Thread: Double tapping the doorbell transformer

Guys,
Since double tapping the doorbell transformer on a breaker is not allowed ( though it is the only means I see in my area) What would be the accepted means of supplying power to it? I only ask because it came up twice today, and my electrician buddies say it's standard practice and has been for years. I normally do not even mention it.

Jim Weyenberg
NE. WI.

Similar Threads:

• Transformer & Low Volt Wiring in Main Panel
• Double taped breakers
• Double p-trap?
• Double at Main
• Double wired breaker

Good question. Just how many circuits are approved for tapping into a 120AC/12DC transformer to ring the chimes? Unless it is an approved for double tap in the panel then that is a no. I do not see the economics in running a 14awg from the panel to the attic. On thinking about it, most I have seen over the years is tapping in the attic of front room circuits, hopefully in a box, but a lot of times cut in to and wrapped with tape.

The modern way is to install a junction box, usually a round box for light fixture, high up the wall in a closet. Then the tranny is mounted on the cover of the j-box. It does not need to be on a dedicated circuit, just any lighting circuit is OK. Sometimes we see them in the crawlspace, clean dry crawlspaces with concrete floors. Attics are considered to be too hot and may cause the insulation on the tranny windings to melt.

Originally Posted by Jim Weyenberg

Guys,
snip .. my electrician buddies say it's standard practice and has been for years. I normally do not even mention it.

Your buddy needs to take the NEC update classes when they come out. The codes are not static. The in-panel installation has not been allowed for some time (when Jerry?). I write it up as a recognized fire and safety hazard not a code violation.

I do not recommend depending upon the advice of friends. Do your own research and get training by at least online classes. If your friend said it was standard practice to test 240V receptacles by standing in a puddle of water on a concrete slab and grabbing hold of wire in each hand, would you have done it?

The worst installation I've seen so far was in the crawlspace under a 1985 modular home. The ding-dongs ran 2 pieces of wire, 120VAC, from under a ceramic light base and connected them to the high side of the transformer. They left the transformer hanging by the wires. Not even tape over the terminal screws.

I agree with Stuart, Transformers should not be installed inside panel box because a service panel box is exactly that. It's not a splice box, it's not a box to throw the transformer into because as Stuart said causes excessive heat build up and is a fire potential hazzard. Do you wire it in directly to a breaker? Lets see, low voltage componet directly to even a 15 amp breaker. The transformer will burn up before the breaker trips in the event of a fault. It's a gray area for some areas out there. Don't ask me for th edirect quote from the NEC but we'd rather see a splice in a light circuit branch going to a breaker than a direct hook up of a transformer to a breaker. Mount the transformer outside the service panel box. everything should be ok that way. Make sense?
Randy

Originally Posted by Jim Weyenberg

Guys,
Since double tapping the doorbell transformer on a breaker is not allowed ( though it is the only means I see in my area) What would be the accepted means of supplying power to it? I only ask because it came up twice today, and my electrician buddies say it's standard practice and has been for years. I normally do not even mention it.

Jim Weyenberg
NE. WI.

lol....well it is a simple fix, remove both wires and wirenut them together with a pigtail to the breaker....ensure the pigtail is of the same size as the original circuit wire attached to the breaker before.

Originally Posted by Marcel Cyr

lol....well it is a simple fix, remove both wires and wirenut them together with a pigtail to the breaker....ensure the pigtail is of the same size as the original circuit wire attached to the breaker before.

Yep that's one. Don't forget to move the transformer out of the panel.

Originally Posted by Stuart Brooks

Your buddy needs to take the NEC update classes when they come out. The codes are not static. The in-panel installation has not been allowed for some time (when Jerry?).

From Day 1.

Things such as that were not allowed back when they first came out as they understand that mixing voltages together was not a good thing.

Of course, though, with improvements in conductor insulation and the belief that better insulation was all that was needed, good wiring practice lost out to 'don't really need to do that now' and things suffered. Then when experience and practice proved the old timers right (the older timers being the ones from Day 1), and their intuition and respect was replaced with experiments and science, those practices came back in - for most, apparently some still have not got the message ...

Guys,
I didn't say the transformer was IN the panel! I find them almost always screwed to the panel with a built on conductor collar through a knock out on the outside of the panel with the lead directly to one side of a 15 amp usually Square D breaker terminal. Saw it again today on a new const very upper end home, by a reputable electrical co. I guess I'll call them and get their view.
But thank you all for help, I'll be writing it up from now on.
Thanks again
Jim Weyenberg

Originally Posted by Jim Weyenberg

to one side of a 15 amp usually Square D breaker terminal.

Hi Jim,

Some of the Square D breakers are designed for two wire connections. If that is the case then it is allowed.

Don,
Thanks for the reply, I know Square D's allow 2 conductors, what the guys are pointing out here is that that is still an undersized conductor on a 15 amp breaker and having low voltage wiring in the panel is not allowed. It seems to me no matter where it's tied into the circuit or the wiring the small wire is attached, so why should it matter if the connection is in the panel (with the trans mounted on the outside of the panel) or tied in through a junction box to the same circuit somewhere else. It's the same thing in a different place. I'm still note clear on what the "proper" way of wiring the trans is, just so when I get called on it I have some back up.

Jim Weyenberg

Despite "Philip"'s assertions, Doorbell transformers are rarely rectifying power supplies, therefore they normally supply stepped down (lower voltage) AC power, not DC power.

Normally this is 30VAC or less for doorbells, usually via Listed Class 2 power supplies (not raw "componant" transformers).

Power limiting circuits and Listed Class 2 power supplies are covered in the NEC (as are Class 3 and Class 1).

Should the location be hazardous (such as near fuel tanks, etc.) Class 1, should the requirements of the system exceed Class 2, might be Class 3.

I noticed no indication that the panelboard mentioned was service equipment.

"Screwing" something to a bonded, listed cabinet obviously doesn't fly, as described.

OK If I read the original post correctly,
The transformer is attached to the panel can. It is not "screwed" to the panel, but rather attached using the listed and approved mounting means on the transformer. That woud be the same method one would use to attach it to a junction box. The transformer has a collar with a setscrew that when tightened it secures the transformer to the panel / box and the 120 volt leads are then inside the panel / box and the low voltage contacts are on the exterior of the panel/box.

The original post was about how to feed the transformer with 120 volts. It seems the most common method is to just double tap a breaker. Unless the circuit breaker is approved for the SIZE of the conductor AND double tapping then it is OK. Most breakers are not APPROVED for double tapping using the size conductor on a transformer. Thus the proper way would be to splice it with a circuit conductor with a tail to a breaker. Or attach it to it's own circuit.

He posted three times, said it was "screwed" on the second post.Still hasn't inidicated if the panel board/cabinet was/is service equipment, a power panelboard, light and appliance panel, etc.

I think some clarification is required here, I probably should have said attached to the panel box with a box collar, just like Ken stated. These appear to be designed just for that purpose. And the panels here are combination service equipment (usually on top) and distribution. One cover accesses both. So the trans collar is directly parallel with the breaker it's attached to.
Thanks Again Guys I'm cool with it.

Jim Weyenebrg