ApprenticeMedium risk

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.

Start fault-finding

Safety first

Control circuits can sit alongside live power terminals. Confirm what is isolated and what is not before probing. Treat the contactor's load side as live unless proven dead.

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
Open or burnt-out coil
Most likely
The coil winding is broken internally. You can still read voltage across it because almost no current flows through an open winding — the voltage is just sitting across the break.
2
Measuring a 'phantom' or floating voltage
#2
A high-impedance meter can show a misleading voltage through a parallel path (snubber, capacitor, parallel coil, or capacitive coupling) even though the supply can't actually drive the coil.
3
Wrong coil voltage rating fitted
#3
A coil rated for a higher voltage than the control supply will read voltage but never develop enough magnetic force to seat the armature.
4
Mechanically jammed armature
#4
Debris, a seized armature, or a stuck mechanical interlock physically stops the moving contacts from closing even with a healthy coil.
5
Weak supply that collapses under load
Least likely
An undersized or failing control transformer/supply holds open-circuit voltage but sags badly the instant the coil tries to draw inrush.

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.

Test 1 of 4

Re-measure coil voltage right at the coil terminals while a colleague (or the logic) calls the contactor in.

Expected reading

Rated coil voltage present and roughly steady at the moment of call-in.

Your actual reading

If it passes

Supply is reaching the coil — the problem is most likely the coil itself or a mechanical jam. Continue.

If it fails

Voltage drops out or never appears under call — the fault is upstream in the control circuit (interlock, contact, supply), not the coil.

Often leads toContactor chattering or buzzing instead of holding in No control voltage in the panel

View all expected readings at once

1. Re-measure coil voltage right at the coil terminals while a colleague (or the logic) calls the contactor in.

Rated coil voltage present and roughly steady at the moment of call-in.

2. Isolate and lock off, then measure coil resistance with the coil disconnected from the circuit.

A low, sensible resistance reading consistent with a coil winding (a small number of ohms up to a few hundred, depending on coil type).

3. With the coil still de-energised, manually push the armature in by hand (where the design safely allows).

Armature moves freely and the contacts make with a clean action.

4. Confirm the coil's printed voltage rating matches the actual control supply voltage.

Coil rating equals the measured control supply.

Fault-finding flowchart

The same logic as a decision tree.

1
start
Coil reads voltage but contactor won't pull in
→ step 2
2
decision
Does rated voltage hold steady at the coil during the call-in?
Yes→ step 3No→ step 4
3
decision
Isolated coil resistance sensible (not open circuit)?
Yes→ step 5No→ step 6
4
result
Fault is upstream: interlock, series contact, or sagging supply. Trace the control circuit.
5
decision
Does the armature move freely by hand?
Yes→ step 7No→ step 8
6
result
Coil is open — replace coil/contactor.
7
result
Suspect a supply that collapses under inrush, or a wrong-rated coil. Verify coil rating and supply capacity.
8
result
Mechanical jam or interlock — clear obstruction or check the interlock logic.

Common mistakes apprentices make

Trusting a digital meter reading without questioning whether it's a real, load-capable voltage or a phantom voltage.
Measuring across the coil terminals but on the wrong pair, so you're actually reading across an open contact in series.
Replacing the whole contactor before checking the coil resistance — often only the coil has failed.
Forgetting to re-check the voltage at the instant of call-in, missing a supply that collapses under inrush.

When to stop & escalate

If the control supply is sagging under load, escalate to investigate the control transformer or supply sizing rather than swapping contactors. If a mechanical interlock is holding the armature open by design, stop and confirm the sequence/logic with the machine drawings before defeating anything.

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

Contactors & relays

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.

5 causes3 test steps

QualifiedMedium risk

General testing

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.

5 causes4 test steps

ApprenticeMedium risk

Forward / reverse circuits

Motor goes one way but won't go the other (e.g. down but not up)

A reversing drive works in one direction only. One command (say, down) runs fine; the other (up) does nothing, or just hums/trips. Common on hoists, doors, and conveyors.

5 causes4 test steps

QualifiedHigh risk