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Old 09-25-2012, 08:27 AM   #1
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Wiring a generator from the garage


Greeting all. I am a DIYer with some slightly more than basic electrical knowledge (4 years of electronics in high school, read many books on wiring, have wired my own switches etc and rewired the attic in our old house by replacing cloth with new romex) and have a question that i think I know the answer to but want to make sure I'm not missing anything.

I live in the North East and in October we were without electricity for 11 days. In order to get us through I killed the house breakers, opened the box leading into our heating system (natural gas but the water pump requires electricity), disconnected the wires and put them into a dummy junction box I affixed to the ceiling beam (2 outlets) and then ran the genny into that same outlet. It ran the heating system just fine and then i was able to run a 100 foot extension cable upstairs to run the fridge and a few LED lights. So essentially it was disconnected from the main electrical and became it's own circuit. All worked well and we got through the outage fine with 14 people staying at the house.

Jumping forward I realized I was lucky we didn't have much snow on the ground because I had the genny in the back yard and opened the basement hatch to run the extension chord into the basement. It occurred to me that had this been an ice storm after 2 feet of snow I wouldn't be able to do that. So I started to think about hardwiring a system in so it's essentially simple (and my wife can do it if I'm not here). So here's what I'm thinking of doing and I'm wondering if i'm missing anything or wrong on something. Please let me know your thoughts and thanks for taking the time.

Sometime before we moved in someone took down the suspended electrical wires that powered the detached garage from the house and ran them underground. I was able to find where they enter the garage and where they enter the basement easily enough and realized for some reason they had run two lines. I did some checking with my non conductive voltage checker and realized that one line was for everything but the exterior light (two garage doors, a few outlets, and a light or two). So I opened up the box for the exterior light and connected that up to the "main" line and disconnected the secondary line. In the basement I disconnected and terminated the secondary line as well so now I essentially have a long piece of underground 3 wire romex coming from the garage to the basement.

So here's what i want to do. Put a male plug on the "dead" line in the garage that can connect to the genny which is positioned near the door and grounded to a grounding rod outside. The genny could run in there with the door and window (directly above) open and should be fine as long as the dog doesn't fall asleep in there.

On the basement side of things I was planning on extending the "dead" line to that dead box I mentioned earlier. That way when the power goes out I can plug in the genny thereby making that "dead" line the only hot line in the house. Then in the basement I can connect the line heading into the pump, thereby making that hot, and run the extension to the fridge as before. It's a totally seperate circuit so i have no issues with backfeeding a line that may be being worked on.

So there ya go. Any thoughts, concerns, etc? Also, while I have thrown the breakers back on and have determined that in fact there is not power coming into the "dead" underground line, it still freaks me out not being able to see the entire thing. If it was a short cable I'd just test it with a continuity tester, but since it isn't, any thoughts on how i can determine that it's the same line without question?

Allright, that's it. Thanks in advance.

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Old 09-25-2012, 09:03 AM   #2
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Wiring a generator from the garage


To reiterate, I assume that the only item in the house to be made live using the generator is an outlet box with some receptacles not connected to the rest of the house electrical system.

First test the existing supposedly unused underground cable for voltage with the power to the house and garage turned on. Test between each combination of two wires and each combination of one wire and ground. Repeat at the other end of the suspected cable.

You want to measure no voltage on any of the measurements.

Do a continuity test from one end to the other this way. Since the meter probes don'r reach both ends of the test subject (the buried line), get a long length of insulated (single conductor) wire (suggest 12 to 16 gauge, any color) to reach with. Do enough tests to verify that each of the three or so wires in the cable have continuity but do not short to each other.

Always turn off the power to the test subject before doing any continuity tests. Also disconnect at least one side of the test subject (screw or wire or terminal) from everything else connected to it before doing the test. (Label everything you take apart.)

By the way, white or yellow Romex is not rated for direct burial and if you find some buried then you have no choice but to abandon it. You need the gray UF variety.

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Last edited by AllanJ; 09-25-2012 at 09:18 AM.
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Old 09-25-2012, 09:06 AM   #3
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Wiring a generator from the garage


Now why didn't I think of that. Makes sense. Any thoughts on the rest of the situation?
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Old 09-25-2012, 09:07 AM   #4
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Wiring a generator from the garage


Don't even think of running the generator in a garage, even detached. You'll have to go into it to service it or shut if off and it will be full of carbon monoxide.

Do it for the dog at least!

You're much better off building a small generator sized shelter so that it is protected from the environment.

3 wire romex? Is that including the ground? You mean UF right? Romex can't be run underground. What gauge? What sized generator?

You could do as you want, but you could also put in an "interlock breaker" so that you could then choose what you want to run on your existing panel, without splicing wires. With the interlock, either the main or your generator can feed the panel. You can't accidentally have both "on" at the same time.

Square D makes a small "transfer" panel that you can run up to 8 circuits - it can hold 4 tandem breakers. Move your well pump and furnace, and some lighting and you just flip a switch.
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Old 09-25-2012, 09:26 AM   #5
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Wiring a generator from the garage


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Don't even think of running the generator in a garage, even detached. You'll have to go into it to service it or shut if off and it will be full of carbon monoxide.

With the windows open and the door and garage doors there's actually less structure than walls. i tried this for an hour and it was fine (and I was kidding about the dog). Plus I should point out that the genny sits in the door way with the exhaust venting outside.

Do it for the dog at least!

You're much better off building a small generator sized shelter so that it is protected from the environment.

3 wire romex? Is that including the ground? You mean UF right? Romex can't be run underground. What gauge? What sized generator?

