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Portable generator for my home

  1. Sep 6, 2014 #1
    I have a portable generator for my home. it puts out a total of 80 amps at 240v with no problem. what it does not have is a single 80 amp connector. I have a 50amp and a 30 amp. my plan is to connect these both to the CB in the transfer box to attain the full 80 amps to my home. a local "electrician " recommended against this, but had no alternative method. I know parallel circuits have equal voltage and their own amperage. the power is all coming from a single source. am I wrong about this connection.
  2. jcsd
  3. Sep 6, 2014 #2


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    If you assume the breakers in the generator connect to the same power feed point, at the full 80 amp draw to the same load in parallel through those breakers it's likely the 30amp breaker will trip first if the current flows equally (40/40) in the connections from the generator, then the 50amp breaker will trip when it has the full 80amp current load.
  4. Sep 7, 2014 #3
    trough 30 A connector you will have 40 A current, this is not good idea.
  5. Sep 7, 2014 #4
    so I need to form a single output line to connect directly to my 80amp transfer box breaker.
  6. Sep 7, 2014 #5


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    Do you have a wiring diagram of your generator? I'm wondering whether it might be feasible to replace the two breakers with a single breaker of 80A ?

    Is the generator for emergency use, or routine use?
    Last edited: Sep 7, 2014
  7. Sep 7, 2014 #6
    no diagram. that's my big problem. it has a large panel with a total of 8 outlets, each with their own CB. 3 are 240v, the rest 120v. suppose I could just combine the lines to the 2 240v outlets into one. and use my 80 amp CB in line to the transfer box. long time since I did electrical work. was electronics/electrician in air force about 42 years ago.
  8. Sep 7, 2014 #7


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    It would be worth trying a google search, using its brand and model number, to see what you can find out about its internals.
  9. Sep 7, 2014 #8


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    This is a bad idea.
  10. Sep 7, 2014 #9

    jim hardy

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    It is not good practice to parallel overcurrent protection devices . That's because it is difficult to make them share current equally. When one of them opens its current is shifted to the others which overloads them and they all open in a cascade . You gain no reliability and probably lose some. Weakest link opens first which causes the rest to follow.

    Also - what did you intend to use for a connector? Biggest NEMA plug i can find is sixty amps, NEMA14.
  11. Sep 7, 2014 #10
    I was hoping to wire directly into a CB . this is a portable generator which I am permanently mounting in a shed next to the transfer box. I will search for a diagram. thanks for the input.
  12. Sep 7, 2014 #11
    80 amps at 240 volts is 19.2 KW. That is an unusually large portable generator.

    Does your transfer switch disconnect the normal service when the generator is connected to the panel? It should and I suspect the connection will require a permit and inspection.
  13. Sep 7, 2014 #12

    jim hardy

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    That might work. Your electrician friend can help you find the big wires inside it and you could put a two pole breaker in it.
    Be aware that wiring it in that way makes it a "separately Derived Source" under the code and i think no longer a "Portable Generator". Your electrician friend can help you get it grounded, bonded, and be sure the disconnecting means is appropriate per code..

    You want this done properly and per electrical code.
    I trust the transfer box is physically interlocked so you cannot backfeed into the power company .
    Improper(therefore illegal) backfeeds electrocute several innocent linemen in the South every hurricane season and the homeowner is directly at fault .

    Please do it right.

    old jim
  14. Sep 8, 2014 #13
    the transfer box was installed by my local REC when they hooked up my meter to the house. it has an interlock that prevents generator from being on without turning off incoming power. I found the wiring diagram. all power goes into a 50 amp breaker, then passed on to the multiple 20 and 30 amp breakers. the generator is rated at 15kw with a surge rating of 22.5kw. I will most likely settle for a 70amp breaker to keep it down.
  15. Sep 8, 2014 #14

    jim hardy

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    There's a good article here

    looks like i was wrong about the generator being "separately derived". So long as your transfer switch doesn't switch the neutral wire you're okay. Good drawings in that link.

    Glad to know you're doing it right.

    15KW at 240 volts is 62.5 amps, divide that by generator's nameplate power factor probably around 0.8 to 0.9

    15KW is 20.1 horsepower. Ventilate the shed well.

    Good luck !

    old jim
  16. Sep 8, 2014 #15
    has 30hp engine on it. plan to run exhaust to outside. transfer uses only 2 hot wires. both grounds are separate and not involved.
  17. Sep 8, 2014 #16


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    Usually, there are few things in a household which require a dedicated 80 A circuit. IDK about 240V houses in Europe, but in the US (with 110V electricity), most home circuit outlets are wired for about 20 A max. A few appliances requiring larger current draws (like central A/C, clothes driers, and hot water heaters) are wired to special circuits which can accommodate their special electrical needs, including higher voltage.
  18. Sep 8, 2014 #17
    Could it be two 50 amp breakers with one wire into and out of each? If so it would seem you are all set!
  19. Sep 8, 2014 #18
    double pole 50A with 2 wires going in and 2 coming out. wires out feed a single 50A receptacle. wires going in travel on to 1 30A 240V, 2 30A 120V, and 4 20A 120V receptacles.50A is separate from the others. so the input to the 50A and the 30A could combine to give me 80A but I am not a pig. 70A will do,
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