Structured wiring for the DSC alarm
DSC alarm panels are usually a veritable rats' nest of wires and strange connectors, so I decided to try and clean up my panel by using structured wiring. This makes a lot of sense, standard Ethernet wiring is good enough for 2 amps for a single pair, which provides more enough power for the DSC panel and alarms.
My house uses a Legrand On-Q enclosure, so I used an AC1015 Network Interface Module to terminate the wires from sensors in individual zones. At this point, I spent some time deciding on the way to map the wiring from the DSC standard to the T-568A Ethernet pinout.
Security alarms typically use cables with 4 wires: Black, Red, Green and Yellow. Sometimes cables might have Blue wires instead of Green ones.
This is the Ethernet wiring mapping that I came up with:
| T-568A | 4-wire | Meaning |
|---|---|---|
| WhiteGreen | ||
| Green | ||
| WhiteOrange | Black | 12V(–) |
| Blue | Red | 12V(+) |
| WhiteBlue | Green (Blue) | KEYBUS |
| Orange | Yellow | KEYBUS |
| WhiteBrown | ||
| Brown |
DSC uses the Black and Red wires for 12V DC power supply, so it's important to make sure that they are not connected to the same Ethernet pair (for example, do NOT connect them to blue and white-blue). This way, if you accidentally plug in a regular Ethernet device into a DSC plug, there won't be any magic smoke emitted.
Additionally, I used RJ11 phone jacks with 4-wire cable instead of the regular CAT6 cable for the zone-to-alarm wiring. It saves a bit of space and makes sure they are visibly distinct from Ethernet jacks. RJ11 jacks are perfectly compatible with the regular CAT6 Ethernet sockets.
Wiring the zones to a patch panel
The first step in organizing the mess was to terminate the wires from zone sensors in the network interface module. This turned out to be pretty easy, I just lined up the wires according to the mapping above and punched them in using a Keystone Punch Down Tool. It can be done with a thin screwdriver, but a proper punch down tool saves a lot of effort.
My alarm wiring shorts the Black wires with Green, and Red wires with Yellow at the door/window sensors. Then the sensor in turn shorts these two 2-wire bundles all together when it's closed. So all four wires end up shorted.
It means that if I connect all these zones to the alarm panel according to the wiring above, I'll end up with shorted +12V and -12V power lines. I have basically two ways to deal with it: I can leave the Black and Red wires (coming up from the sensors) disconnected inside the Network Interface Module, or I can use patch cables that don't have Black and Red wires to connect the door/window sensors to the alarm terminals.
Leaving the wires disconnected inside the Network Interface Module will make any future upgrade from passive sensors to powered motion sensors harder, but it's completely safe. Fortunately, it turned out that shorting the +12V and -12V is not a big deal for the DSC alarm panels, they simply shut down as a result and come back up once the fault is removed. So I decided to just use appropriate patch cables.
Here's how the alarm zone panel looks:
Using extender for zones
Another thing is that I wanted to move my alarm panel into the basement, out of my living room. This is mainly to get rid of an ugly metal cabinet in my food pantry, and also because my wiring cabinet was getting congested.
I added several conduits leading from the basement up into my living room, so there was plenty of space to just run the wires to the panel downstairs. But then I had an idea, I could use a zone expander and just run one wire from it to the control panel!
It worked well, I was able to use just one Ethernet cable to connect the zone expander with the main panel downstairs. Here's how the living room panel looks, and it also holds an Envisalink 4 board that exposes the DSC alarm state for my HomeAssistant:
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And this is the main alarm panel:
Super-tidy!
For comparison, this was the initial look.
Expander wiring
Zone expanders for the DSC alarm systems use the same KEYBUS standard for 4-wire cables. But we need two more modifications: 1. I also need to send the bell (siren) signal up from the main alarm panel. 2. I'd like to have some headroom for power. I have 3 keypads and 1 security camera powered by 12V from the expander, and this is just a bit too close to the maximum rated amperage for the CAT5 cable pairs. So I used up the remaining twisted pair for an additional power line.
This is the updated mapping for the expander-main connection:
| T-568A | Expander | Meaning |
|---|---|---|
| WhiteGreen | Additional Red | MORE POWER |
| Green | Bell (–) | Siren |
| WhiteOrange | Black | 12V(–) |
| Blue | Red | 12V(+) |
| WhiteBlue | Green (Blue) | KEYBUS |
| Orange | Yellow | KEYBUS |
| WhiteBrown | Additional Black | MORE POWER |
| Brown | Bell (+) | Siren |
As a note for myself, here's the zone mapping between locations and zones, they go in the descending order, from upstairs to downstairs:
| Location | Expander Zone | Global Zone |
|---|---|---|
| 4th floor door | 8 | 16 |
| 3rd floor: balcony door and living room PIR | 7 | 15 |
| 2nd floor balcony door | 6 | 14 |
| 2nd floor bedroom PIR | 5 | 13 |
| 2nd floor entry hallway PIR | 4 | 12 |
| 2nd floor entry door | 3 | 11 |
| 1st floor bedroom door and window | 2 | 10 |
| 1st floor elevator door | 1 | 9 |
| garage PIR | Main Panel | 8 |
PIR stands for Passive InfraRed, in other words, motion detectors.