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small invertor gen and subpanel?

Post in 'DIY and General non-hearth advice' started by briansol, May 17, 2013.

  1. woodgeek

    woodgeek Minister of Fire

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    Dave, your procedure exactly as described will 'work', without requiring any new permanent wiring. Indeed, it is exactly what many folks with generators do. BUT, it does not have a safety interlock, and puts linemen at risk. If someone flipped the breaker back while you were running (ignoring your tag) your genset would backfeed the grid.

    Instead, get an interlock panel, and it will mechanically force one (new) 240V 30A breaker to be 'off' whenever the main breaker is on...that 30A line can go to a (new) locking outlet, located wherever you like, that will be dead whenever you are on grid power. Use that with the same cabel you made up for your idea, and you are 'safe'. I was saying (confusingly) that if you moved your dryer to that new breaker, it could never connect to grid power...it would be locked out.

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  2. Highbeam

    Highbeam Minister of Fire

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    The legal way to do it is with a cheap interlock kit and a generator inlet circuit. Functionally, this is exactly the same as backfeeding through a four wire dryer plug using a double male "suicide" cord. I recommend a backfeed that utilizes both the ground and neutral along with the hots.

    Especially with your goofy subpanel setup I would be most inclined to only send genny power to your main panel using the appropriate interlock and genny circuit. Sometimes subpanels have isolated grounds.
    Ashful likes this.
  3. Dave A.

    Dave A. Minister of Fire

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    Just checked my dryer plug and it's a 3 prong (no separate ground).

    What would be the risk in combining the ground and neutral at the dryer outlet -- pretty sure they are combined in the sub panel.

    As I said, haven't used the gen yet and sort of hope I don't have to. And not planning on being in this house more than a couple years so don't want to have to invest in something unless it's really necessary. Am confident the main could be kept off while the gen ran. Another point is that my panel is filled, even the 1/2 breaker slots are maxed out -- I probably could move some things around if I had to but would rather not.

    The gen says floating neutral -- does that mean you don't ground it? (probably in the directions but they aren't handy). That would kind of imply neutral and ground are joined at the gen. That can't be right, am guessing that they are assuming you're going to be backfeeding or using a transfer switch and relying on the house ground and if you use extension cords you need to run a ground to something?

    What's the risk of using my 3 wire dryer plug from the sub? I know the neutral goes back to the main though there may be an additional ground to the water pipe near the sub.

    And what's the problem with a separate ground on the sub?

    J, WG, HB, thanks for the replies.
  4. Dave A.

    Dave A. Minister of Fire

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    Maybe I'm not following but I was thinking in terms of only connecting one of the hots. I.e Black to Black, White (neutral) to white, Red not connected. Certainly would never connect a neutral to a hot. One problem I foresee would be that it's possible a certain one of the hots is necessary for the motor and controls and I'd have to connect to the correct one. I wouldn't think you could cause damage to the dryer with only one hot connected. The question is whether it would even work -- I mean I saw something about someone wanting to connect an elec WH to 120v and the response was it would work but take longer to heat.
  5. Highbeam

    Highbeam Minister of Fire

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    On a three wire circuit, such as to your dryer, the ground is often undersized. It is not a neutral, but a chassis ground and only needs to carry enough current to trip the breaker. That's the first problem.

    It is poor form to use a ground for a neutral. In a 120 circuit, both the hot and neutral are current carrying conductors. To use the dryer plug ground for a neutral means you will be energizing the ground system which energizes the metal exterior of your toaster. Do you really want to do that?

    The ground and the neutral are not combined at the sub, only the main.
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  6. Highbeam

    Highbeam Minister of Fire

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    Find a four wire plug somewhere.
  7. Ashful

    Ashful Minister of Fire

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    Maybe we got off track here, as this conversation has taken a few turns, so I'll just summarize what's normal, here:

    240V dryer outlet is typically three-pronged, and is wired with black, white and green. Back at the breaker panel, the other end of the black and white conductors are connected to the two poles of a double-pole breaker, such that both black and white are "hot". They're the opposite ends of a single 240V "phase". Green is always ground.

    In some unique situations, you will come across a 4-prong 240V receptacle. These are more often used for kitchen ranges, but I suppose there may be some 4-pronged dryers out there, as well. In this case, you will have a cable with black, red, white, and green, and it is normal then to use black and red for hot, white for neutral, and green for ground, when connecting this wire at the breaker panel.

    As just about everyone knows, in a 120V receptacle, there are typically 3 wires, black (hot), white (neutral), and green (ground).

    I've come across very few houses that don't have at least one wiring mistake or non-conformity, so it's always best to check voltages, rather than relying on colors.

    Now, the trouble with back-feeding 120V thru a standard 3-prong dryer outlet is that the white wire in that dryer outlet is not connected to the common rail in your breaker panel. It's connected to one of the "hot" rails.

    Also, to answer the prior question about using ground for common, if everything is properly wired, this is technically possible. However, it is unsafe and illegal. Ground connections are not always continuous or direct. Code dictates that ground and neutral only be bonded at ONE place in the house, and that is where service enters the house, again for safety reasons.
    woodgeek likes this.
  8. ironpony

    ironpony Minister of Fire

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    like the house I worked on where whoever wired it believed black should be ground and white hot and green neutral, talk about a mess
  9. Dave A.

