KUKA KRC2: “Safety Circuit for Drives Not Ready” — Find the Open ESC Signal
Drives won’t enable on a KUKA KRC2 with “Safety circuit for drives not ready”? Use the ESC diagnosis to localize the open safety signal at X11 before swapping any board.
“Safety circuit for drives not ready” — read the chain, don’t swap boards
The drives contactor stays dropped because one monitored safety input in the ESC chain is open.
The ESC chain (redrawn)
Read it & fix it
- Message = ESC has not released the drives; power to drives is shut off on any interrupted input.
- Monitored: local/ext E-STOP, operator safety, enabling, drives off/on, qualifying, mode.
- Every signal is two channels (A + B) — a break on one side = single-channel discrepancy.
- Unused X11 inputs must be jumpered: enabling
5-6 / 7-8, drives-off17-18, qualifying14→13 / 16→15. - Don’t jumper a real open input to silence the message — that defeats a safety function.
- Don’t swap KPS/CI3/KCP before the ESC diagnosis names the fault.
Diagnostic path
Sources: KUKA KRC2 ed05 Operating Instructions — §2.6 ESC (p.23–25), §11.13 ESC diagnosis (p.132–136); KUKA KRC2 ed05 Interface X11, Direct Connection — §2.3 terminals (p.10–11), §5.1 jumpers (p.17); KUKA KSS System Messages (p.29/34/55).
“Safety circuit for drives not ready” — find the one open signal, don’t swap boards
The drives contactor will not pull in. This is the ESC safety chain doing its job — the task is to read which monitored input opened it.
The question
Everything looks fine to the operator, yet the contactor stays dropped. The real question is not “which part do I replace” — it is “which node or input in the safety chain is holding the drives off, and how do I localize it without swapping parts blind.”
Short answer
Monitor > ESC Diagnosis: it shows every monitored signal in colour and flags the offending node. Then localize the culprit input at the X11 terminal strip. The ESC mechanism and this diagnostic path are confirmed by the KRC2 ed05 manuals.
What the message means (verified)
The ESC is a dual-channel, computer-aided safety system that permanently monitors every safety-relevant input. The manual is explicit: “In the event of a fault or interruption in the safety circuit, the power supply to the drives is shut off” (KRC2 ed05 Operating Instructions, §2.6, p.23). The drives-off you see is that shut-off. The signals it watches are exactly the ones an operator would call “the safety chain”:
| What the ESC monitors | Behaviour if the signal is interrupted (per manual) |
|---|---|
| Local E-STOP (KCP) | Drives contactor drops out immediately |
| External E-STOP | Drives contactor drops out after a delay |
| Operator safety (safety gate) | Drops out after a delay (optionally immediately) — effective in AUTOMATIC |
| Enabling switch (1/2) | Drops out immediately — effective in TEST |
| Drives OFF / Drives ON | External Drives-OFF contact opens → drives off; Drives-ON needs a positive edge to close the contactor |
| Qualifying input (QE) | 0-signal causes a category-0 STOP in all modes (used by external axes / loading stations) |
| Operating modes (AUTO/TEST) | AUTO and TEST asserted together → drops out immediately |
Signal list and interrupt behaviour: KRC2 ed05 Operating Instructions, §2.6 & §2.6.1, p.23–25. ESC components (CI3 board, KCP master, KPS600, MFC passive node): §2.6, p.23.
Where it sits: the ESC chain to the drives contactor
Any open input anywhere in the dual-channel loop → AE output drops the drives contactor
Structure redrawn from the ESC description (KRC2 ed05 Operating Instructions, Fig. 2-14 / §2.6, p.23–25) — original diagram, not a manual reproduction.
Step 1 — read the chain with the built-in ESC diagnosis (don’t swap blind)
The controller has a dedicated tool that tells you exactly which signal is open. Open it from the menu: Monitor > ESC Diagnosis. It determines the current structure of the ESC circuit and shows the connected controllers and every ESC node (Operating Instructions, §11.13 & §11.13.1, p.132). In the state display each signal is colour-coded, updated cyclically; on a fault the view switches automatically to the error display and the relevant node flashes (§11.13.5, p.134):
- Local / External E-STOP — red = pressed, gray = released.
- Operator safety — red = open, green = closed.
- Enabling switch — green = pressed, gray = not activated; a separate Panic state exists.
- Qualifying input / Drives OFF key — red = Not OK, green = OK.
- A “Dual channel” box shows
Errorwhen the two channels of a signal disagree (single-channel fault).
Log on softkey writes EscDiagnosis.log to C:\KRC\Roboter\Log (§11.13.2, p.133).
ESC diagnosis is a live reading of the running safety system on an energized controller. Do not defeat any input to “clear” the message. Interpretation and any subsequent work: qualified personnel only.
