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Thread: Back fed breakers

  1. #11
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    Quote Originally Posted by shortcircuit2 View Post
    texie [Fliz]...705.12(D)(6) permits us to omit the use of a additional fastener required by 408.36(D) for utility interactive inverters. This is allowed because if the breaker were removed the inverter output disconnects under the UL 1741 requirement.
    Just to clarify, that applies only to load-side connections. It does not apply to line-side connections (i.e. a breaker that also serves as a service disconnecting means).
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  2. #12
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    Quote Originally Posted by Smart $ View Post
    Just to clarify, that applies only to load-side connections. It does not apply to line-side connections (i.e. a breaker that also serves as a service disconnecting means).
    If you are discussing line-side connections in which the backfed breaker is the main breaker of a sub-panel, i.e. feeding POCO voltage from wired terminals through the breaker to the bus, then I agree with you.
    But if you have a line side tap running to an MLO subpanel with one or more backfed breakers in the normal branch circuit part of the panel, I would think that the exception should still logically apply, whether the Code is clear on that or not.

  3. #13
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    Quote Originally Posted by GoldDigger View Post
    If you are discussing line-side connections in which the backfed breaker is the main breaker of a sub-panel, i.e. feeding POCO voltage from wired terminals through the breaker to the bus, then I agree with you.
    But if you have a line side tap running to an MLO subpanel with one or more backfed breakers in the normal branch circuit part of the panel, I would think that the exception should still logically apply, whether the Code is clear on that or not.
    I'm still trying to figure out how a backfed breaker could be a service disco. I guess the main breaker in a panel which is connected to a service with no other disconnecting means is the disco, and it is backfed if there is solar in the panel, but aren't main breakers normally tied down anyway?

  4. #14
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    Quote Originally Posted by GoldDigger View Post
    If you are discussing line-side connections in which the backfed breaker is the main breaker of a sub-panel, i.e. feeding POCO voltage from wired terminals through the breaker to the bus, then I agree with you.
    I don't know where you are getting this out of my post, but no I'm not discussing backfed breaker as a service disconnecting means for a panelboard.

    But if you have a line side tap running to an MLO subpanel with one or more backfed breakers in the normal branch circuit part of the panel, I would think that the exception should still logically apply, whether the Code is clear on that or not.
    I'm referring to an MLO panelboard where each breaker is a service disconnecting means, one or more of which is a disconnect for power production equipment (such as a PV system's GTI). Such breakers must meet 408.36(D) secured-in-place requirement for plug-in-type breakers, regardless of UL1741 listing, as 705.12(D)(6) only applies to load-side connections [see general text of 705.12(D)].

    And I see no exception to any of the referenced sections...???
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  5. #15
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    Quote Originally Posted by ggunn View Post
    I'm still trying to figure out how a backfed breaker could be a service disco. I guess the main breaker in a panel which is connected to a service with no other disconnecting means is the disco, and it is backfed if there is solar in the panel, but aren't main breakers normally tied down anyway?
    IMO if under nominal conditions current can flow relatively opposite the voltage (phase angle deviation greater than 90°), then it is a back-fed device.

    Any disconnecting means connected to a service conductor or bus or tap is a service disconnecting means.

    Main breakers are for the most part secured, but not all.
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  6. #16
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    Quote Originally Posted by Smart $ View Post
    IMO if under nominal conditions current can flow relatively opposite the voltage (phase angle deviation greater than 90°), then it is a back-fed device.

    Any disconnecting means connected to a service conductor or bus or tap is a service disconnecting means.

    Main breakers are for the most part secured, but not all.
    Voltage flows?

  7. #17
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    Quote Originally Posted by ggunn View Post
    Voltage flows?
    I didn't say voltage flows.
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  8. #18
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    Quote Originally Posted by Smart $ View Post
    I don't know where you are getting this out of my post, but no I'm not discussing backfed breaker as a service disconnecting means for a panelboard.


