The safest way is to get an electrician to install a transfer box and plug into that with a NEMA plug.
Lawyer's stuff: Electrical work can KILL YOU and EVERYONE in your home. Don't do it incorrectly. My instructions do not constitute a perfect method and you have to determine if it is right for you. Consult an electrician if you're unsure about any part of my instructions, and even if you are sure, consult one anyway because I don't need the hassle of having your lawsuit thrown out of court.
After this latest power outage, I had half a dozen people ask me how I set up my little portable generator into my mains box. You can buy a transfer switch and do it, or you can make a home made setup that is safe and easy and cheap. I wrote this in an email and decided to post here.
EDIT : Please note that the setup can be improved by adding an SPDT switch. I am going to go back and add one to mine, and that will add about $3-4 to the cost, but will make the system much safer.
I found a way to do it for ONE circuit that is safe -- provided you do and use it correctly -- and does not violate IRC code.
..and it only cost me $6 (not including the tester). All prices are from my home depot.
The only downside is that you can only do this with a SURFACE MOUNT mains box. If yours is mounted in the wall, then you'll need to find another place to mount the handy box. My setup puts the handy box right on the side of the mains.
I assume you have a generator with a 120vac outlet and a 3-prong extension cord with at least 14ga wire.
You'll need the following:
1. voltage tester. Any kind will do, as long as it has leads. This kind costs $5
(http://lh4.googleusercontent.com/public/qkA5vZuBTMVqw6A3NaKKsSX-Swqf1Hwajf5ENRENyDs9seIrQdKv8p3zxXP1o7Hiy3YLPunY3V-ADvpVotRwOq71kQHC2voWbVsGfUw0kCz3J7whfwaRqcW0o_Y5Gg5Ge_IwcF_aanGhyVIwQlODS6gEBQ3v2hY2M-tFSa1mw2FAtTu0nsDDuOpiXD7XCPNaBIWg6QH2WXu7FMbc7TVpQocAJdLgCoPirXcXDRsLP8t2mygQ6gYPScsb-xb7lX2bHYiQcU8FIn5Ckb8189NOLfe2YQBzow)
2. A single-gang handy box, deep type. $1
(http://images.grainger.com/B341_22/images/products/250x250/Handy-Box-4A238_AS01.JPG)
3. Single gang handy box cover for single outlet: $0.81 (at home depot)
(http://images.grainger.com/B341_22/images/products/250x250/Handy-Box-Cover-4YF17_AS01.JPG)
4. A NEMA 5-20A single receptacle $2
(http://images.grainger.com/B341_22/images/products/250x250/Single-Receptacle-1PKB9_AS01.JPG)
5. A NEMA 5-20A plug $2 -- i prefer the angle type as it won't pull out.
(http://www.stayonline.com/images/products_240x240/3600.jpg)
6. An old 3 prong extension cord. At least medium duty 14 gauge wire. 12ga is better. You are going to cut it down to about 15ft and put the plug in #5 onto it (free, i had one that was cut. if you have to buy one, then you blow the budget).
7. A 1/2" chase nipple and locknut - $0.50
(http://lh3.googleusercontent.com/public/7CYOD2qY55Xt6WV-S58IgK8UNQm3gTQvYTP2dAz492TeCUgGO7IzAyrJR-bCsF14C3NnXeeFirdjVVjKJ_eOD4ul-e2mJ_9FZFbujaGIn0gONoMcgBm_FXLdnYPAkKM17sbt87qZDwkyzXVxTEyi-zC8hiLCbEo57Vhk3e9qgnSswB6JXIp9OvfQYjmGCrl95w2BLYJKSAaIExggNAAD1pg_WUz-m0lg7B9_DOSKDzp1C0j6p5Svfixyr3Jtkk4WD3GN3hRqPV31joM-BCyzeBycs0pbT0TQ7eNTcr-dB3s)
8. Tools: screwdrivers, wire cutters/stripper.
9. Wire. I had some 12 ga laying around. You need to use house-spec single conductor copper wire. You can use 14ga for this provided you only do one circuit and you don't exceed 20a (it's only a foot) but 12ga is preferable. You'll need about a foot max. if you have to buy it, get them to cut you 1 foot of 12-2 ROMEX NM cable, which is sheathed. One white, one black and one with no insulation (ground) (NOTE: If you plan to do two circuits, get 12-3/3 conductor)
(http://img.ehowcdn.com/article-preview/ehow/images/a02/5j/g3/understand-different-household-wire-types-1.3-800x800.jpg)
10. OPTIONAL: glass fuse holder.. recommended but not required. They usually run about $5
(http://images.grainger.com/B341_22/images/products/250x250/Fuse-Holder-1CV90_AS01.JPG)
How to do it:
1. Open your mains box. Marvel at the mess. You need to find the circuit you want to back up with your generator. I assume it's your fridge, but you can do whichever one you want. You can also do more than one, but I am only going to cover doing ONE here (and mention how to do TWO). If you understand all this, then you can figure out how to do more. The key is to know which breaker you want and make sure the load on it is small enough for your generator to handle. BE CAREFUL NOT TO TOUCH ANYTHING.
