Low voltage wiring a fire hazard??

jonnymac44

jonnymac44

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Sep 27, 2007
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Ok, let's see if anybody can help me out here:o

There was an alarm system installed in my house when we bought it a few years ago. Standard ADT type system with sensors on doors, windows, motion in the hallway, etc. Anyway, we've never really used it because it was a bit older and annoying. Always meant to have a new system installed, but that hasn't happened.(I know I know:p)

Anyway, the other night when I was cooking I had to check on the kids and things got a touch smoky. The damn alarm starting going crazy inside the house and the ear splitting bell was going off on the outside. The keypad control is long gone and we don't have any monitoring, so I just opened up the control panel and pulled a couple wires until it finally stopped.

This is my question, is this control box inside the house a fire hazard. It's got a ton of the really small gauge low voltage wires going into it from the wall, the kind that phone systems and thermostats use, I assume leading in from all the sensors around the house. There is a little red LED lit on the circuit board and the heatsink is warm. Not too hot to touch, but warm. A couple months ago I removed the backup battery because it seemed overheated. Are these type of wires a danger at all. I'm leaving for a few days over thanksgiving and want to know if I need an electrician over here ASAP. I'm ok with hammers and nails, but I don't mess around with electricity, even low voltage!

Any advice? Thanks all.
 
If you can pull the primary on it. If not there is no chance those wires would ever carry enough current when shorted or otherwise, unless they were shorted across a higher current/voltage line. Unlikely.

Likely the wires don't carry voltage to the board, but away. So when pulled they are dead. Confirm with a multimeter (you should have one if you're doing home work)
 
How old is the house? It's slightly possible for low voltage wires to get overheated if there is modern spray foam insulation covering the wires, which thereby eats through the wire sheathing and can cause the warm temperature.
 
I've never heard of a problem with lo vo overheating. The heat you felt was likely from the transformer. It converts your 120V to 12Volt and does generate heat. But its no different than the transformer for your doorbell. (Doorbells run on 12V and have a transformer plugged into the regular house wiring somewhere in the system. They run for decades and never have issues.)

You can disconnect the transformer if you want, but if it were mine I'd probably not worry about it. It's a non-issue.
 
The low voltage 12 vdc in the panel would be protected from shorts with fuses. You should see them on the circuit board, probably 3 of them. One for the bell, one for the loop, one for the 12vdc power. I would not expect much of a problem with low voltage wiring. Like knarfeng mentioned, why not cut the 120 v power going to the panel and be done with it?
 
Don't worry about it, you have a better chance of getting hit by lighting while eating your turkey. All the small wires you see go to sensors and door triggers, most just work on a sense voltage and are of very low amperage. Even if you had a dead short I don't think it would be able to create enough heat to cause a problem, DC voltage does not do the crazy things AC voltage does.

Speaking of dead shorts, that might be one of the reasons for the alarm acting up. If a small animal chewed on the wires and the wires were touching it would be sending a signal to the panel that a sensor has been tripped. Like others have said, pull the main power so it does not cause any more problems and don't be worried of a fire hazard.
 
komondor said:
How old is the house? It's slightly possible for low voltage wires to get overheated if there is modern spray foam insulation covering the wires, which thereby eats through the wire sheathing and can cause the warm temperature.
Click to expand...


Where did you get this information?
 
Thanks for the responses guys:thumbup: I feel better about leaving for a few days now.

I'll definitely be disconnecting the main power........after this crazy holiday week, when I've got time to take the whole box down off the wall and get behind it to find that darn thing!:D

Again, I appreciate all the info.

Jonny
 
Wow. I didn't know this was whine & cheese.

Why the pissy comments? :confused:

Anyways, there is not a lot of information available on this subject, unfortunately. Not yet at least. But I did find this discussion from a couple years back:

http://www.avsforum.com/avs-vb/showthread.php?t=832496

It's certainly very possible for two part spray foam to melt the plastic sheathing on wires-- probably even more so on thin, low voltage ones. It can be seen as a fire hazard. The heat generated by expanding and curing foam can be tremendous, especially if one doesn't install it properly and goes for more than 2" deep at a time.

I'm not saying any fire has ever been started because of this, but it's possible, and people need to be careful of this issue as spray foams become more and more popular.
 
I'm gonna say a big no to that, I've been a low voltage tech for 13+ years 6 of that in new construction. That spray foam does not build that much heat and dries in a matter of minutes, and just because the wire is thinner means nothing. On average the insulation on the wire should be able to handle up to 600 deg F. If this was a issue it would also be a issue for your high voltag AC wiring. All materials have a fire rating including insulation, believe me if it was a issue I would have probably heard of it, I had to know all kinds of codes for new con and I'm also the son of a Fire Chief/fire investigator.
 
Alarm circuits are Class II power-limited circuits and generally considered safe from both an electrocution and fire standpoint. But, I would suggest removing power from the alarm if you don't use it. The power for these alarms generally comes from a plug-in transformer. It's often plugged in in a hidden place. Look behind your refrigerator as that is a favorite.
 
Knifenut,

I agree mostly with what you are saying. I really don't think it is a huge problem-- it certainly doesn't seem to be based on the lack of information on the net.

However, I don't agree with the spray foam comment. Two part foam can reach temperatures of over 300°F. Is this hot enough to melt the thermoplastic sheathing on wires? Maybe not, but it's hot enough to get people talking.
 
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