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Generator Transfer Switch: Combining Multiple House Circuits on One Switch Circuit?

Discussion in 'Home Power and Microgeneration' started by (PeteCresswell), Dec 6, 2012.

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  1. Just had a cutover switch installed, but it only supports six
    circuits and I actually have 9 that I'd like to have power to
    when running a gennie.

    The three combined circuits would be a couple of bedrooms and a
    bathroom. i.e. expected use would be just a few electric lights
    and a couple of radios.

    Seems like two breakers will now become unused and all 3 circuits
    will be running off of a single 15-amp breaker - which, in turn,
    would be served by one circuit from the generator transfer
    switch.

    Not knowing anything about electrical stuff, I'm wondering what
    the downside exposure is here.

    My hope would be that putting a 20-amp fuse in the transfer
    switch's circuit (which is allowed per the maker's specs) would
    make it so if, for instance, somebody plugged an electric heater
    into a bathroom outlet, the breaker in the breaker box would trip
    and that would be the end of the problem.

    What I'm worried about is maybe a wire melting somewhere - which
    seems tb a really dangerous situation.

    Other considerations?

    Code violations?
     
  2. mike

    mike Guest

    I'm trying to get my head around the math. If you have six and combine
    two more on one of the six, doesn't that make 8?
    Not sure what you're planning, but if there is ANY wire smaller than
    #12 anywhere in the system before or after your 20A breaker, you've got
    a problem.
    Acting on answers you get on the web is risky.
    Some people here know exactly what they're talking about...some don't.
    It's impossible to tell which is which.

    There are two people who care.
    1)The local building inspector who'll sign off on the inspections that
    come with the permit. Call 'em up.
    2)Your insurance carrier. They'll probably not care if the building
    inspector is happy.
    You are gonna get a permit and have the work inspected??right???

    Around here, an electrical permit costs way more than a lifetime supply
    of batteries for bedroom emergency flashlights.

    You don't say where you are, or exactly what's happening, but I expect
    your solution will be "frowned upon" by the inspector. Call 'em up and ask.

    As usual, the time to think about 9 circuits is BEFORE you have six
    installed.
     
  3. Per mike:
    Five house circuits, each served by a single transfer switch
    circuit.

    One transfer switch circuit left. Proposal is to combine three
    of the remaining house circuits on to it.
    A licensed electrician did the job, so I'm assuming it's all
    good-right-and-holy with the powers that be.
    I like the idea of calling the building inspector.... I'll do
    that.

    Actually, I did. But this type of transfer switch only comes
    with six circuits for a 120-v generator (which I have).

    http://tinyurl.com/csv3g2y

    It's claim to fame is that it doesn't cost that much more than a
    conventional switch, but can shed circuits and re-acquire them
    automatically in light of circuit loads, generator capacity, and
    user specs. Supposedly, this lets one get significantly more
    use out of a smaller generator without having the generator's
    breaker repeatedly tripping and/or running the generator over
    it's continuous load capacity.

    My generator is a dinky little Honda EU2000.

    Push-comes-to-shove, I can buy a second one and run them parallel
    to double the capacity.... but experience over the past few years
    (using no transfer switch but lots of extension cords) suggests
    that a single one can do it.

    The 10-circuit models are looking for 220v input. People report
    jury-rigging the 10-circuit/220v switches to work with a 120v
    generator, but I didn't want to go there - perhaps mistakenly...
    because now I'm probably talking about a much more serious crime
    against nature in combining circuits...

    Bottom line though is that we're thinking "lifeboat" and not
    "cruise ship".... dinky little gennie, low gas consumption...

    With the five individually-served circuits, we have phone
    service, internet service, lights in the kitchen, and TV... plus
    I can do my work (which needs a PC and LAN server).

    The two extra circuits are nice-to-haves (bathroom
    light/radio/electric toothbrush, bedroom lights/radio...) but
    certainly not a big deal.

    I'll still try to get the local building inspector's comments,
    but it sounds like we already know what he's going to say.... and
    flashlight batteries are sounding a lot more sensible.
     
