Will this old security system kill me?
April 8, 2020 2:38 PM   Subscribe

Photos here. We just bought and moved into a house built in 1970. I want to remove the obsolete security system control box from my coat closet. Can i just start cutting wires? Prior owner doesn’t know anything about it and there’s no alarm company info on it.
posted by Talia Devane to Home & Garden (18 answers total) 1 user marked this as a favorite
I wouldn't start cutting wires until you've established whether there is mains voltage in there. You're probably in the USA so it's likely to be 140 volts, or 240 if you're in the UK; either can hurt/kill you. Do you have a live wire tester? The red and the black wires at lower right are most likely the power connection, and the rest most likely go to sensors and alarms.
posted by anadem at 2:56 PM on April 8, 2020 [2 favorites]

love the scorch marks on the wiring diagram.

one of those sets of wires is a live 120V feed that goes into a transformer and then into a battery which is both. backup and I guess some sort of basic power supply. You need to figure out which wires those are. This is eventually connect to some breaker in your main electrical panel so you need to turn that off, disconnect the mains connection to the box and properly cap off those wires. But those should be the only dangerous wires, the rest you can probably just cut. At least that's what that very basic wiring diagram seems to indicate.

This also seems to be wired into your phone system - I don't know exactly what to do but those wires need to be capped off somehow and shouldn't be left loose in a metal box.
posted by GuyZero at 2:56 PM on April 8, 2020 [2 favorites]

Is it even still active? The backup battery is missing (the red and black wires in the lower right of the first pic) and there's no mains transformer that I can see. If there is one, just pull the power cord and remove the box, all it contents and the wiring with as much violence as you desire to apply.
posted by Stoneshop at 2:58 PM on April 8, 2020 [3 favorites]

Also, just for fu, the huge. metal piece in the middle of the top photo is a heatsink connected to a LM317T which is apparently a voltage regulator and based on the placement of the scorch mark on the wiring diagram and the discolouration above it, it gets really really hot! Like unsafely hot! So yeah even if you don't remove this completely, find and disconnect the main power wires for sure.
posted by GuyZero at 3:00 PM on April 8, 2020 [1 favorite]

If I'm reading the diagram right, there's an 18V supply coming in to the top two contacts of the vertical strip on the left, from a transformer. Following the brown wire from there should take you to the transformer (which I presume is one of the boxes at the bottom). I'd expect to see a mains input into that transformer, which you might be able to trace back to a breaker.
posted by pipeski at 3:27 PM on April 8, 2020 [2 favorites]

I assume you unplugged the white extension cord that's powering it?

It has the ability to interrupt a phone call (disconnect your home phones) so it can call out. If you just chop those wires, your phone jacks will probably all be dead. If you care about that, have someone check it out.
posted by fritley at 3:35 PM on April 8, 2020 [3 favorites]

The conduit in the lower left rear probably contains the 120V wires for this system. You'll want to make sure that a) there is no power on those conductors currently before you go messing with the system and b) they can't be energized in the future if they aren't safely contained in a box.

If your electrical is all via conduit then you should be able to pull those wires out of the conduit completely. It would then be safe to cap off that conduit and just leave it there if you don't want to remove it. Other wise you can get a shallow handy box to contain the end of the wires. Put marrettes on the ends of the wires and install an appropriate cover.
posted by Mitheral at 5:57 PM on April 8, 2020 [1 favorite]

Best answer: There is mains voltage in there. Potentially.

The big cube at the bottom with the black wires coming off it, black wires with the red crimp terminals, hooked to screw terminals, that's the power transformer. It takes 120V in.

This transformer is supposed to be installed externally and is supposed to be screwed into a standard outlet. You can see the retention screw tab on the opposite side from the terminals. It would look something like this, new.

It looks like some doofus has wired this inside the panel with a cord and an old "make-your-own-cord" style IDC end. It looks to me like the transformer is already unplugged, as the 120V prongs are visible. It is very important that you carefully follow any cord coming out of the white "make-your-own-cord" to whereever it is plugged in, somewhere outside the can. Unplug it. It's possible that this goes into conduit, possibly somewhere where you can't find it. Better pictures might help clarify.

Once the transformer is unplugged, the unit is "safe" as the battery has been removed (black and white wires in the lower right corner). You MUST make sure the AC power cord is de-energized before it is safe to demolish, however, otherwise there is still "power inside the can."

Unscrew the black cable with the red crimp terminals from the screw terminals on the transformer. This should allow you to remove the transformer from the enclosure. Most other wires appear to be thin, which implies low voltage, which everything SHOULD be, but sometimes dumb things are done. The zone wires are connected to the twelve screw terminals at the bottom. It is safe to loosen each screw, one at a time, remove the wires on the terminal, and cut them back as far as you can within the can. This will help increase visibility into what is going on. There is no risk there. In theory you should also be able to remove everything from the lefthand terminal strip, but there's more risk because there are relay contacts and you never know if someone ran line voltage for a klaxon or something dumb.

