Short version: if you own a portable generator and you’re willing to flip two breakers in a storm, the interlock kit wins on cost and flexibility. If you want a fixed set of circuits that switch over with zero thinking, the transfer switch earns its price. And if you never want to touch anything, that’s a standby with an automatic transfer switch. I install all three, so this is the honest comparison, not a sales page.
All three options do the same fundamental thing: they let generator power feed your house while making it physically impossible to backfeed the utility lines. The difference is how much house you can run, how much thinking the switchover takes, and what you pay for it.
An interlock kit is a steel plate on your existing panel plus a dedicated inlet outside. Your whole panel becomes available, and you choose which breakers to run based on what your generator can handle. A manual transfer switch is a separate small panel next to your main one, with a fixed set of circuits you picked on install day, usually six to ten. A standby system is a permanently installed generator with an automatic transfer switch that starts itself and swaps the house over before your ice cream softens.
Most people around Lake Keowee who already own a portable generator get the most value from the interlock. The exceptions are real, though, and they’re covered below.
| Interlock kit | Manual transfer switch | Standby + automatic transfer switch | |
|---|---|---|---|
| Installed cost | $800–$1,500 | $1,500–$3,000 | $9,000–$18,000 |
| What you can run | Any circuit in your panel, your choice on the fly, within generator wattage | Only the 6–10 circuits chosen on install day | The whole house, or a managed load list |
| Switchover | Manual: plug in cord, main off, generator breaker on | Manual: plug in cord, flip the transfer switch | Automatic, even when you're not home |
| Generator | Your existing portable | Your existing portable | Permanently installed unit, propane or natural gas |
| Panel space | Uses your existing panel, needs one open two-pole slot | Adds a second small panel beside the main | Full separate equipment install |
| Best for | Portable owners who want the whole panel available for the lowest cost | Households that want a fixed, foolproof circuit list | Second homes, medical needs, or anyone who wants zero involvement |
| Code and permit | Listed kit matched to your exact panel, permit and inspection | Listed equipment, permit and inspection | Permit, inspection, gas and electrical trades |
All three are legal and code-compliant when installed with a permit and a listed device. What is not legal is a double-male cord into a dryer outlet, which is the thing all three of these exist to replace.
Generator running, main breaker left on: your generator energizes the utility lines, and the lineman restoring your power gets hit with everything your generator can produce
Grid power back on, generator breaker left on: the exposed prongs on your inlet or cord are now live at 240 volts, waiting for someone to touch them
Both scenarios come down to the same root cause: two power sources connected to one panel with nothing but human memory keeping them apart. In a blackout, at 2 AM, in the rain, human memory is not a safety device.
The interlock plate and the transfer switch each solve this mechanically. The interlock physically blocks the generator breaker unless the main is off, and blocks the main unless the generator breaker is off. The transfer switch can only connect one source at a time by design. Either way, the dangerous state cannot exist, no matter who touches the panel or what they forget. That mechanical guarantee is the entire reason inspectors sign off on these and treat unprotected backfeed setups as seriously as they do.
This is my full walkthrough of a 50-amp inlet and interlock kit install, including the two danger scenarios above drawn out on the actual panel, everything that comes in the kit, and how the plate physically blocks the wrong breaker combination. A customer told me this video is why he hired us, so apparently it’s worth sixteen minutes.
One detail from this job worth knowing: my panel needed a slightly custom interlock plate because of a clearance issue at the top, and the kit manufacturer made one to fit. That’s the kind of thing that separates a listed, panel-matched kit from a generic plate off a marketplace.
Six honest signals, three of them point at each option. If you’re still unsure after this, text me a photo of your panel and I’ll tell you straight.
A portable in the garage plus an interlock and inlet is the cheapest legal path to whole-panel backup. Nothing else comes close on dollars per circuit.
Run the well pump this hour and the water heater the next. With an interlock you manage loads by flipping breakers, not by living with a list you chose years ago.
If the person doing the switchover might not know what a two-pole breaker is, a transfer switch with six labeled circuits is the safer bet. Flip one handle, done.
Interlocks need an open slot in the right position and a listed kit for your exact panel. Crowded panel, odd brand, or no kit available: the transfer switch sidesteps all of it.
Second home, medical equipment, sump pump, or freezers full of venison: if an outage while you’re away is a real loss, automatic switchover is what you’re buying.
A standby with an automatic transfer switch is genuinely the best product. It is also ten times the price of an interlock. If that number doesn’t bother you, get the standby.
Have a question not listed here? Call or text (864) 436-8680. I’m happy to talk through it.
Text a photo of your panel with the door open to (864) 436-8680. I’ll tell you which option fits, what it costs, and whether a listed kit exists for your panel, before any work starts.
Mon–Fri · 8am–6pm · Same-day emergency service available
Storm-season warning: Never connect a generator to your house with a double-male cord through a dryer or welder outlet. It backfeeds the utility lines, it can kill the lineman restoring your power, and it can destroy your generator when the grid comes back. Every option on this page exists so you never have to do that.