Using house wiring during an outage

Hi,

New guy here, just learning the solar ropes. I live in what's called a patio home without a lot of ground space and with a homeowner's association that frowns on planting panels all over the roof. So, I'm starting out with small projects to experiment with that will light my porch and rear alley, but it will also serve as backup power. I do have a small backup generator, but fuel is more finite than sun.

I'm learning a lot reading these forums but one item crossed my mind that might help in the midst of an emergency power outage (I live in earchquake country) - I have an inverter and considered fashioning a two-plug (one on each end) extention cord. Providing the cord is of the proper gauge, would it be feasible to open selected circuit breakers and plug the inverter into a wall socket so as to use the house wiring to power low-wattage fluorescent lamps.

It seems fairly benign but there might be a no-no that I haven't though of. There might be some code problem with that but in the event of disaster, I'm more concerned with safety and practicality of doing this rather than any codes specifically.

Thanks,
Ed

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,494 admin
    Re: Using house wiring during an outage

    Yes, there are major issues when using home wiring for emergency backup...

    You need a transfer switch. There are manual, automatic, small, large, etc... A random link to small 6 circuit one:

    http://www.electricgeneratorsdirect.com/catalog/product_info.php?cPath=21_31_102&products_id=333

    And, depending on the inverter (cheaper, modified sinewave types--used to be called modified squarewave), they may not work on house wiring were you have a grounded neutral wire (all US 120 VAC circuit homes have a grounded neutral).

    Basically, if you have to ask, this is probably not a good, first home project for your experience. A licensed electrician is usually mandatory for these projects (building code/insurance reasons).

    I live in earthquake country too... And have installed a manual transfer switch for use with a generator. If improperly installed, you can cause a fire and/or electrocute a utility lineman.

    Also, if you are using a generator near a home, get a couple of carbon monoxide detectors for sleeping / living quarters--generators too close to home (fumes), storage of fuel (fire, fuel going bad), theft (generator has to be outside to run safely), and noise (look at the Honda eu1000i / 2000i / 3000i for some quieter possibilities) are some of the issues to be worried about.

    Regarding Solar, I believe in California (if that is where you are), there is a state law that allows, within reason, for home owners to install solar panels even if local homeowner associations or city planning departments explicitly prohibit such roof modifications.

    Hope I answered your questions...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Using house wiring during an outage
    ...a homeowner's association that frowns on planting panels all over the roof.
    This link may be a place to start in determining solar access rights in CA.

    HTH,
    Jim / crewzer
  • FrankFrank Solar Expert Posts: 54 ✭✭✭
    Re: Using house wiring during an outage

    The biggest issue is accidental backfeeding into the grid. Circuit breakers can "leak" and it's better to use a knife-blade switch.

    Does your homeowners assoc. "frown" on panels or is it written into a contract somewhere that you can't use them? I don't understand groups that try to shoot down progress! Why not try to get it changed?
  • System2System2 Posts: 6,290 admin
    Re: Using house wiring during an outage
    Frank wrote:
    The biggest issue is accidental backfeeding into the grid. Circuit breakers can "leak" and it's better to use a knife-blade switch.

    Does your homeowners assoc. "frown" on panels or is it written into a contract somewhere that you can't use them? I don't understand groups that try to shoot down progress! Why not try to get it changed?
    Sorry, I disappeared for a while. Priorities...

    Thanks to the replies so far. They've proven useful.

    Frank's response is sorta what I was looking for. I need to clarify some things that I didn't state well in my previous post.

    Yes, I do have that Honda generator, the EU2000i - excellent, and quiet.

    No, I wasn't planning to plug the generator into the wall socket. I figured when I got to that stage that the transfer switch would be the way to go.

    I do have a deep cycle battery (so far) and was considering that if power lines were down (nothing for a lineman to even work on, much less get shocked) would there be any harm in attaching an inverter to house circuit just to run some lights, =IF= the circuit breaker switch were opened. From Frank's response it apparently is not a good idea. This is what I was looking for.

    But also, thanks, Jim, for the link to solar access rights. Yes, I'm in southern California (Orange County) and I was not aware of the details of California law. I used to be on the board of our homeowner's association and vaguely remember some restrictions in the CC&Rs but haven't looked at them in quite some time. However, according to the details in that link, they are fairly moot at this point.

    This opens some doors.

    And thanks, Bill, for the advice on CO detectors and possibility of generator theft. I hadn't considered that possibility. Along that train of thought, how good is the prospect of running the generator in the garage with the exhaust piped outside? - provided, of course, that the system is adequately foolproofed. ...granted, at this point I don't see an effective way to connect to the EU2000i muffler.

    Thanks, again!

    Ed
  • BB.BB. Super Moderators, Administrators Posts: 30,494 admin
    Re: Using house wiring during an outage

    Whether you plug a generator or an inverter into a wall outlet to power a few lights...

    1. You can open a circuit breaker--I have not heard of any voltage/current leaks with standard breakers
    2. HOWEVER, if you forget to flip the breaker and turn on the gen/inverter, you can (in theory) kill somebody.
    3. If you have utility power and plug the gen/inverter in accidentally, you will probably pop a few fuses/circuit breakers/devices.
    4. A transfer switch (like that I put in my link above) is both safe and legal. Allows a load to be safely switched between two sources and prevents back feeds (many also include a watt meter so that you can watch total loads supplied by gen-set).