Step 2 — localize the culprit input at X11 (wiring + jumpers)
If the ESC diagnosis points to a peripheral input (E-STOP, operator safety, enabling, drives-off, qualifying), the fault is almost always in the external wiring or a missing jumper on the X11 interface — the standard customer interface with the CI3 Extended board (Interface X11, Direct Connection, §2.3, p.8). Unused inputs must be jumpered or the chain stays open. On the ed05 direct-connection terminal strip:
| Input | Terminals | If not used |
|---|---|---|
| External E-STOP A / B | 2 / 4 | dual-channel input; must be closed by the periphery |
| Enabling switch A / B | 6 / 8 | jumper 5–6 and 7–8 (effective in TEST only) |
| Safeguard / operator safety A / B | 10 / 12 | close via gate switch (effective in AUTOMATIC only) |
| Drives OFF external (ch. A) | 17 / 18 | jumper 17–18 if the input is not used |
| Qualifying input A / B | 14 / 16 | jumper 14→13 (TA) and 16→15; a 0-signal forces a category-0 STOP |
| Drives ON external (ch. B) | 20 | needs a pulse > 200 ms; must not be permanently active |
Terminal assignment and jumper requirements: KRC2 ed05 Interface X11, Direct Connection, §2.3, p.10–11.
Because every safety signal runs on two independent channels (A and B), a wire that is broken, high-resistance or intermittent on only one side produces a single-channel / dual-channel discrepancy rather than a clean open — which is exactly what the “Dual channel” box in Step 1 catches. So test both channels, not just one:
- Power down the affected circuit before touching wiring (the X11 cable must not be energized — §4.2, p.15).
- At the flagged input, unmate both ends of the run and check continuity pin-to-pin on channel A and channel B separately; compare the two — a difference is the fault.
- Check for shorts to 0 V / shield and for a loose crimp at the terminal strip.
- Wiggle test: with the meter connected, flex the cable and connectors at both ends while watching for a break — catches the intermittent single-channel dropout.
- Confirm the mandatory jumpers above are actually present for every input you are not using.
Using an X11 jumper plug to “get past” the message deactivates the corresponding safety function; the manual states plainly that with a jumper plug fitted “safety functions are deactivated and the robot is not subjected to safe monitoring” and it “may only be used for the brake test during start-up and must be removed immediately afterwards” (X11, §5.1, p.17). A jumper is a legitimate part of a documented start-up procedure only — never a fix for a real open input. While it is fitted, the robot can move without that protection. Qualified personnel only. Remove it immediately after.
Could it be a board or power-supply fault instead?
It can — but that is the second question, not the first, and the symptoms differ. A genuine hardware fault inside an ESC node (KPS600, CI3/MFC, KCP) usually declares itself with its own node/error entry in the very same ESC diagnosis error view (byte-timeout, CRC, crossed-connection, output error, “Drives contactor auxiliary contact error”, §11.13.6, p.135–136), and the KPS600/KSD have their own dedicated trip codes (§11.12.12–13, p.131–132). So let the ESC diagnosis arbitrate: a clean “input open” points at wiring/jumpers; a node error points at the board. On a dated KRC2, also keep a lost or corrupted configuration in mind — but a live safety-input message like this one is most often a real open channel, not a software fault.
Open points / to verify
- Message-number mapping is a corpus gap. The exact string
"Safety circuit for drives not ready"is not in the loaded message manuals, and in the KSS System Message list in the corpus number 310 is “Drive disabled (extern)”. The message text/number varies by KSS build, so treat the number as indicative and rely on the text and the ESC diagnosis, not the number. - Cabinet generation. The pin/terminal numbers above are for the KRC2 ed05 X11 direct-connection terminal strip. The earlier KR C2 uses a different X11 connector layout — verify against your cabinet’s circuit diagram before jumpering.
- Interface variant. Standard X11/CI3 vs a SafeRobot / SafetyBUS p gateway changes where and how the chain is diagnosed; confirm which interface this robot carries first.
Monitor > ESC Diagnosis, state/error display, X11 pinout & jumper rules) — all confirmed in the KRC2 ed05 manuals. Medium on the exact fault-number mapping and on the case-specific root cause, which depend on the KSS build and the actual wiring.Sources: KUKA KRC2 ed05 Operating Instructions — §2.6/2.6.1 (ESC, p.23–25), §2.6.3 (CI3, p.26), §11.13 ESC diagnosis (p.132–136), §11.12.12–13 (KPS600/KSD trips, p.131–132); KUKA KRC2 ed05 Interface X11, Direct Connection — §2.3 (terminals, p.10–11), §4.2 (cabling, p.15), §5.1 (service jumpers, p.17); KUKA KSS System Messages — message list (200/220 drives contactor, 310, p.29/34/55).
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