Updated October 2026
Straight answer
A generator interlock and inlet in Boston lets a portable generator power your panel through one cord, without backfeeding the utility lines. The interlock is a sliding plate that makes it impossible to turn on the main and the generator breaker at the same time. The inlet is a weatherproof box outside where the generator cord plugs in.
Using your portable generator through the panel
Most people who own a portable generator run extension cords through a window during an outage. That powers a fridge and a lamp, but not a furnace, a well pump or hardwired lights. An interlock and inlet change that. The generator feeds a breaker in the panel, and you choose which circuits run by switching breakers on and off. Hardwired loads like a boiler or a well pump finally get power during an outage.
This setup is the lower-cost alternative to a standby generator. It does not start itself, and it is limited by the size of your generator. In exchange, the hardware is simple, the install is short and the generator you already own does the work. We match the inlet, cord and breaker to the generator output so nothing is overloaded on the first storm.
The plate, the inlet and the generator behind them
Interlock kits
An interlock kit is a metal plate made for your specific panel. It slides so that either the main breaker or the generator breaker can be on, never both. That is what stops generator power from flowing back onto the street, where it could hurt a lineworker or damage the generator when the grid returns. A listed kit has to match the panel brand and model, and it needs the generator breaker in the top position near the main. Older or crowded panels sometimes have no kit made for them. Then the choice is a manual transfer switch, which does the same isolation in a separate box, or replacing the panel.
Power inlet boxes
The inlet is a weatherproof box with a male receptacle, mounted outside where the generator will sit. We place it so the generator runs well away from windows, doors and vents, because exhaust drawn into the house is a carbon monoxide hazard. A short cable runs from the inlet to the generator breaker. Inlets come in 30 and 50 amp versions, and the inlet, cord and breaker all have to match your generator output. Some inlets have a built-in meter or indicator light so you can see the panel is energized. We mount it at a height that stays clear of snow and roof drip.
Portable generator sizing
A portable generator has a running rating and a higher starting rating. Motors such as a well pump, a sump pump or a furnace blower draw a surge when they start, so the starting rating matters more than people expect. We list the circuits you want during an outage and add up their running and starting loads to see what your generator can carry at once. Most mid-size portables run heat, refrigeration, a few lights and outlets, but not central air or an electric range. If your generator is too small for what you need, we tell you before you buy an inlet sized for it.
Still running cords through a window in an outage? Call about an interlock and inlet.
Call (617) 843-6591What decides the cost of an interlock and inlet
An interlock and inlet is one of the smaller backup power jobs. The price moves with these factors.
- Panel compatibility. A panel with a matching kit and an open top slot is straightforward. One without needs a transfer switch.
- Inlet amperage. A 50 amp inlet needs heavier cable and a larger breaker than a 30 amp one.
- Distance to the inlet. An inlet on the wall behind the panel is short. One on the far side of the house is not.
- Panel space. Moving breakers to free the top slot for the generator adds time.
- Permit and inspection. Work that needs a permit adds the filing and an inspection.
Interlock kit or transfer switch
An interlock and a transfer switch both keep generator power off the grid. They do it in different ways.
| Option | How you switch over | Best fit |
|---|---|---|
| Panel interlock kit | Slide the plate, flip main off and generator on | Panels with a listed kit and an open top slot |
| Manual transfer switch | Throw switches for prewired circuits | Panels with no kit, or a set list of circuits |
| Automatic transfer switch | No action, it switches itself | Standby generators, not portables |
Storm outages and flood-prone yards
An interlock is the simplest way to run a portable generator through your panel when the grid stays down for days, and New England storms make that more than a hypothetical: nor'easters have left big parts of the Eversource system dark for that long. Where we place the inlet matters as much as the interlock. In Quincy, storm surge has flooded parts of the city badly enough that residents had to leave. If your property floods, we mount the inlet box well above the waterline you have seen and plan a dry, ventilated spot for the generator.
How the install runs
Check the generator and panel
We note generator output and whether a listed kit fits your panel.
Plan the inlet spot
Away from openings, above snow and storm water, close to the generator spot.
Install the interlock and breaker
Generator breaker placed at the top, interlock plate fitted.
Mount and wire the inlet
Inlet mounted, cable run to the generator breaker.
Run a test with your generator
We start it, switch over and show you the outage routine.
What you handle and what we handle
Safe for a homeowner
- Run the generator outdoors, well away from doors, windows and vents
- Turn off big loads before switching to generator
- Keep fuel stored safely and run the generator monthly
- Test your CO alarms before storm season
Leave to an electrician
- Installing the interlock plate and generator breaker
- Mounting and wiring the inlet
- Any connection to the panel or service
- Working out which panels have a listed kit
Never plug a generator into a dryer or range outlet with a double male cord. It can backfeed the street, injure a lineworker and put live prongs in your hand.
Interlock and inlet questions
A listed interlock kit, installed on the panel it is made for, does the same job of keeping generator power off the grid. It just uses your existing panel as the switch.
No. A double male cord can backfeed the utility lines, shock a lineworker, and energize exposed prongs in your hand. It also bypasses every breaker in the house.
It depends on the generator. Match the inlet to the largest 240 volt outlet on the generator, and use a cord rated for the same amperage. We check the generator panel before we order parts.
Usually heat, refrigeration, a sump pump, some lights and outlets. Central air, electric ranges and electric water heaters are usually beyond a portable, so those breakers stay off on generator.
No. Exhaust from an open garage still reaches the house. Run it outdoors, well away from doors, windows and vents, and keep working CO alarms inside on every level.