    Plugging an Inverter into house wiring:

    1. First, see above... treat inverter and generator as the same type of device (power source)
    2. If it is a cheap inverter (i.e., a few hundred watt inverter for less than a few hundred dollars), it is probably a modified sinewave inverter. Those will not usually work well (or at all) if connected to a grounded neutral in house wiring and the DC side of the inverter is also negative grounded to to house ground. It is possible if the 12 vdc negative lead is not grounded (but the AC neutral is earthed), that the whole 12 vdc side wiring/battery (plus and minus leads and possibly the metal case of the inverter) could become electrically "hot" wrt to earth ground... Not a problem unless you touch the battery terminals and didn't expect 120 VAC or so on exposed metal/DC connections (or connect a battery charger that may be grounded output itself).
    3. Usually, only the "true" sinewave inverters can have their neutrals and 12vdc inputs safely grounded.

    Regarding a generator and CO... You could build a box in the garage with am electric fan and a vent stack.... But I would not trust it. If you have ever idled an old car in the driveway or near the garage--many times it does not take long for the exhaust fumes to be noticed in the home (depending on many factors).

    Instead, I would put the generator at the end of a 25-50 foot heavy (12 awg with ground wire or heavier for 15 amp circuit) duty extension cord far away, and cross or down wind from ALL HOMES (not just my own). Wind can shift (or no wind)--there is probably no way to generically describe where to safely place a generator. Where ever you place it (hopefully away from direct view of street), make sure you can lock it up with a heavy chain/cable to a large tree, ring in concrete, etc.. In any case, your home will stick out like a sore thumb because it will be the only one with its lights on. If power fails for days, you may wish to run the generator more during the day to keep your food cold and not run it too much at night when folks are on the prowl.

    Some folks purchase an RV style generator and run the stack up towards the roof (following rules for chimneys).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Using house wiring during an outage
    BB wrote:
    Instead, I would put the generator at the end of a 25-50 foot heavy (12 awg with ground wire or heavier for 15 amp circuit) duty extension cord far away, and cross or down wind from ALL HOMES (not just my own). Wind can shift (or no wind)--there is probably no way to generically describe where to safely place a generator. Where ever you place it (hopefully away from direct view of street), make sure you can lock it up with a heavy chain/cable to a large tree, ring in concrete, etc.. In any case, your home will stick out like a sore thumb because it will be the only one with its lights on. If power fails for days, you may wish to run the generator more during the day to keep your food cold and not run it too much at night when folks are on the prowl.

    Some folks purchase an RV style generator and run the stack up towards the roof (following rules for chimneys).

    -Bill

    I'm totally off the idea of plugging into a wall socket. I figured it probably wouldn't be a good idea but had to ask anyway to see what others might have come up with. Thanks for all the input there. I don't really need to do that anyway but pondered the possibilities.

    And that's very good perspective on generator placement. I'll give that much thought.

    I was planning on running only a few low-wattage interior lights off solar/battery system and the generator was for keeping the fridge going till it's eaten clean. I only wanted to store no more fuel than is necessary to keep it going for maybe several days. I have the Duration tank for the EU2000i. I rarely let my Tundra get much more than half empty, so there's more there if I need it.

    I once lived through a 4-day outage, an ice storm in the east, but I moved the food out onto a balcony in the frigid air. In southern California I don't have that same "luxury" in the event of an outage.

    Regarding the solar/battery setup, I have a deep cycle battery so far that's just being held to "full" with an automatic charger. Next I'll need a suitable panel and charger. This is my "hobby" project for lighting a fluorescent floodlight in the alley behind our garage. I'll probably "grow" it from this small beginning.

    Thanks for all the input!

    Ed

  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: Using house wiring during an outage

    Just about all of the light weight modified sinewave portable inverters have two primary power conversion circuits. The first is a ferrite transformer based DC to DC switching power supply that take battery voltage up to about 155 vdc. The second circuit function is a full wave H-bridge MOSFETS that sequences the output AC plug in a short, +155 vdc, short, -155 vdc, short at a 60 Hz rate to produce the modified sinewave.

    This is okay for directly pluging in a light or appliance but the problem with the H-bridge driver is the normal neutral (wider of two AC plug prongs) can not be grounded which will be the situation if you tie into the house electrical wiring. The neutral is ground bonded at the main breaker box.

    If you do attempt this, as soon as you ground the inverter case it will shut down (or blow out). If you do not ground the inverter case and you touch the case and any grounded item you will get a nasty shock. You may also get a nasty shock if you touch one of the battery terminals and ground.

    Backup inverters like Xantrex DR series have an isolation transformer from the H-bridge output to AC output which allows the output to have a neutral that can be ground bonded in a house electrical hookup.

    Basically, if it is not heavy, don't try to wire it into the house wiring.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: Using house wiring during an outage

    ps, by the way, inverter generators in the less then 3KW class have the same issue with grounding the neutral side of the plug.

    I have a Yamaha EF3000sei that I connect to my SW inverters for charging batteries but I have a large isolation transformer connected between the inverter generator and SW inverter.
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