![]() ![]() Bus stabs without notches do not allow for tandem breakers installation but will allow for non-class CTL tandem breakers (QO) as replacements only. Panelboards with notched bus stabs allow for installation of CTL tandem breakers (QOT). With this code, manufacturers are required to list the number of max number of circuit breakers allowed and to provide a “rejection feature” to help prevent people from installing tandem breakers where they are not allowed to be installed. The 2008 National Electrical Code (NEC) got rid of the “lighting and appliance” designation and now says, “A panelboard shall be provided with physical means to prevent the installation of more overcurrent devices than that number for which the panelboard was designed, rated, and listed.” At various points in time, Square D has labeled tandem circuit breakers with part numbers that did not hold true to this rule.Īll panelboards must adhere to UL standards and included in this requires “lighting and appliance” panelboards to be class CTL. QO (e.g., QO2020) are circuit breakers are designed for use in the older “non-class CTL” QO load centers that were manufactured before the change in code. In general, QOT (e.g., QOT2020) are the new version of tandem breakers designed to be used in present class CTL QO load centers. Horizontal Switch with Hook Horizontal Switch w/o Hook Vertical Switch w/ Hook Class CTL & QO vs QOTĬlass CTL (Circuit Total Limiting) is a classification of load centers from the 1965 National Electrical Code (NEC). Usually if a breaker has a hook it is referred to as a “QOT” and if it does not then it would be considered a “QO Twin or Tandem”, but this is not always the case. Some use a common clip while others use a larger “hook”, which only allows the breakers to be mounted into specific spots on a panel. ![]() ![]() The hook refers to the way the back of the breaker clips into the panel on the bottom side. Vertical (Stack) Switch Horizontal Switch Hook The horizontal version is the newer design. ![]() Vertical units are stacked top to bottom whereas horizontal units have the switches side-by-side. The vertical vs horizontal refers to the switches on the face of the breaker. Let’s learn more about what these mean… Vertical vs Horizontal Here are the four varieties of Square D QO tandem breakers:įrom left to right we have the vertical switch with hook, horizontal switch with hook, horizontal switch without hook, vertical switch without hook. This is a normal and legitimate practice as long as the panelboard is designed for tandem circuit breakers and these breakers are installed on the panelboard where they are specifically allowed. For this reason, they’re usually used on panelboards that has filled to capacity with standard breakers. Some may confuse tandem breakers with two-pole circuit breakers, however, tandem breakers do not get connected to two different poles at a panelboard and do not have a common trip or handle tie for simultaneous disconnecting of two poles - unlike a two-pole circuit breaker.Ī tandem circuit breaker is a double circuit breaker that takes up one circuit breaker space on a panelboard. Tandem breakers are known by different names, such as duplex, slimline, twin, half-height, half-inch, double and wafer breakers. Let’s get things straight once and for all… Tandem Breaker definition The thing is, although many Square D QO tandems have the same part number, they don’t all interchange. What is it about tandem / twin breakers that confuse so many of us? Maybe if they gave these bad boys a more specific part number then it wouldn’t be so bad, right? Need something different? Other sizes, voltages and configurations are available. ![]()
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