Generator Transfer Switch Table
| Method | Powers | Parts cost | Watch |
|---|---|---|---|
| Extension cords, direct | 2-4 appliances by cord | $100-200 in 10 AWG cord | never through a window at 100 ft; the gauge table rules |
| Manual transfer switch | 4-10 chosen circuits | $400-900 installed | flips loads off utility before generator on - the furnace and well, wired in |
| Interlock kit | whole panel, you manage loads | $150-300 parts + electrician | cheapest legal whole-panel route; you shed big loads yourself first |
| Dryer-outlet backfeed | everything, briefly | $0 | illegal and lethal - energizes dead lines that linemen believe are dead |
A generator in the yard is half a backup power system; the other half is how it connects to the house - and that choice decides whether an outage means four extension cords snaking through a window or one switch flipped at the panel. The methods are: direct extension cords, a manual transfer switch (chosen circuits, wired in), an interlock kit (whole panel, you manage loads), and the dryer-outlet backfeed that is free, common, illegal in most jurisdictions, and has killed linemen.
Bottom line: for a 5,000-watt portable - the most common size - the interlock kit is the value pick: a few hundred dollars of hardware plus an electrician turns the whole panel into generator territory, with the discipline that you shed the big loads yourself. The manual transfer switch buys pre-wired circuits and simplicity at roughly double the money. Both exist to enforce one physical rule: the generator and the utility can never be connected at the same time.
The honest part: the backfeed route - plugging the generator into a dryer outlet to energize the panel - works, which is exactly why it is dangerous: it pushes full voltage out onto lines a lineman three streets away believes are dead. The interlock plate costs less than a nice dinner and makes that impossible by geometry rather than by memory.
How to use
- Size the ambition before the hardware: cords reach 2-4 appliances; a transfer switch or interlock reaches the panel - decide what an outage actually requires (fridge, furnace, well pump, lights, phone) before picking.
- Budget the ladder: 10 AWG cords per the gauge table for the direct route; $150-300 interlock kit plus electrician; $400-900 manual transfer switch installed with 4-10 chosen circuits.
- Get the permit and the electrician for anything panel-connected - the interlock kit must match your specific breaker panel brand and model, and the inspection is part of the point.
Frequently asked questions
What is the difference between a transfer switch and an interlock kit?
A manual transfer switch is a separate sub-panel holding pre-chosen circuits - flip it and those circuits move from utility to generator power, nothing else. An interlock kit is a metal plate installed on your existing main panel that mechanically prevents the generator breaker and the main breaker from being on together - the whole panel becomes available, and you choose what runs by switching off what the generator cannot carry. The switch is simpler operation; the interlock is cheaper and more flexible.
Can I plug my generator into my dryer outlet?
No. It backfeeds your house wiring and the utility grid at full voltage, energizing lines that a utility worker believes are dead - linemen have died this way, which is why the connection is illegal in most jurisdictions and why interlocks and transfer switches exist. It also skips every protection: no overload limit, no disconnection from the grid, noinspection trail. The hardware is cheap; the failure mode is not.
How much does it cost to install a transfer switch?
Roughly $400 to $900 installed for a manual transfer switch covering 4 to 10 circuits, parts plus licensed electrician, depending on panel access and circuit count. An interlock kit runs cheaper - $150 to $300 in parts plus an hour or two of electrician time - because it reuses your existing breakers. Whole-house automatic standby switches are a different product at ten times the money and belong to standby generators, not portables.
What size generator needs a transfer switch?
Nothing requires it - cords are legal for any size - but beyond about 3,500 watts the cord route strands capacity: a 5,000 or 7,500-watt generator on extension cords simply cannot deliver most of what it makes. The rule of thumb: cords for the fridge-and-phones tier, interlock or transfer switch once the furnace, well pump, or a second big appliance joins the outage plan.