Installation / Operation / Maintenance Manual
10/28/2019
16
5.
MOLDED CASE SWITCHES
5.1.
GENERAL INFORMATION
The molded case switches used in transfer switches are the standard devices supplied by molded case switch
manufactures. Figure 2 (page 16).
Thermal magnetic or magnetic trip units may be installed (Accessory 23) for thermal overload and short circuit
protection. When these trips are provided, a bell alarm contact is included inside the breaker to indicate to the transfer
switch circuit that the breaker has tripped due to an overload. This breaks the motor circuit and prevents the transfer
switch from cycling between the Normal and Emergency positions.
If either breaker trips due to overload, it can be reset by manually operating the transfer switch to a position so that the
breaker resets. After resetting, return the transfer switch to the proper position. A shunt trip may also be provided. This
allows the breaker to be electrically tripped from a remote location and can also be reset manually.
5.2.
INSPECTION AND MAINTENANCE
Terminal lugs and trip units must be tight to prevent overheating. Due to the inherent wiping action built into the
moving contacts of all molded case switches, operating the switch several times under load will remove any high
resistance film that may have formed. Under normal conditions, additional cleaning of contacts is not required.
However, should operating and/or atmospheric conditions make it desirable to clean the contacts further, the following
procedure is recommended. (Refer to Figure 2).
Remove cover, arc chutes, and cable terminal assemblies. Wipe contact surfaces with a clean, lint free cloth. If surfaces
are excessively oxidized or corroded, scrape lightly with a fine file before wiping.
The auxiliary micro switches are mounted internally to the molded case switch.
Figure 2
