Electrical Transfer Switch
Managing a power outage is not a minor event. Food can thaw or spoil in a few hours. If you have electric pumps in your water or sewer systems, they can create issues as well. Providing heat or air conditioning and cooking food are other concerns you must address. Fortunately, using a backup generator can provide limited electricity during an outage. However, you must have a safe way to connect the unit to the correct electrical circuits. An electrical transfer switch is a safe way to integrate a backup generator into your home or business.
Understanding how electrical transfer switches work
An electrical transfer switch mounts directly beside your home electrical panel. If a generator directly connects to a home electrical system, there is a risk of electrical overload when switching from utility power to the generator. The electrical transfer switch acts as a barrier between these two power sources, preventing electrical back feed. Keep in mind that your generator is an emergency electrical source, so it will not power every circuit.
Most electrical transfer switches are open-transition switches, which are also called break-before-make switches. The switch completely disconnects from one power source before engaging the second power source. This results in a short power delay each time the switch transfers between sources. Nearly all residential transfer switches are open-transition switches.
The switch has three positions: LINE, OFF, and GEN. LINE means the home is receiving power from the utility company. Having the OFF position in the center prevents fire hazards by keeping the generator from short circuiting with the utility line. When the switch is in the GEN position, limited circuits receive power from the generator. The switch does not simply protect your home; it also protects linemen working on nearby electrical lines from dangerous power surges.
Transfer switch operation follows three basic steps. First, an interruption or failure occurs in the primary power source. Second, the transfer switches to the secondary source once it is stable and reaches the correct voltage and frequency. This transition can happen manually or automatically. The third step takes place when the primary source engages again and is stable. The switch transitions power from the secondary source back to the primary source. This final step can also be manual or automatic.
Other types of switches
Other types of electrical transfer switches are primarily used in industrial or healthcare settings. In these environments, even brief power delays could cause a significant loss of life or data breach that would impact the public.
- Closed-transition transfer switches have a make-before-break action. In other words, the switch briefly engages both power systems at the same time when switching from primary to standby power. This provides an uninterrupted flow of power in hospitals, data centers, and other critical operations hubs.
- Bypass isolation transfer switches use two parallel transfer switches. The switches add redundancy to the system to prevent power interruptions. Healthcare and data centers use this type of switch as well.
Deciding between an automatic or manual electrical transfer switch
Electrical transfer switches can be automatic or manual models. An automatic electrical transfer switch provides homeowners with the convenience of hands-free operation. However, manual transfer switches are less expensive and easier to install. Take a look at how both types of transfer switches work to determine which switch you need.
Automatic electrical transfer switch
An automatic transfer switch constantly monitors electrical power. When the power fluctuates too much or fails, the generator receives a start command. When the generator reaches a stable operating level, the switch transfers power from the utility grid to the generator.
When the utility power comes back on for a predetermined time, the switch operates in reverse. After 20-30 minutes of stable utility power, it switches back to the power grid. At the same time, it sends a signal to the generator, telling it to power down. After a short cool-down period, the generator shuts off.
Automatic switches can also be configured to power predetermined circuits. Some systems monitor power fluctuations and shut off minor circuits if power demands exceed the generator’s capability. For example, you might prioritize food refrigeration or home heat over television use. If the system detects a potential overload, the switch can shut down the television circuit without compromising your heat or food storage needs.
Manual electrical transfer switch
To turn on a manual transfer switch, refer to your owner’s manual for the correct startup procedure. However, the steps below outline the general steps for transferring power to a secondary source.
- Connect the generator to the transfer switch.
- Flip all circuit breakers on the main electrical panel to the OFF position.
- Start the generator and wait for it to reach full operating capacity.
- Flip the generator switch to the OFF position, then move it to GEN.
- Turn on circuit breakers one at a time to avoid overloading the generator.
When the power comes back on, you must flip the transfer switch back to LINE, then restore any circuits that are still off. You will also have to turn off and disconnect the generator.
If this does not sound too complicated, remember that you may be performing these steps in the dark with a flashlight. Furthermore, you cannot use a gas-powered generator cannot indoors. They emit carbon monoxide, a deadly odorless gas. When the weather is bad, you must brave rain or snow to turn on the generator. It is also important to identify the location and power load for each circuit prior to an outage. Without this information, you could overload the generator.
Installing an electrical transfer switch
Before you decide to install a transfer switch, keep in mind that you must meet national and local electrical code standards. If you do not have significant electrical experience, you should hire a licensed electrician to install the transfer switch for you.
Determining your power needs
Select the appliances that must operate during an emergency and note their individual and combined amperage. Select a generator that meets those needs. However, the combined amperage can be more than the generator capacity provided you do not run all appliances at the same time.
Selecting a switch
The switch amps should match the amperage of the main breaker in your electrical panel. This ensures the switch can handle the correct amount of power. If your home runs on 200 amps of power, you will need a 200-amp electrical transfer switch.
Steps for installation
Follow these steps to install the transfer switch.
For simplicity, the steps below refer to two separate breaker mechanisms: the transfer circuits and the breaker circuits. The transfer circuits are breakers located within the transfer switch. The phrase breaker circuits applies to the main electrical breaker for the home.
- Mount the transfer switch beside the main electrical panel, about 1.5 feet from the panel’s center point. Number the breaker circuits and note the corresponding appliance. Label each transfer circuit with its assigned appliance. Load sizes in the transfer circuit must be equal to the corresponding breaker circuit.
- Cut the power by switching the main circuit breaker OFF. Remove the transfer switch and electrical panel covers. Trim the transfer switch insulating tube to access the wires and attach connectors with PVC cement.
- Draw the wire bundle through the insulating tube in the bottom of the transfer switch. Trim 5/8-inch of the plastic covering from each wire to expose the copper. Connect the wires to the transfer switch following the number system you created in Step 3. Label each wire with the correct number.
- Attach unused black wires to the 2-pole utility transfer switch breaker. There is a neutral area in the center of the transfer switch; connect the white wire to it. The green wire connects to the grounding bar at the lower left of the switch. Refer to your owner’s manual to verify the correct connections. When you finish, replace the transfer switch cover and verify that the main power breaker is OFF before moving on to step 5.
- Detach the wires for each appliance from the breaker circuit. This only applies to appliances or circuits that will run during an emergency. Trim the wires as in step 3, then use the numbered wiring system you created to attach each wire to the correct transfer switch location with wire connectors.
- Connect miscellaneous black wires with the new 2-pole breaker. Detach each pair of individual pole breakers for assigned appliances. Connect the white wire with the neutral bar and the green wire with the ground bar. If no ground bar is available, connect the green wire to the neutral bar.
- Drill a 1.5-inch hole through the outside of the house. Mount the electrical box that came with your transfer switch over this hole, then run an electrical cable between the box and transfer switch. Consult your owner’s manual to connect the cable and the electrical receptacle you received with the transfer switch. Mount the receptacle in the electrical box. Connect the other end of the cable to the transfer switch.
- Test your work. With the house power still off, start the generator and plug it in. Flip the transfer switch from LINE to GEN. Verify that the selected circuits are receiving power.
Once the switch is in place, have an electrician inspect your work. Failure to meet electrical code standards could result in fire, electrocution or death.
Electrical transfer switches provide a safe way to transition between primary and secondary power sources during an outage. A properly installed transfer switch can protect your home and help keep you comfortable during power failures.