My fridge has a 6.1A MAX rating. My generator has a 1200W max, 900W nominal. 6.1A x 120V = 732W. My generator can handle the fridge. I put a white stripe of paint on the surface of my breaker so I know that's the one even in limited light.
2. Remember surface mount mains only here. Find a 1/2" punch-out hole near the breaker for the circuit you want to back up. Punch it out. Punch out the middle 1/2" hole in the handy box. Now take the 1/2" chase nipple and put it thru the inside of the handy box and mount it to the mains punch out with the lock nut. You should now have a handy box attached to the side. Mount it in a place the cover will still attach properly. Tighten the nut carefully. Does your mains cover fit securely? Good. Keep it off for now.
3. Take out the NEMA 20A receptacle. Notice the screws for the wires are different colors. The brass one is for hot and the silver one for common. Trim your ROMEX wire and attach the black to the brass screw, the white to the silver and the bare/ground to the ground screw.
4. Run the wire thru the chase nipple you installed, taking care to route your wire away from the panel. Strip the sheathe and trim your common/white and ground/bare. Attach the white wire to the commons rail in your mains and the ground to your ground. Most older mains panels ground into the box itself, newer ones have a ground rail. Screw in the receptacle to the handy box, make sure everything is secure.
5. TURN OFF the breaker for the circuit you want to back up. Loosen the wire screw which holds the black (or red) wire, then run your new black wire from your handy box into the same place as the existing black/red wire. (some will use either depending on the wiring. Once you've got both wires back in place, screw down tightly and DO NOT TURN YOUR BREAKER BACK ON YET. First check everything to make sure you wired it right. White on silver, black on brass, etc.
6. Plug your tester wires into the leads of the receptacle. You just want to test the power. Turn the breaker ON. You have a hot receptacle there so watch out. Got current? If no, turn off the breaker, and double check your wiring connections. If yes, remove the tester. Put the cover on the handy box. You're done here.
7. Now cut down your extension wire to about 10-15ft, keeping the MALE three prong. Install the NEMA 20A plug on the end. The correct way to do this is to strip ONE main wire back, keep it away from the ground or anything else, then plug the male end in and test the exposed wire against GROUND with your tester. You want to find the hot wire. If the wire is hot, that one goes to the brass screw in the plug. If you have nothing, then that's the common and attach that to the silver screw in the plug. YOU NEED TO MAKE 110% CERTAIN YOU'VE CONNECTED THE RIGHT WIRES TO THE RIGHT SCREWS HERE. Test before, and then after. And then turn the breaker off, plug both ends in and test it again. Once you are sure you've kept the right wiring thru, then you're completely done.
Now, the next time the power goes out, crank up your generator. TURN OFF the breaker for your fridge, then plug in the special cord. You have power for that circuit.
What happens when the power comes back on? Nothing. Since you turned off the breaker and you connected HOT-HOT and COMMON-COMMON, the generator will keep plugging away until you turn it off. When power comes back on, UNPLUG FIRST, then turn on the breaker. Don't leave the plug in.
=====
Adding an inline fuse.
1. I recommend this, but it's more advanced so you have to have more understanding. One note, there isn't any place to do this that is IRC code compliant. If you want to be code compliant, you have to install an external fuse into a separate box or even in a double-gang handy box, but that won't fit on the side of the mains box.
2. Do the install as above, but instead of connecting the black/hot from the handy box to the breaker wire, you are going to connect it to the fuse lead. I mounted mine right next to the handy box one the side of the panel. You might even be able to do it IN the handy box front cover but I haven't tried.
3. Connect the other fuse lead to the breaker as above. You have to use the NM type wire and solder them on. For my 10A connection, I used an LGR-type 10A/300v fast acting fuse (part 0LGR010.V).
====
Wiring for 2 circuits with 12-3 wire
1. Everything is the same.
2. Instead of one black from the receptacle, you have one black and one red. There are always two connection locations on every receptacle for each lead. Just put the black on one and the red on the other and each one to a different circuit as above.
