Electric Strike and Maglock Power, Inrush, and Standby Budget

ScopeBecause standby is a different problem. Three separate failures hide behind one supply. STEADY CURRENT is the easy one and the one everyone computes: 14 maglocks at 0.45 A holding is 6.3 A, and a 12 A supply covers it comfortably. INRUSH is the second. A strike or magnet energizing draws several times its holding current for a few tens of milliseconds, so those same 14 locks at 1.5 A of inrush momentarily demand 21 A. A fail-safe maglock releases by LOSING power, so the alarm itself costs nothing; the inrush arrives when the alarm resets and every lock re-energizes at once, and a supply sized on holding current alone sags then and leaves doors hanging open that should have relocked. STANDBY is the third and the most commonly wrong: standby hours at the quiescent load plus the alarm period at the alarm load (zero for fail-safe locks, which are released). 6.3 A for 24 hours is 151.2 Ah, and derating to 80% for battery age and temperature makes it 189 Ah: sixteen of the 12 Ah batteries that fit in a typical enclosure. That is an external battery cabinet or a shorter standby requirement, and it is a design decision rather than something to discover at commissioning. Sizing a battery to nameplate ignores that a battery at end of life and at low temperature delivers considerably less, which is why the derate exists and why battery replacement is scheduled rather than failure-driven. The quiet fourth failure is voltage drop: a magnet at the end of a long small-gauge run sees less than its rated voltage and holds with less than its rated force, and the symptom reads as a lock problem when it is a wiring problem -- that calculation is the low-voltage DC drop calculator and is not repeated here. A load and standby calculation from device data the user supplies. Device currents, and especially inrush, must come from the manufacturer's specifications; nameplate holding current alone will undersize a supply. It does not address the fire alarm interface requirements, which govern both the standby duration and the manner in which locks must release on alarm and which are life-safety requirements rather than design choices. It does not evaluate egress: electrically locked egress doors are heavily constrained by the building and fire codes, and a lock that fails secure on a door required for egress is a violation regardless of its power budget. The adopted building and fire codes, the device manufacturers' specifications, and the AHJ govern.

Formula or tablesteady current = device count x holding current; peak inrush = device count x inrush current; amp-hours = steady current x standby hours + alarm current x alarm minutes / 60; battery required = amp-hours / derate factor.

Source and editionThe standby amp-hour and inrush sizing method by name, with the fire alarm and egress interface requirements named as governing the standby duration and the release behaviour. Device currents, and especially inrush, come from the manufacturer's specifications.

Free accessMultiplication on device data the user reads off the manufacturer's specification; no product table is reproduced.

What governsEstimate. AHJ and licensed professional govern.

API field namesdevice_count, holding_current_a, inrush_current_a, standby_hours, battery_derate, supply_rating_a, installed_battery_ah, steady_current_a, peak_inrush_a, amp_hours_required, amp_hours_after_derate, batteries_needed

• Inrush is not holding current several times it, briefly, and simultaneously across every fail-safe lock when the alarm resets and they re-energizedevice manufacturer data
• Standby duration is often set by the alarm interface not by the access control system's own needsadopted fire code
• Derate the battery age and low temperature deliver materially less than nameplatebattery manufacturer data