24 Volt transformer blowing

get a fuse in the secondary side if you want troubleshoot without replacing transformers

another trick is to put a 24v lamp in series with the xfrmr secondary, it will limit the current so you can look for the short without blowing the fuse.

Transformers aren't cheap. Try this: Should be in everyone's toolbox.

https://www.amazon.com/POP3-Lil-Popper-Fuse-Tester/dp/B07FWFZCSF

https://www.youtube.com/watch?v=9gEd-VDf0QE

so it is just this with a big markup:

There are Tatle Tales that you place across the controls to find what one it tipping. Ive never needed them, but they do work.

There are many techniques to find a short circuit. Focusing on mostly one here. IMO the best way is not to accumulate burned up transformers and/or blown fuses if the circuit has a fuse or if a fuse has been added.

I would find the Li'L Popper very annoying, since it requires constant resetting, it is just an appropriately sized circuit breaker with convenient wires and wire terminations added. But it is better than accumulating burned up transformers and blown fuses. I have not used the LED device so I have no comment about it.

The oldest but probably most forgotten method is to put an incandescent lamp (tungsten filament) in series with one side of the transformer's secondary wires (a lamp on the transformer's primary side may work too but you have the transformer's properties that may muddy up the technique a bit.)

The incandescent lamp technique, commonly called a Dim Lamp test or Dim Bulb test (look on YouTube) has to be set up correctly to be most effective. And this means the incandescent lamp(s) need to be sized correctly. The lamp need to be the same voltage as the circuit under test. Also the load current of the lamp should be in the ball park of what the transformer can safely source.

So for example if the 24 VAC transformer is rated at 40 VA the lamp should be in the 40 Watt ballpark or a bit less. The lamp provides a maximum safe load for the transformer and any fuses in the circuit. So no more burned up transformers or blown fuses. Two 12 volt lamps in series can be used too.

The benefits: No more burned up transformers, blown fuses, it is self resetting, provides good visual indication of the circuit status providing diagnostic information.

The down sides: 24 Volt lamps are more rare, incandescent lamps are more fragile, you would probably have to build the tester.

Using this technique I have founds shorts in seconds where others have failed using other methods (the looks on their faces were priceless).

In this situation it appears the Orange and Blue annotations are shorted together somewhere. With the test lamp in circuit it will be bright until the short is removed, then it will get dim. Often the circuit will actually work with the dim lamp in circuit (the short has been repaired obviously). In this case the Orange or Blue annotations can be disconnected one at a time to locate the part of the circuit that is defective. Also if there are crushed or chaffed wires the lamp may help identify where they are with the self resetting ability and the good visual indication. Also although not shown here one side if the transformer's secondary may be bonded to ground and/or the jacket of the heating equipment.

I hope @BruceSteinberg looks at this discussion before he buys anymore transformers.

@Jamie Hall have watched bot Pine Hollow and South Main Auto. Eric is the best and is a riot.

more or less. it will be more difficult if it is intermittent or if it is something that gets switched on at some point in the cycle. the light limits the current to less than the rating of the fuse. if you chose a light that is close to the va rating of the transformer the system will probably still operate if it needs to get part way in the cycle to turn on whatever is shorted.

That's about it. However " because power is being consumed by the light ", the light limits the power that can be drawn from the transformer to a safe amount even though the original circuit has a short circuit.

The short circuit defect creates significant excessive current flow way exceeding the transformers rating so the transformer fails (it burns up). The lamp limits the current.

This technique leverages the difference between the Hot and Cold resistance of a tungsten filament.

Also keep in mind even with disconnecting one part of the circuit that part may branch out down stream into multiple paths and only one of those branches may be shorted. (The wiring diagram often helps) That is where the self resetting and visual indication is so beneficial. All you have to do is explore the circuit and not mess with resetting the test equipment with every test.

If you use the lamp and the Li'L Popper the Li'L Popper should never trip.

Use the popper, by breaking the 24v common to transformer. put it in line there and again I would just leave it for future issue. And save transformers and 3 amp fuses.

Pro Short Tool (and others), from what I can find on-line, it seems usable there are a few different versions. The lack of published specifications does not help my enthusiasm. One thing I don't like is they seem slow, one states 5 to10 seconds to reset. Personally I like the fact you can see an incandescent lamp flicker and they are bright (with a short) not a little LED.

Pro Short Tool (and others) not sure what the current is limited to, with an incandescent lamp there is enough current that it can be traced with a clamp on Ammeter.

I guess what it comes down to is what you like and understand.