What the C152 alarm means

The TCP approached a configured safety plane/boundary and the safety system stopped the robot to keep it inside the protected workspace. We see this alarm constantly when servicing Universal Robots CB3 / e-Series (UR5/UR10/UR16/UR20) systems, and the first on-site pass usually pins down the cause.

Most common causes

  • Safety planes configured too tight for the real program path
  • Workpiece or fixture inside the safety zone
  • Safety settings changed without updating the program
  • TCP offset set incorrectly so the real tool tip is outside the computed zone
Field note: Based on our handling experience the first cause is the most frequent — use it as your starting point.

Step-by-step field fix

  1. Verify the 3D graphics position matches the real robot before anything else
  2. Adjust the safety plane limits in Installation > Safety to match the real cell
  3. Correct the TCP if the offset is wrong
  4. Move the fixture/workpiece out of the safety zone
  5. Run the program at reduced speed to confirm clearance
Safety first: For Universal Robots c152, this alarm is the safety circuit itself: jumpering a door switch or forcing a contactor removes the protection entirely - no protective action when something happens, and no defensible account of responsibility. What you can check yourself first is Verify the 3D graphics position matches the real robot before anything else; the e-stop chain and safety circuit handling is not a DIY job.

How we diagnose safety-chain faults on site

Universal Robots c152 belongs to the safety chain & e-stop family. On Universal Robots c152 the failing stage is configurable safety functions (limits, safety IO, force and power limits; finer on e-Series) on the UR control box (CB3 / e-Series) - continuity of one series loop: e-stop buttons, door switches, light curtains, safety relays and the enabling device. We start reading Universal Robots c152 at the PolyScope event and alarm pages; codes carry a C prefix (C15x, C5x, C7x).

The chain involved in Universal Robots c152 runs: e-stop / door / curtain -> safety relay (dual channel) -> controller safety input -> motor-off and brake apply.

On Universal Robots c152 the field usually reports Safety planes configured too tight for the real program path, but the check that matters is not continuity: The point of a safety loop is not whether it conducts but whether both channels conduct together. The relay compares channels; if one opens tens of milliseconds early it latches as a channel fault. The commonest causes are plain: oxidised door-switch contacts raising contact resistance, or one loose terminal. We measure segment by segment - pendant e-stop, panel e-stop, external e-stop, safety door - and lock onto whichever segment reads differently on the two channels.

Field notes on this page cover Universal Robots c152 (Protective Stop — Position Close to Safety Plane Limits); written by the Henghuan repair team, updated 2026-10-01.

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Related Safety Chain & E-Stop alarms

C191A1 — Safety Violation — Joint Position Limit Violated C191A2 — Safety Violation — Joint Speed Limit Violated
Same family: this code belongs to the Safety chain & e-stop alarms family - the page collects all Safety chain & e-stop-family codes we have handled, with the common inspection order and spares.
Other brands: we also keep field-fix libraries for Kawasaki · Staubli · Epson and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the Universal Robots c152 alarm mean?

The TCP approached a configured safety plane/boundary and the safety system stopped the robot to keep it inside the protected workspace. We see this alarm constantly when servicing Universal Robots CB3 / e-Series (UR5/UR10/UR16/UR20) systems, and the first on-site pass usually pins down the cause. Universal Robots c152 sits in the safety chain & e-stop family; on our work orders the highest-frequency trigger for this code is "Safety planes configured too tight for the real program path".

QCan I clear a Universal Robots c152 alarm myself?

Whether Universal Robots c152 clears on its own depends on the outcome of "Verify the 3D graphics position matches the real robot before anything else". Finish the flow with "Run the program at reduced speed to confirm clearance" to confirm Universal Robots c152 - do not skip it. If that step is clean, the second most frequent cause on Universal Robots c152 is "Workpiece or fixture inside the safety zone". When Universal Robots c152 keeps coming back it is not a one-off trigger - especially if Run the program at reduced speed to confirm clearance is where you get stuck. Do not keep producing through Universal Robots c152.

QA safety-chain fault like Universal Robots c152 stops the line - how fast can you be here?

The commonest causes we see on Universal Robots c152 are "Safety planes configured too tight for the real program path, Workpiece or fixture inside the safety zone, Safety settings changed without updating the program", so we stock the van against those. For Universal Robots c152 specifically, we stock along the loop: safety relays, common door switches, e-stop buttons, light-curtain pairs and terminal blocks. For Universal Robots c152, a safety-chain fault stops the whole line, so we rank it top priority and pre-triage by phone: door switch, e-stop or relay. Before we roll, tell us what Universal Robots c152 shows on the PolyScope event and alarm pages; codes carry a C prefix (C15x, C5x, C7x) and what the machine was doing - phone or video triage is free.

This page on Universal Robots c152 was compiled from actual repair records of the Henghuan Robotics repair team. Alarm notes are our own summary for troubleshooting reference only and may vary with controller and software version — please consult Universal Robots documentation or contact us if in doubt. Henghuan is an independent service provider, not affiliated with or endorsed by Universal Robots.