EUCHNER's MGB2-L1-MLI family combines an ISO 13850 illuminated e-stop, up to three illuminated pushbuttons, and a Category 4 / PL e guard lock in one IP65 housing that delivers 2000 N of locking force and runs on a closed-circuit current principle [S1]. The locking module connects to a separate MBM bus module, with the 166693 variant adding an OM.R 2-channel key-operated rotary switch for mode selection [S1].
Older MGB-L1 (closed-circuit) and MGB-L2 (open-circuit, solenoid-force) modules remain in catalogue use, with PROFINET/PROFIsafe versions (MGB-L1HEB-PNA-L-124575) carrying 5 illuminated pushbuttons, 1 non-illuminated pushbutton, and an integrated RT switch plus escape release [S3]. On the Allen-Bradley side, the Guardmaster 442G-MAB series matches the same architecture: e-stop, enabling switch, guard and bolt position, and guard locking in a single housing with rated insulation voltage Ui 75 V and impulse withstand Uimp 0.5 kV [S9].
Locking principle: spring (closed-circuit) vs solenoid (open-circuit)
The closed-circuit (MGB2-L1, MGB-L1) principle holds the door locked by spring force and releases it only when voltage is applied to the solenoid, so a power loss or cable break leaves the door locked, the safe state for personnel protection [S1][S3]. The open-circuit (MGB-L2) principle instead locks by solenoid force and releases on power loss, which is the correct choice for process protection where a stopped machine must allow operator escape but still resist unauthorized opening during a run [S6][S7].
Locking force FZh on both MGB2-L1 and MGB-L1HEB is rated 2000 N, with mechanical life of 1 x 10⁶ cycles total and 0.1 x 10⁶ to 0.2 x 10⁶ cycles when the module itself is used as the door stop with 1-2 Joule impact energy [S1][S3]. Switching frequency is capped at 0.25 Hz on the MGB family, matching the 1 Hz maximum specified for the 442G-MAB and limiting cycle counts on high-traffic cells [S9].
Safety ratings and switch-off timing
Control of guard locking on the MGB2-L1-MLI reaches PL e, SIL 3, Category 4, with PFHD 2.62 x 10⁻⁹ and a 20-year mission time per EN ISO 13849-1 and EN IEC 62061 [S1]. The PROFINET MGB-L1HEB-PNA-L reports PFHD 4.07 x 10⁻⁸ at 99% diagnostic coverage for combined guard-locking and guard-position monitoring [S3].
Switch-off times diverge by signal path. MGB-L1HEB-PNA-L specifies 250 ms for emergency stop and enabling switch and 550 ms for door position, bolt position, and guard locking [S3]. The Allen-Bradley 442G-MABE1 / 442G-MAB B-U narrows those numbers: 100 ms for e-stop and enabling switch, 250 ms for guard position, bolt position, and guard locking [S9]. The e-stop response of the 442G is therefore the tightest of the three families, a meaningful delta for short-cycle cells where stop-time budget drives the safety distance calculation.
Electrical ratings and environment
All three families share the same 75 V Ui / 0.5 kV Uimp / Class III / Pollution Degree 3 envelope from EN 60947-1, with 24 V DC UB tolerating -15% to +10% on the PROFINET X1/X2 supplies [S3]. Current draw caps at 350 mA on MGB2-L1-MLI, 500 mA on MGB-L1HEB-PNA-L, with a 4000 mA maximum feed-in allowed at the connection block [S1][S3].
Ambient temperature windows are -30 to 55 °C on MGB2-L1-MLI and -20 to 55 °C on MGB-L1HEB-PNA-L, both at UB = 24 V DC, with storage to 70 °C [S1][S3]. IP65 in the closed state (with all submodules and cables fitted) is the rule for MGB2; MGB-L1HEB-PNA-L drops to IP54 [S1][S3]. The 442G-MAB family reaches the same IP65 / NEMA 13 equivalent for washdown cells [S9].
