Does this bell transformer have overload protection?

[Selfmade]

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).

 

[Selfmade]

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.

Thanks, sounds like a good plan. Shame they couldn't have built this in like others did decades ago.

 

[Selfmade]

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.

 

[MDJ]

you are not going to wire that up to a chair are you !

PMSL, I choked on my pint there, definately post of the week, brilliant.

 

[Selfmade]

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_sc 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_sc does not exceed the breaking capacity of the fuse I buy, though I doubt that would be an issue in practice.

 

[Selfmade]

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).

 

[Selfmade]

I think he means the seconhairy side.

Yup second hairy. On the primary I'm just connecting it to its own circuit consisting of a 6A MCB and very short length of 1.5mm T & E. The MCB will protect the cable and the transformer can look after itself.

 

[Selfmade]

MFT will not run the Isc test at this voltage, so I guess I'll just have to buy the fuses.