Portable generators and interlocks, explained

A portable generator converts mechanical energy into electrical energy, running on gasoline, diesel or propane. During an outage it keeps a refrigerator cold, a furnace running and the phones charged.

Safety is paramount when using one. They run outdoors, always, well away from windows and doors — carbon monoxide is the leading cause of generator deaths and it is entirely preventable.

Three variables: power output, fuel type and runtime. Size it to what genuinely has to stay on rather than to the whole house, and be realistic about how often you want to be refuelling it at 3am.

Whatever you buy, how it connects to the house matters more than the badge on the front.

A generator interlock is a mechanical device on the panel that makes it physically impossible to have the main breaker and the generator breaker on at the same time.

That prevents backfeeding — pushing generator power out onto the utility lines. Backfeeding can electrocute the line worker restoring your power, and it can destroy your generator when the utility comes back. The interlock removes the possibility rather than relying on anyone remembering.

Both solve the same problem. An interlock is generally more cost-effective because it uses your existing panel, and it lets you choose which circuits to run.

A transfer switch is more automatic and more foolproof. Which is right depends on your panel, your budget and how much you trust a procedure at 3am in the dark.

Verify licensing and insurance before anyone touches the panel. Ask to see it — a legitimate contractor will not be offended.

Read reviews, and pay attention to how clearly someone explains the options. Anyone who cannot explain backfeeding in plain language should not be installing your interlock.