Contactors & relays
Coils, contacts, chatter, and switching faults.
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.
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 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.
Control relay coil not energising
A plug-in or interface relay isn't picking up — its indicator stays off and its contacts don't change, so whatever it controls never operates.
Auxiliary contact not making — seal-in or interlock fails
The contactor pulls in, but an auxiliary contact (used for seal-in, interlock, or status) doesn't change state, so the circuit won't latch, an interlock misbehaves, or status feedback is wrong.
Contactor drops out on its own / won't stay latched
The contactor pulls in when you press start but drops out the moment you release the button, or randomly during running — the seal-in (latch) isn't holding it.
Overload relay won't reset
After an overload trip, the reset won't take — the starter won't re-arm, or it resets and trips straight back. The control circuit stays broken at the overload's contact.
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.
Star-delta starter not transitioning to delta
A star-delta (wye-delta) starter starts the motor in star but never switches to delta — the motor runs weak/slow, or trips, because it stays in the starting connection.
Latching / impulse relay stuck in one state
A latching (impulse) relay won't change state on a pulse — lighting or a load stays on or off regardless of the switch, because the relay isn't toggling.
Phase-failure / monitoring relay has tripped the circuit
A phase-failure or phase-sequence monitoring relay has dropped out and is holding the control circuit off, stopping the equipment — even though the panel looks powered.
Contactor noisy only when the load is connected
The contactor pulls in and holds quietly with no load, but buzzes or hums once the load is connected and drawing current.
Control relay contacts sticking or welded
A control/interface relay's contacts stick closed (or won't make cleanly) — the controlled circuit stays on when it should be off, or switches unreliably.