A very common cause of electrical equipment failures is relay or contactor failure. Relays can stop working as intended due to burned contacts, dirt, electric arc, but they can often be easily repaired by following the steps below.
This procedure does not apply to state relays and solid state contact forms, since these relays have no moving parts and are manufactured as a complete sealed unit that cannot be disassembled. However, for most mechanical relays, where the contacts can be reached by removing a plastic housing and some parts, repair is possible and relatively simple.
The industrial relay in Figure 1
Figure 1 shows a newer Schneider relay with its plastic parts held together with small tabs, while in Figure 2 the relay is held together with screws, one of which is indicated with a red arrow. But both are practically twins when you come in. The frame has several contacts built into it (how many depend on the purpose of the relay), a coil and a piston-style luminaire rest on a large spring, the purpose of which is to return the anchor to its normal position while activated.
For each contact pair on the frame, there is a contact list on the anchor that will connect or disconnect them.
Finding Bad Contacts
Step 1 – Checking with Multimeter
The first thing to do is determine which contacts are defective. Figures 3a and 3b show the red arrows pointing towards the anchor, which is the blue part which is more clearly shown in figure 3b with the covers removed. Fig. 3b also shows six sets of threaded connection screws at the bottom of the image, which are connected to the corresponding screw terminals opposite to the other side of the relay (on top of the picture).
Place the probes on a multimeter set to continuity or ohms over a pair (set) of connecting screws while measuring resistance – once with the armature in normal position (up), and again when pushing the piston all the way down. Compare the readings, which should show open circuit in one case and closed circuit in the other. Either of the six sets of contacts showing open or closed circuit in both cases is incorrect. These bad contacts should be identified and noted.
Step 2 – Repeat for each contact set
Repeat the process for each set of contacts. If the readings are good for all contact sets, the cause of the error is probably a little dirt or dust that causes an intermittent connection problem.
Open the relay
Examine the relay to get a clear understanding of how the lid was installed over the frame and how many parts it has. If there are no obvious screws holding the unit together, look for small plastic tabs around the lid parts (see red arrows in Figures 4 and 5).
Step 3 – Carefully pull the tabs
Use a small flat screwdriver (shown in Figure 6 below) to easily pull the tabs – the parts should come apart easily and reveal the inner frame. It is very important to be careful not to stretch or break any of the plastic tabs. Figure 4 clearly shows the lid (bottom of the picture) removed from the frame (top of the picture) and exposes the screw connections and the anchor.
Remove the frame
Step 4 – Unhook the Frame
What really happens within a relay is quite obvious when the frame has been disassembled. In this case, there is a tab on each side of the frame that needs to be relaxed (Figure 6). When this is done, the frame will be split into two parts, revealing the anchor in its core (the blue part in Fig. 7). The contact points should now be fully exposed and ready for maintenance.
Cleaning contacts and insides
Now that points are fully exposed, they should be carefully examined for corrosion, pit, dirt or other deviations. For example, if the contractor is used in a woodworking environment, there may be small sawdust particles floating around. If small debris problems are the root of the problem and the points are not damaged, you just need to clear it.
However, if the contacts show any damage, the procedure must be taken one step further. Remember to never burn or archive relay contacts, never use grease and other coatings that may collect dirt or dust, and only clean with a well-known brand of electronic contact cleaner – low or medium current contacts often have very light gold or silver plating applied to those that could easily be removed without proper care.
Step 5 – Apply Cleaning Solution
The two parts of the frame and anchor must be handled with great care and attention, as they consist of many small parts that can easily fall or get lost. Delicate focus on this point is extremely important. A pair of latex gloves should be worn for the next step.
The first half of the frame can be picked up with one hand so that the contacts are visible. With an aerosol with a cleaner contact, on the other hand, continue spraying the contact points properly. These products are designed to clean contacts and remove all traces of oxidation without leaving any residue.
If professional contact cleaner is not available, vinegar is the best household.
Step 6 – Brush the contacts  After using the solution, take a small nylon brush (or toothbrush) and gently scrub the contacts.
Step 7 – Clean and Brush Frame
The second part of the frame can then be sent to the same processing (from steps 5 and 6).
Step 8 – Clean and brush the fixture
Be extra careful with the anchor as its contacts (points) are extremely flexible and could easily come off. Spray the anchor with contact cleaner and gently scrub it with the brush, with extreme care.
Step 9 – Reset Frame
After completing the final cleaning, reverse the disassembly to get the relay back again and work again.  Step 10 – Check contacts again
Repeating steps 1 and 2 with the multimeter tell you if the process was successful. If so, the reset relay can be reset. Good luck!