I received the "MOWABI Generator Interlock Kit Compatible with Square D QO & Homeline 150 or 200 amp Panel - Generator Lockout Kit, Interlock Switch - 1 3/8" Spacing Between Main and Generator Breaker" in early February 2025. For the purposes of this review, I shall refer to this product as the "MOWABI-GEN-LOCK"Having a backup generator presents some challenges. You can spend a LOT of money on control systems that are designed to "synchronize" the generator output with other power sources such as Commercial ("from the Utility Company") Electricity. If properly "tuned" to match the frequency, phase, and voltage, a generator can be hooked to Commercial Power and actually, intentionally, used to send power into the commercial system. People sometimes do this to make their "meters run backwards" and thereby "selling power" to the Utilities. The two (2) main disadvantages to this scheme are: 1) it is expensive to install and maintain; and, 2) the generator needs to be cut off from commercial power when that commercial power source fails; otherwise, people working on downed power lines or other system problems may encounter live voltages unexpectedly -- such as when repairing the feed to someone's house when there is a "back feeding" generator operating.If you are not trying to "sell" power, you can install an Automatic Transfer Switch (ATS). The ATS is designed to bring your generator online ONLY when Commercial Power is out. Many have provision to start your generator as well as "transfer" your load to the generator. An ATS is expensive; but, once upon a time, that was THE major way of having a Standby Generator installed and protected. In some places it may still be the ONLY legal way.The third (3rd) may method was to "turn off the main breaker, THEN fire up the Generator and turn on its Breaker." If you think that sounds like Human Error -- such as turning on the Generator Breaker before turning off the Main Breaker -- could be a problem, you are right! Generators have been destroyed and people injured or killed because somebody did the order backwards or, worse, only closed the GenSet Breaker and forgot to open the Main Breaker...Enter the Electrical Panel, Generator Interlock. If properly installed, it makes it mechanically impossible to have both breakers closed ("on") at the same time! You cannot close either breaker without the other one being open ("Off"). These devices are inexpensive, robust, and reliable. You don't get the unattended actions of an ATS, but you don't have the maintenance expense, either...The MOWABI-GEN-LOCK proved to be of quite simple, but effective design. The MOWABI-GEN-LOCK, when properly installed, provides a "mechanical interference" between the Main Breaker and the "Upper Right" Breaker in a Square-D electrical panel.Disadvantages1. REQUIRES the installation of a Main Breaker. Main Breakers for Square-D Panels may be as much as three to five times (3-5X) as expensive as a standard, "two pole" Branch Circuit Breaker. As a result, small, branch circuit panels are sometimes installed without a dedicated main breaker by using a "reverse fed" Branch Circuit Breaker as the panel's Main Breaker. While this interlock is inexpensive, the Consumer may spend considerable money on the REQUIRED Main Breaker.2. REQUIRES the Generator Feed Breaker -- the "branch circuit breaker" that is "reverse fed" from the Generator and becomes the panel's de-facto Main Breaker (see #1 Above) when the GenSet is in operation -- occupy the upper-right breaker position. If have something else there, you'll have to move it!3. REQUIRES careful installation -- IF THE PLATE'S MOUNTING SCREWS ARE NOT IN THE CORRECT POSITION, THE INTERLOCK WILL NOT WORK!4. REQUIRES careful installation -- after marking the panel as shown on the seller's Amazon Page, do NOT drill the cover while it is in place! There are energized wires and buss bars behind that panel that do not react well to being pierced by steel drill bits. Even you CAN drill the panel without contacting any energized parts with your drill bit, you do NOT want the metal swarf from your drilling operation ending up INSIDE a live electrical panel.5. It may not be legal in your jurisdiction; or, if legal, it may not be legal for YOUR to make the installation. Check your local codes and laws.6. Square-D makes several DIFFERENT versions of Load Center (Breaker Panel); if you do not measure carefully before purchasing and you buy the wrong Interlock, it WILL NOT WORK.Advantages1. Even if you have to buy a new Main Breaker, it is MUCH Cheaper than paying for an ATS.2. Even if you have to buy a new Main Breaker, it is MUCH Cheaper than paying for a dead Generator.3. Even if you have to buy a new Main Breaker, it is MUCH Cheaper than paying for a dead Utility Worker.4. If you have reasonable mechanical and electrical skills, you can (are able to) install this yourself. (Whether or not you "may" install it is another matter -- See Above.)5. It is quick and easy to operate.6. This kit comes with most everything you need -- including screws and drill bit and warning labels.Bottom Line: Would I recommend the MOWABI-GEN-LOCK?Yes!Then, why am I giving them Four Stars (4*) instead of Five Stars (5*)? Because the Web Page shows the Interlock Being Installed without removing the cover to do the drilling. That is dangerous!

Instructions were terrible and part did not line up with square D 200 panel properly

............a simple device when using a portable generator. It forces the operator to shut the main breaker off before letting power into the panel from a generator which does two things: It keeps power from the generator from going back into the Utilities distribution system and it prohibits generator power from colliding with Utility power. They provide everything you need to install the device. (see pics)  If your a homeowner doing this for the first time be advised you must drill your holes (provided drill bit) in the panel cover in the right spot so be extra careful that the device is lined up correctly. (see provided installation pics)  The lock washers (see pics) go on the "inside" of the panel cover in other words the side of the cover facing the panel. They give you 2 "Allen keys" to tighten the screws (see pics). One for one side and one for the other. Tighten till it stops, it will automatically be at the correct spacing for the device to move freely.  Once installed the only way this safety device can be defeated is to remove the panel cover so keep it on during a power outage.  This is a "generic" device designed to fit Square D's "QO" and "Home Line" panels. Square D makes their own version of this device which is probably more expensive but this one works just as good. 

3/17/2025This interlock did work, but I was never 100% satisfied with it. With the screws tightened, the movement was extremely tight. I had to shim the backplate to clear the breakers (due to the design of my panel) and the movement was still really tight. The problem is that the holes in the backplate are big enough to accommodate the shoulder screws from the front, and the screws coming from the back aren't long enough to work otherwise. The result is that tightening the screws clamps the panel, backplate and front plate all together tightly. You have to loosen the screws enough to allow movement. I ordered another kit that was actually less expensive, and the holes in the backplate were only large enough for the screws coming from the back of the panel. The shoulder screws (with internal threads) butt up against the backplate by design. The result is that the shoulder screws have the correct spacing to allow tightening of the screws without ever squeezing the two plates together. It just secures the backplate to the panel and retains the front plate with the heads of the shoulder screws. I still had to shim the backplate (I actually just used the backplate from this kit as the shim) and simply picked up some 1/8" longer screws to make up the difference. The new interlock slides easily, still does its job, and the screws are all tightened down.All that would need to be done to fix this design would be to drill smaller holes in the backplate so that the shoulder screws butted up against it, and include longer screws for the back.Original:An interlock is a simple device that is pretty specialized, which I suppose explains the high prices many manufacturers demand. This is an inexpensive, but well designed, sturdy alternative that works perfectly. Its sole purpose is to prevent the main breaker and generator breaker from being on at the same time, and this interlock works perfectly with a Square D panel with a 1 3/8" gap between the main breaker and other breakers. It meets code and protects the linemen who work hard to get our power back on. It came with everything you need to install it, and was simple to get going.

This interlock, actually a little piece of aluminum, and all of its parts, would fit in your pocket easily. But it's a lot easier than fabricating one.