While our customers are wholesalers, Packard knows that you, the contractor, have a choice. You are often presented with many buying options, and being well-informed about your purchase can help make your job easier and more successful. Our Tech Tips are also very helpful for our wholesalers as we present product information that can help as contractors have questions.
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Can a 2 pole contactor be used to replace a 1 pole contactor?
The quick answer is yes. But let’s look at the contactors and see how they function.
In Figure 1 above, the terminals have been labeled L1, L2, T1, and T2. The “L” represents line, the source of power. With single phase power there would be two legs of power that would be connected to L1 and L2. The “T” represents load, such as a motor, compressor, or some other device. Think of a simple motor connection where two leads from the motor are connected to the two lines of power. In the case of a contactor, those two motor leads would be connected at T1 and T2.
Look closely at the 2 pole contactor. Notice the brass colored material between L1 and T1. This consists of an upper and lower section. The upper section makes contact with the lower section when the contactor coil is energized. This closes the circuit, allowing the power from L1 to pass to T1. There would be continuity between L1 and T1 when the coil is energized. Note that the power energizing the contactor coil may be a different source of power than that which is connected to L1 and L2. When power is removed from the coil, the sections separate and the circuit from L1 to T1 is open and there is no continuity. Each pole on a contactor functions in the same way.
Look at the 1 pole contactor. It’s identified as a 1+ pole! Notice that there is only one set of contacts (the brass colored material), hence 1 pole. The circuit between L1 and T1 would operate as we previously discussed. But why the “+” sign and no contacts between L2 and T2?
Notice in Figure 2 below that between L2 and T2 there is a “shunt”. It is a solid brass bar connecting L2 to T2. The circuit between L2 and T2 is always closed and there is always continuity from L2 to T2. The “+” indicates that there is an additional circuit, but it is not switching between opened and closed.
With a 1 pole contactor, the shunt circuit is used when the device being operated is always to have power to it, such as in the case of a crankcase heater.
When replacing a 1 pole contactor with a 2 pole remember that L2 to T2 would be opening and closing as the coil is energized. If a crankcase heater were connected through this path it would not always be energized. So how could a 2 pole replace a 1 pole and provide the same operation? The crankcase heater or any other device that should be constantly energized would be connected to the same side as the power, L2. It would then be constantly energized. Some might say attach a jumper between L2 and T2. This would provide constant power to the crankcase heater. However, you would lose the ability of opening and closing the circuit of L2 and T2. Opening and closing both legs of power can be looked at as a safety feature.
Yes, a 1 pole can be replaced by a 2 pole, and the 2 pole provides additional switching capabilities. But be certain to determine if any devices on the shunt side of the 1 pole need to be constantly energized and, if they do, make any needed connection adjustments.
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