Contactor contacts welded closed — load won't switch off
The contactor won't drop out when the coil is de-energised. The load stays powered even with the control circuit off, because the main contacts have welded together.
Safety first
Welded contacts mean the load cannot be switched off by its normal control. Never rely on the coil to make it safe — isolate upstream and prove dead. Treat the load as live.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Full detail — causes, the why, and common mistakes.
Likely causes
Ranked from most to least likely.
- 1
High inrush or fault current welded the contacts
Most likelySwitching a heavy inductive or motor load, or closing onto a fault, can draw enough current to fuse the contact faces together.
- 2
Worn / pitted contacts arcing on each operation
#2Aged contacts with heavy pitting concentrate current on small points, building heat until they weld.
- 3
Undersized or wrong-rated contactor
#3A contactor rated below the actual switching duty wears and welds far sooner than expected.
- 4
Chattering that arced the contacts together
Least likelyProlonged chatter from a weak coil supply arcs repeatedly and can weld the faces.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
De-energise the coil and check whether the load actually drops out (observe / measure downstream).
Load de-energises cleanly when the coil is released.
Contacts are releasing — the fault is elsewhere, not a weld.
Load stays live with the coil off — a weld is confirmed.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Contactor won't drop out
→ step 2 - 2decision
Does the load stay live with the coil de-energised?
Yes→ step 3No→ step 4 - 3decision
Are the contact faces welded/badly pitted?
Yes→ step 5No→ step 6 - 4result
Contacts release fine — look elsewhere (control logic, not a weld).
- 5result
Welded contacts — replace, then find the over-current cause and correct rating.
- 6result
Clean but stuck — suspect a mechanical jam in the contactor.
Common mistakes apprentices make
- Assuming the control circuit failed when the contacts have actually welded.
- Replacing the contactor without finding why it welded — it will happen again.
- Relying on the coil/control to isolate a welded contactor for working on the load.
- Fitting a like-for-like device when the duty really needs a higher rating.
When to stop & escalate
If the load can't be positively isolated by its normal means, treat it as a safety issue and isolate upstream before any work. Repeated welding points to a sizing or fault-current problem that should be designed out, not just re-fitted.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
Related faults
Contactor chattering or buzzing instead of holding in
The contactor rapidly clicks/buzzes, pulls in and drops out repeatedly, or hums loudly without seating cleanly. Often comes with arcing noise and heat.
Contactor has voltage at the coil but won't pull in
You measure the rated control voltage (e.g. 24V) across the coil terminals, but the contactor refuses to energise — no clunk, no pull-in, contacts stay open.
Motor overload keeps tripping
The thermal/electronic overload trips repeatedly, either on start or after the motor has run for a while. Resetting only buys you a short run before it trips again.
Learn the theory
How the gear and circuits behind this fault actually work.