I recently was installing my nest hello doorbell in my old doorbell system with a conventional mechanical chime, that I purchased new, that said it was compatible with the nest hello doorbell. My old tranfsformer was 16V/10va . Worked fine for about three days and then the chime began to buzz and get hot, as well as the transfomer got rather warm. I began looking into the situation and purchased 2 new transformers - one a 16V/30va and the other a 24V/40va. My research said, depending on what I find I may require the larger of the two to run my system. After tracing the system out I discovered that after installing either of the above new transformers that they both were putting out 19.8 and 27.8 volts respecitvely after wiring them into the electrical panel (no doorbell wiring was connected at this time, just straight off the breaker at this time). Connecting the existing doorbell wiring from the chime area to the transformer and checking the voltage on the transformer wire at the chime area location gave me the same readings as the initial test straight off the breaker. Upon wiring in the nest hello doorbell and the mechanical chime I found that the buzzing continued and both transformers heated up as the original system did. I checked the voltage at the doorbell and discovered there was very minimal voltage, perhaps one or two volts. I also went back to the transformers and checked their voltages after the humming and found these results: old original transformer still read 16 volts, both of the new transformers were now reading 0 volts. Checked the wire continuity and it said there was continuity but I still didn't have enough voltage for the system. Decided there had to be a short somewhere in the wire so I found the wire in the attic and decided to replace it. Couldn't pull it through the outside wall due to access and/or the fact that it was stapled or had some sharp corner that it was snagging on. So I cut the wire and decided to test to see if perhaps the short may have been on the opposite end that I was able to pull from the interior wall. Hooking this wire up to the transformer and testing the voltage using my old transformer gave me what I needed, somewhwere around 19.8 volts. This told me that my short was obviously in the other end of the wire that I could not pull from the outside wall leading down to the doorbell.
Sooo, new plan, without being able to pull a new wire from the attic my new course of action is to go down, instead of up, into a space below in the crawl space under my landing. I can access the back of an existing room outlet and run wiring in conduit to a new box under the front door area - hook up my transformer to that new box wiring and run new wiring from the transformer to the front doorbell. I have decided to not use the mechanical chime and will instead use my hub as well as a couple of google speakers as my actual "ringer". My ultimate question is which transformer to use? The old, original transformer 16V/10va, which cannot be connected using a knock out on the new box? The new 16V/30va if I discover that it did not get burned up in my testing? Or the new 24V/40 va if I discover that it is still in working order.? So I will basically be running the system straight off my transformer (whichever one) and completely getting rid of the mechanical chime and using just the google prodducts as my "ringer". Which of the transformers should I use and will any or all of them be adequate and safe to use without causing any electrical safety issues or problems for the doorbell?