Connectivity and pushbutton options
Pushbutton count and labelling are the biggest model-to-model differentiator inside each family. MGB2-L1-MLI base configurations give 3 illuminated pushbuttons with 5-color lens sets (color selectable at install) [S2]. MGB-L1HEB-PNA-L lifts that to 5 illuminated plus 1 non-illuminated pushbutton, ships with adhesive labels (RESET, START, MAINTENANCE, REQUEST ACCESS, CYCLE STOP / UNLOCK, etc.), and includes a 12-pin RC12 terminal plug for an enabling switch [S3]. The 166693 MGB2 variant layers an OM.R 2-channel key switch on top of the 3 pushbuttons and e-stop, aimed at run / setup / service mode selection [S1].
Bus-side, the EUCHNER PROFINET module uses 7/8" power plus M12 D-coded Ethernet per IEC 61076-2-101, runs PROFINET RT (IEC 61158 type 10) with PROFIsafe (IEC 61784-3-3) for the safety protocol, and has an internal RT switch so cells can be daisy-chained point-to-point without an external switch [S3]. MGB2-L1-MLI uses a modular MBM bus module that can be swapped to match the fieldbus, which is the practical way to standardize one mechanical subassembly across PROFINET, EtherCAT, EtherNet/IP, or PROFIBUS cells [S1].
Selection criteria: matching module to risk and topology
For personnel protection on a cell where a stop must hold even on loss of power, pick a closed-circuit L1 (spring-force) module; for process protection where a stop must release on power loss, pick an open-circuit L2 (solenoid-force) module [S1][S6]. Both choices still need to hit the same PL e / SIL 3 target on guard locking, and both need an e-stop and at least one pushbutton if the operator must acknowledge or request access from the door [S1][S2][S3].
Beyond the locking principle, four practical filters narrow the catalogue. (1) Bus protocol: PROFINET/PROFIsafe users go MGB2-MLI + MBM or MGB-L1HEB-PNA; EtherNet/IP or simpler hard-wired users go MGB-L1-ARA/MGB-L2-ARA with M12 or cable entry [S1][S3][S5][S6]. (2) Pushbutton count: 1-2 for minimal request/reset, 3-5 for full request/reset/start/maintenance/mode-select [S2][S3][S5]. (3) Switch-off time: 100 ms e-stop on 442G is the tightest, 250 ms on MGB, with the longer guard/bolt times on both dictating the safety distance math [S3][S9]. (4) Enclosure: IP65 for washdown, IP54 for dry cells, and a die-cast zinc / glass-filled plastic housing if the door doubles as the door stop and will see mechanical impact energy above 1 Joule [S1][S3][S9].
Failure modes, maintenance, and what the e-stop hardware still does
The e-stop on every MGB / MGB2 / 442G module is built per ISO 13850, mechanically latching, and typically supplied as a 30 mm or 40 mm mushroom head with separate yellow guards that accept up to 20 padlocks for lockout-tagout, a common 30 mm guard detail shared across the 442G and equivalent EUCHNER hardware [S4]. Reset is always intentional, never automatic, and the e-stop signal is wired into the safety logic separately from the guard-lock signal so a single e-stop press will not on its release leave the door locked (on closed-circuit systems) or released (on open-circuit systems) without the safety controller's decision.
Two failure modes the catalogue ratings do not paper over. First, the e-stop and the guard locking share the same housing but are two independent safety functions, so a module that lists "Category 4 / PL e for the evaluation of all safety functions" still requires the downstream safety controller to evaluate them as separate signals, and the system's overall PL is set by the worst of those channels [S1]. Second, the 550 ms switch-off on door/bolt/lock paths of the MGB PROFINET module is longer than the 100 ms e-stop path, and that delta flows directly into the safety distance formula: a higher-response e-stop with a slower guard-lock monitor still needs the slower number carried into the stop-time calculation [S3][S9].
What to track next
Two signals will move this category through 2026: CIP Safety on PROFINET (CIP Safety is more common on EtherNet/IP but is being layered onto PROFINET profiles) and the MGB2 modular line taking share from legacy MGB-L1 in cells that need a swap-in bus module rather than a new mechanical subassembly [S1]. Watch also for any MGB2 variants that compress the 550 ms door/bolt switch-off toward the 100 ms e-stop number, which would directly reduce the safety distance and free up floor space in compact cells [S1][S3].
Detailed specification references: locking assembly, emergency stop, and emergency stop button.
This topic is covered further in Cylindrical vs Conical Ladle Shells: Heat Loss and Pouring Control in 2026.