Generators can supply a portion of a home's power if service is interrupted from the electric utility. The amount of power the generator can supply is limited; requiring decisions about which circuits to power during an outage. Typical installations power one or two lighting circuits: a fridge, freezer, furnace or sump pump. Wire the generator to a transfer switch and not to the main service panel.
Transfer switch installation
Mount the transfer switch box near the main service panel. Turn off the main circuit breaker and remove the screws holding the cover in place. Remove each circuit breaker for the branch circuit the generator will power by prying it gently from the centre with a flat bladed screwdriver. Label each wire with the circuit breaker amperage from the breaker's switch handle.
Loosen the wiring terminals on the circuit breakers with a screwdriver and remove the wires. Locate the corresponding white neutral wires and bare ground wires; remove them from their respective bus bars. Route the sheathed cables for these wires to the transfer switch box.
Hook the 250-volt, 40-amp circuit breaker on the main panel's bar and press firmly until it clicks into place. Route the 8-gauge sheathed cable between the transfer switch and the main panel. Strip the sheathing from the cable inside the panel and connect the bare ground wire to the ground bar. Strip 9 mm (3/8 inch) of insulation from the neutral and two hot wires. Connect the neutral wire to the neutral bar; connect the two remaining wires to the circuit breaker terminals. Replace the main service panel cover.
Route the 8-gauge sheathed cable into the transfer box and remove the sheathing from the cable inside the box. Connect the bare ground to the ground bar and the white neutral wire to the neutral bar. Connect the two coloured hot wires to the terminals on one of the two breakers in the transfer switch.
Note: The ground and neutral bus bars may be the same in the main panel, but the same arrangement is dangerous and against code in the transfer switch. The two bars must be separate and not connected.
Install the new circuit breakers in the transfer switch box. For each circuit, connect the bare ground wire to the ground bar, the white neutral wire to the neutral bar and the black wire to a circuit breaker of the correct amperage according to the labelled wires.
Mount the outdoor receptacle box within six feet of where the portable generator will be placed during operation. Route 8-gauge sheathed cable between the receptacle box and the transfer switch. Strip the sheathing from the cable at both ends.
Connect the ground wire from the receptacle box to the ground bar and the white neutral wire to the neutral bus inside the transfer switch box. Connect both hot wires to the terminals on the second circuit breaker in the transfer switch.
Connect the bare ground wire to the ground terminal on the 250V recessed plug and the white neutral wire to the receptacle terminal labelled "W." Connect the two coloured hot wires to the two remaining terminals. Mount the receptacle in the weather-tight box with the supplied mounting screws.
Strip the sheathing from several inches of 8-gauge cord on each end to expose the wires. Disassemble the 250-volt plug and receptacle. Feed the cord through the strain reliefs. Strip 2.1 cm (7/8 inch) of insulation from each wire on both ends and make identical connections to the plugs and receptacle. Connect the green wire to the green ground terminals, the white wire to the terminals labelled "W" and the two coloured wires to the remaining terminals. Reassemble the plug and receptacle and tighten the strain reliefs.
Install the transfer switch cover using the supplied screws. Turn the circuit breaker in the main panel supplying the transfer switch to the "On" position. In the transfer switch, move the toggle switch to the "Main" position.
In the event of a power failure, connect the generator to the receptacle with the cord. Start the generator, then move the transfer switch to the "Generator" position.
In the main panel, the wires coming from the electric meter are always hot. Never touch or allow any wire or other object to touch these terminals. Never bond or connect a sub-panel or transfer switch box neutral to ground.