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Thread: Piggyback Circuit Breakers - U.S.

  1. #1
    Join Date
    Sep 2002

    Default Piggyback Circuit Breakers - U.S.

    “Piggyback” Circuit Breakers – U.S.
    In an earlier post it was indicated that piggyback breakers, i.e. two breakers occupying the space of one breaker can only be installed in those panel boxes exhibiting an “A” and “B” per breaker number. Why is this? What’s the reasoning behind this? It’s not because they won’t function in a ‘normal’ box.

    I was touring a house on the market and another party was quizzing the owner about the amp service and a chance peek inside the box revealed three such piggyback devices. The owner said that they were installed in 1983 and have worked fine. Why is the NEC against the devices and what is the NEC article number prohibiting their use.

  2. #2


    NEC 110.3.B demand that you install electrical products meeting the manufacturer's installation instructions and as they are listed and labeled.

    If you can find a piggy back breaker that is UL listed for your brand name and model of your panel then by all means the NEC says you may use it.

    However the fit all piggy back breaker is bypassing tabs on any breaker that is not desigend nor listed for a piggy back breaker.

    You have a limit of 42 branch circuits in a panel. If you installed all piggy back breakers then you may have as many as 84 piggy back circuits in a maximum 42 circuit panel.

    Then the thickness of each different brand of panel is different. If you do not use the proper breaker listed for use with that panel then you may be installing a breaker designed for a fat buss bar and be installing it in a panel that has a skinny buss bar. About 6 months ago if it were not for a neighbor of a vacationing home owner that home owner would have come back to a foundation only. There were piggy back breakers installed not listed for that panel. Exactly the condition above existed. The piggy breakers installed did not make a tight connection to the buss bar. Looked good but over a period of time due to heating and cooling the buss overheated broke down burnt through the nonconductive backing and shorted to the frame. The neighbor went over to check the house and decided to get a coke out or the fridge. He discovered the fridge was without power. He went into the basement in a corner under the stairs [tight area to have a panel but did meet the 30" wide and 36" clear approach requrements]. The neighber found the main breaker tripped. He reset the main breaker casually and when he turned it back on a fire ball blew out of that panel through every crack in that panel cover. He was not hurt except to hit his head on the bottom of the stair runner. When he turned the breaker on after it had been damaged due to the warped buss bar the main breaker exploded and dead shorted the unfused main service conductor to the panel. The fire department could do nothing until the power was cut at the pole. If they had tried to remove the meter under that kind of dead short unfused load it would have blown like a bomb in their face. The firemen called the power company and had a service man sent out to cut the lines. While this was going on fire was enveloping the home. Before the lineman got there the primary fuse at the transformer finally blew allowing the firemen to the do their job.

    The house was saved the home owner's vacation was cut short and it took about 6 weeks to repair the damage so they could again live in their home.

    All the above happened because a nonlisted piggy back FIT ALL breaker was installed in that panel causing a break down of that buss bar and the above chain of events.

    Many people want to use breakers but don't care if they are listed for that panel. I have found many panels with damaged buss bars before anything like the above happened. It cost them a new service upgrade to repair the minor damage to the buss.

    The above is why you must use only breakers listed for the panel brand and model that you have. Even two panels of the same brand will often have different thickness of buss bars. The wrong breaker causing a mismatch of contact between buss bar and nonlisted breaker will over time cause you to have to replace your panel at the least. If you are unlucky you may experience the above.

    There is a reason for about anything the NEC does and writes. However often times we have no explaination to those reasonings.

    In this subject I have seen the results showing the reasoning of NEC 110.3.B requiring only approved and listed equipment to be used for any electrical product. Those reasons are quite clear to me through experience of what I have seen on this subject of using non listed breakers in panels.

    The NEC is not opposed to using piggy back breakers but does demand that that panel is designed to accept piggy back breakers and the proper breaker listed for use in that certain panel be used.

    Be careful and safe;

    Hope this helps


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