Figure 3-7.--Schematic and wiring diagram of ABT-1A2.

also has a manual switch for selecting the

capable of transferring the load between two

normal or emergency power sources and a test

sources of power available to the ABT. The two

switch.

sources are identified as normal (ship's service)

For purposes of explanation, the 3-phase

and alternate (ship's service) or normal (ship's

model will be discussed. The ABT-1A2 is

service) and emer-gency (service).

designed to transfer automatically from normal

Three-way transfers indicate that the

to emergency supply upon a decrease in voltage

ABT is capable of transferring the load between

to within the 81- to 69-volt range across any two

three sources of power available to the ABT.

of its three phases in a 120-volt system. Upon

These three sources of power are identified as

restoration of the voltage to the range of 98 to

normal, alternate, and emergency. Either the

109 volts, the unit is adjusted to retransfer to

normal or alternate source may be selected as

the normal source of supply. An intentional time

the preferred source.

delay of 0.3 to 0.5 seconds is included in the

One of the more common ABTs used with IC

circuitry for both transfer and retransfer. This

switchboards is the ABT-1A2. This model operates on

allows for surges in line voltage and short

120-volt, 60-Hz, single- or 3-phase systems.

duration losses of power.

The ABT-1A2 (fig. 3-6) has a control

Automatic operation (refer to fig. 3-7) is

disconnect switch that allows the ABT to be

accomplished when the normal supply voltage drops

operated in the manual or automatic mode. It

Figure 3-7.--Schematic and wiring diagram of ABT-1A2.

3-9