    I'm referring to an MLO panelboard where each breaker is a service disconnecting means, one or more of which is a disconnect for power production equipment (such as a PV system's GTI). Such breakers must meet 408.36(D) secured-in-place requirement for plug-in-type breakers, regardless of UL1741 listing, as 705.12(D)(6) only applies to load-side connections [see general text of 705.12(D)].

    And I see no exception to any of the referenced sections...???
    I was getting confused thinking about the situation in which you have a feeder tap rather than a service line-side tap. The fastening requirement of 408.36(D) is the only one that is waived by 705.12(D)(6); any other tie down requirements would still apply. And, yes, 705.12(D) explicitly applies only to the load side of the service disconnecting means.

  9. #19
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    Quote Originally Posted by Smart $ View Post
    I'm referring to an MLO panelboard where each breaker is a service disconnecting means, one or more of which is a disconnect for power production equipment (such as a PV system's GTI). Such breakers must meet 408.36(D) secured-in-place requirement for plug-in-type breakers, regardless of UL1741 listing, as 705.12(D)(6) only applies to load-side connections [see general text of 705.12(D)]
    Quote Originally Posted by Smart $ View Post
    IMO if under nominal conditions current can flow relatively opposite the voltage (phase angle deviation greater than 90°), then it is a back-fed device..
    Wow, I wouldn't agree with any of that.

    I think that a back-fed plug-in type breaker, for the purposes of of 408.36(D), is simply a breaker that has the supply conductors connected to the terminals, rather than to the busbar that connects to the 'plug in' part. In other words, it's a breaker whose parts can remain energized when the breaker is unplugged, opposite the way that most plug-in type breakers get installed. The requirement is there simply to prevent someone in a hurry from missing the fact that an unplugged breaker could shock and kill them. 705.12(D)(6) overrides that requirement precisely because a utility interactive inverter does not continue to energize the breaker if it's unplugged. It basically recognizes that GTIs aren't a 'supply' for the purposes of 404.36(D), and that the danger doesn't exist.

    The first quote doesn't jive with the second. Multiple breakers used as service disconnecting means in an MLO panel aren't backfed according to your definition in the first quote. I would say they aren't backfed because they are energized from the busbars, hence if unplugged they are no longer energized. (It might be wise in many such installations to have tie downs to prevent accidental movements in the vicinity of high fault currents, but I don't think that 408.36(D) requires it.)

    I've seen plenty of back-fed breakers set up as service disconnecting means. But like ggunn I'm struggling to visualize how such a breaker could fall under 705.12(A).
    Last edited by jaggedben; 07-12-13 at 10:29 PM.

  10. #20
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    Quote Originally Posted by jaggedben View Post
    Wow, I wouldn't agree with any of that.

    I think that a back-fed plug-in type breaker, for the purposes of of 408.36(D), is simply a breaker that has the supply conductors connected to the terminals, rather than to the busbar that connects to the 'plug in' part. In other words, it's a breaker whose parts can remain energized when the breaker is unplugged, opposite the way that most plug-in type breakers get installed. The requirement is there simply to prevent someone in a hurry from missing the fact that an unplugged breaker could shock and kill them. 705.12(D)(6) overrides that requirement precisely because a utility interactive inverter does not continue to energize the breaker if it's unplugged. It basically recognizes that GTIs aren't a 'supply' for the purposes of 404.36(D), and that the danger doesn't exist.

    The first quote doesn't jive with the second. Multiple breakers used as service disconnecting means in an MLO panel aren't backfed according to your definition in the first quote. I would say they aren't backfed because they are energized from the busbars, hence if unplugged they are no longer energized. (It might be wise in many such installations to have tie downs to prevent accidental movements in the vicinity of high fault currents, but I don't think that 408.36(D) requires it.)

    I've seen plenty of back-fed breakers set up as service disconnecting means. But like ggunn I'm struggling to visualize how such a breaker could fall under 705.12(A).
    100% agree
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