Door chimes: replacing 1970s unit

[mike004]

I am replacing an old 1970s door chime unit. It runs from a Friedland mains transformer which is fixed in the loft. I would like to keep the existing transformer and bell push wiring and just swap-out the wired chime unit.
So, I have bought a basic bell unit as below:

http://www.partmaster.co.uk/cgi-bin/product.pl?PID=472835


The transformer supplies power via a pair of bell wires -- one is 9V, the other earth.
But the replacement unit I have does not have an earthing connection. It just requires a single-wire power input.
Do I need to earth the spare wire?

Mike

 

[slippyr4]

The transformer supplies power via a pair of bell wires -- one is 9V, the other earth.

No, one is live and one is neutral.

But the replacement unit I have does not have an earthing connection. It just requires a single-wire power input.
Do I need to earth the spare wire?

It may not require an earth (highly likely it doesn't require an earth in fact). But it does require both live and neutral, + and - if you like.

I suggest you read the instructions again, and remember that earth is not the same as the neutral.

---------------------------
edited: I assumed the product was DC. It's not; the bell is 9VAC.

 

[smokeyJoe]

Those clever people at Friedland designed door chime solenoids that worked with AC as well as DC.
I suspect that the output from your Friedlland bell transformer is 6V AC, which might read around 9V AC with a multimeter or even higher with no load (bell) or doorpress lamp being driven; the regulation on these transformers is poor, but they are perfectly suited to powering a doorbell.
My best advice would be to leave the transformer where it is so that you don't have to touch mains wiring.
The secondary (6V AC) wiring doesn't need to be earthed. It doesn't matter which way round you connect the bell terminals.

 

[mike004]

Thanks Joe.
I am keeping the existing transformer as you suggest and am also removing the wiring loop to the back door, which is never used!
That leaves a much simplified wiring arrangement.
I can then see that I just need to connect one of the pair of power wires to the front door bell push loop and everything should work OK.

Mike