General - hdbk109220040154

DOE-HDBK-1092-2004

9.7.1

GENERAL

Interlock systems are not a recommended disconnecting means for cabinets and equipment

having potentially dangerous currents and/or voltages present. (See Section 9.6.4)

Permanently connected equipment and multi-phase equipment should employ a listed switch or

circuit breaker as means for disconnection.

All cord-connected equipment should have one of the following as a disconnecting device:

1. A switch or circuit breaker,

2. Plug that can be disconnected without the use of a tool, or

3. A separable plug, without a locking device, to mate with a socket-outlet in the building

Where equipment is connected to the source of supply by flexible cords having either an

attachment or appliance plug, the attachment or appliance plug receptacle may serve as the

disconnect (NEC 422.33).

Where a switch is not part of a motor, motor circuit or controller, the disconnecting means

should be within 50 feet and in sight of the operator and marked as the disconnection device for

the equipment.

Where a disconnecting means is not part of the equipment, the disconnecting means should be

near the equipment, within easy reach of the operator during normal operation of the equipment,

and marked as the disconnection device for the equipment.

If a disconnecting device is part of the equipment, locate it as close as practical to the input

power source.

9.7.2

EMERGENCY SHUTDOWN

The emergency shutdown switch should be within arm's reach of the operator, be easily

identifiable, deenergize all power to all equipment associated with the system, be separate from

the routine on/ off switch, and be located to protect the employee from moving parts. However,

the emergency shutdown switch should not disconnect auxiliary circuits necessary for safety

(such as cooling).

9.7.3

SPECIAL CONSIDERATIONS

The disconnecting means should interrupt the source voltage for secondary or remote controlled

equipment, such as those using thyristor controls. Do not rely on disconnecting the control

voltage.

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