An electromagnetic holding lock (maglock) clamps a steel armature plate to a frame-mounted coil only while current flows, so it is fundamentally a fail-safe device; a solenoid bolt uses an electromagnetic coil to drive a mechanical bolt into a keep, and is typically wired as fail-secure so the bolt stays home on power loss [S3][S4]. The two converge on "magnetic action" but diverge on holding force versus latching geometry, which is the line that drives every other spec on the data sheet.
On machinery guards, ISO 14119 (Type-B2 standard) treats them as separate categories inside "electrical guard locking": purely electromagnetic devices hold the guard by magnetic force only, while electromagnetic/mechanical devices combine a solenoid-released latch with a mechanical catch, the latter being the typical solenoid-bolt pattern [S2]. For OEM builders, the choice therefore starts with the safety function, not the catalogue page.
How Each Device Actually Holds the Door
An electromagnetic holding lock has two main parts, an electromagnet fixed to the frame and an armature plate on the door leaf; apply DC and the magnetic field clamps the plate against the magnet, remove power and the field collapses, releasing the door immediately [S4]. A solenoid bolt is a single assembly containing a wound coil, a moving plunger, and a deadbolt or pin; the coil, when energised, pulls the plunger and drives the bolt into a keep in the frame, where it stays latched either by spring pressure (fail-secure) or by sustained current (fail-safe) [S7][S8]. Holding force on a maglock is therefore proportional to coil area and ampere-turns across the full armature face, whereas holding force on a solenoid bolt is set by the bolt's mechanical geometry and the spring or keeper design, not the contact area between door and frame.
The "solenoid" inside a solenoid bolt is the same electromagnetic device class used in industrial actuators, and the same continuous-duty derating rules apply: small cabinet-style strike solenoids are commonly rated for energisation of only a few seconds before overheating, which is why a true guard-locking solenoid bolt is built as a continuous-duty, frame-mounted unit with a separate power supply sized for the duty cycle [S5].
Fail-Safe vs Fail-Secure: The Real Decision Axis
On a maglock, loss of power releases the door, so the device is fail-safe by construction and is the typical pick for emergency exits, fire doors, and any door that must allow free egress when the building loses power [S3][S4]. On a solenoid bolt, the default is fail-secure: the bolt stays engaged when power is removed, which is the desired behaviour for high-security rooms, vaults, and server halls where the priority is keeping assets contained even during a black-out [S1][S3].
Both functions are available in each technology with extra hardware: bistable (or "low-consumption") solenoid bolts change state on a short pulse and then hold that state without continuous current, which is the option to specify when the duty cycle keeps the door locked for hours and continuous power is not practical [S1]. For maglocks, a battery-backed PSU is the standard way to convert a fail-safe device into a controlled-egress lock that still meets life-safety codes, since the lock itself cannot be re-engineered into fail-secure behaviour without a mechanical catch [S3].
Where ISO 14119 Fits, and Why It Pushes You Toward Solenoid Bolts on Guards
ISO 14119, the Type-B2 standard that defines interlocking and guard-locking devices for movable guards, separates "electrical guard locking" into electromagnetic, electromechanical, and electrical sub-types, and the standard expects the locking function to be either mechanically held (so power loss does not release the guard while a hazard exists) or actively monitored with a performance level consistent with the risk assessment under ISO 13849-1 [S2]. In practice this is the reason that machinery-guard specifications almost always end up on a solenoid-bolt or spring-locked guard switch, not a bare maglock: a plain electromagnetic holding lock cannot satisfy the "lock held by mechanical means" reading of ISO 14119 on its own, because removing power opens the guard at exactly the wrong moment.
The performance-level language in ISO 14119 is the part engineers trip over: PL d or PL e under ISO 13849-1 is the typical target for hazardous-motion guards, and that target drives component choices (dual-channel monitoring, coded actuators, force-monitored solenoids) that the catalogue line "solenoid bolt" alone does not guarantee, so the spec must call out the achieved PL and the category, not just the technology [S2]. For comparison, building-door maglocks are commonly specced to UL 294 or IEC 60839-11-x for access control, a different compliance regime, and mixing the two is a common audit finding on integrated facilities.