    Dave A. Minister of Fire

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    Now I see what you were saying here. It just didn't fit my situation (and I didn't understand how an interlock worked at that point). But my dryer breaker is in a sub panel box, not in the main panel so would not be effected by the interlock. For the interlock to work as intended you can't backfeed into a normally working breaker. (As you know), it really needs a dedicated to gen breaker which must be turned off before the main can be turned on and vice versa.

    Starting to think about installing an interlock (at some point). Have seen kits for $150 but that includes a breaker which I wouldn't really need. At one point I had a 240v AC breaker in the first position in the main. But when my 18000 btu wall unit died, I replaced it with a smaller 1 ton (12000 btu) 120v unit. The 1.5 ton unit was much larger than needed. Anyway the other side of that 240v, I was going to use for something else. I have to think about it.

    First thing though is buying or making up the extension cord for the gen. My gen is 120v so I need plugs for that (3 wire 30a) but am thinking about using a four wire cord to support a (future) 240v gen. And then buying the parts for the dryer/gen dual male "suicide" cord and making that up.

    Trying to find some link for Highbeam's idea of joining the two hots of a 240 to the one hot from the 120 gen but can't find anything. Would like to see some more support, details for that.

    Backfeeding without an interlock installed, I can see you really need some way to mechanically lock the main breaker off, or remove it (in a safe way).
  10. briansol

    briansol Minister of Fire

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    After all this talk i'm debating my intended purchase again and wondering if getting a 240 is a better idea. :/
  11. Highbeam

    Highbeam Minister of Fire

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    Getting a 240 genset sucks. You won't have the same options for a quiet, inverter set to produce high quality power efficiently and quietly. Instead you will be stuck with full RPM contractor screamers that suck vast quanitities of fuel.

    The only inverter 240 genset I have seen is the biggest honda and it was like 5000$.
  12. Ashful

    Ashful Minister of Fire

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    Highbeam makes a good argument, but I would not even consider buying a 120V generator. For those that already have them for running portable power tools, that's one thing... but there are too many 240V appliances I want to run in my house.

    Running a resistive heater like an electric water heater on half voltage is one thing, but you generally don't want to do that with appliances containing motors or electronics. No 240V means no water, for my house.

    Of course, this is why so many favor the two-generator setup. The 240V rig for the well, and the 120V inverter for everything else.
  13. Dave A.

    Dave A. Minister of Fire

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    Have looked at a few youtube videos about these suicide plugs. And there's very little warning about where one of the real problems with them is. Only saw it mentioned once as to what I think is the glaring problem with them which goes against all normal usage of electric plugs and cords.

    And that is that with these cords with 2 male plugs you can easily end up with a live male plug if you're not careful. In everyday normal usage with electricity you plug the non-energized male into an energized female socket/receptacle.And when you unplug something the exposed male end is never hot. You don't expect the metal contacts to be live and don't need to take care not to touch them.

    With a suicide plug otoh, if you don't have the house end plugged in before turning on the gen set or remove the house end while gen set is on, you have a live male plug, something most people would normally never expect. The bare metal contacts are live/hot. You can't touch them or allow them to get shorted together, touch metal or ground. So it's important they be plugged in and unplugged in the correct sequence. And anyone using these devices needs to be necessarily vigilant and warn/prevent others from unplugging them.

    Another risk comes in having them left in place after line power is restored. They must be removed before the main breaker is turned on.

    They clearly are dangerous and it is understandable why their use should not be encouraged.
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  14. Ashful

    Ashful Minister of Fire

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    Umm... hence the name, "suicide plug".
  15. briansol

    briansol Minister of Fire

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    I have city water/sewer and live above the road (gravity takes the stuff away from the house should the pump fail), no well.
    I rarely have less than a few cases of Poland spring in the house as well.
    my property contains a 'babbling brook' and I have filtering capabilities if absolutely necessary to get water. I also use rain buckets for the garden.
    I have a boiler, thus no electric hot water heater.
    I don't care about cooking on the electric range.... i'll use my grill
    I don't care about using the clothes dryer in an emergency. I have a ton of clothes to get by for a few weeks with out doing laundry.
    I don't care about a/c... can live without.

    I don't know what the boiler runs on. Is that a 240 ringer? I assume its not much as its the fuel that burns it.

    What else is 240 that I would NEED in an emergency? I can't think of anything.
  16. maple1

    maple1 Minister of Fire

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    Everyones NEEDS are different. Sounds like you've got yours covered. I've got mine covered without needing any electricity until about the time the freezer gets to thawing. That's my NEED point. Aside from that, if we run out of water from all the places we've got it & I don't feel like carrying a couple of buckets from the well, I can hook my well pump into my generator - it's only a 120v jet pump. My boiler keeps us lots warm with no electricity at all by convection flow. Extra tank for the BBQ. I'm set.

    The wife & kids though tend to get a bit needier after only about an hour...
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  17. Dave A.

