Mystery stepdown

[Calculus]

This is curiosity rather than a practical problem. This doorbell and push switch have been part of the house since I moved in thirty years ago, and probably date to the time the house was built (1952). The push switch is inside the porch, the white wire leading to a second (modern plastic) push switch on the front door. The are no screws on the old switch (pictured) and it doesn't twist either way, though I didn't risk turning it too hard. There is no clue where the switch is wired from.

The bell is in the kitchen. The supply wires emerge from the plaster and there is no clue what path the wiring from the push switch takes.

I tested the voltage on the bell today and it was 6 volts AC. I'm guessing the push switch is also 6V. What I am curious about is that voltage. The bell and switch must be mains powered and something, somewhere, must step the voltage down to 6V. Any ideas where that might be happening?

 

[JohnW2]

I tested the voltage on the bell today and it was 6 volts AC.

What do you mean by that? If there was a voltage literally being supplied to the bell, it would probably be ringing!

I'm guessing the push switch is also 6V. What I am curious about is that voltage. The bell and switch must be mains powered and something, somewhere, must step the voltage down to 6V. Any ideas where that might be happening?

If not battery-powered (and any batteries would presumably have died decades ago), doorbells are usually supplied by a very low voltage produced by a transformer of some sort, of in the vicinity of (sometimes even 'in') the consumer unit/fuse box.

However, it's also possible that what you are measuring are 'spurious' (rather than real) voltages. What are you measuring it with?

Do I take it that this bell doesn't work?

Kind Regards, John

 

[Calculus]

Hi John, the bell works fine, I took the actual bell part off it because it was deafening, but it still makes a sufficiently loud rattling to serve its purpose. I measured the current by getting someone to push the switch while I held a mutlimeter cross the inputs to the bell. Tried DC first and the needle barely moved, but switching to AV it showed a clear 6 volts. I didn't think of the consumer unit. I'll have a look tomorrow and see if there's anything that looks like a transformer....not that I would recognise it if it's there.

 

[JohnW2]

Hi John, the bell works fine, I took the actual bell part off it because it was deafening, but it still makes a sufficiently loud rattling to serve its purpose. I measured the current by getting someone to push the switch while I held a mutlimeter cross the inputs to the bell. Tried DC first and the needle barely moved, but switching to AV it showed a clear 6 volts.

Oh - fair enough!

I didn't think of the consumer unit. I'll have a look tomorrow and see if there's anything that looks like a transformer....not that I would recognise it if it's there.

If you're lucky, then if/when you find it, there could well be clues to its recognition - like "Bell Transformer" written on it

Kind Regards, John

 

[skenk]

I've seen bells of this age wired in cotton insulated cable, the black moulded bit may unscrew from black base section, but don't attempt unless required for fixing that surface cable bodge as wood can split. Transformer maybe cream or brown thing the size of a small remote control (and overpainted?) , maybe long since boxed in, or near the distribution board? I have also seen them in lofts where there may have been/is a more extensive -indoor- bell system (using that style of bell) in posh houses.

 

[Jackrae]

I've seen bells of this age wired in cotton insulated cable,

A little bit of history : Silk (DSC) was preferable to cotton (DCC) as the cotton tended to absorb moisture. Windings were usually double wound (the D in D..) in opposing directions (so forming a sort of cross helix pattern) to prevent exposure of the core due to adjacent windings separating.

 

[Gerrydelasel]

The switch assembly will unscrew, but no doubt it is ceased up. Try putting a little oil in the bits that look like joins, warm it with a hair dryer, and gently try unscrewing it back and forth until it gives.

 

[bernardgreen]

A little bit of history

and in the past the insualtion was wound by hand.

It could mean hand winding insulation on many yards of wire before the wire could be used to make a coil for a piece of apparatus ( motors transformers etc etc )

 

[Calculus]

Solved - John and Skenk were right, there is a transformer (white box) next to the consumer unit in the garage. Thanks to everyone for items of electrical history.

 

[JohnW2]

Solved - John and Skenk were right, there is a transformer (white box) next to the consumer unit in the garage.

Well done! I told you that there might be a clue to identification in what was written on it

That transformer is probably relatively 'modern' in comparison with the bell and bell-push - white electrical items is a relatively 'new' phenomenon (newer than 1952!).

Kind Regards, John

 

[jg321]

Wow! That electric meter is around 25 years old! And that bell transformer is probably the newest item in the picture!

 

[Calculus]

Hi John, the house was rewired about 25 years ago. Part of the job was putting in a consumer unit in place of the original fusebox, so presumably the electrician replaced the old transformer.

 

[JohnW2]

Hi John, the house was rewired about 25 years ago. Part of the job was putting in a consumer unit in place of the original fusebox, so presumably the electrician replaced the old transformer.

It looks as if he didn't actually put in a new consumer unit - he 'adapted' the existing fuse boxes by replacing their fuses with plug-in MCBs and adding an external RCD. However, you're probably right that the transformer was changed at that time.

Kind Regards, John

 

[Calculus]

Hi jg321, in the pic you can see a piece of blue card left by Manweb when they changed the meter; barely legible but I think the date on it is 30/01/93

 

[jg321]

I was just about to write "were they still installing those boards in 93?" - but John suggested the most likely set of events.