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Thread: Back-up to the Back-up

  1. #1
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    Back-up to the Back-up

    I had installed manual transfer switch and outside receptacle for gas generator , so if I loss power I could plug into receptacle start generator , go in the house and flip transfer switch and have power. Now I was given a whole house generator . I install everything , automatic transfer ( 200 amps ) etc.. This house generator is good for 30 amps. Could I if I wanted to use both at the same time by flipping manual transfer switch to generator and have both going at the same time. I'm just thinking here don't think I would ever do it but could I.
    gusco

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    You can run them at the same time, but you can't power the same house or the same circuit(s) with more than one generator unless they're phase- and frequency-synchronized, something that most small standby generators are incapable of doing.
    Last edited by drcampbell; 01-10-19 at 08:56 AM.

  3. #3
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    Plus, the ATS is wired in line with the panel main breaker, while a properly-installed manual interlock requires the panel main be switched off.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    What if I turn the breaker off in the main panel that feeds my manual transfer switch?
    gusco

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    Quote Originally Posted by guschash View Post
    What if I turn the breaker off in the main panel that feeds my manual transfer switch?
    You need a interlock, no promises to turn the main off if running a generator are going to cut it.

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    As another stated, no because there is no synchronization of the 60hertz cycle between the two generators. You’re going to burn things up.

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    If the whole house automatic TS is up stream of the portable Gen TS, such that the portable Gen TS is switching the upstream supply, be it POCO or whole house sourced, I don't see any issues with this configuration. The critical thing is the portable Gen TS must be positioned to switch the circuit regardless of the source (POCO or whole house), thereby preventing any possibility of feeding any circuit with more than one source.

    I have a somewhat similar configuration, but use two backup sources...one a generator and one a battery inverter. I have a 4 circuit (4 switches) Transfer Switch 1 (TS1) and a ten circuit (10 switches) Transfer Switch 2 (TS2). TS1 decides between POCO and Inverter (mix or match among the four circuits). Those four decisions are feed to Transfer Switch 2 (TS2), along with six additional circuits. TS2 decides between generator and the other input. Six of the other inputs are POCO, and four are whatever is fed from TS 1 (POCO or Inverter). This allows me to mix and match the four circuits between gen, POCO, and inverter without any chance of a double feed.

    In a nutshell, I have cascading Transfer Switches where the decisions are made in a sequence to physically avoid any possibility of feeding the same circuit with two power sources. A similar approach would work with an automatic whole house and a separate gen switch. Again, the key is the cascading nature of the two switches must ensure no possibility of energizing the same circuit from two sources.

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    Quote Originally Posted by JPinVA View Post
    ... The critical thing is the portable Gen TS must be positioned to switch the circuit regardless of the source (POCO or whole house), thereby preventing any possibility of feeding any circuit with more than one source. ...
    Also critical: The transfer switch configuration must assure that no two generators (including the power company as a "generator") can ever be connected to each other, even if they're not connected to any loads.

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