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Hi Folks

I bought one of these Door Bell Transformer | Stevenson Plumbing & Electrical Supplies - https://www.stevensonplumbing.co.uk/door-bell-transformer.html?gclid=EAIaIQobChMIwLOp8p7A3QIV7grTCh3TzQvbEAkYAiABEgIxmvD_BwE as it's SELV and supports illuminated pushes, but can't find any reference to built-in overload protection. Yet the instructions and wiring diagrams do not indicate separate overload protection is needed. I've emailed Greenbrook a few days ago but got no response. I wonder if anyone know either wither it has overload protection, or how I can find out? (I've had the cover off and there are no obvious fuses like in some old transformers).
 
Thanks for all your replies folks, you've got me wondering now. Thought I remembered reading (perhaps on here) that bell transformers have to have it, plus the old one I've removed has a couple of cartridge fuses visible when the cover is removed. But now I come to think of it as it's a single load maybe it's not necessary. Although I can't help thinking short circuit protection would be in order. Thinking and reading cap back on I guess...
 
Then it will not require circuit protection.
OK thanks, I'm just trying to imagine what would happen in the event of a short circuit. Could this not lead to overloading of the bellwire and/or transformer in the absence of any protection? And why do at least some of the old transformers have fuses?
 
I'd probably fit a small in-line fuse holder and a 1 Amp slow-blow fuse on the secondary side if I was installing it in my house.
 
Those little tiny transformers are often so innefficient as to limit the secondary fault current to safe levels but I can't see a symbol on it to indicate it's impedence protected.
 
Many power transformers have a thermal fuse embedded in the winding's of the transformer.They usually have a symbol on them somewhere to indicate such. But with cheap Chinese, anything is possible. so instal a fuse if you are concerned, it's good practice anyway.
 
Hi - the instructions don't mention any additional fusing being required. That said, I would not direct wire this into a power circuit.
 
It would probably melt the secondary wires if it shorted much like a fuse.
Just what I was worrying about. Only the secondary wires are not as easy to replace as a fuse, and nor are they enclosed to prevent them damaging surrounding materials like a fuse.
 
Those little tiny transformers are often so innefficient as to limit the secondary fault current to safe levels but I can't see a symbol on it to indicate it's impedence protected.
I guess I could try to measure I<sub>sc</sub> with my MFT. Not sure if it'll work at 8V but worth a try to see if I can save spending money/time buying fuses and holders. I guess I should do this anyway to make sure I<sub>sc</sub> does not exceed the breaking capacity of the fuse I buy, though I doubt that would be an issue in practice.
 
Many power transformers have a thermal fuse embedded in the winding's of the transformer.They usually have a symbol on them somewhere to indicate such. But with cheap Chinese, anything is possible. so instal a fuse if you are concerned, it's good practice anyway.
What would the symbol look like? Is it in the regs book anywhere (just had a quick look in the index and can't see anything about impedance protection).
 

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