How to connect a generator to the electrical panel of the house

The connection of a generator to your house or apartment requires the use of a changeover switch, which means a switch that, unlike the one that turns on or off an electrical equipment, allows to switch from one electrical source to the other.

Such switches are widely available and can be manual, motorized, or motorized and automatic.
The latter is called Automatic Transfer Switch or ATS.
This pictorial explains how to install a transfer switch and wire the Mains source, the Generator and the House to it.

Understanding where to install the transfer switch

Whether you chose to install a manual transfer switch or ATS, the installation is the same.
It will be inserted upstream the main breaker of your house, so installed within a separate box or panel.
You should then do the following:
  1. Bring a cable from the generator to the box of your transfer switch "Cable 2"
  2. Extend the Mains cable that connects to your main breaker to reach that same box, after disconnecting it, "Cable 1"
  3. Add a cable between the transfer switch box and your house's main breaker "Cable 3"
  4. Wire all cables as shown in the below diagram

Wiring diagram of a generator (genset) connection through an automatic transfer switch

The below diagram shows how to connect the ATS in both 2P (single phase) and 4P (three phase versions).
Note well that:
> Cable 1 described above is the one shown as Common Incoming Line
> Cable 2 is the one shown as Standby Incoming Line
> Cable 3 is Load Output
The control lines are required for the automatic operation:
  • Upon a Mains failure, the switch will automatically transfer to the generator (standby) position, as soon as the latter is turned on and provides power.
  • Upon the Mains return, the switch will automatically transfer to the Mains (common) position.
The additional unwired contacts on the ATS can be used to turn on or off the generator if you wish, although this is not recommended for small portable generators, since these should always be visually inspected prior to turning them on.
Buy your automatic changeover generator switch from our partners:

Connection diagram of a diesel or gasoline generator (genset) to the house through a manual knife switch:

> Cable 1 described above is the one shown as Common power input
> Cable 2 is the one shown as Standby power input
> Cable 3 is Load Output
Buy your knife transfer switch from our partners, be aware of cheap products using thin copper, we did select some better choices for you. Nevertheless, and as a safety measure, always select a knife switch which Amps rating is one size higher than your main breaker, i.e. if your breaker is 32A, buy a 60A switch, not a 32A switch.

Buy your portable generator here:

See also our pictorials and tips for engine and generator repair: