Transfer Switches & Connection
The Best Generator Interlock Kits
Fit is decided by millimeters of breaker spacing. Every published figure is in the table below — measure before you order.
Written byMike M.
Published
Disclosure: we earn a commission on purchases made through links on this page, at no cost to you. It does not affect what we recommend or what we say about it — how we are funded.
The short answer
Eaton's own BRMIKBR is the pick if you have an Eaton Type BR 100-125 A panel: a factory kit with a stated National Electrical Code Article 702 basis, which removes both the fit risk and the inspection risk for about four times the price of a third-party plate. For other panels, match the published breaker spacing exactly — 3/4 to 7/8 inch on a 100 A Square D, 1 1/4 to 1 7/16 inch on an Eaton BR 150/200 A, and Siemens panels differ between plug-on-neutral and non-plug-on-neutral variants.
An interlock kit is a steel plate that bolts to your panel cover and makes it mechanically impossible for the main breaker and a new generator breaker to be on at the same time. It costs a fraction of a transfer switch and gives you access to every circuit in the panel rather than a pre-chosen six or ten.
The short answer
Quick picks
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 |  Eaton BRMIKBR Factory Interlock Kit 100-125A Pay the premium for this one: a factory interlock with a stated NEC Article 702 basis removes both the fit risk and the inspection risk. | Factory kit that satisfies inspectors | 8.9/10 | $84.00 |
| 2 |  SPZOCE Interlock Kit — Square D QO/Homeline 150/200A The cheapest correct way to connect a generator to the whole panel, provided your panel is a Square D QO or Homeline with the exact spacing stated — measure first. | Square D QO and Homeline, 150-200A | 8.5/10 | $26.99 |
| 3 |  XMK Interlock Kit — Siemens/Murray 100A The best-documented interlock kit here on the question that actually matters — it tells you the spacing for both Siemens neutral variants. | 100A Siemens, both neutral types | 8.3/10 | $19.99 |
| 4 |  XMK Interlock Kit — Square D QO/Homeline 100/125A The correct kit for an older, smaller Square D panel — and the published spacing range means you can confirm fit before ordering. | Smaller Square D panels | 8.2/10 | $19.99 |
| 5 |  EXCELFU Interlock Kit — Eaton BR 150/200A The affordable option for an Eaton BR panel, with the spacing published so you can verify fit — but check whether your inspector wants the factory kit. | Eaton / Cutler-Hammer BR panels | 8.0/10 | $19.99 |
| 6 |  SPZOCE Interlock Kit — Eaton BR 100/125A A complete, cheap kit for a smaller Eaton BR panel, as long as your main and generator breaker positions can be adjacent. | Smaller Eaton BR panels | 8.0/10 | $26.99 |
| 7 |  SPZOCE Interlock Kit — Siemens/Murray 150/200A The main third-party option for a Siemens or Murray panel — identify your plug-on-neutral variant before ordering. | Siemens and Murray panels | 7.8/10 | $26.99 |
#ad Prices as of October 5, 2026; they may have changed since. Scores are our editorial judgment from published specifications, not test results — how we pick. How we are funded.
The published fitment figures, all in one place
| Panel | Amperage | Published spacing | Kit |
|---|---|---|---|
| Square D QO / Homeline | 150 / 200 A | Stated by manufacturer — verify | SPZOCE SD200A |
| Square D QO / Homeline | 100 / 125 A | 3/4 - 7/8 in | XMK GK-007 |
| Eaton / Cutler-Hammer BR | 150 / 200 A | 1 1/4 - 1 7/16 in | EXCELFU GK-PN200 |
| Eaton / Cutler-Hammer BR | 100 / 125 A | Adjacent main + gen breaker | SPZOCE SP-ECSD |
| Eaton Type BR (factory) | 100 - 125 A | Factory fit, no measuring | Eaton BRMIKBR |
| Siemens / Murray | 150 / 200 A | Stated by manufacturer — verify | SPZOCE SP-SM200 |
| Siemens / Murray | 100 A | 7/8 in PoN, 1 1/4 in non-PoN | XMK GK-009 |
The best-documented kit in the table is the XMK GK-009 for 100 A Siemens panels, because it publishes both neutral variants' spacing: 7/8 inch for plug-on-neutral panels and 1 1/4 inch for non-plug-on-neutral. That is exactly the information you need, and most listings do not give it.
Why the factory kit wins despite costing four times more
Eaton's BRMIKBR is the manufacturer's own plate for its own panel. Three consequences:
- Fit is certain. Eaton made both the panel and the plate. No measuring, no ambiguity about which production run yours came from.
- Code basis is stated. Eaton's listing says the kit meets National Electrical Code Article 702 requirements — the article covering optional standby systems. That is the version no inspector argues with.
- It converts the load center officially. Eaton describes it as allowing the load center to function as a generator panel, which is the language an inspector is looking for.
Against a third-party plate at a quarter of the price, you are paying to eliminate two risks: the plate not fitting, and the inspector refusing it. On a job that already involves a licensed electrician and a permit, that is usually money well spent.
Is a third-party plate acceptable?
Often yes, and millions are installed. But the answer varies by authority having jurisdiction: some inspectors accept third-party plates readily, others want the panel manufacturer's listed kit. That is a local question, and the time to ask it is before you order.
Ask your electrician — they will know what your inspector accepts. If the answer is "factory only" and no factory kit exists for your panel, a transfer switch becomes the route instead. Discussed further in are interlock kits legal.
What the cheap kits include, which is more than you expect
The SPZOCE kits publish a genuinely useful package: the interlock plate, three screws and nuts, a 3/16-inch steel drill bit for the panel cover, a generator start-up procedure label, and reusable labels.
That start-up procedure label is not a gimmick. With an interlock, the sequence matters — main breaker off first, always, then the generator breaker — and having it printed on the panel door is where that instruction belongs. A transfer switch manages the sequence for you; an interlock relies on whoever is standing there at 2am.
What an interlock does not do
Load management. A transfer switch's circuits were chosen at installation to total less than the generator can carry, so overloading is hard. With an interlock you have access to the whole panel, and nothing stops you switching on more than the generator can deliver.
That is the real trade, and it is a genuine one rather than a safety compromise: the interlock prevents back-feeding just as absolutely as a switch does. It simply hands you the load discipline. Work out your standing set from the wattage chart and keep kitchen appliances strictly one at a time.
A generator with a live wattage meter helps considerably here — DeWalt's DXGNR8000 publishes one — because you can see the load rather than calculate it.
- Panel
- Eaton Type BR
- Panel size
- 100-125 A
- Code
- NEC Article 702
#1 · Factory kit that satisfies inspectors
Eaton BRMIKBR Factory Interlock Kit 100-125A
Pay the premium for this one: a factory interlock with a stated NEC Article 702 basis removes both the fit risk and the inspection risk.
#ad Price as of October 5, 2026; it may have changed since. How we are funded.
What is good
- The manufacturer's own kit, listed for the panel, citing the NEC article it satisfies — this is the version no inspector argues with
- Fit is certain: Eaton made both the panel and the plate
- Removes the measure-and-hope step entirely
What is not
- Roughly four times the price of a third-party plate
- Only covers Eaton Type BR 100-125 A — the wrong part for anything else
- Still requires a licensed install, a generator breaker and an inspection
Published specification & our scoring
- Eaton BRMIKBR Type BR mechanical interlock kit (manufacturer)
- Allows the load center to function as a generator panel (manufacturer)
- Prevents utility and generator supplies being energized simultaneously (manufacturer)
- Manufacturer states it meets National Electrical Code Article 702 requirements
- Panel fit certainty
- 10
- Code basis
- 10
- Circuit flexibility
- 9
- Completeness
- 8
- Value
- 6
Specification figures are the manufacturer’s published values. Scores are our editorial judgment from those figures and are never published as structured review data — how we pick.
- Panel
- Square D QO / Homeline
- Panel size
- 150 or 200 A
- Includes
- Plate, drill bit, labels
#2 · Square D QO and Homeline, 150-200A
SPZOCE Interlock Kit — Square D QO/Homeline 150/200A
The cheapest correct way to connect a generator to the whole panel, provided your panel is a Square D QO or Homeline with the exact spacing stated — measure first.
#ad Price as of October 5, 2026; it may have changed since. How we are funded.
What is good
- An interlock kit costs a fraction of a transfer switch and lets you back-feed ANY circuit in the panel rather than a pre-chosen ten
- Square D QO and Homeline are the two most common residential panels in the US, so this fits a large share of homes
- The included start-up procedure label is not a gimmick — the correct sequence matters and it belongs on the panel door
What is not
- Panel fit is decided by millimeters of breaker spacing. Open your panel, read the exact model, and measure the spacing before ordering — a kit for the wrong spacing simply will not install
- An interlock requires a generator inlet breaker added to the panel, which is licensed work and in most places requires a permit and an inspection
- Unlike a transfer switch, nothing stops you overloading the generator — you manage the load manually, by deciding which breakers to turn on
Published specification & our scoring
- Compatible with Square D QO or Homeline 150 A or 200 A panels (manufacturer)
- Manufacturer specifies the required spacing between the main breaker and branch breakers — verify yours matches before buying
- Includes a 3/16-inch steel drill bit for the panel cover
- Includes the interlock plate, three screws and nuts, a generator start-up procedure label and reusable labels
- Panel fit certainty
- 7
- Circuit flexibility
- 10
- Completeness
- 9
- Code basis
- 8
- Value
- 10
Specification figures are the manufacturer’s published values. Scores are our editorial judgment from those figures and are never published as structured review data — how we pick.
- Panel
- Siemens / Murray
- Panel size
- 100 A
- Spacing
- 7/8 in PoN, 1 1/4 in non-PoN
#3 · 100A Siemens, both neutral types
XMK Interlock Kit — Siemens/Murray 100A
The best-documented interlock kit here on the question that actually matters — it tells you the spacing for both Siemens neutral variants.
#ad Price as of October 5, 2026; it may have changed since. How we are funded.
What is good
- This is the only listing here that publishes BOTH neutral variants' spacing — exactly the information you need to identify your panel
- Covers the older 100 A Siemens and Murray panels that most kits skip
- Very cheap
What is not
- You still have to open the panel and identify which variant you have
- 100 A service limits total back-feed capacity
- Licensed install
Published specification & our scoring
- Compatible with Siemens / Murray 100 A panels (manufacturer)
- 7/8 inch spacing for plug-on-neutral panels, 1 1/4 inch for non-plug-on-neutral (manufacturer)
- Prevents mains and generator supply being live simultaneously (manufacturer)
- Panel fit certainty
- 9
- Circuit flexibility
- 9
- Code basis
- 7
- Completeness
- 7
- Value
- 10
Specification figures are the manufacturer’s published values. Scores are our editorial judgment from those figures and are never published as structured review data — how we pick.
- Panel
- Square D QO / Homeline
- Panel size
- 100 or 125 A
- Spacing
- 3/4 - 7/8 in (mfr)
#4 · Smaller Square D panels
XMK Interlock Kit — Square D QO/Homeline 100/125A
The correct kit for an older, smaller Square D panel — and the published spacing range means you can confirm fit before ordering.
#ad Price as of October 5, 2026; it may have changed since. How we are funded.
What is good
- The manufacturer publishes the exact spacing range, which is the only figure that determines fit
- Older 100 A and 125 A panels are exactly the homes where a transfer switch install is most awkward
- Very inexpensive
What is not
- A 100 A service limits what you can back-feed regardless of the interlock
- Measure the spacing: 3/4 to 7/8 inch is a narrow window and panels vary by production year
- Licensed install plus a generator inlet breaker
Published specification & our scoring
- Compatible with Square D QO or Homeline 100 A and 125 A panels (manufacturer)
- Single-handle horizontal throw, left to right, with 3/4 to 7/8 inch spacing between main and branch breakers (manufacturer)
- Prevents the main breaker being on while the generator breaker is on (manufacturer)
- Panel fit certainty
- 8
- Circuit flexibility
- 9
- Completeness
- 7
- Code basis
- 8
- Value
- 10
Specification figures are the manufacturer’s published values. Scores are our editorial judgment from those figures and are never published as structured review data — how we pick.
- Panel
- Eaton / Cutler-Hammer BR
- Panel size
- 150 or 200 A
- Spacing
- 1 1/4 - 1 7/16 in (mfr)
#5 · Eaton / Cutler-Hammer BR panels
EXCELFU Interlock Kit — Eaton BR 150/200A
The affordable option for an Eaton BR panel, with the spacing published so you can verify fit — but check whether your inspector wants the factory kit.
#ad Price as of October 5, 2026; it may have changed since. How we are funded.
What is good
- Eaton BR is the second most common residential panel family after Square D, and third-party kits for it are harder to find than Square D kits
- Published spacing range, including the plug-in-neutral variant that trips people up
- A quarter the price of Eaton's own kit
What is not
- Eaton BR spacing varies more between production runs than Square D does — measure, do not assume
- A third-party plate on an Eaton panel may draw an inspector's question; Eaton's own BRMIKBR does not
- Licensed install
Published specification & our scoring
- Compatible with Eaton / Cutler-Hammer BR series panels, including BR with plug-in neutral and CH variants (manufacturer)
- Single-handle horizontal throw, left (on) to right (off), with 1 1/4 to 1 7/16 inch spacing between main and branch breakers (manufacturer)
- Ensures the main breaker cannot be on while the generator breaker is on (manufacturer)
- Panel fit certainty
- 7
- Circuit flexibility
- 9
- Code basis
- 7
- Completeness
- 7
- Value
- 10
Specification figures are the manufacturer’s published values. Scores are our editorial judgment from those figures and are never published as structured review data — how we pick.
- Panel
- Eaton / Cutler-Hammer BR
- Panel size
- 100 or 125 A
- Layout
- Adjacent main + gen breaker
#6 · Smaller Eaton BR panels
SPZOCE Interlock Kit — Eaton BR 100/125A
A complete, cheap kit for a smaller Eaton BR panel, as long as your main and generator breaker positions can be adjacent.
#ad Price as of October 5, 2026; it may have changed since. How we are funded.
What is good
- States the layout requirement — adjacent main and generator breaker — which is as important as the spacing
- Complete with drill bit and labels
- Inexpensive
What is not
- The adjacent-breaker requirement may mean rearranging breakers, which adds to the install
- Older 100 A Eaton panels vary considerably
- Licensed install
Published specification & our scoring
- Compatible with Eaton Cutler Hammer BR Series 100 A and 125 A panels with adjacent main and generator breakers (manufacturer)
- Includes a 3/16-inch steel drill bit
- Includes the interlock plate, three screws and nuts, a start-up procedure label and reusable labels
- Panel fit certainty
- 7
- Circuit flexibility
- 9
- Completeness
- 9
- Code basis
- 7
- Value
- 10
Specification figures are the manufacturer’s published values. Scores are our editorial judgment from those figures and are never published as structured review data — how we pick.
- Panel
- Siemens / Murray
- Panel size
- 150 or 200 A
- Includes
- Plate, drill bit, labels
#7 · Siemens and Murray panels
SPZOCE Interlock Kit — Siemens/Murray 150/200A
The main third-party option for a Siemens or Murray panel — identify your plug-on-neutral variant before ordering.
#ad Price as of October 5, 2026; it may have changed since. How we are funded.
What is good
- Siemens and Murray panels are common in homes built from the 1980s onward and are the least-served by third-party kits
- Complete kit with drill bit and labels
- Inexpensive
What is not
- Siemens panels come in plug-on-neutral and non-plug-on-neutral variants with different spacing — identify yours exactly
- Murray was absorbed into Siemens; older Murray panels vary
- Licensed install
Published specification & our scoring
- Compatible with Siemens or Murray 150 A and 200 A panels (manufacturer)
- Manufacturer specifies the required main-to-branch breaker spacing — verify before buying
- Includes a 3/16-inch steel drill bit, interlock plate, screws and nuts, a start-up procedure label and reusable labels
- Panel fit certainty
- 6
- Circuit flexibility
- 9
- Completeness
- 9
- Code basis
- 7
- Value
- 10
Specification figures are the manufacturer’s published values. Scores are our editorial judgment from those figures and are never published as structured review data — how we pick.
Questions people actually ask
What is the best generator interlock kit?
Eaton's own BRMIKBR for an Eaton Type BR 100-125 A panel, because a factory kit with a stated NEC Article 702 basis removes both the fit risk and the inspection risk. For other panels, the right kit is whichever one publishes a breaker spacing that matches your panel exactly.
How do I know which interlock kit fits my panel?
Open the panel cover, read the brand and the main breaker amperage, then measure the spacing between the main breaker and the branch breakers. Published fitment ranges are as tight as 3/4 to 7/8 of an inch, so this measurement is what decides fit — not the brand alone.
Are third-party interlock kits acceptable to inspectors?
It varies by authority having jurisdiction. Some inspectors accept them readily, others want the panel manufacturer's listed kit — Eaton's BRMIKBR, for example, states that it meets NEC Article 702 requirements. Ask your electrician what your inspector accepts before ordering.
Is an interlock kit cheaper than a transfer switch?
Much cheaper for the part — tens of dollars against several hundred — and it gives access to every circuit in the panel. The installation still requires a licensed electrician and a generator inlet breaker, and you take on load management yourself.
What does an interlock kit come with?
The better third-party kits publish the plate, screws and nuts, a 3/16-inch steel drill bit for the panel cover, a generator start-up procedure label and reusable labels. The start-up label matters, because with an interlock the sequence is manual: main breaker off first, always.
Does an interlock kit stop me overloading my generator?
No, and that is the real trade-off. It prevents back-feeding absolutely, but it gives you access to the whole panel, so nothing stops you switching on more than the generator can deliver. A transfer switch's pre-chosen circuits manage that for you.
Sources
- Eaton BRMIKBR Type BR mechanical interlock kit — manufacturer listingManufacturer statement that the kit meets National Electrical Code Article 702 requirements, quoted wherever this page discusses code basis.
- Eugene Water & Electric Board — Generator Sizing ConsiderationsPublished appliance running-watt figures used when working out how many circuits a household actually needs.
- US Consumer Product Safety Commission — Portable Generator Information CenterThe 20-foot placement guidance that sets the minimum practical cord length referenced on this page.
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