I recently walked through a few homes here in SW Florida that had just been "roughed-in". I immediately noticed that Cat-5 cable was used to wire not only the telephone system, but also the chime and garage door opener systems.

The Cat-5 is labeled as type CMR cable and is listed as a communications cable under the requirements of Article 800. The conductors are #24 AWG. Both the chime transformer and the grage door unit control are powered from a class 2 source. I reviewed section 725.61(G) and the companion Table and Figure for that section. It appears that type CMR can be used as a substitution for Type CL2 cable. So, I guess there is no violation for using Cat-5 for these purposes.

My concern and question is that typical CL2 cable has conductors sized at #18 AWG. It also appears that CL2 cannot be used as a substitute for type CM which seems odd.

Do any of you have a concern with type Cat-5 being used for a class 2 circuit?

I imagine you will end up in the manufacturer's instructions if you want to find a violation. Since this is a "power limited" circuit I don't see a danger but if this was a mechanical ringer you might have a voltage drop issue. If it is an electronic chime it probably runs on 10ma or so.

BTW Doorbell wire is usually 22ga, not 18