Eaton ATC-900 Automatic Transfer Switch Controller Background

Safety precautions

All safety codes, safety standards, and/or regulations must be

strictly observed in the installation, operation, and maintenance of

this device.

Background

Transfer switches are used to protect critical electrical loads

against loss of power. The load’s normal power source is backed

up by a secondary (emergency) power source. A transfer switch is

connected to both the normal and emergency sources and supplies

the load with power from one of these two sources. In the event

that power is lost from the normal source, the transfer switch trans

fers the load to the secondary source. Transfer can be automatic or

manual depending upon the type of transfer switch equipment being

used. Once normal power is restored, the load is transferred back to

the normal power source.

In automatic transfer switch equipment, the transfer switch’s intel

ligence system initiates the transfer when normal power fails or falls

outside a preset threshold. If the emergency source is a standby

generator, the transfer switch initiates a generator start and will

automatically transfer the load to the emergency source when the

generator voltage and frequency are within setpoint tolerance. When

normal power is restored, the transfer switch automatically transfers

the load to the normal source and initiates a generator shutdown.