Tech Tip: How To Use Aux Contacts with Your Contactor

In many applications you'll want to know if a contactor got a command to actuate and if it actually did it. Attaching an aux contact that closes its contacts when the contactors poles close is an inexpensive way for your PLC to keep any eye on things and tell you the status of the contactor. And they're easy to use. Here is a small Fuji contactor and here is a side mount aux contact. This post simply gets pulled up or down by the contactor which opens and closes these aux contacts. You just align the receptacle in the contactor by pushing the contactor in. Connect the PLC to the normally open or normally closed contact, and you're done. The PLC can now monitor this aux contact to see if the contactor is responding to commands. These side mount aux contacts can be mounted on either side and they work across multiple sizes of contactors. And some contactors come WITH aux contacts already installed, like this E7 Fuji which comes with a left and a right set of aux contacts. The Fuji contactors also have a top mount aux contact you can use. You just slide it on and you're ready to go. This little button now becomes your contactor test button. There's a 2 pole and a 4 pole version and you can get them with different numbers of normally open and normally closed contacts. One thing to beware of -- adding aux contacts places and extra load on the contactors coil because now it has to move the contactor AND the aux contact. So most manufacturers will put limits on how many of these aux contact you can add to a single contactor -- especially contactors with low power coils. If we look at the Fuji data sheet for example, we see you can have 2 side mounted or 1 front mounted only. So don't try to add more aux contacts than they specify. If you do then there is no guarantee the contactors coil will be able to move all of that hardware. While most contactors have side and top mount options for aux contacts like the Fuji we were just looking at, these WEG mini contactors are a little bit different. Three pole WEG Contactors have one aux contact built in and if you want to add more aux contacts, your only option with WEG is to add a top mount aux contact. This little slide button here becomes your contactor test button. They come in 2 pole and 4 pole modules, and you can get them in pretty much any combination from 4 normally open to 4 normally closed. Are there any limitations on the number of aux contacts that a WEG contactor can handle? Yep. If you are using a low power coil -- a 12 volt or 24 Volt coil -- you can only add a 2 pole aux contact. The WEG contactors are available in 3 power pole and 4 power pole versions. On the 3 pole WEG contactors, the fourth pole IS an aux contact, so you get that one for free and you can add more on top of that with these aux modules. Note that there is one set of aux contacts for the three pole contactors, and a different set for the four pole contactors. Now honestly, they are functionally identical, they fit the same hole and do the same job. The only difference is the terminals are labeled differently. That's so they comply with the IEC standard. The one exception with the WEG family are the 22 amp contactors. They can only support two additional aux contacts because more power is required by the coil to pull those heavier 25 amp contactors closed. Because of that, the 25 amp contactors have their own special aux contact module -- the regular 3 pole or 4 pole aux contact modules won't work with these 25 amp guys. If you look here you can actually see they have a different mounting configuration so you can't confuse the two. So make sure you get the right aux contact for the contactor you selected -- whether it be 3 pole, 4 pole or the 22 amp -- they are all different for the WEG family contactors. The 22 Amp WEG contactor also doesn't have that extra aux contact that the other three pole contactors have. That's because the heavy duty 22 amp contacts in this guy take up all the space in the box. If you need any help, please don't hesitate to reach out to AutomationDirect's FREE award winning tech support during regular business hours -- they will be happy to help you out. And don't forget the forums -- there are lots of folks there that love to share, so don't be shy about posting questions there too -- just beware that the AutomationDirect support team doesn't always monitor those forums on a regular basis, so you don't want to post any questions directed at Tech Support on the forums -- they may not see them.