Auxiliary contacts are secondary switching devices that work with primary switching equipment. They are used for interlocks, latches, and remote indication of status and trip. They come in normally open or normally closed contact points and are smaller and rated at lower current ratings than the primary device. They can be built-in or added as modular units.
Auxiliary contacts are secondary switching devices that work in conjunction with primary switching equipment such as circuit breakers, relays, and contactors. These contacts are physically connected to the main switching mechanism and activate simultaneously. They are commonly used as interlocks or latches on the primary device’s control circuit and often used to give an indication of its operating status. Many contactors and circuit breakers feature auxiliary contact sets as integral parts or can be snap-fit modular units that can be added or removed as needed. They are available with normally open or normally closed contact points or a combination of both.
Main circuit switching devices, such as circuit breakers and contactors, often require additional switching functions beyond those of their primary contacts. These include remote status indication, trip function indication, electrical interlocks and starting circuit lockout devices. These functions have no physical impact on the main circuit and are independent. Also, the voltage used for these auxiliary circuits will typically be much lower than that of the main circuit. To achieve this simultaneous but separate switching, the auxiliary contact points activate together with the main device. These are generally much smaller and rated at lower current ratings than the primary device.
One of the main uses of auxiliary contacts is in the latching circuit. This is a control circuit function that allows the use of pushbutton-type momentary switches to start motors and other equipment. Another common function of these contacts is remote indication of status and trip. A separate low voltage circuit is passed through the auxiliary to a remote indicator light which illuminates when the device is triggered or tripped. Auxiliary contact points can also be used to turn on auxiliary equipment, such as starter panel cooling fans, when the contactor activates.
There are two basic types of auxiliary contacts: those which are closed in the non-activated state or those which are open. These are known as normally closed (N/C) and normally open (N/O) contacts. NC contacts are, for example, used as electrical interlocks where two contactors are used for forward/reverse operation. The control circuit of one contactor will pass through the N/C auxiliary of the other. This means that one cannot be inadvertently started while the other is running. The NO contacts are typically used to turn on the status indicator lights and act as a holding circuit.
Many breakers and contactors have built-in auxiliary contacts as an integral feature. However, if necessary, additional contact groups can be added. These modules typically slide on top of smaller relays or clip into your existing auxiliary set.
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