FANUC External E-Stop Wiring: Dual-Channel Discipline, TBOP Jumpers, and Why SRVO-007 Returns After You Bypass It

You wired the external e-stop button into the FANUC operator panel, the cabinet powered up, and within seconds the alarm screen is full of SRVO-007 (external emergency stop) that will not clear with a reset. Or worse, the alarm comes and goes randomly while the cell tries to run. The instinct on a bench setup is to jumper the inputs, prove the robot works, and worry about wiring later. That instinct is exactly what produces a week of intermittent safety trips at Probot Systems’ customer sites every month.

This post is for integrators and machine builders wiring an external e-stop, fence, or safety relay into an R-30iA Mate, R-30iB, R-30iB Plus, or CRX-10iA cabinet. If you are at the design stage and have not cut wire yet, read this first.

How FANUC dual-channel safety inputs actually work

FANUC’s safety inputs (EES1/EES2 for external e-stop, FENCE1/FENCE2 for fence, EAS1/EAS2 for external auto stop, SVOFF1/SVOFF2 for servo off) are dual-channel monitored circuits. The controller polls both channels continuously and compares them. If one channel closes faster than the other, or one opens faster than the other, or one is stuck open while the other is closed for longer than the mismatch tolerance (typically 500ms), the controller reports a safety fault and locks the cabinet out.

This is not optional, and it is not the same as a single-channel input. A single wire jumper across EES1 alone leaves EES2 hanging, which the controller sees as a permanent mismatch.

The FANUC alarm code manual entry for SYST-045 captures one common confusion: “The mode selector is in AUTO and the TP ON/OFF switch is in the ON position. Remedy: Turn the TP ON/OFF switch to OFF. Press RESET.” That alarm is not e-stop wiring per se, but it shares the same operator panel terminal block (TBOP) and the same dual-channel discipline. Touching one wire on TBOP and forgetting the other generates similar symptoms.

Most common causes, in order of probability

1. Single-channel jumper on a dual-channel input. Number one root cause on bench setups and refurbished cells. EES1 is bridged, EES2 is left open, the cabinet locks out. The SRVO-007 External emergency stop thread describes this exact pattern.
2. Missing factory jumper kit on a re-purposed robot. When a cell is decommissioned and the robot moves to a new home, the OEM jumpers that ship with the cabinet often do not come with it. The Need help fixing my Fanuc 200IC thread suggests jumping the estop string as a starting diagnostic, but only as a temporary measure with both channels bridged.
3. External safety relay with a stuck or failing contact. Pilz, Sick, or Banner safety relays age. A force-guided contact that hangs in the open state will throw SRVO-007 every time. The Emg stop light flashing but no alarm thread is a textbook intermittent-relay symptom.
4. Loose terminal at a daisy-chain junction. Multiple e-stop buttons in series, one terminal block partially seated, intermittent loop. Visible by wiggling the wires while watching the safety signal screen.
5. Wrong terminal on the operator panel. TBOP-6, TBOP-7, CRMA93, and CR43A are different terminals on different controller generations. The I/O Auto Configuration thread mentions checking CR43A on the E-Stop board, which is the right terminal block on some R-30iB Mate variants but not on R-30iB Plus.

How to diagnose in under 10 minutes

Step 1. With cabinet locked out and powered down, open the operator panel side. Locate the safety terminal block (TBOP on R-30iB, CR43A on some Mate variants, CRMA93 on others). Pull the controller maintenance manual for your specific cabinet before touching any terminal.

Step 2. Meter continuity across each channel of the external e-stop loop. EES1 should be closed (continuity) when the button is released and open when pressed. EES2 should match exactly. Both should change state simultaneously when you press or release the button.

Step 3. If a safety relay is in the loop, watch the relay’s status indicators while operating the button. Pilz PNOZ and similar safety relays have channel-by-channel status LEDs. A relay whose output stays closed when the input opens is failed.

Step 4. Power the controller back up, go to MENU > 4 STATUS > Safety Signals, and watch the EES1 and EES2 (or the FENCE1/FENCE2 if that is the input in question) toggle as you press and release the e-stop. Both should change together. A safety input that flips alone, while the other stays put, is a wiring or relay fault.

Step 5. If both channels meter correctly and the alarm persists at power-up, suspect the operator panel board. The thread Errors SPOT-473 and SPOT-472 points to CRMA93 on the E-stop board as the critical electrical landing, and a damaged trace at the terminal will produce the same symptoms.

How to do it right

Re-purposed robot with no external safety hardware. Install the factory jumper kit. Both EES channels and both FENCE channels need their OEM jumpers in place, each as a separate piece of wire. Do not bend one wire into both terminals. The Teach mode for a CRX robot, with an open-fence thread covers a related case on CRX where the fence is intentionally bridged but using a safety device (SFDI) rather than a raw jumper.

Wiring a real e-stop button. Use a dual-contact NC + NC e-stop. EES1 to one contact pair, EES2 to the other. No shared wires anywhere in the loop. Same rule for door interlocks (use dual-contact safety switches), light curtains (use dual-channel safety relay outputs), and presence sensors.

With an external safety relay. Pilz, Sick, Schmersal, or Banner relays output dual contacts that map straight to FANUC’s dual channels. Connect each contact to its own EES channel. Keep the safety relay separately powered, and tie its reset button to a monitored loop you can verify with a meter.

Daisy-chain of multiple devices. Each device must have dual contacts in series. A six-device chain has two parallel series-strings, one per channel. Both strings must close together for the loop to be healthy.

Intermittent relay symptoms. Replace the relay. A safety relay with degraded contacts is a lost cause; it is also the cheapest part in the cabinet next to the wire itself.

When to call a specialist

If you have verified both channels close, the wiring matches the controller maintenance manual, and SRVO-007 still locks the cabinet at power-up, the next suspect is the operator panel or E-stop board itself. Swapping one requires a controlled start and a panel calibration, and is not bench work.

If your cell is being commissioned for production and the safety wiring is going to be audited, the wiring that “works” is not the same as the wiring an auditor will accept. Document the e-stop loop, every junction, and the safety relay’s parameter set before the cell ships.

contact us for an external e-stop integration or audit, or set up a maintenance preventive contract that includes an annual safety-circuit verification.

Related errors to check

• SRVO-007 External emergency stop: the direct alarm for an EES channel break, see this post for the wiring side.
• SRVO-218 Servo disconnect (external e-stop on R-30iA Mate): same family of fault, different alarm number on Mate cabinets.
• SRVO-213 Safety Signal Mismatch: the channel-mismatch warning that fires when EES1 and EES2 disagree but both have some signal. If you see this first, the dual-channel tolerance is already telling you about a half-wired loop.
• SRVO-378 DCS chain fault: on CRX-10iA, the DCS safety chain is a related but separate set of inputs. The Fanuc CRX-10iA/L SVRO-378 error thread covers the CRX side.
• SYST-045 TP enabled in AUTO mode: shares the operator panel terminal block, common when TBOP wiring is partially in.

Probot Systems is a FANUC integrator based in Lévis, Quebec. We commission palletizers and provide preventive maintenance across Canada and the US, and external e-stop wiring is one of the first things we audit on a new install. If you have a new cell that needs the safety wiring reviewed before production, that is a contact us conversation.