By Kent · Lock Depot Staff Writer

You are at a door you did not install

The frame is painted over, the strike has no markings, and the cutout matches nothing in the catalog. The job is Friday. Order the wrong strike and the frame gets cut or the job slips a week. That is what the SDC 45 Series is for: a field-selectable, multi-frame-application strike configured on site for more than one frame condition.

The SDC 45-A field-selectable strike is the base of the family. The SDC 45-AK adds a keeper open/closed status output. There is also a 45-4SU, same series and finish. The letters after the series number set the configuration, and I am not guessing at them from the parking lot. Send us the part string off the old strike, or a photo of the prep, and we will confirm which ships.

Picking an electric strike for an unknown frame type starts with the frame

Most bad strike orders start the same way. Somebody reads the lock brand off the lever, orders the strike that goes with that brand, and never measures the frame. Selection is driven by the frame and the latch, not the lock.

The frame decides the pocket. Hollow metal, aluminum, and wood prep differently, and the depth behind the face decides whether a strike body fits. The latch decides the keeper: a cylindrical latch, a mortise latch with a deadlatch plunger, and a rim exit device are three different loads.

Assuming ANSI prep is the most common failure. Plenty of openings were prepped before that was standard, or by whoever had a router. If you have not put a tape on it, you do not know. Our guide to choosing an electric strike for a metal frame walks it.

What field selectable buys you

A screwdriver instead of an RMA. A wrong guess at the desk becomes an adjustment at the door. On a retrofit where nobody knows the frame, that is the whole value.

Fail-safe or fail-secure

Fail-safe unlocks when power is lost: the keeper releases and the door opens from the outside. Fail-secure stays locked. Either way the door still opens from the inside by lever or push bar, because the strike never touches free egress from the secure side.

The SDC 15 Series shows it in both voltages:

• SDC 15-4F12U 12VDC Failsafe
• SDC 15-4F24U 24VDC Failsafe
• SDC 15-4S12U 12VDC Failsecure
• SDC 15-4S24U 24VDC Failsecure

Same series, same finish, four different behaviors.

The building decides, not the customer's preference. A fire-rated assembly, a stair, a required exit path, a door tied into the fire alarm: those conditions constrain what function is allowed, and the AHJ tells you which.

Fail-safe on a fire-rated door is a classic way to fail an inspection. A fire door has to stay latched when power is lost, and a strike that releases on power loss defeats that. Confirm the rating and the AHJ's requirement in writing before the part ships. I have watched an install get red-tagged over this: a second trip and a second strike.

Voltage

A 12VDC strike belongs on a 12VDC supply, a 24VDC strike on a 24VDC supply. Do not mix them. Long runs lose voltage, and a strike marginal at the panel chatters or fails to release at the door.

When you do not know the supply in the closet, the SDC 25-4U Dual Voltage Failsecure Electric Strike takes the decision off the table. Same part, either supply: the 45 Series hedge applied to power instead of frame.

Monitoring: why the 45-AK earns it

The 45-AK carries a keeper open/closed status output. Without it, your system knows only that it sent an unlock command, not whether the door secured. A keeper that got caught, a door held open by a box on the floor: none of that reaches the log, and the history reads clean while the opening sits unsecured.

With keeper status the log reflects reality. On a controlled perimeter, a server room, or anything auditable, order the monitored version.

Rim exit devices

If the door has a rim panic bar, you need a rim-mount strike: the SDC 30-4-12 12VDC Failsecure Rim Mount or the SDC 30-4-24 24VDC Failsecure Rim Mount. A rim device latches into a strike on the frame face, not a pocket cut in the frame. A mortise-frame strike on a rim panic bar is a wasted trip.

SDC electric strike comparison

Series	Application	Voltage	Fail mode	Keeper status
45-A	Field selectable, multi-frame	Confirm	Confirm	No
45-AK	Field selectable, multi-frame	Confirm	Confirm	Yes
45-4SU	Field selectable, multi-frame	Confirm	Confirm	No
15-4F12U	Frame mount	12VDC	Failsafe	No
15-4F24U	Frame mount	24VDC	Failsafe	No
15-4S12U	Frame mount	12VDC	Failsecure	No
15-4S24U	Frame mount	24VDC	Failsecure	No
25-4U	Frame mount	Dual voltage	Failsecure	No
30-4-12	Rim mount, rim exit device	12VDC	Failsecure	No
30-4-24	Rim mount, rim exit device	24VDC	Failsecure	No

Every cell comes off the product name. Where it says "Confirm," the name does not state it and I will not invent it. Call us with the opening. More of the line sits on the SDC hub.

The trap: preload

A strike will not release if the door is pushed against the keeper. That is preload, the most common "the strike is defective" call we get that is not the strike.

Three things cause it. A closer adjusted too tight holds the door into the frame. Wind on an exterior opening pushes it closed. Stack pressure in a stairwell or unbalanced HVAC does it quietly, all day. The keeper carries side load the solenoid cannot swing.

The fix is not a bigger strike. It is a strike rated for preload, or an adjustment to the door and closer so the latch is not loaded when closed. Replace it without addressing the load and the new one fails the same way.

What to confirm before you order

• Frame material and depth behind the face.
• Prep dimensions, measured.
• Latch type: cylindrical, mortise, or rim exit.
• Voltage at the opening and length of run.
• Fail-safe or fail-secure, per the AHJ and fire rating.
• Whether monitoring is in scope.

Then send us a photo of the frame prep with a tape in the shot. We will tell you which part string to order.

Common questions

Can I use one electric strike for an unknown frame type?

Yes: that is what the 45 Series field-selectable, multi-frame-application design is for. It is configured at the opening, not at the desk. You still confirm the latch type and the fail mode.

What is the difference between fail-safe and fail-secure?

Fail-safe unlocks when power is lost; fail-secure stays locked. Free egress from the inside is unaffected either way, because the lever or push bar retracts the latch mechanically. Which one you may use is set by the building and the AHJ.

Do I need 12VDC or 24VDC?

Match the strike to the supply already in the closet and account for voltage drop over the run. If you do not know what is there, the 25-4U is dual voltage.

Why would I pay more for the 45-AK?

Because it tells the access control system whether the keeper actually closed, not just that an unlock command went out. Where the audit trail matters, order the monitored version.

My electric strike buzzes but will not release. Is it bad?

Usually it is preload, not the strike. The door is being pushed into the frame by a closer, wind, or stack pressure, and the keeper carries side load the solenoid cannot overcome. Back off the closer first.

Which strike works with a rim exit device?

A rim-mount strike, the 30 Series in this line. A rim panic bar latches into a strike on the face of the frame, so a mortise-frame strike will not work. Confirm the device is rim before ordering.