Decision Matrix: Maglock vs Solenoid Bolt on Four Criteria
On holding force per unit footprint, maglocks win: a 300 kg (about 660 lbf) maglock is a single commodity SKU, while an equivalent solenoid bolt reaches comparable retention through the bolt's shear geometry rather than distributed magnetic face pressure [S4]. On fail-state behaviour, the maglock is fail-safe, the solenoid bolt is fail-secure, and that single line typically decides the application before any other spec is read [S1][S3]. On continuous power draw, maglocks draw current for as long as the door is closed (typical 300 mA to 500 mA at 12/24 V DC for an office-grade unit), while bistable solenoid bolts draw current only during the transition pulse, dropping to zero holding power once latched [S1]. On suitability for a hazardous-motion guard under ISO 14119, the solenoid bolt (in a PL-rated guard switch form factor) is the appropriate pick, and the maglock is generally rejected because it cannot demonstrate mechanical latching on power loss [S2].
If the application is an emergency exit on a stairwell door, choose a maglock with a fire-alarm release contact and a battery-backed PSU; if the application is a robotic-cell guard door requiring PL d under ISO 13849-1, choose a solenoid-bolt guard switch with coded actuator and dual-channel monitoring; if the application is a multi-cabinet storage rack where the door must stay latched for days without heat or power, a bistable solenoid bolt is the only one of the three that meets the energy budget [S1][S2][S3].
Limits, Failure Modes, and Engineering Gotchas
Three concrete failure modes drive the "maglock will not do" list. First, maglocks leave no mechanical latching, so any control-circuit fault, power dip, or intentional defeat releases the door, which is the reason UL and IEC access-control standards require a release device (request-to-exit, fire alarm contact) on every maglocked egress door [S3][S4]. Second, solenoid-bolt strikes of the cabinet-latch form factor are usually rated for energisation of a few seconds only; running them continuously will burn the coil, an issue that the engineering community has documented on the Digi-Key TechForum as the reason a 40-lock cabinet array was redesigned with a bistable mechanism [S5]. Third, both technologies are sensitive to misalignment: a maglock's holding force drops sharply as the armature-to-magnet air gap grows, and a solenoid bolt's plunger can jam or fail to seat if the door sags more than a few millimetres, so the install spec must include a maximum gap tolerance rather than just a holding-force number.
Integration-wise, maglocks and solenoid bolts are not protocol-agnostic: door-position and bolt-state feedback need to land on the access-control panel or the safety relay, and a maglock typically reports only "power applied" via a bond-status contact, while a solenoid bolt in a guard switch reports "bolt home" and "actuator present" as discrete inputs, which is what ISO 14119's monitoring and verification clause actually expects [S2][S4].
Component Selection, Duty Cycle, and What to Put on the Data Sheet
For a solenoid bolt on a guard, the spec sheet must carry: achieved PL and category under ISO 13849-1, holding force in N, coded vs uncoded actuator level (low, high, unique per ISO 14119), continuous-duty current at the rated voltage, and the maximum door-mass / misalignment the bolt can tolerate before the keeper jams [S2]. For a maglock on a building door, the spec sheet must carry: holding force in kgf or lbf, voltage (12 V DC or 24 V DC being the two commodity rails), current draw at full holding, monitored bond-status contact rating, and the residual magnetism figure, which is the small holding force that remains after power removal and which dictates whether a separate door operator or anti-residual-magnet pin is needed [S4].
For a bistable bolt in a low-power enclosure, the spec sheet must carry: pulse energy (mC or mAh equivalent), latching force in both directions, mechanical life in cycles, and the explicit statement that the device is not a guard-locking device under ISO 14119, since bistable bolts are typically used in cabinet and enclosure security rather than in hazardous-motion guarding [S1]. Industrial buyers comparing across the three should also note the supply-chain reality that a holding-electromagnet on a holding furnace door or a solenoid coil on a process valve shares the same continuous-duty winding rules as a guard-locking solenoid bolt, so the same vendor audit (winding class, insulation class, duty cycle) applies when qualifying a new supplier.
Trackable Signals to Watch
Three concrete signals will move this specification area in the next two quarters: the publication of the next ISO 14119 amendment (any tightening of the mechanical-latching language will push more guard-door specs toward spring-locked solenoid bolts), the rollout of Ethernet-APL access-control panels (which changes how a maglock's bond-status contact is wired, since digital communications replace discrete I/O on many new builds), and the wider availability of PL d / PL e solenoid-bolt guard switches at sub-300 euro list price, which historically has been the cost gate that kept designers on mechanical-only guard switches. For a deeper dive into how solenoids are specced in adjacent industrial subsystems, see the engineering note on locking assembly and the reference page on locking nut designs, both of which use the same force-versus-duty trade-off as a guard-locking solenoid bolt. [S2]
See also our earlier report, UPE vs UPN channels: parallel versus tapered flange decision reference.