3. Your generator better be at least a 2000/2400W type. If you do this on a small generator into two 15A circuits you can get the gen overloaded. I would not do more than the fridge and a single light circuit. Do your math for power and add 20% for safety.
Most places this would not be acceptable since the breaker can be on with the generator connected, back feeding the grid if I understand your method (a wiring diagram would help). You need a handle interlock or a SPDT switch to guarantee only one source of power is going to the panel at any time.
mitt
Here is a better way for $99
http://www.northerntool.com/shop/tools/product_200196724_200196724 (http://www.northerntool.com/shop/tools/product_200196724_200196724)
mitt
Quote from: mitt on August 29, 2011, 08:57:09 AM
Most places this would not be acceptable since the breaker can be on with the generator connected, back feeding the grid if I understand your method (a wiring diagram would help). You need a handle interlock or a SPDT switch to guarantee only one source of power is going to the panel at any time.
mitt
Mitt,
You missed something. The patch-in for the generator is a
receptacle. When the breaker is on, it's just a 20a receptacle and you can plug anything normal into it. The only "problem" is the cord, and I specifically chose that plug to keep you from using it elsewhere. Having a male-to-male cord is basically useless for anything else. Yes, "someone" could find that cord and cause a problem.
The best way to deal with the backfeed problem is the fuse.
Quote from: mitt on August 29, 2011, 08:59:37 AM
Here is a better way for $99
http://www.northerntool.com/shop/tools/product_200196724_200196724 (http://www.northerntool.com/shop/tools/product_200196724_200196724)
mitt
Better in every way, except price.. ;-)
Quote from: ducatiz on August 29, 2011, 09:02:05 AM
Mitt,
You missed something. The patch-in for the generator is a receptacle. When the breaker is on, it's just a 20a receptacle and you can plug anything normal into it. The only "problem" is the cord, and I specifically chose that plug to keep you from using it elsewhere. Having a male-to-male cord is basically useless for anything else. Yes, "someone" could find that cord and cause a problem.
The best way to deal with the backfeed problem is the fuse.
When the breaker is ON, and the utility is down, and you plug your generator into the receptical, what prevents the voltage from the generator going out of your house to the mains?
The fuse will only blow if there is a load greater than the fuse.
mitt
Quote from: mitt on August 29, 2011, 09:06:21 AM
When the breaker is ON, and the utility is down, and you plug your generator into the receptical, what prevents the voltage from the generator going out of your house to the mains?
The fuse will only blow if there is a load greater than the fuse.
mitt
I see your point. The only thing that prevents it is the brain of the operator. There's no easy way to put in an SPDT, maybe route the house wiring thru the box into the SPDT. That just increases the complexity. It works for me, and probably a few other people out there.
Running the wire from the house to the SPDT and then one from the breaker and one from the gen might be too much wiring for it.
I am going to see if I can cram an SPDT into the handy box. The whole thing works well because of that size, but the more I think about it, I'd rather have that in place too.
Quote from: ducatiz on August 29, 2011, 09:09:46 AM
I see your point. The only thing that prevents it is the brain of the operator. There's no easy way to put in an SPDT, maybe route the house wiring thru the box into the SPDT. That just increases the complexity. It works for me, and probably a few other people out there.
Running the wire from the house to the SPDT and then one from the breaker and one from the gen might be too much wiring for it.
I am going to see if I can cram an SPDT into the handy box. The whole thing works well because of that size, but the more I think about it, I'd rather have that in place too.
the link I posted - that box from reliance - is exactly that - a SPDT switch - one input side coming from the breaker, one input side coming from the generator, and the common output going to the circuit (in my case - a furnace - I installed one a couple years ago).
generator__________
\____________ furnace (or fridge) circuit
utility (breaker)_____
It is a 1 dollar SPDT switch in a $5 sheet metal box with a nice male receptacle (no hacking of extension cords) and a power on LED, but for 99$ and having a UL label, to me is is worth it.
I have been in your shoes before though in an emergency and just wired my generator straight to a switch on my furnace bypassing the panel altogether, so I know how it goes when sh!t is hitting the fan. I just don't want people taking an emergency solution as a good long term solution.
I have designed 2 whole house transfer systems in the last 5 years for work, they are never as simple as most DIY'rs think when all the standards UL and NEC are taken into account.
mitt
LOL...
I hear you. My hack works well.. [thumbsup]
shame on you for not using a union electrician
;)
[laugh]
A breaker isn't a disconnect.
Please don't do this. Spend the money and get a real disconnect.
Your local utility worker appreciates it.
I'm going to revise it to include the SPDT.
Quote from: bobspapa on August 29, 2011, 09:37:30 AM
shame on you for not using a qualified electrician
;)
[laugh]