetallic raceway as the raceway material cannot serve as a grounding conductor.

When cable trays are mechanically discontinuous, a bonding jumper sized per NEC 250.102 must connect the segments to maintain electrical continuity.

Connections in busbar grid rails must use listed insulating devices and remain accessible after installation to comply with NEC safety standards.

Power feed bus rail conductors must be at least 16 AWG or have an equivalent crosssectional area for safety and compliance.

Combination raceways must separate lighting/power circuits from signaling systems and clearly identify the compartments using stamping, imprinting, or color coding.

Cable tray covers must be made of a material that is compatible with the cable tray to ensure durability and protection.

Dead ends of underfloor raceways must be securely closed to prevent entry of debris, moisture, or unintended access, ensuring compliance and safety.

Concealed knob-and-tube wiring is allowed only for extensions of existing installations or where special permission is granted, as it is no longer widely used in modern installations.

For 4/0 AWG or larger cables in a solid bottom tray, the sum of the diameters of all cables must not exceed 90% of the tray width, ensuring proper spacing and heat dissipation.

Each length of surface metal raceway must be clearly and durably identified as required in the first sentence of NEC 110.21(A), ensuring proper use and installation.

Single conductors in ladder cable trays must be 1/0 AWG or larger, ensuring safe and compliant installations.

Surface nonmetallic raceways cannot be used in concealed locations, hazardous areas (unless permitted by other articles), or where subject to severe physical damage or ambient temperatures beyond their ratings.

Concealed knob-and-tube wiring cannot be used where insulation, such as loose, rolled, or foamed-in-place materials, envelops the conductors. This insulation can trap heat and increase the risk of overheating or fire.

Suspended ceiling power distribution systems are not allowed in damp or wet locations, hazardous (classified) areas, or concealed spaces to ensure compliance with safety standards.

Metal cable trays must be grounded as an equipment grounding conductor or bonded in compliance with NEC requirements for safety.

Cable trays containing conductors over 600 volts must display a permanent, visible warning notice stating “DANGER — HIGH VOLTAGE — KEEP AWAY,” placed every 10 feet.

Splices and joints in cable trays must be accessible and approved to ensure compliance and allow for maintenance.

Surface metal raceways are permitted in dry locations and Class I, Division 2 hazardous locations when meeting NEC 501.10(B)(3), and under raised floors as per 645.5(E)(2).

Conductors in underfloor raceways must not exceed 40% of the interior cross-sectional area to comply with NEC requirements and ensure proper heat dissipation.

Surface nonmetallic raceways are permitted in dry locations and may extend through dry walls, partitions, and floors if the raceway remains unbroken.

Open wiring on insulators cannot be installed where it is concealed by building structures, as it must remain exposed for maintenance and inspection.

When passing through walls or partitions, cable tray installations must comply with NEC 300.21 to maintain fire and smoke barriers.

The disconnecting means for the Class 2 power supply must be accessible and located within sight of the Class 2 power source to facilitate safe servicing and maintenance.

Open conductors must maintain at least 50 mm (2 inches) of clearance from metal raceways, piping, or other conducting materials, or be separated by a fixed nonconductor.

Suspended ceiling power distribution systems are limited to operating at 30 volts AC or less and 60 volts DC or less, ensuring safety for Class 2 power levels.

Single conductors used as equipment grounding conductors in cable trays must be at least 4 AWG to ensure sufficient current-carrying capacity.

Cables in cable trays exposed to sunlight must be identified as sunlight-resistant to prevent degradation.

Cable trays serve as mechanical support systems for cables and are not raceways as defined in the NEC.

Outdoor overhead conductors over 1000 volts are permitted for use outdoors in free air and can serve as service conductors, feeders, or branch circuits, ensuring compliance with high-voltage safety standards.

Cable trays in corrosive environments must be corrosion-resistant or protected as specified in NEC 300.6 to ensure longevity and safety.

Engineered design documentation by a licensed professional engineer, covering applied voltage, conductor size, support structure spacing, and environmental conditions, must be available upon request to ensure safe and compliant installation.

Raceways and cables entering a cable tray must be secured with listed clamps, adapters, or fittings to ensure stability and compliance.

Splices and taps in surface nonmetallic raceways with accessible covers are limited to filling no more than 75% of the raceway’s cross-sectional area to comply with safety standards

Underfloor raceways are permitted beneath the surface of concrete or other flooring materials, and in office occupancies when installed flush with the concrete floor and covered with appropriate flooring.

Insulators must be rated for the applied phase-to-phase voltage, the mechanical strength needed for the installation, and the impulse withstand BIL, ensuring durability and compliance with high-voltage standards.

Splices and taps in surface metal raceways with removable covers are limited to filling no more than 75% of the raceway’s interior cross-sectional area to ensure safety and functionality.

Strut-type channel raceways are not permitted where concealed, as they must remain accessible for conductor installation and maintenance.

Strut-type channel raceways must be made of steel, stainless steel, or aluminum, ensuring strength and corrosion resistance for various applications.

Open wiring on insulators is allowed indoors or outdoors, in dry or wet locations, and in areas with corrosive vapors, provided appropriate insulation is used.

Messenger-supported wiring cannot be installed in hoistways or locations where it is subject to physical damage, as these conditions compromise safety and system integrity.

Surface metal raceway enclosures must have a means for connecting an equipment grounding conductor, such as a grounding terminal screw or lug, to comply with NEC requirements

Junction boxes must be leveled to the floor grade and sealed to prevent the free entrance of water or concrete. For metal raceways, the boxes must be metal and electrically continuous with the raceways.

Bushings for open wiring through framing members must be made of noncombustible, nonabsorbent insulating materials, with waterproof sleeves used when the bushing is shorter than the hole.

The minimum size for load-side utilization conductors is 18 AWG. However, conductors as small as 24 AWG are permitted for Class 2 circuits if they are fully enclosed and comply with specific conditions.