Rack Power Distribution

DOE-HDBK-1092-2004

9.4

RACK POWER DISTRIBUTION

The following guidelines will provide the necessary information to correctly install power

distribution equipment within instrumentation racks containing electrical and electronic

equipment.

9.4.1

GENERAL REQUIREMENTS APPLYING TO ALL AC POWER EQUIPMENT

WITHIN OR ATTACHED TO INSTRUMENT RACKS

9.4.1.1 LOADS

Knowledge of the loads that will be connected within a rack cabinet is necessary before starting

design of a rack power distribution system. All components must be sized correctly for the loads

and should provide for expansion.

Equipment enclosures may or may not contain a power distribution unit. A rack power

distribution unit contains a main overcurrent protection device and multiple branch circuits that

are individually protected against overcurrent. Without a power distribution unit, the power wiring

is considered part of one branch circuit.

Branch circuit loading shall meet the requirements of NEC Article 210. (See NEC 210.21

through 210.23).

External convenience outlets should be connected to a separate circuit breaker.

Where three-phase, four-wire service is utilized, the loads should be evenly distributed on all

phases and there should be consideration of sizing the neutral conductor for certain loads (such

as computer equipment) due to the presence of harmonic currents. (See NEC 210.4 and

310.10).

9.4.1.2 OTHER GENERAL EQUIPMENT REQUIREMENTS

Rack power distribution components or assemblies must be listed by an NRTL, or have AHJ

approval (See Section 2.5).

9.4.2

CONDUCTORS AND CABLES SPECIFIC REQUIREMENTS.

Each type of internal wiring for equipment or an accessory shall be acceptable for the particular

application when considered with respect to (1) the current, ambient temperature, voltage, and

other conditions of service to which the wiring can be subjected, and (2) exposure to oil or

grease.

The term "cables" refers to groupings of wires typically used for control signals, data, or DC

power. The term "cords" refers to AC power cords.

The basic insulation on each wire shall be rated for at least the maximum voltage to which the

wire is connected, and for at least the temperature it attains. Additionally, the insulation should

be rated for the maximum voltage of nearby conductors and wire to which each wire may be

exposed. Insulating tubing, sleeving, and tape shall be rated for at least the maximum voltage

against which it insulates, and for at least the temperature it attains. Power and signal wires

should be routed separately within a chassis.

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