    Dave A. Minister of Fire

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    My 120v receptacles are almost all 2 wire + ground (black, white, bare (ground)). Have never seen romex with a green wire. BX, less common in my locale, has a green insulated ground wire.

    Now I see where you guys are coming from on these 2 wire plus ground dryer hook-ups. Never thought that was really acceptable or standard.



    Mine is certainly not done that way. I have three insulated #10 wires black, red, white. Ground strap connected to neutral on the dryer, and white wire is neutral back to the sub panel.

    Had a 240 a/c unit connected that way when I moved in and it shorted out badly. Whole house wiring got messed up knocking out one side of the panel. Not sure if the meter caused but it also was ruined and had to have the meter box replaced and a new meter put in. But the elec co denied any responsibility even though the electrician claimed it was the fault of the meter. The only damage to the house wiring was on that 14 2 wire plus ground romex line to the a/c. That had the thinner gauge bare ground wire.

    Am pretty sure that current romex is not like that. The bare ground has to be the same gauge as the insulated wires and been that way for awhile.
  18. Dave A.

    Dave A. Minister of Fire

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    Nothing really goofy or bogus about it. Builder built in a development. Was quite common back in the mid 1950's when this house was built in this area especially ones without NG service having lots of elec appliances in the kitchen requiring many circuits, d/w, range g/d washer/dryer, etc. Main residential panels tended to be limited to about 12 breakers then, so a sub panel with the same # of breakers helped increase the capacity and made the house easier to wire, I guess.
  19. Dave A.

    Dave A. Minister of Fire

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    Sometimes that's necessary. But I prefer to check continuity with the power off when possible.
    Edit: And testing outlets with plug in wiring testers is a good idea
    also.

    Okay mine is not like that. But even if the white wire is used for a hot it's done so continuously. When you're backfeeding into a dryer plug (assuming you do that) you're not going to even see that wiring which is inside the receptacle. And if you check voltage and continuity, then you'd be connecting to the correct wires unless things were really screwed up before hand and likely there would have been evidence of that.

    Where is anything being done much different than with line power by hooking up a gen if you don't do something really stupid like reversing hot and neutral when hooking up your gen extension cord/s assuming you make them up yourself. I can't see it.
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  20. Ashful

    Ashful Minister of Fire

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    Ground is referred to as green, because in a flexible cord set, it is always the green wire. Bare copper also turns green. The ground screw on your receptacles and junction boxes are colored green. You get the point. Yes, it's normal to find uninsulated copper used for ground in Romex/

    This is correct when dealing with smaller gauge wiring. With current-carrying conductors larger than gauge 6, all ground wires are typically kept at gauge 6.

    The house in which I spent most of my childhood was built in 1953, and had three Edison fuse panels, 24 channels each. They were all original construction. None of these three panels was the "main" or "sub", in our current sense of the words. Power came into the house thru an old knife-blade disconnect with dual cartridge fuses, and then into a large lug box into which all three panels were connected. Pretty standard big house or light commercial stuff for that period.

    One thing that was real interesting about that house was that we had no toggle switches for lights. We had momentary contact buttons which controlled enormous banks of relays, all located in the garage or basement. Each relay controlled a lighting circuit, and there were many momentary contact buttons to control each relay. I've seen the same rig in a few churches and schools, but never another house.
  21. nate379

    nate379 Guest

    I don't know who exactly started this big scare about killing lineman, bald eagles, baby seals, etc but it's b/s. Unless a person has a BIG gen set (like 50-100Kw... or larger) it wouldn't be able to power the grid even if you wanted to. With a normal homeowner size unit (4-10kw) as soon as it fed onto the grid it would either trip the breaker on the gen set or stall the engine because of way too much load on it.

  22. woodgeek

    woodgeek Minister of Fire

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    I agree with you completely. If your residential service line was down, you could zot the guy fixing it I suppose, with 120V. If they don't have proximity voltage testers, you were backfeeding (with the main on), they didn't hear your genny AND you didn't hear them drive up.

    Advice over the internet and electrical code both tend to an overabundance of caution. I do not own an interlock panel, and run cords all over my house during the rare outage.
  23. semipro

    semipro Minister of Fire

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    This assumes that the house with the generator is still connected to a grid that can suck up all that power. In the rural area I live in there's a lot of space between houses and only a few may be served by a circuit protected by an inline fuse. If that inline fuse is tripped the power from the genny has no place to go but into an unwary lineman.
  24. briansol

    briansol Minister of Fire

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    same. I have some good amount of meat in my freezer and plan to buy a half-cow (free range grass fed filtet!) this fall as well so it would be painful to watch that melt away.

    I guess the quest is on to get this working on 120v.
    had a read through this thread, and it looks promising:
    http://www.garagejournal.com/forum/showthread.php?t=156864
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  25. Highbeam

    Highbeam Minister of Fire

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    In case you all want to know what an interlock panel looks like, here is my home panel. I installed it about 5 years ago and it passed inpection. The cover is off but the interlock is part of the panel. THis is the more expensive way to do an interlock but I needed a new panel anyway.

    Attached Files:

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