There are some additional modules attached that aren't entirely obvious to me as to what they are, but appear to be low voltage stuff.
posted by jgreco at 6:13 PM on April 8, 2020 [3 favorites]

Best answer: Mine is slightly more modern than yours, though not by much - the transformer looks identical. Additional to other points, if you feel that one day in the future you might want to add a security system back, then the house wiring from this might be reusable by a new system (all the crap on the left, basically). To do that you would want to keep the cables long enough to reconnect one day, and take some better notes about what wires are attached to the board and where so that your hypothetical future installer can work out what they're looking at. The wiring diagram makes clear what's a detection circuit, the siren and so on, so either you would work out what wire does what and label them up or just take copious pictures from better angles and keep them with the wiring diagram picture. Then stuff the wires into the crawlspace rather than cutting them all short.

Also from the comment above about phone connection, there are two possibilities there:

- you'll note on the wiring diagram the phone connectors are bottom right on the board and the bottom right of the board has no wires connected, so it looks like you're in the clear on that part.
- the dangly board top-right in the actual box is undocumented and is clearly connected in series with something with green/red/black/yellow wiring; that could be a phone connection, in which case I would find some terminal block and just replace the onboard connector with that.
posted by How much is that froggie in the window at 7:58 PM on April 8, 2020

Once the transformer is unplugged, the unit is "safe" as the battery has been removed (black and white wires in the lower right corner).

Black and red, the ones with the isolated Faston connectors on the end. The schematic also says BLK and RED.
posted by Stoneshop at 11:24 PM on April 8, 2020

Upon moving into a new house I once disconnected a security system that was way less scary-looking than yours, and then had to listen all night while the alarm rang. Obviously, in retrospect, it was designed to set off the alarm when the power to the box with the noisy thing was cut. That box was right under eaves on the front of the house, and my ladders didn't get me anywhere near it. The battery in the box had more or less given up by the following mid-morning, when I came home from the tool hire place with long ladders so I could reach it and kill it. I made a great first impression on my new neighbours.

So, don't be me. Disable the potentially noisy part first.
posted by rd45 at 1:25 AM on April 9, 2020 [1 favorite]

Looking at what jgreco has written I believe this is the best advice give. Once the power is removed from the unit I would let is sit for a day or two so all components that may be energized have time to discharge, before attempting to remove. Although it does appear to be unplugged now.
posted by tman99 at 6:08 AM on April 9, 2020

I strongly suggest having a licensed, bonded, and insured electrician do this work.
posted by evilmonk at 11:04 AM on April 9, 2020

jgrego gave a good explanation. The big tan colored block at the bottom is the wall-wart transformer, which appears to be unplugged, so your system is unpowered. And the battery is also gone.

The white block on top of the transformer is the end of an AC extension cord. You need to trace that cord back to its source at an electrical outlet and unplug it. Once you have done that, there is no power to the system and you should be able to hack away.

One thing to consider is on the far right on the expansion circuit board. Those red, green, yellow, black wires look like they could be telephone wires. The connections look like they daisy chained the phone lines to those screw terminals so if you disconnect them, you might lose your landline. To prevent that, after you remove the wires from the terminals, just splice them back together, red to red, green to green, etc.
posted by JackFlash at 11:07 AM on April 9, 2020 [1 favorite]

Response by poster: Thanks for all the great answers. The wall wart is unplugged as was noted by several. I’ll get a live wire checker before i start taking it apart. Most of the wires run through metal conduit out the top and bottom through the ceiling and floor so i can’t chase them to far. Everything will be capped if necessary.
posted by Talia Devane at 11:33 AM on April 9, 2020 [1 favorite]

This security system was either not installed by any sort of professional or heavily modified since. I wouldn't assume that the zip cord is/was being used for input power; it is as likely to be used for an indicator light or something. I also wouldn't assume that just because you have unplugged the zip cord that there are no other sources of power in the panel. You really want to at least pass a non-contact voltage tester around before you start cutting anything.
posted by Mitheral at 11:34 AM on April 9, 2020

Response by poster: Im going with non-professional and heavily modified. I started tracing the extension cord, it had already been cut and painted over.
posted by Talia Devane at 11:40 AM on April 9, 2020 [1 favorite]

Also, just for fu, the huge. metal piece in the middle of the top photo is a heatsink connected to a LM317T which is apparently a voltage regulator

It is a voltage regulator indeed, and one that can easily be used as a charge controller for a battery, especially for the AGM batteries you would find in alarm systems, emergency lighting and such from that era.

In this design it would regulate the rectified 18V AC (about 24V DC) down to the battery voltage, 12V. If that battery has failed the regulator would still try to keep it at 12V, increasing the charge current, ultimately to 1.5A. That would result in that poor 317 theoretically having to dissipate 18 Watts, which that heatsink (ahem) is totally insufficient for. Even with that 18V coming out of the transformer dropping due to the load, it'd still be way more than that heatsink can stow. Hence, scorch marks.
posted by Stoneshop at 9:25 AM on April 10, 2020 [1 favorite]

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