Contactor coil overheating / burning smell
The contactor coil runs hot, discolours, or gives off a burning smell, and may eventually fail. It might still operate for now but won't last.
Safety first
Overheating coils are a fire risk and can fail short. Isolate before touching a hot coil. Investigate promptly rather than leaving it in service.
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
Over-voltage on the coil
Most likelyA coil fed above its rated voltage draws more current and overheats.
- 2
Armature not seating fully
#2If the armature can't pull fully home (dirt, wear, mechanical jam), the coil keeps drawing high inrush-level current and overheats.
- 3
High ambient temperature / poor ventilation
#3A hot, sealed enclosure pushes the coil beyond its temperature limits.
- 4
Wrong coil or partial short in the winding
Least likelyA miswound, wrong-rated, or partially shorted coil dissipates more heat than it should.
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.
Measure the coil voltage and compare to its rated value.
Coil voltage at its rating, not above.
Voltage is correct — check the armature seats fully.
Over-voltage — correct the supply to the coil.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Coil overheating
→ step 2 - 2decision
Is the coil voltage at (not above) its rating?
Yes→ step 3No→ step 4 - 3decision
Does the armature seat fully when energised?
Yes→ step 5No→ step 6 - 4result
Over-voltage — correct the coil supply.
- 5result
Check ambient/ventilation and the coil for a partial short.
- 6result
Partial seating holds high current — clear jam / clean faces.
Common mistakes apprentices make
- Leaving an overheating coil in service until it fails (and possibly arcs).
- Not realising a partly-seated armature holds the coil at high current.
- Ignoring a baking-hot enclosure with no ventilation.
- Fitting a wrong-voltage coil from spares.
When to stop & escalate
A persistent over-voltage or a consistently hot enclosure points to a supply or ventilation problem to address at design level. A burning smell with discolouration means take it out of service and replace.
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.
No control voltage in the panel
Nothing in the control circuit will operate — contactors won't pull in, indicators are dead, the PLC may be off. The control voltage that should be there simply isn't.
Learn the theory
How the gear and circuits behind this fault actually work.
Transformer
Transfers electrical energy between circuits by magnetic coupling, stepping voltage up or down.
Power factor
How much of the current actually does useful work — and why a poor figure costs you capacity and money.
Back-EMF & inductive kick
Why a spinning motor generates its own voltage, and why switching a coil produces a damaging spike.