WiremanWireman · Relay or timer not working: troubleshooting for electricians · 2023 NEC ·
Relay or timer not working
Coil voltage first, then the contacts, then the timing mode and settings.
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How it works
A control relay is a coil that moves a set of contacts. Nothing happens on the load side unless the coil is energized and the right contact (normally open or normally closed) is wired. A timing relay adds a delay: an on-delay closes its contact some time after the coil is energized, and an off-delay holds its contact closed for some time after the trigger goes away. Most multi-function timers have a mode setting, so a timer set to the wrong mode looks broken.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- Test: Measure the coil voltageExpect: The coil’s rated voltage, within about 10%.
- No voltage at the coilThe relay isn’t being told to operate
- Voltage, but no click or LEDFailed relay coil or a bad socket
- It clicks, but the load doesn’t respondTest: Check the contact that drives the loadExpect: Near 0 V across a closed contact. Full voltage across it means it’s open.
- Full voltage across it (open)Is it a timer, and is the mode and time setting what the circuit needs?
- Wrong mode or rangeTimer mode or range is wrong
- Settings correct, or a plain relayBurned or wrong contact
- Near 0 V (closed), load still offThe relay works; the problem is past it
- Full voltage across it (open)Is it a timer, and is the mode and time setting what the circuit needs?