Raceways and Trays

DOE-HDBK-6004-99

Instrumentation cables should be multi-conductor, No. 16 AWG, twisted and shielded, and should

have 600 V insulation. Shield grounding should be in accordance with the equipment manufacturer's

recommendation. Multi-paired cables should be used wherever possible between terminal boxes and

the cabinets. The insulation and jacket material should be the same as specified for the control cable.

All thermocouple circuits should be No. 18 AWG or 20 AWG with twisted and shielded leads.

Multi-paired cables should be used wherever practicable.

Coaxial and triaxial cables should conform to the specifications of the suppliers of the systems in

which they are used.

All individual load circuit conducts should be capable of carrying 125% of rated full load at ambient

temperature with due allowance for cable grouping. Transformer primary and secondary feeder

cables should be capable of continuously carrying 115% of the maximum transformer rating. Cable

size should meet the requirements of short circuit duty, and limit the voltage drop to 5% (2% in

supply feeder cable plus 3% in branch circuit feeder equals 5% overall voltage drop).

Cable current carrying capacity (ampacity) information contained in IPCEA Publications P-46-426

and P-54-440 should be used to select cable size. For circuits which will be routed partly through

conduit and partly through trays or underground ducts, the cable size should be based on the

ampacity in the portion of the circuit with the highest conductor temperature.

The conductor size should be large enough to ensure that the conductor temperature, after a short

circuit, (assuming rated conductor temperature prior to the short circuit) will not exceed 2500 C.

For purpose of sizing the cable, it should be assumed that over load operation at the emergency

temperature of the conductor will be limited to 100 hours per year, and that such 100-hour overload

periods will not occur more than five times during the life of the facility. The emergency temperature

rating is 130o C for cross linked polyethylene and EPR insulated cable.

Raceways and Trays

Underground, exposed, and embedded conduits should be used through the facility where the use of

trays is not economical or practicable.

Underground conduits for other than safety-class circuits should be type PVC ducts encased in a

concrete duct bank. Underground safety-class circuits should be run in cable trenches, tunnels, or

duct banks designed to withstand the SSE. The minimum size of conduit used in duct bank should

be 2 inches.

The top of duct banks should be buried a minimum of 2 feet below grade. Underground conduit

within duct bank for non-Category I (non-seismic) installation should be non-metallic type DB. The

duct encasement should be reinforced concrete. The surrounding encasement should be a minimum

of 3 inches thick. PVC type DB encased in reinforced concrete should be used for a Seismic

Category I duct bank. Rigid steel conduit encased in reinforced concrete should be used for isolated

runs. Single conduit leaving a duct bank between manholes or groups of conduits should be rigid

steel galvanized encased in un-reinforced concrete with 3 inch cover all around. The top surface of

the electrical duct banks should be covered with red dye on the surface to distinguish them from other

underground structures.