What they have in common
An interlock kit and a manual transfer switch are two ways to do the same essential job: let you power circuits from a portable generator without ever back-feeding the utility line. Both are safe, both are code-compliant when installed correctly, and both require a permit and inspection. The difference is in how they get you there.
The interlock kit, in plain terms
An interlock is a small, listed metal plate that mounts on your existing electrical panel. It physically prevents the main breaker and the generator breaker from being switched on at the same time. When the power goes out, you flip the main off, flip the generator breaker on, and then you use your panel's own breakers to choose which circuits to run.
- Any circuit in your panel is available, you are not locked to a pre-chosen list.
- Low cost and low clutter, it uses the panel and breakers you already own.
- You manage the load, you turn breakers on and off to stay inside your generator's output.
The manual transfer switch, in plain terms
A manual transfer switch is a separate box installed next to your panel, usually pre-wired with a fixed set of six to ten circuits. When the power goes out, you flip those circuits over to the generator with switches on the box.
- Pre-selected circuits, simple to operate, the same circuits every time.
- Fixed set, you are limited to the circuits wired into the switch when it was installed.
- More hardware and space, it is a larger unit with its own wiring, which costs more.
Side by side
| Panel interlock | Manual transfer switch | |
|---|---|---|
| Circuits available | Any breaker in the panel | Fixed set (often 6 to 10) |
| Typical cost | Lower | Higher |
| Panel space | Minimal, mounts on your panel | A separate box to mount |
| Operation | Main off, gen breaker on, pick breakers | Flip the labeled switches |
| Flexibility later | Change which circuits you run anytime | Limited to what was wired in |
| Code-compliant | Yes, when listed + installed right | Yes |
Which one we usually recommend, and why
For most homes connecting a portable generator, we install an inlet box and a panel interlock. It gives you access to every circuit in your panel, costs less, and adds almost nothing to your wall. You are not paying for a second box, and you are never stuck with a circuit list you picked years ago.
A transfer switch can still be the right call in specific cases, for example if your panel physically cannot accept a listed interlock, or if you genuinely want a dead-simple fixed set of switches and never want to think about load management. We will tell you honestly if that is your situation. We recommend what fits your home, not what we would rather sell.
What the interlock route costs
- Weatherproof inlet box (30A or 50A)
- Listed interlock kit for your panel
- Generator breaker installed
- All wiring, conduit, weatherproofing
- The permit and inspection
- One-day labor, no return trips
What this connects (so the scope is clear)
Either option connects the portable generator you already own to power your selected essential circuits through your panel, the fridge, the furnace blower, the well pump, some lights, the internet. It is not a whole-home standby system. If a standby unit is the better fit for you, we will say so.
Not sure which one your panel can take? That is exactly what we figure out for you. See how the portable generator hookup works, read the full inlet and interlock guide, or get your price below.