Field guide ·
Field guide · Oct 28, 2026
Transfer Switch or Interlock Kit: Explaining the Choice to Homeowners
Every outage season the same question arrives with the generator already in the garage: can you just wire it into the panel? The safe versions of that idea are a transfer switch or a listed interlock kit, and the difference is worth a page of plain explanation, because homeowners comparing quotes will meet both prices.
Both devices do the non negotiable job, making it mechanically impossible for the panel to take power from the utility and the generator at the same time. Backfeeding a line can kill a line worker, so this is the part of the page with no shortcuts in it.
What each option actually is
A transfer switch is a separate panel or switch that feeds selected circuits. You choose the circuits in advance, fridge, well pump, furnace, a few lights, and the switch moves those loads to generator power. Capacity is fixed at install, and the setup is forgiving to use under stress.
An interlock kit is a listed plate on the existing panel that slides between the main breaker and a generator breaker so only one can be on. It can feed any circuit in the panel, within the generator's capacity, which makes it flexible and cheaper, and puts load management on the homeowner, breaker by breaker.
Where the money and the discipline go
Interlock installs usually cost less in parts and labour, assuming the panel has space and a compatible listed kit exists for it. Transfer switches cost more and answer with simplicity: in an outage, at midnight, a tired homeowner flips one switch to a prepared set of circuits.
The service page that explains this honestly, including that a portable generator still has limits no switching device removes, converts better than a page promising whole house power from a portable unit. See also Whole Home Surge Protection Pages: What Homeowners Actually Need to Read.
Permits and inspection are part of both quotes
Either route is electrical work that belongs under a permit with an inspection in most jurisdictions, plus an inlet box mounted properly and a cord rated for the load. A quote that skips those items is not cheaper. It is incomplete, and the missing parts are the safety parts.
Say so on the page. Homeowners cannot comparison shop a line item they have never heard of, and naming the permit is the fastest credibility signal an electrician can send. Related reading: Your Google Services List Is Probably Wrong: An Electrician Audit.
Frequently asked questions
Is an interlock kit legal and safe?
A listed interlock kit, made for your specific panel, installed under permit and inspected, is a recognised method in many jurisdictions. It works by mechanically preventing the main and generator breakers from being on together. Local code and the inspector have the final say, which is why the permit step matters.
Which is cheaper, a transfer switch or an interlock?
The interlock route is usually cheaper in parts and labour when the existing panel is compatible and has space. A transfer switch costs more upfront and gives a simpler, pre selected set of circuits in return.
Can a portable generator run my whole house through an interlock?
An interlock can connect the generator to the whole panel, but the generator's capacity still rules. You would run selected loads at a time and manage them manually. Whole house comfort on a portable generator is a load management exercise, not a switch setting.