600 v sunlight resistant (UL) Operation (#) Ammcoflex 12/2 with ground. That's what is written on the line. Asssuming that means 2 12 gauges with ground?

You could do as you want, but you could also put in an "interlock breaker" so that you could then choose what you want to run on your existing panel, without splicing wires. With the interlock, either the main or your generator can feed the panel. You can't accidentally have both "on" at the same time.

Square D makes a small "transfer" panel that you can run up to 8 circuits - it can hold 4 tandem breakers. Move your well pump and furnace, and some lighting and you just flip a switch.
Thought about that but I prefer to have a dedicated circuit so there is literally no possibility of crossover. So all that said, think I'm kosher in what i'm considering?
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Old 09-25-2012, 09:29 AM   #6
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Wiring a generator from the garage


On the CO question I should point out that the genny is in the entrance way venting outside and all doors are open so it's really no problem. I tested for an hour and it was fine.

The wire that's there says Product of Jose Albuquerque, 600v UF sunlight resistant (UL) operation (#) Ammcoflex 12/2 with ground

Thought about a switch but for my tastes I like the idea of a dedicated seperate circuit. No possibility of any crossover in case a switch fails etc.

Thoughts?
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Old 09-25-2012, 09:36 AM   #7
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Wiring a generator from the garage


Your idea is fine and will work. Basically you're just hard wiring an extension cord.

I disagree with you on the CO. Many accidents happen every year. You know you can't smell it.
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Old 09-25-2012, 09:38 AM   #8
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Wiring a generator from the garage


Point taken on the CO. Thanks.
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Old 09-25-2012, 11:11 AM   #9
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Wiring a generator from the garage


"So here's what i want to do. Put a male plug on the "dead" line in the garage that can connect to the genny which is positioned near the door and grounded to a grounding rod outside. The genny could run in there with the door and window (directly above) open and should be fine as long as the dog doesn't fall asleep in there".

This is called a suicide cord in the electrical trade and is not only dangerous, it is illegal. That dead end connects to something and that something can be turned on. That will make the male plug hot.
Why not do it the right way? Install a generator inlet outside where the generator will sit. Then buy an interlock kit for your panel. This the right way to to do it.
The power company also might have something to say about this installation you suggest. I know that when a power company lineman hears a generator running, he will do nothing to restore your power until he knows whaT YOU have done is safe. Remember what happens when you back feed a transformer. You did study electronics and you do understand now, I hope.

Ps...........Never ever put a generator in any structure. It must be outside in the open air. You can build a top or roof for it, but it can never be run inside. NEVER. Even in an outbuilding. This is deadly.
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Old 09-25-2012, 11:31 AM   #10
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Wiring a generator from the garage


I'm confused. A suicide chord has males on both ends I believe. What I'm proposing is a male on one end and a femsle(outlet box) on the other. It has nothing to do with the house system and is essentially the same as an extension chord. What am I missing?
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Old 09-25-2012, 11:36 AM   #11
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Wiring a generator from the garage


You are making a long extension cord with the uf, which is a violation.
Put an inlet box in the garage and you will be compliant.
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Old 09-25-2012, 12:04 PM   #12
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Wiring a generator from the garage


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Put an inlet box in the garage and you will be compliant.
That is, use a male receptacle in an outlet box as the "plug", which is rigidly fastened to the garage wall instead of at the end of a loose cord.

Use an ordinary extension cord, probably not more than 15 feet, to get from the inlet box to the generator.

If the underground cable did not stick out enough to reach where it needed to reach, additional Romex can be spliced on with a junction box required at the splice point. Indoor rated Romex can be used for a run wholly in a stud bay or other fully dry indoor location.

The generator must have breaker protection limiting the output to 20 amps at 240 volts (or 20 amps at 120 volts) if either of the following conditions are true:

1. The wires to the house are 12 gauge. (Fourteen gauge wire has a 15 amp limit.)
2. The box with receptacles for generator power in the house does not have individual breakers of no more than 20 amps for each receptacle or group of receptacles (if the box is not a subpanel with breakers).
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Last edited by AllanJ; 09-25-2012 at 12:22 PM.
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Old 09-25-2012, 12:11 PM   #13
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Wiring a generator from the garage


I just did an install with a Reliance branded manual transfer switch and inlet box. Easy install and seamless transition to power the selected circuits from either line or generator. There is no real possibility of cross connect. Sure, one of the transfer switch 3-way breakers (they also have a middle "off' position) could fail and leave a circuit unpowered but that's unlikely. GenTran is another major maker.

The panels come in many sizes. I got the 10-circuit model and am using 8 of the positions. I don't really need all that stuff at once but having them connected makes it easy to go to different parts of the house and have lights, etc. w/o having to move ext cords or flip breakers.

Also, concur that NO WAY should you be running a generator in any enclosed environment, even with windows and door open. Go to a local hardware store and get a CO detector and do another test. I bet that will change your mind.
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Old 09-25-2012, 01:22 PM   #14
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Wiring a generator from the garage


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.......
So I opened up the box for the exterior light and connected that up to the "main" line and disconnected the secondary line. In the basement I disconnected and terminated the secondary line as well so now I essentially have a long piece of underground 3 wire romex coming from the garage to the basement.
........
What did you terminate this line to ???
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Old 09-25-2012, 01:46 PM   #15
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Wiring a generator from the garage


Allan J, thanks, that makes sense.

Oso, apologies for my terminology. The line went from the fuse box into a junction box into the basement where it connected to the line out to the garage. I disconnected the wires, trimmed the ends from the junction box as they were long, wing nutted them and crimped them and then tucked them back into the box. That's what i meant by terminating it.

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