Maintenance Detective: The Conveyor That Ran Backwards
- Mac Davis
- Jun 23
- 2 min read
Let's play a game for all the maintenance players out there.
You've got a conveyor. The overload trips. Standard stuff - you reset it and put it back in service.
Except now the conveyor is running backwards.
What's the most likely cause?
Answer:
The backwards rotation and the overload trip are both signatures of single phasing. That means one of your wires is not carrying continuity to the motor.
When you lose one leg of your three-phase supply, the motor loses its phase sequence reference. It may run forwards, backwards, or just trip the overload repeatedly.
The motor will run very hot and it won't have as much power as it should. If you keep running it like that, it will fail quickly.
Single phase usually originates in the wiring, not the motor and not the overload. That means you're looking at terminal strips, lug connections, and upstream distribution points. Something is probably loose, corroded, or intermittently open.
The test is straightforward. First, confirm you have all 3 phases on the inbound side of the motor starter.
Then, put your meter in resistance mode and check each of the three legs at the bottom of the overload. All three should read essentially the same (should be within 10% of each other). If one leg is reading higher than the others, or open, you found your problem. That's where your single phase is coming from.
If you're good above the starter and below the starter, then you need to check the starter itself.
Before you pull a motor or call for a rewind, check your connections. The answer is usually at a terminal strip or wire nut in a junction box that came off.
Maintenance Detective articles focus on solving specific equipment failures and troubleshooting challenges.
While every failure has a technical cause, recurring failures often point to larger issues involving process control, standardization, training, or accountability.
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