Generator transfer switch
A generator transfer switch shifts your home between the utility line and the generator, then shifts back again. The two power sources never feed your wiring together.
What a transfer switch actually does
With no switch in place, a running generator can push electricity back through your meter and out onto the street line. People call this back-feeding, and it is illegal. It can kill a lineworker who believes the line has no power.
The switch holds the two sources apart. That is also why most areas ask for a licensed electrician and a permit, and why your utility company may need to hear from you.
If you intend to run extension cords from the generator into individual appliances, you can skip the transfer switch. The generator stays clear of your house wiring in that setup.
Automatic transfer switch for a standby generator
This kind of switch pairs with a home standby generator, the type that sits outside on a pad. It notices the outage, gets the generator running and moves the house onto generator power in about 10 seconds. Nobody has to touch a thing.
It can power every circuit in your panel, or only a load center, which is a small second panel that holds just the circuits you picked, like the fridge, furnace and a few lights. These switches are offered in sizes from 100 to 400 amps.
Working with a manual transfer switch
This kind of switch pairs with a portable generator, and you take on the steps an automatic switch handles on its own. During an outage, you get the generator going, hook the cord up to the inlet and throw the switches. That inlet is a weatherproof socket on an outside wall, and the generator cord plugs into it.
Manual switches usually handle 6 to 10 circuits you choose, with ratings of 30 or 50 amps. The price sits above an interlock kit, since each of those circuits needs rewiring to the switch, and below an automatic switch.
| Automatic transfer switch | Manual transfer switch | |
|---|---|---|
| Used with | Home standby generator | Portable generator |
| Switching | Senses the outage, starts the unit, switches in about 10 seconds | You start the generator, plug it into the inlet and flip the switches |
| Circuits | The whole panel, or a load center of chosen circuits | Usually 6 to 10 chosen circuits |
| Rating | 100 to 400 A | 30 or 50 A |
Which switch suits a portable generator?
A portable generator gives you 2 safe choices. The first is a manual switch rated 30 or 50 amps that feeds 6 to 10 circuits. The second is an interlock kit, a metal plate fitted to your current panel that keeps the main breaker and the generator breaker from being on together.
An interlock kit with its inlet box runs $600 to $1,500 once installed. It costs less than a manual switch because your circuits stay where they are and nothing needs rewiring.
Generac standby switch prices
Generac sells Guardian standby units in 10 to 24 kW sizes, with or without the switch. Compare the two list prices: the automatic 200 amp switch adds roughly $850 to $1,060 to what the same generator costs on its own.
For a whole house generator, the switch is part of the overall job. Installing a standby system usually costs $3,000 to $5,500 in labor, based on ranges from Home Depot, Angi and PowerOutage.us. That covers the switch, the wiring to the generator and getting it started up.
| Item | Cost | Basis |
|---|---|---|
| Interlock kit with inlet box, installed | $600 to $1,500 | Plate, inlet box, 2-pole breaker, power cord and labor |
| 200 A automatic switch, hardware | $850 to $1,060 | The gap between Generac's list prices with and without the switch, 10 to 24 kW units |
| Standby install labor, switch included | $3,000 to $5,500 | Price ranges published by Home Depot, Angi and PowerOutage.us |
Do you need a 200 amp switch?
The rating of a switch lines up with the main breaker it sits behind, so check the large breaker near the top of your panel. Most homes have 200 amp service, so they take a 200 amp switch; that is why this size is the usual whole-house choice.
A smaller switch than your service can still work. It just powers only your essential circuits, through a separate load center, instead of the whole house.
Generac prices for both versions are on Generac generator cost, and the full standby job is on whole house generator cost.
Questions about transfer switches
Is a transfer switch something a homeowner can install?
Usually not. The switch ties into your service panel, so the work needs a licensed electrician and an electrical permit. Your utility company may also need to know before the generator gets used.
Do I have to switch off the main breaker when I run the generator?
The switch handles that for you. It disconnects the house from the utility line first, then lets the generator supply it, so nothing depends on your memory. On a manual switch, you do this by flipping its switches.