Why Is This Door Lock Burning Up?

AC or DC?

Failsafe or Failsecure?

I'm no lock specialist but sounds like a *****y lock if you've had to regularly change several already. Have you checked how much power it draws? Is there a mechanical way to short circuit it? Are all of them the same batch? I'd ask the vendor.

First, I would be surprised if the manufacturer did not have some feedback on that.

It looks like heat damage, I would guess that it stays energized for long periods of time ( and that is just a guess since I am not an access control guy, and have never even heard of Cisa before). Either it is not rated for such long durations of operation, or other parts of the door are supposed to be acting as a heat sink and are not.

If it is just doing that while idle, and the power supply is the proper voltage it would seem like a manufacturing defect.

Will be curious to see what the final resolution is, if you figure it out.

Try installing a Diode at the door strike. See if it burns out the Diode before the strike atleast...but it sounds like you have a short somewhere or it's getting more power than it should and burning out. 

Cisa is owned by Allegion, and is an well established brand outside the US.

Continually energized strike (fail safe) not designed to be so?

24V strike driven by 12V, therefore pulling double current?

Since it's so intermittent, sounds like the door lock power is getting stuck on and keeping the lock energized for long periods of time.  Otherwise in order to do that much heat damage in a short period of time the lock would need to see very high current for a short period of time...which is unlikely assuming the door lock power is fused or uses a PTC device for overcurrent mitigation.

On the really weird side, we would always switch the (+) leg on a DC lock since many power supplies have the negative rail at ground (more or less).  I have occasionally seen strange things like this happen if you are keeping the (+) always on and switching the (-) side.  If the lock wiring or sometimes the case on a metal door shorted to ground, it could keep the lock energized.

Here is what I would try:

1.) Measure the current for the lock and make sure it is within the manufacturer's stated specs.  Since you stated that the power supply is 12 VDC, 5 A, and I'm guessing the lock current is less than 500 ma, if the 2 REX normal press switch for that door is getting stuck in the on position it could definitely cause this.

2.) Make sure the power leg for that lock has a suitable fuse in line from the 12 VDC, 5 A power supply.  If so and the lock still burns up, most likely cause is voltage sustained longer than just a few seconds at a time.  Sometimes this can also be determined if the lock handle is warm to the touch.  

3.) Check with the Allegion/Cisa to see if they have a bad batch of lock solenoids, etc.  Have seen this happen with Schlage in years past.

Please let us know what you find out in the end.  Good luck!

Im having a difficult time trying to figure out what I am looking at. Which of the locks in your link refereeing to? Your pic looks like a blow torch was taken to it.  

Cisa is a well known product in Europe. I believe it is HQed in Italy.