Installation / Operation / Maintenance Manual
10/28/2019
11
1.
CONSTRUCTION
All of the molded case switches and/or circuit breakers are electrically interlocked through control relays and auxiliary
switches, and mechanically interlocked through a walking beam mechanism which is located on the rear of the
baseplate. This mechanism is a fulcrum and lever device which positively prevents both molded case switches or circuit
breakers from being on the ON position simultaneously. It provides a “Fail-Safe” design.
The gear motors can operate on either AC or DC, and the gear reduction unit is permanently lubricated so that no
maintenance is required.
All transfer switches are provided with an insulated operating handle to enable personnel to manually operate the
transfer switch should this become necessary. The handle is permanently mounted and readily accessible in an
emergency.
All relays are of the industrial type to ensure long life and minimum maintenance. All relays are rated for continuous
duty to eliminate overheating of coils. The only relays that are continuously energized are the Phase Failure Relay
Normal (PFRN), Time Delay to Pickup (T) and the Normal Control Timer (TNR).
All timed control relays are of the pneumatic type.
Standard wiring harnesses are manufactured from 16-gauge insulated machine tool wire. All control circuits are
protected with fuses.
2.
DESCRIPTION OF OPERATION
Normally, the transfer switch operates on the preferred power source with the Normal molded case switch in the closed
position and the Emergency molded case switch in the open position. (Refer to Wiring Diagrams, Pages 7, 9 and 11.
Note:
These wiring diagrams are for reference only and should not be used in place of wiring diagrams are for
reference only and should not be used in place of wiring diagrams for a specific switch.)
All Phases of the preferred power source are continuously monitored by a voltage sensitive relay which is adjustable
from 70% to 90% of nominal. In the event of a drop in any phase of the preferred voltage below the drop-out set point
the voltage relay, the TNR Timer begins timing.
Upon completion of this ten second delay, the transfer switch motor is energized through the emergency relay and TNR
contact opening the Normal switch and closing the Emergency switch, thus affecting the power source transfer. With
the switch now operating on the emergency source, the voltage relay continues to monitor the preferred source.
When all phases of the preferred source return to the pickup level of the voltage relay, the “T” Timer begins timing,
upon completion of this 10 second delay, the transfer switch motor is energized through the “TNR” contact, opening the
Emergency Switch and closing the normal switch, thus affecting the power source transfer.