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Instructions on How to Wire a Transfer Switch

Swapnil Srivastava Sep 29, 2018
A transfer switch switches load between two power sources, i.e. a primary source and a secondary source. Let's see the step by step procedure on how to wire a transfer switch.
Transfer switches are basically used for switching power from a primary power source to a secondary power source. They are useful in case of sudden power outage, where there is a need to switch to other source. They may be a manual switch, automatic switch, or a combination of both.
It becomes necessary to transfer power from a primary source to secondary source in case the incoming power quality deviates from the set limits. A transfer switch is made up of an actuator and a toggle mechanism.
An actuator can be activated either manually or automatically, in order to supply energy to the movable contacts on the toggle mechanism. These switches prevent the damage of utility equipment by allowing for operation of the generator without back-feeding to the utility.
The automatic switches are controlled with the help of a programmable logic controller (PLC), a relay logic, or an embedded controller. These circuits monitor the public utility power source constantly for any kind of fault.
Once a fault with the utility power is identified, the embedded controller automatically switches to the secondary source of power. Wiring is important for a household generator. For this purpose, it is necessary to connect the properly sized wires to the three position switch.
As a basic security measure, it is important to turn off the power before attempting any type of main electrical power wiring. On taking a closer look at a transfer switch, one can observe six termination points on the switch, along with three grounding screw terminals and three neutral terminals.
The grounding screw terminals are connected directly to the frame of the switch, whereas the connection of rest of the termination and neutral points is made according to the next few steps.
1. Remove a small part of insulation from the wires which come from the generator, the power utility meter, and the circuit breaker box. There should be four wires from each component. Out of these four wires from every set, one is used as the earth ground, one as neutral wire, and the remaining two as power wires.
2. Connect all three of the grounding wires, each coming from a set, to the grounding bar mounted to the rear of the transfer switch. Connect the neutral wires to the ground connection bar which may also be tied to the rear.
3. Next step involves the connection of the remaining two power wires from each set, to the two center lugs on the transfer switch. These lugs are connected to two large knife blade connectors.
Attach the wires coming from the power utility meter to the two lower set of lugs on the transfer switch. The two wires from the generator should be connected to the two top lugs on the switch, thus completing the wiring part.
4. All transfer switches do not have a remote start/stop contact block. However, if it's there, make a connection between the start/run wires from the generator and the auxiliary screw terminal mounted on the side of the switch.
Automatic transfer switches monitor the incoming utility power for anomalies, like, brownouts, spikes, or surges and works accordingly. If no anomalies occur for a set time, the transfer switch transfers back to utility power and commands the generator to turn off. These steps may help a person to safely make proper connections of a transfer switch wiring.