replacing door bell transformer

I need to replace the transformer for my door bell and I have some questions on good wiring practices.
The existing (defective) transformer is attached to a metal junction box in the middle of a cable whose primary duty seems to be providing power to the furnace fan motor. There is also a porcelain light bulb socket (luminaire seems too fancy a word for this fixture) attached directly to the 'broad' face of the junction box. This house is 40 years old so who knows what's been done around the wiring, I've had surprises before.
I expect that when I lock out the breaker and open the junction box there will be 4 black wires on one wire nut (1 black wire coming in, 1 black wire going out, 1 black wire for the luminaire, and 1 black wire to existing transformer), 4 white wires on another wire nut (similar distribution as for black wires), and 3 grounds on a third wire nut (same as before except that the porcelain luminaire likely isn't grounded) or else attached to the metal box.
Is this a realistic assumption for a properly designed connection?
The reason I ask is that I had a another set of assumptions for a similar junction box that was on a switched circuit. Here the reality didn't match my preconceived notions; instead the white wire from the bathroom ventilator fan was attached to a sloppy-looking birds nest of ground wires; and that's the only way it would work.
Also, is it all right to connect 4 wires with one wire nut? Information from Ideal shows UL listed wire combinations for number/size of conductors for each model number of Wire-Nut(R), so presumably this is okay. But is this commonly done as good practice and relatively safe? Would it be better to pigtail off so that I have 3 conductors under one wire nut with the pigtail connecting the existing light and the replacement transformer with another wire nut?
thanks!
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Just note where the wires of the existing transformer are attached and connect the new one the same. Make sure your wire nut connections are tight

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RBM wrote:

Hi, First, turn off 120V going to the x-former. I'd buy a heavy duty x-former which will last longer. It is just s step down x-former 120V AC to 24V AC.
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Is the OP CERTAIN that transformer isnt for the furnace thermostat? its a logical place to be....
sometimes its easiest to abandon something old like this transformer and install a new one somewhere else, bell wire is cheap
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I don't know where you retrieved this old post from, but, if it's a bell transformer, it isn't 24 volt, and if it is 24 volt, it would probably be for the heating system, but certainly not the doorbell
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SOME doorbells use 24 volts. Most are 18?
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Most chimes are 16, bells and buzzers are 6-8. I've never seen a 24, but maybe up in your neck of the woods
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My house came with chimes and I think 18 volts. When I got a better chime for the first floor and moved the first chime to the basement (where I used to work and never hear the first chime, the transformer wasn't powerful enough for both so I had to get heavy duty. (Otherwise I think the original light duty one would have lasted forever) Then the chime on the first floor was so loud, it tripped the breakage detectors on my burglar alarm anytime a delivery man rang the doorbell. I only use the alarm when I'm not home and no one told me about this for a year or two!
Then I used a a potentiometer, variable resistor to find a value that would quiet the chime so it woudln't set off the alarm, but was still as loud as possible. Once I had the value, I replaced the pot with a fixed resistor.
Then I started using the computer a lot, with the radio on and couldn't hear the bell on the first floor. No easy way to run wires so I got a 4 dollar wireless doorbell, soldered a wire across the button switch, and powered it not from a 9-volt battery but from the 18 volt transformer, only when someone at the door pushed the button. 18 volts was AC and I ran that through a little diode, and got about 9 volts DC which is what the electronic-doorbell-button wanted.
I hate it when people have surface mount buttons at their door, and it's even worse when they have two buttons at the same spot.
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RBM wrote:

I just installed a doorbell for a customer and it was a 16 volt system with a lighted button. 24 volts would work but the light may not last very long. Many door- bells are 10 volt units. If you look in the door chime section of Lowe's/Home Depot you may only find 10 and 16 volt transformers.
TDD
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