A basic home electrical service looks like this (grounding circuits and wires have been left out in order to make the drawings less cluttered):Figure 1-Home electrical service before the installation of a standby generator and transfer switch
The meter is fed from the utility via an overhead or underground conduit as shown in figure. The electrical service main disconnect and electrical distribution panel are shown as 2 separate items, however newer circuit breaker distribution panels have the main disconnect located at the top of the electrical distribution panel (large circuit breaker).
Adding a standby generator into your electrical service system
The circuits that you want to be powered by both the electrical utility and the standby generator are transferred to the generator electrical distribution panel. The generators electrical distribution panel should be fed from a double (2-pole) breaker in the main distribution panel.
Figure 2 - Standby generator and transfer switch installed in a home electrical service.
Simplified inner workings of the transfer switch are shown in Figures 3 and 4. For clarity have been shown with a manual lever. If you have an automatic transfer switch the electrical switching function works in the same manner as the manual switch.
The drawings also show the switching of the neutral wire (white). Many systems do not switch the neutral wire and tie the three neutral wires together. Verify the method of wiring with your transfer switch and generator before installation.
Figure 3 - Wiring Diagram Of A Manual Transfer Switch In The "Off" Position
Figure 4 - Wiring Diagram Of A Manual Transfer Switch In The "ON" Position
When utility power is functioning the wires from the circuit breaker in the main electrical distribution panel are connected to the generator sub-panel. If utility power fails, the switch connects the generator's power to the circuits in the generator sub-panel.