Cat 5 for Doorbell transformer??


Old 07-26-03, 07:58 AM
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Cat 5 for Doorbell transformer??

My doorbell was wired using stranded Cat5. During the finishing of our basement, the transformer (attached to a light in the ceiling) had to be moved to a utility room and there wasn't enough wire. The existing wire was extended using Cat5! Somewhere in the ceiling, there is a piece of Cat5 joined to the end of the wiring that eventually leads to my doorbell button. The wiring that leads to the doorbell mechanism, and all other, is intact (it's a 4-strand phone-like variety installed by the builder). Here's a diagram:

~~~ = cat5 wire

BUTTON ________~~~~~~ TRANSFORMER_________ BELL
| |

The doorbell never worked after the construction was completed. I am wondering now if the Cat5 wire can even handle the low voltage from the transformer, which is no more than 24 volts. I can't find any info on what the maximum voltage is on a Cat5 strand. I'd like to avoid cutting into the drywall blindly trying to locate where the patching took place if possible, however, if there's a potential fire hazard (which I am concerned about), then I'll just do what is necessary.

Any help is greatly appreciated!
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Old 07-26-03, 09:04 AM
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Cat 5 is a little thin for a doorbell, thermostat (#18 or so) is a better choice.
You are probably dropping so much voltage over the Cat5 that the system cannot operate.
Old 07-27-03, 05:19 PM
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Iv'e seen cat5 used on doorbells before, I personally totally dislike the idea, however when in a pinch, it can be used. What is important if using cat 3/5/5e/6 is to use both wires from a pair for one standard 18AWG low voltage wire. For example, if you have a red and a white 18AWG CL2 wires going to the D.B., use both the blue and wh/blue stripped conductors in the cat5 for the white 18awg, and both the org and wh/org stripe cat5 for the red 18 AWG. Also, I want to make sure your definition of stranded is correct, stranded wire is when there are multiple strands of copper inside a single conductor, and solid is where there is one large strand of wire inside a conductor. If the Cat5 is stranded (meaning Patch Cord), definitly replace it with Class 2 low voltage cable. If solid, it could be reused, even though it is not advisable to do so unless absolutely necesary.

Hope I have clarified a few things!
Old 07-27-03, 05:43 PM
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Although a technicality, you are not supposed to parallel wires less than 1/0awg, so don't combine two wire together in the Cat5 cable and hope to get double tha ampacity from the circuit.
I don't know the VA size of the door bell transformer nor the ampacity/voltage rating of Cat5 cable to help with your problem.
I think it is 24awg which is not recognized by the NEC's ampacity tables.
So, I would say no to use of the Cat 5 cable to carry 24V at all. It might be capable, but not code compliant.
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