SJE Electrical Installations
Backup Generator Installers
- Auto mains transfer switch installation
The auto transfer switch monitors utility power, when normal power is
interrupted the electronics send a signal to start the generator. A contactor
within the auto transfer box switches from the utility supply cable to the
supply feed from the generator.
When normal power is restored the system is reversed.
When using an auto transfer switch arrangement more wiring is required than
manual changeover.
A mains feed cable from the generator along with a control cable to the auto
box.
The supply feed cable will normally be a 3-core swa, (assuming single phase) but
much depends on the location of the generator in relation to the location of the
auto transfer switch.
The size of the supply feed is determined by the generator maximum load and the
distance of the generator to the auto transfer switch. (the auto switch is
fitted as close as possible to your normal mains incomer
A further cable is also needed, usually a multi-core from the auto box to the
generator, this is a control cable only and the size can be greatly reduced.
Normally a 12-core 1.5mm swa is used, all cores may not be needed but at least 9
will be used.
Normally auto transfer is used in conjunction with generators over 10Kva.
However, smaller sets can be used but will only auto transfer single dedicated
circuits and not a full installation.
