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I'm setting up my home alarm (a dsc 1832) using cat5 cables (these were the closest I could find in my country to the specs recommended by the 1832 manual).

I've had to make some splits since the cat5 cables has 8 wires and most sensors only need 4, but joining each wire individually is a bit of a mess.

¿Would using rj45 connectors to join the wires have any drawbacks? I already have the rj45 crimper and tester so I'm hoping that could simplify the installation.

More context: Old house, there was a single pipe we could spare for networking, alarm and doorbell, and given the topology there was no choice but having to join some wires since we couldn't fit more cables in the pipe to run everything end to end. All concrete walls here, getting a new pipe in for cables is very expensive. RJ45 connectors are very very cheap.

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  • What do your instructions say?
    – FreeMan
    Feb 11 at 20:11
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    Please explain a little more what you mean by splits and joins. The alarm panel has screw-down terminals, and most devices do too. You should be running wires point to point and screwing down the bare ends. If you don't use all 8 conductors that's fine. What are you splitting or joining? What has RJ45 in your system? All I can imagine is that you are splicing wires together by putting RJ45 plugs and sockets on them, but that would be very overcomplicated. Please explain more.
    – jay613
    Feb 11 at 20:54
  • Old house, there was a single pipe we could spare for networking, alarm and doorbell, and given the topology there was no choice but having to join some wires since we couldn't fit more in the pipe to run everything end to end. All concrete walls here, getting a new pipe in for cables is very expensive. Feb 12 at 16:26
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"split wiring" is a networking term that is specific to ethernet networking it's not surprising others don't understand what you are doing.

Yes, home running everything even when you leave 2 dead pairs in the cable is the best shot since you never know 10 years from now if you might actually want Ethernet there. And cable is cheap.

Typical RJ45 connectors are rated up to a half amp. You can get specialty ones rated to 1.5 amp. As long as your sensors are not drawing much power you are fine with them. Needless to say the cost of rj45 jacks and plugs exceeds the garbage-grade connectors typically used by alarm wiring companies which is why you don't see them used in alarm work but the worst you could do is almost certainly going to be better than the best that a typical alarm wiring guy does. I've never seen an alarm installation wiring that wasn't an utter mess up inside of the ceiling or anywhere that wasn't immediately visible to the customer.

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  • Thanks, I'll check the amp requirements but I think they'll do then! Feb 12 at 16:35
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There's no sensible application for RJ45s in a proper alarm system install, unless some alarm company comes out with control panels and sensors equipped with them. The alarm you mention is not...

The sensors and control panels don't work with them, being designed for screw connections to stripped wires, and your cables should run from each sensor to the alarm control panel unbroken. Adding connectors in the middle just adds points of failure that not having connectors removes.

You chose to make some splits. You didn't have to, and it's not a best practice, which is one complete cable to each sensor, and if you have extra wires you don't need right now, no big deal, as opposed to cutting cable jackets open midway and extracting a couple of pairs, which is a hack, and an additional potential point of failure. Or chopping off the cable and having a junction to two other cables, which is a worse hack.

I can't see any way that crimping RJ45s in the middle of a cable running between screw terminals at the control panel and screw terminals at the sensor "simplifies" anything. You'd need to connect jacks to the sensor and alarm panel, which is still "joining each wire individually" and more places to fail.

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  • I agree with most of what you said, as I added in my edit, there were other constraints that forced the decision of splitting. RJ45 connectors can simplify stuff for me because i can use ethernet testers for connectivity, and avoid splicing which is messy. I'm just splicing 8 wires (an 8 wire cable split in two), i already have the RJ45 crimper and tester. Feb 12 at 16:29

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