Poor Man's Generator Transfer Switch

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Poor Man's Generator Transfer Switch

Here are the details of what I did to find and install an affordable generator transfer switch into my house electrical panel. Like many of you, I have been looking for a proper manner in which to hook up my genset into my house electrical circuits.


A DISCLAIMER: I want to make it clear that I do not work for Home Depot or Square-D. The only proper and safe manner to hook a generator into your house electrical wiring is through a UL approved Generator Transfer Switch, designed for this purpose. There are many excellent articles throughout the 'net on this subject. Read them and adhere to them. Messing around with 120 and/or 240 volts is not for novices!! Get professional help if you do not know what you're doing, and/or your local building code requires you to do so. Nuff said!


After searching the Internet for some time, and seeing all those $300-450 plus generator transfer switch panels, I called a few local suppliers. Their units and prices were no better than what I had found on the 'Net.

I found the Popular Mechanics article (http://popularmechanics.com/popmech/homei/9803HIHIAM.html) on this subject and phoned Lowes in an effort to purchase the Square-D unit recommended in the article: 4-circuit generator panel, model QO4-8M60DS-GP). As I have come to expect from Lowes, they didn't have a clue, nor were any help at all.

I contacted Home Depot, and their electrical manager was able to cross reference the Square-D unit and special ordered one for me. HD's sku # is 515-664 (Square-D model 82434) It cost $87.50 and I had it within a week.

I spent quite a bit of time with the electrical manager on the purpose for the unit. He is a master electrician and was more than helpful with ideas and all. He did make it clear that he could not install it nor inspect it for me due to company policy. I had offered to pay him for his time to perform an inspection, thinking the law required it. I have a lot of experiance with electronics and electrical wiring and informed him of this. He asked me exactly where I lived, then informed me that the building code allows me to perform an install of this type, without a permit nor an inspection. Certain areas of Texas are like this.

I drew up a schematic of how I wanted to wire it in and brought it by for him to review. He blessed my plans and the next weekend I installed the unit and tested it.

This Square-D unit comes with 2 main 60 amp 240 volt input breakers linked together mechanically in such a way that only one may be "on" at a time. This arrangement feeds an electrical buss that can house either 4 "normal" or 4 "tandem" (2 circuits per breaker) Square-D circuit breakers.

I have a rather old and cheap existing electrical panel. I want to be able to have power to all my 120 circuits possible and perform power management myself. My house has 9 120 volt circuits, so I chose the 8 most important and wired them into this new panel, which I mounted next to the existing panel. I removed the 8 circuits from the old panel and routed them to the new panel, loading both sides of the new panel's 240 volt circuits just as they were in the existing panel.

I left the one remaining 120 volt and all the 240 volt circuits in the existing panel. I don't plan on running the drier or air conditioner from the generator anyway. I brought over the main 240 volt circuit (2 120 volt legs) from the existing panel by connecting 6 gauge stranded wire, via terminals, directly to the mounting screws of the 100 amp 240 volt MAIN breaker (on its output side), then routed these wires to both sides of one of the 60 amp 240 volt input breakers in the new panel.

I was fortunate that the 100 amp main breaker had these mounting screws. Otherwise, I would have to purchase a dual 60 amp 240 volt breaker for the existing panel and source the 240 volt panel to panel connection from it. Of course I brought over a good main ground and the neutrals and grounds from the old to the new panel and wired them accordingly.

I had to extend the length of several of these wires. I did so by soldering the extra length(s) needed and then protecting the connections with 2, count them, 2 layers of heat shrink tubing. I could have merely used wire nuts for such a wire extention, but I wanted an extra good job done.

I did have to purchase 4 new "tandem" (2 breakers each) type circuit breakers to use in the Square-D panel because my existing panel's circuit breakers were a different mounting type. These 4 new breakers cost me about $13 each. I could have used 4 new "normal" type ones, if I only wanted to power 4 circuits from the genset.

