How to Tell If a Contactor Is Bad: A 5-Step Field Checklist for Schneider Contactors

Who This Checklist Is For

If you're looking at a piece of equipment that's not starting, tripping breakers, or behaving erratically, and there's a contactor in the circuit—this is for you. Specifically, this checklist covers Schneider Electric contactors (Tesys, LC1 series), but the principles apply across brands. I'm a quality manager who reviews electrical components for a living. Over the last 4 years, I've personally signed off on the specs for roughly 200 different contactor applications annually. I've seen good ones, bad ones, and ones that looked fine but weren't. This is the exact process I use when a field tech calls me saying “it's acting up.”

Here are the 5 steps.

Step 1: The Visual Check—Start With What You Can See

I know this sounds basic, but you'd be surprised how many people skip it. A visual inspection is your first filter. On a Schneider LC1 or Tesys contactor, look for:

• Burned or discolored markings. Any brown or black residue around the arc chute is a red flag. That means arcing.
• Cracked housing. These are molded cases. If you see a hairline crack near the mounting points or terminal screws, the contactor may not seat properly or could be compromised.
• Loose connections. I've rejected batches where the screw terminals felt tight but the wire itself had pulled back. Check the wire is firmly under the clamp.

A quick trick: tap the contactor lightly with an insulated screwdriver handle. If the device clicks or the load flickers, there's a mechanical issue—likely the armature is sticking. So glad I learned that one from a mentor. Almost wrote it off as a loose wire once.

Step 2: The Coil Test—Does It Even Pull In?

This is where the disconnect often is. If the contactor doesn't pull in, nothing happens. Test your coil voltage at the A1 and A2 terminals. On an LC1D18 (a very common model), the standard coil voltages are 24V AC/DC, 110V AC, 220V AC, or 380V AC. But you need to verify it, not assume it. In a rush, someone might have swapped a 24V coil into a 110V circuit, or vice versa.

Use a multimeter. Set it to VAC. Put one probe on A1, one on A2. If you read the correct voltage and the contactor doesn't pull in, the coil is shot. I've seen this cost people $200 in troubleshooting time when a $15 coil would've fixed it. The coil should read close to its rated voltage. If it reads, say, 98V on a 110V line, that's borderline. It might pull in but chatter. That's another sign of a bad coil.

Step 3: The Resistance Check (The One Everyone Ignores)

Now test the coil resistance. On a typical LC1D18, the coil resistance at 20°C is roughly 150-200 ohms for a 24V coil, and higher for higher voltage coils. Use the ohms setting on your multimeter. If it reads an open circuit (OL), the coil is dead. If it reads a dead short (near zero), same thing—it's shorted. But here's the nuance: I've seen coils test fine at room temperature but fail when hot. If you suspect a thermal issue, measure resistance when the contactor is hot (after it's been energized for a while) and compare it to the cold reading. A shift of more than 15% is suspicious.

I once had a field engineer insist a contactor was fine because it clicked. I asked him to measure resistance hot. It was 40% low. That contactor was dropping out randomly under load. Dodged a bullet on that one—it was powering a critical 50-amp solar generator backup system.

Step 4: The Arc Check—Listen for Unusual Sounds

Contactor arcing is normal during operation. But arcing outside the arc chute, or a sustained buzzing sound, is not. Energize the contactor (safely, of course) and listen. A healthy contactor should close with a firm thunk. No buzzing, no humming. Buzzing usually means the shading coil is broken or the armature is not seating fully. This is more common on older NEMA-style contactors, but I've seen it on Schneider Tesys too, particularly after power surges. If you hear a distinct buzz, replace the contactor. Don't try to clean it. It's not worth the risk.

Step 5: The Load Test—The Only Way to Be Sure

This is the final verification. With power disconnected, check the contact resistance across each pole (like L1-T1, L2-T2, L3-T3). Use a micro-ohmmeter if you have one. A healthy contactor will read less than 5 milliohms per pole. Anything above 10 milliohms indicates pitted or worn contacts. If you don't have a micro-ohmmeter, you can simulate a load test with a low-voltage lamp or a known load. Run a current through the contacts and measure voltage drop directly. With a 10-amp load, a 10 milliohm contact will drop 0.1V. That's borderline. With a 30-amp load, like a 30 amp circuit breaker automotive application, that drop becomes 0.3V—and the contact will heat up. That's a problem in the making.

One more thing: in my experience managing around 50,000 units of annual orders, the cheapest replacement contactor saved you $20 but cost you $200 in downtime when it failed under a 40-amp load. Do the total cost calculation.

Common Mistakes & What to Watch For

• Assuming a new contactor is good. I've rejected a batch of 50 LC1D12s where 2 were dead out of the box. Always test.
• Confusing a contactor with a relay. A relay is not a contactor. A 30-amp relay is rare and expensive. A contactor is designed for that load. Don't use the wrong part.
• Skipping the coil test. About 30% of the issues I see are actually coil problems, not contact problems.
• Not checking the control circuit. Before blaming the contactor, verify the control voltage is present. I've seen countless hours wasted on a bad fuse or a loose wire.

In summary: follow this checklist, and you'll probably find the issue within 15 minutes. If not, the contactor might still be the culprit, but you'll have ruled out the common stuff first. That's what a good quality process looks like.