Applicable Systems
EFC
FEX
FEI
HNC
Symptoms
Both travel limit switches activated simultaneously. The drive has detected that both the positive and negative travel limit switches are triggered at the same time, which is a logical impossibility indicating a wiring or switch fault.
Possible Causes
- Limit switch wiring error (both switches connected to the same input)
- Both limit switches mechanically stuck in the triggered position
- Limit switch wiring shorted together
- Limit switch power supply failure causing both to report triggered
Troubleshooting Steps
- Step 1: Check the wiring of both limit switches at the drive input terminals
Each switch connected to its own designated input; no cross-wiring - Step 2: Test each limit switch mechanically for proper operation
Each switch triggers only when the corresponding direction limit is reached - Step 3: Check limit switch power supply (typically 24V DC)
24V present at each switch; no power supply fault - Step 4: Replace any stuck or defective limit switches
New switches operate correctly
How to Reset
1) Inspect limit switch wiring. 2) Test mechanical operation. 3) Check power supply. 4) Replace defective switches. 5) Reset fault.
Frequently Asked Questions
- Q: Why is it impossible for both limit switches to be active?
The positive and negative travel limits are at opposite ends of the axis. The motor cannot physically be at both ends simultaneously. Both being active indicates a fault.
- Q: What type of limit switches are typically used?
Mechanical roller plunger or non-contact inductive proximity switches. Both types provide a dry contact or PNP signal to the drive's digital inputs.
Source: Rexroth IndraDrive HCS/HMS Fault Code List, Bosch Rexroth AG
Category: PLC & VFD