Emergency Stop & Safety Relay Wiring Diagram — the Complete Circuit, Terminal by Terminal

How Do an E-Stop Button and a Safety Relay Work Together?

The red button does less than most people assume. Mechanically it is just a pair of switch contacts that open when struck; it cannot check its own wiring, supervise a restart, or notice that the contactor it was supposed to drop has welded shut. All of that judgement lives in the safety relay — the button reports, the relay decides. This division of labour is why every serious emergency stop circuit has two parts, and why the wiring between them follows rules rather than habits.

It also explains how an e-stop differs from a light curtain in the same cabinet. A curtain feeds the relay active, self-tested signals (its OSSD pair drives the inputs high and pulses them); an e-stop feeds it passive contacts that simply open. Evaluation relays handle both — on the DAIDISIKE DA31 the same S1/S2 channel pair accepts either input style, which is why one relay model ends up supervising both the curtain on the feed opening and the mushroom button beside it. If the curtain side is your question, the light curtain safety relay wiring guide walks that variant of the loop; this page owns the button side.

Inside the Button: Why Two NC Contacts?

Open any properly specified e-stop station and you find not one switch but two: a pair of normally-closed, positive-opening contact blocks on one plunger. Positive opening (the ISO 13850 requirement) means the actuator mechanically forces the contacts apart — a spring cannot fail closed. Pressing the head opens both contacts at once; twisting or key-releasing the head closes them again but, in a correctly wired circuit, does not restart anything by itself.

The duplication is not ceremony. A single contact on a single wire has no way to reveal its own failure: short that wire to supply and the relay reads "not pressed" forever. With two contacts on two separate conductors feeding two relay channels, every single fault — one broken core, one short, one welded block — shows up as a disagreement between channels, and the relay refuses to run. Route the two conductors separately where practical; two channels in one crushed cable is one fault, not two.

The Complete Circuit: E-Stop → Safety Relay → Contactors

Here is the whole loop on published DA31 terminals. Supply first: 24 VDC to the relay's (+) and (0V) terminals, with a 5 A gL/gG fuse in the positive leg. Inputs next: button channel 1 into S1, channel 2 into S2. Outputs: the DA31 carries three force-guided NO safety contacts — 13/14, 23/24, 33/34 — and the classic arrangement puts contactor K1's coil through 13/14 and K2's coil through 23/24, leaving 33/34 spare. The two contactors' main contacts sit in series in the motor circuit, so either one alone can break the power. The 41/42 normally-closed auxiliary is signalling only — a stop lamp, a PLC status bit — never part of the safety path.

Press the button and both channels open; the relay drops all three NO contacts in under 30 ms, both contactor coils lose power, and the series main contacts open the motor circuit twice over. Contact ratings on the published sheet: AC-1 6 A / 250 VAC per contact, total load capped, minimum load 10 mA / 5 V — small enough that the 41/42 status circuit stays reliable.

Wiring Multiple E-Stop Buttons in One Circuit

A line with several operator stations chains its buttons in series: every station's channel-1 contact in one loop into S1, every channel-2 contact in a second loop into S2, in the same station order. Any button pressed opens both loops and stops the whole line — which is exactly the intent. The trade-offs are physical and diagnostic: long series loops accumulate line resistance (check it against the relay's input specification before committing a 60-metre run), and a series loop cannot tell the maintenance team which station tripped. Long lines therefore add a per-zone status contact into the PLC, or move to individually monitored inputs, purely for fault location — the safety function itself stays the simple series pair.

Reset Modes: Manual vs Automatic at SR/SRC

On the DA31 the choice is one terminal pair: SR–SRC open with a momentary button in the loop = manual reset; SR–SRC shorted = automatic reset. For emergency stops the default is manual, and the logic is human, not electrical: the person who twists the button back out has not necessarily checked that the jam is cleared or that a colleague is out of the machine. Manual reset inserts exactly one deliberate act — verify, then press — between "button released" and "machine live". Automatic reset has legitimate duty elsewhere (guarded zones nobody can stand inside), but on an e-stop circuit it must be justified in the risk assessment, not defaulted into.

EDM Feedback: Making the Circuit Notice a Welded Contactor

The stop element of this whole circuit is a pair of contactors — and contactor contacts weld. EDM (external device monitoring) is the circuit's answer: wire K1's and K2's normally-closed auxiliary contacts in series back into the relay's monitoring input. When both contactors have genuinely dropped out, both auxiliaries are closed and the loop is complete; a welded main contact holds its auxiliary open, the loop stays broken, and the relay refuses the next reset. The failure gets discovered at restart time, standing at the panel — not at injury time.

One honesty note that matters when ordering: the DA31's EDM terminal detail is not published in the current public factory sheet — the feedback principle above is standard, but request the DA31 manual and wire that loop from the factory drawing, not from this or any other web page. The EDM feedback wiring examples guide covers the loop's diagnostics in depth.

Connecting Brand Safety Relays: the Universal Checkpoints

Whether the relay on your DIN rail is a Pilz PNOZ, an Allen-Bradley Guardmaster, a Siemens SIRIUS 3SK or a DAIDISIKE DA31, the circuit you just read does not change — dual-channel input, supervised reset, force-guided outputs, feedback loop. What changes is the label printed next to each terminal, and that is where cross-brand rewiring goes wrong. Five checkpoints cover it:

• Supply naming: A1/A2 on most European relays equals the DA31's (+)/(0V) — confirm voltage and polarity, not just position.
• Channel naming: S11–S12 and S21–S22 pairs equal S1/S2 — some brands source the channel from one terminal and return it to another, so trace the loop, not the number.
• Reset naming: S33–S34, Y1–Y2 or X1–X2 all play the SR/SRC role; verify whether the brand expects a monitored (rising-edge) or simple reset button.
• Feedback/EDM naming: often Y1–Y2 or an S34 loop — never assume it is optional just because the demo wiring omitted it.
• Coil ratings: the force-guided outputs are near-universally numbered 13/14, 23/24, 33/34, 41/42 — but contact ratings differ, so re-check your contactor coils against the new relay's sheet.

Function-level comparisons of the DA31 against Pilz PNOZ, Allen-Bradley Guardmaster and Siemens SIRIUS 3SK relays live on their own pages, including when a configurable controller is the better answer than any hardwired relay.

The Six E-Stop Wiring Mistakes We Actually See

• Single-channel "economy" wiring — one NC contact, one wire. Saves a conductor, deletes the fault detection. The second channel is the safety function.
• Two contacts merged onto one conductor — electrically one channel wearing two connectors; a single short defeats both.
• A maintained switch on the reset input — taped-down or selector-style reset turns every cleared fault into an unattended restart.
• No EDM with contactor stop elements — the one failure mode the circuit exists to catch goes unwatched.
• Missing or shared fusing — the 5 A gL/gG belongs in this circuit's own supply leg, not borrowed from a neighbour that may be sized for ten times the current.
• Using 41/42 as a safety contact — it is a status auxiliary; the safety path runs through the force-guided NO contacts only.

Commissioning: the Test That Makes It Real

An e-stop circuit is commissioned by proving it fails correctly, in this order: verify wiring and polarity dead; power up and confirm the relay arms only after a deliberate reset; press every station in turn and watch both contactors drop each time; confirm the twist-release alone does not restart anything; short K1's auxiliary to simulate a welded contactor and confirm the reset is refused; then log the results in the machine's safety file with the date and your name. Repeat after any work on the buttons, the relay, or the contactors.

For the light-curtain leg of the same cabinet, the complete light curtain wiring diagram library (27 diagrams + free PDF handbook) is the companion to this page.