Product Manual

2. Introduction 8-2018

2.2 Transfer Switch Application

Transfer switches are an essential part of a building's standby or emergency power system. The utility line

(normal power), is backed up by a generator set (emergency power). The transfer switch switches the

electrical load from one source to the other.

The load is connected to the common of the ATS (Figure 5). Under normal conditions, the load is

supplied with power from the utility (as illustrated). If utility power is interrupted, the load is transferred to

the generator set. When utility power returns, the load is retransferred to the utility. The transfer and

retransfer of the load are the two most basic functions of a transfer switch.

No. Description No. Description

1 Utility (Normal Power) 4 Over Current Protective Device (Customer

Supplied)

2 Over Current Protective Device (Customer

Supplied, Unless Service Entrance)

5 Generator Set (Emergency Power)

3 Load

FIGURE 5. LOAD TRANSFER SWITCH (TYPICAL FUNCTION)

2.3 Transfer Switch Function

Automatic transfer switches, capable of automatic operation without operator intervention, perform the

basic function of transferring the load to the available power source.

This automatic transfer switch, capable of automatic operation without operator intervention, is designed

for utility-to-generator applications. In utility-to-generator applications, the transfer switch performs the

following functions:

1. Senses the interruption of utility power

2. Sends a utility unavailable signal to the generator set

3. Receives transfer command from generator set control