  4. Per mike:
    Electrician I asked said something that I interpreted as similar.
    I'm having trouble with this one and think either something
    hasn't soaked in yet or I talk too fast/write too verbosely and
    am muddying the waters.

    For the sake of argument:

    - One 15-amp breaker (NOT 20.... the twenty amp fuse
    is in the switch's circuit feeding the 15-amp
    breaker)

    - Three circuits hung on that single breaker.

    - Each circuit's wire is spec'd to handle up to
    15 amps.

    - Seems to me like no single wire can experience more
    than 15 amps because the breaker will trip at 15.

    - The 20-amp fuse in the switch (instead of a 15-amp fuse)
    is so that the breaker will take the hit on overload
    and the fuse will be less likely to blow.

    Do I have it right? If not, where am I going wrong?
     
  5. mike

    mike Guest


    I read the installation and operator's manuals. Way cool device.
    Would be interesting to know the details of the load shedding.
    My place was wired by an idiot. I've got the living room, bedroom
    and two bathrooms on one 15A circuit. The stuff I could shed is
    on the same circuit as the thing I want to power.
    Having the computer crash every time I turn on the microwave isn't
    an attractive option ;-) I'm stuck with manual load management.

    I have a new 5kW generator and a manual transfer switch in the garage.
    Impulse garage sale purchase.
    Learned that the permit cost more than the hardware, so there they sit.
    Power doesn't go out much here anyway.
    Power outage is a good excuse to take a nap ;-)
     
  6. Vaughn

    Vaughn Guest

    I see nothing dangerous here, but it may turn out to be inconvenient if
    your load is more than you think it is. There is no chance that you
    will want to run window units in any of those bedrooms?

    When I installed my 6-circuit transfer panel I believe I combined a
    couple circuits.
     
  7. mike

    mike Guest

    I'm no expert. I know about how electrons behave.
    I don't know a lot about the details of the electrical code.

    The electrical code is like a lawbook. Evolved over the ages to
    codify acceptable behavior. But the devil is in the details.
    You may do something that you think is perfectly reasonable
    and still be in violation. That's why we have inspectors.
    And they don't always agree.

    What follows is based on logic and conjecture. The electrical
    inspector is the one you need to ask.

    Assume for the sake of argument that a 15A breaker actually tripped
    at 15.00 AMPS. Assume you have #14 wire in the circuit.
    If you load any point on any downstream line to 15.1A, the breaker
    should trip. There is no way you can overheat any part of the
    wire as long as the breaker is functional.

    If you have a #14 wire from the input side of the 15A breaker to the
    output side of a 20A breaker, you could logically argue that
    the wire can never experience more than 15A because of the second
    15A breaker.
    And the inspector might agree with your logic as he wrote
    "fail" on the inspection report. ;-(

    I made all that up. Ask the inspector or a licensed electrician.

    Just flashed on another issue.
    If you have 240VAC service, your 120VAC loads will be split with an
    attempt to balance the load on the two halves.
    If you have a 120VAC generator, the switch will have to combine
    circuits from two phases onto a single phase generator.
    That might make for some interesting transients when the power
    comes back on.
     
  8. Per mike:
    So would I.... -)

    But the manual is the absolute pits for understanding what's
    going on. It's all "Trust us, we'll do the right thing.".
     
  9. Per Vaughn:
    Right now, we're thinking "Lifeboat", not "Cruise Ship".

    OTOH, I did buy an itty-bitty microwave for use during outages
    and maybe a very small window box would not be out of the
    question.... OTOOH, we very seldom have outages during hot
    weather and when we have they've been fixed within hours.
     
  10. Per mike:
    Waited for my better half to go shopping today and fooled around
    with the gennie/xfer switch for a few hours.

    It seems to tolerate cutting/resuming utility power with no
    problems that I can see. Delicate stuff like the TV, LAN
    server, computer are on UPS', so maybe that helps.

