What Size Transfer Switch Do I Need?
Most homes need a 30-amp transfer switch for essential circuits (fridge, furnace, lights) with a portable generator, or a 100 to 200-amp switch for whole-home backup with a standby generator.
Transfer Switch Sizing Calculator
Select the appliances you want to power during an outage. We'll calculate the amperage and recommend the right transfer switch size.
Select your appliances
What Is a Transfer Switch?
A transfer switch is a device that safely connects your generator to your home's electrical panel. It prevents dangerous backfeed into utility lines (which can electrocute line workers) and lets you power hardwired circuits like your furnace, well pump, and refrigerator directly from the panel instead of running extension cords.
Transfer switches are required by the National Electrical Code (NEC) whenever a generator is connected to a home's wiring. Most municipalities enforce this, and many insurance policies require one for coverage during generator use.
Manual vs Automatic Transfer Switches
Manual Transfer Switch
- You flip the switch to transfer power
- Works with any portable generator
- Lower cost ($100 to $500)
- Best for occasional outage protection
Automatic Transfer Switch
- Senses outage and switches automatically
- Designed for standby generators
- Higher cost ($500 to $1,500+)
- Best for frequent outages or medical needs
Transfer Switch Size Guide
| Switch Size | Best For | Generator Size |
|---|---|---|
| 30A | Essential circuits (fridge, lights, furnace) | 3,500 to 7,500W portable |
| 50A | Essential circuits plus 240V appliances | 7,500 to 12,000W portable |
| 100A | Most of the home including AC or dryer | 10,000W+ portable or standby |
| 200A | Whole home including all 240V loads | 15,000W+ standby |
Not Sure What Generator You Need?
Use our generator sizing calculator to find the right wattage for your appliances, then come back to size your transfer switch.
Use the Generator Sizing Calculator