I installed a L6-30 amp Twist-Lock female plug on the bottom of the generator transfer panel in a small weatherproof box to serve as a connection for my generator's output. I also fabricated a generator-to-panel cord from 10 gauge 3 wire stranded "outdoor" cord, ($0.90 per/foot at HD) with a male L5-30 amp on the generator end and a male L6-30 amp on the panel end. Sure, I could have used L5's on both ends, but my RV's 30 amp service is L6 so I used the L6 on the panel end to allow me to hook my genset into the house or the RV.

It is important to note that I decided to use a 120 volt "backup power" wiring scheme, verses a 240 volt one. To do this, I use the full-power 120 volt output of my generator to feed my 8 circuits, rather than use the generator's 240 volt output. I believe this scheme is better for the generator, no need to worry about balancing the 2 120 volt outputs. Another benefit of this scheme is that powering my house at night with my Heart 120 volt 2000 watt inverter and battery bank will be a snap because everything is already setup for 120 volts.

To accomplish this, I wired both inputs of the 240 volt generator transfer panel "genset" main breaker to the black (hot) portion of the L6-30 amp Twist-Lock female plug on the bottom of the generator transfer panel. This sends the 120 volt output fo the genset to each leg of the 240 volt buss, therby connecting all 4 circuit breakers to a single 120 volt circuit. This arrangement is ONLY in effect when the "genset" main breaker is switched on.

During normal commercial power operation, the "commercial" main breaker is engaged on the generator transfer panel supplying normal 240 volt power, via the 2 120 volt leg buss, to my 8 120 volt circuits, electrically just as things were before in the existing panel.

I use a Generac 4000 XL generator as my power backup. This generator is rated for 33 amps maximum "continuous" output on the 120 volt full-power L5 outlet. Using 10 gauge wire to connect it to the generator transfer panel is acceptable even though this size wire is rated for 30 amps safe-maximum. I don't expect to be running my generator to it's 33 amp maximum output anyway. Motor starting surges and such are no real problem and did not warrant an upgrade to 8 gauge wire.

I am very happy with the Square-D generator transfer panel and I recommend it to anyone wanting to safely hook up their genset to their house electrical circuits. It is well designed and very affordable, even if you have to purchase 4 new breakers as I did.

The total cost of this project was (tax included)

$ 93 for generator transfer panel $ 56 for the 4 new breakers $ 30 for the L6 male & female plugs $ 40 genset-to-panel connection wire $ 20 various small parts and such

$239 total

Your costs could be much less is you can use your existing breakers, don't use the expensive Twist-Lock plugs, and keep your genset close to the electrical panel.

Home Depot has since decided to stock these Square-D units in some of their Houston area stores, so you Houstonians can thank me for that. As with anything Y2K related, you ought to purchase it sooner rather than later.

The Home Depot folks went out of their way to help me with this project. I went back several times with questions, and each time found smiling, helpful folks who know what they are talking about.

If anyone has any suggestions or comments I would appreciate them. We're all here to learn from each other and to share what we find. I hope the information I have presented here helps another Y2K'r out.

-- Buffalo Bob (buff@hal.com), February 18, 1999


I copied this to my brother, who has also installed a back-up generator. He replied:
Soldered splices are OK in electronics (in fact, they're routine), and this guy's background is in electronics, so I guess that's why he thought he was doing an extra good job by soldering. But 120/240v power transmission is another kettle of fish, because at these voltages and amperages a certain amount of heat is generated along the transmission line - from all those excited electrons shoving each around other in the wire. So, all the electrical codes I've read require either continuous runs or wire-nut splices rather than soldering. You terminate the old wire in a utility box with a strain-relief coupling, and bring the new wire into the box, also through a strain-relief coupling, and then splice them with the appropriate size wire nut. With heavy gauge wire, the splice is done with a copper nut and bolt. Solder's a no-no, because of its low melting point.

Hope this helps.

-- Tom Carey (tomcarey@mindspring.com), February 18, 1999.

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