    Once I figure out how to have come control over which circuits
    get shed in what order when there's too much for the gennie, I
    think I'll be a happy camper with this thing - albeit critical of
    the manuals.... but then I'm one of those compulsive fault
    finders and I can write a single-spaced 8x10 page of negative
    rants on almost any product I buy.... -)
     
  11. mike

    mike Guest

    The interesting thing about the "shedding" section of the manual
    was that the graph has no dimensions.
    Shedding works well when the incremental loads are insufficient to
    stall the system, or when you sit between the event that initiates
    the function and the function itself so you can shed loads BEFORE
    adding loads and sensing overload.

    When you have a 2kW generator and a 1500W microwave and a 1300W bathroom
    heater and a 700W furnace air handler and...and...and...
    You might want minimum on/off times for the furnace and fridge.
    Starting the microwave might leave you with nothing that can be shut
    down and a stalled generator.
    That kinda puts you in the position to manually shed loads before
    you start the new one.

    It wasn't much more expensive than a manual switch, so, no big deal,
    but I'm not optimistic that it's all the marketing hype would lead
    you to believe.
    It'd be more interesting if you could install it before the wiring
    went in so you could have direct access to the loads you want to
    focus on.

    I have this vision of the stairwell lights going out just as
    you step off the top platform with a heavy box of junk.
    "Honey, I'm microwaving some coffee...want some?"
    ;-)
     
  12. Vaughn

    Vaughn Guest

    Yes, but if you combine your circuits, you will be power-limited all the
    time, not just when you are on emergency power.

    I asked about the window shaker because that's one of the more common
    big power users you will find in a bedroom. Other possibilities include
    space heaters and medical equipment such as oxygen concentrators.
    Things are a bit different here in south Florida.

    Vaughn
     
  13. Per mike:
    I had a similar vision of The Better Half chopping celery in the
    kitchen and Yours Truly stupidly turning on the bathroom lights
    where a heater was plugged in.

    I discovered a circuit parm called "Delayable" that *sounds* like
    it exempts the circuit from being shed if set to False.

    "Delayable Circuits The factory default setting is NO. Setting
    a circuit to YES, enables the UTS to run ALM for the individual
    circuit selected."

    Next time I have the house to myself, I'm going to try some more
    stress testing and see what happens when I do various things.

    I'm thinking a 1,500 watt electric heater or two will be useful
    tools in that regard. Also, I have found that just a toaster
    takes almost 1,000 watts.
     
  14. Mr Clarke

    Mr Clarke Guest

    Whole lot could be sensed and controlled using existing wiring; I`m sure
    you`re aware of the
    various mains carrier transceiver kits available?
     
  15. mike

    mike Guest

    Yep.
    Problem with delaying shedding is that it's determined after the fact.
    If the heater stalls the generator, you're hozed.
    I think a good outcome will be critically dependent on which stuff is on
    which circuit.

    Keep posting your evaluation results. Interesting topic.
     
  16. you

    you Guest

    GE, SquareD, and Cutler/Hammer ALL make double Breaker Modules that
    have TWO Breakers in a single Breaker Form Factor. Usually these are
    15Amp Duals.... Just Say'en..... That would double your available
    individual Breaker circuits, and they are ALL UL Approved, so No Code
    Violations.....
     
  17. Per Mr Clarke:
    Maybe in somebody's dreams.

    I'll Google it.

    Thanks.
     
  18. Vaughn

    Vaughn Guest

    Another little surprise will be the defrosting heaters in your
    frost-free refrigerator. They take the best part of a kilowatt and come
    on at unpredictable times.
     
  19. mine is "only" about 500 watts.

    - oh, and a similar surprise to anyone using (most of the) newer
    natural gas stoves/ovens. They tend to have electric "spark"
    ignition for the stove top - which isn't too messy electriclaly.

    But... they also tend to use electrically heated "glow plates"
    in the oven to ignite the gas. And these stay on the during the
    entire "lit up" cycle..

    Add in another 500 watts there...
     
  20. Per Vaughn:
    Luckily (?) we don't have gas for cooking, but the refrigerator
    defrost thing is news to me.

    Knowing that will probably save me an hour or so beating my head
    against the wall wondering where the extra load is coming from.

    Thanks.
     
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