Siemens alarm 21550: [Channel %1: ] Axis %2 Travel from hardware limit switch not possible. Reason: %3

What it means

The axis rests on a hardware overtravel switch and the NCK cannot move it back into the allowable traverse range. The reason code distinguishes cases such as missing reference point, inhibited direction, or both limit switches approached.

Likely causes

• axis jammed against the mechanical/hardware limit switch
• opposite direction of travel inhibited by PLC or interlock
• axis not referenced, so controlled retreat is not enabled
• limit switch stuck actuated giving a false trip

Replacement parts

We supply the following units for this alarm — tested, warranty-backed:

• hardware limit switch per machine builder

  cable · Check if others ruled out

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