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Thread: What happens if I bridge L1 and L2 on a 120 genset

  1. #16
    Electrical Contractor/Instructor jwelectric's Avatar
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    Several things come into play with these generators. The size generator that you have chosen will only deliver 120 volts at 1600 watts which is little power.

    This type generator can also be used with a companion generator but that companion generator must be a designated generator and not just any old generator will work. Not even two of the same make and model will work together it must be a companion generator.

    When two are connected together you will still only have 120 volts. There is no way to achieve 240 volts using two at one time. To jumper from one leg to the other leg in order to make both sides of the panel hot is a very bad idea and even dangerous.

    Under full load this little box will go through a tank of fuel in about 2 (from experience) hours and when two are being used the fuel use doubles. Not much savings when two small generators are being used in the place of one larger one.

    In order to be installed in a code compliant manner they must be connected to the premises wiring through a transfer switch that switches the neutral or they must be connect to the premises wiring as a Separately Derived System.

    These types of generators are designed to be used with cords. In order to save money and I think that is the purpose of using one of these, plugging a cord into the receptacle of the generator and into the load being used is the proper method of use.

    If it is your intention to use one of these for heat you might want to rethink your design and spring for something of value like a 30kw type generator. Unless you heat with gas or oil this little bugger will not be of much help and if you do have gas or oil it will be all that little box can do to start the fan motor to running if it will start it at all. It will take about 4000 watts to start a HP 120 volt motor which is more than two of these units will pull.

    Then we come to the best part, the warranty. Unless this generator is installed and used according to its listing and labeling then the warranty is void. For more information to the listing of this generator see UL White Book FTCN. The information about the warranty voidance can be found in the equipment manual.

  2. #17
    Jack of all trades DonL's Avatar
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    I Don't understand why you would want to connect a Inverter to 2 circuits when it will barely power 1 circuit.

    You should get a Real Generator if you go thru the trouble of putting in a transfer switch.

    You could have bought a Good Gasoline or NG Generator that puts out 240 for what you paid for them 2 Honda Play Toys.

    Were they on Backdoor Special ?
    Theory only works perfect in a vacuum.

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  3. #18
    DIY Senior Member chefwong's Avatar
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    Noise, portability, Fuel.

    The EU is fine for the current application.
    My home in NC in the sticks has a propane fueled generac but that is the Right genset for the application.

    For my primary residence, I get a brownout -- maybe once every year in the summer. Anywhere from 45 minutes to maybe 3-5 hours ? The last power outage aside from Sandy was the great Northeast blackout.

    So these small sipping gensets use less fuel. I can run LEAN to run the stuff I need to . I'll let it throttle to 3600 RPM when full and it will just idle back when it needs to.

    Bigger is not necessarily better given the application. I don't look at how many W per $ I am getting when looking at the APPLICATION for this genset.
    I have a friend who has both a small inverter and a big diesel. Even with a 2 week outage, he will run his single 2K inverter and then run the diesel to run the well, etc.

  4. #19
    Jack of all trades DonL's Avatar
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    Sounds like you have a plan.

    That type of Generator is good for what it is designed for. It is Overrated when it come to continuous full load use.

    I think Charging a battery would be good for when you run out of fuel then you can at least have lighting.

    Good Luck.

    Be careful playing with electricity, It can be a shocking experience.
    Theory only works perfect in a vacuum.

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  5. #20
    Consultant cwhyu2's Avatar
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    I have a brand new 18000 k/w B&S sitting at the shop that wants a home.It can run N/G or propane transfer switch included.
    Last edited by cwhyu2; 12-04-2012 at 08:15 PM.

  6. #21
    Moderator & Master Plumber hj's Avatar
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    According to the Honda manual, they make a "parallel" wiring cordset to connect two EU2000i gensets together to double the capacity. But, just connecting two 120 v. generators together will NOT give you 240 power, because they will not be 180 degrees out of phase, if that is what you are trying to do.
    Licensed residential and commercial plumber

  7. #22
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by hj View Post
    According to the Honda manual, they make a "parallel" wiring cordset to connect two EU2000i gensets together to double the capacity. But, just connecting two 120 v. generators together will NOT give you 240 power, because they will not be 180 degrees out of phase, if that is what you are trying to do.

    They work good when they are 360 degrees out of phase.

    Still a Inverter Play Toy , Good for charging a battery.

    I would not waste money using a transfer switch.

    Extension cords are cheap and safer.
    Theory only works perfect in a vacuum.

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  8. #23
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by DonL View Post

    Still a Inverter Play Toy , Good for charging a battery.
    You've obviously never used one of these things.

  9. #24
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by Speedy Petey View Post
    You've obviously never used one of these things.
    I have used one and it worked very good for what it was designed for. Not that exact model but it is a Inverter.

    I have worked on the cheap overrated ones because people expect to much, and they don't run right, or make the Advertized power, and end up frying electronics.

    Wiring something like this into your House on a main change over is the part that don't make sense.

    For no longer than it will be used a extension cord would be fine.
    It is made to use as a household outlet, Not a complete Home.

    Enjoy it while it is working. And hope you do not loose things that you forgot were plugged into some outlet in the house.

    Follow the smell and smoke and keep spare parts , and keep a smoke detector in hearing range.

    A breaker or fuse will not protect everything, It is all about timing.
    Theory only works perfect in a vacuum.

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  10. #25
    Retired Defense Industry Engineer jadnashua's Avatar
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    Quote Originally Posted by DonL View Post
    They work good when they are 360 degrees out of phase.
    For those uninformed, something 360-degrees out of phase is misleading, as that really means that they are perfectly IN phase. Now, any phase error other than a multiple of 360 has problems, with something 180-degrees out of phase (with the same waveform) would cancel the voltage and maximize the current and fry things quickly if connected together. It is a finely balanced dance to join multiple generators together and have everything work efficiently and without smoke.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  11. #26
    Electrical Contractor/Instructor jwelectric's Avatar
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    With a three phase Delta or Wye transformer the three phases will be 120 degrees away from each other.

    In a single phase 240 volt system there is nothing that is out of phase. There will be one 240 volt phase not two 120 volt phases. Each leg of the 240 volt winding will be referenced to the middle for 120 volts.

    When we connect a scope to this midpoint ground of our panels we are doing the same thing as standing in the grass between four lanes of traffic. For the sake of this discussion let’s say that two lanes are going north and two lanes are going south. When we stand in the middle and look at the south bound lanes the traffic is coming from the right and leaving to the left. Now turn around and look at the north bound lanes. The traffic is coming from the right and leaving to the left. Just as the scope we are looking at each lane of traffic directly. The sine wave will be coming from one end and leaving the other end.

    The current through that 240 volt transformer will be no different than a two D cell flash light. While one end of that winding is on the negative sine wave the other end of the winding will be positive and should we tap the middle just as with the flash light we will have two winds of 120 volts each with the same polarity as the batteries.

    The laws of physics will not let the 240 volt winding have two different sine waves at the same time. Our home is nothing more than one 240 volt winding that has a center tap. Should we connect two 120 volt systems to our homes that were 180 degrees out of phase we would have the 4 of July going on for a couple of seconds.

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