what relay switch

Joined
19 Jan 2012
Messages
9
Reaction score
0
Location
Avon
Country
United Kingdom
Hi wonder if any one can help me with the correct relay to put in a 240v bell system. The system is already in place & works well but I now need to also control it from another 240v supply in another place meaning switching from one supply to another to activate the bell.
Hopefully Skippy
 
Sponsored Links
Do you mean the bell has to operate from either supply source with no manual intervention from anyone and that the bell is operated by an AC supply. If so, then each supply has to activate a dedicated relay to operate the bell. However, whichever relay operates first has to isolate the other relay to ensure both electrical supplies are not paralleled together. This is essential as there is a possibility that the two supplies may be out of phase with each other.

So, each relay needs two NO poles to feed the L and N supply to the bell. Each relay also needs one NC pole which is used to isolate the power feed to the other relay. Typically a 3PDT relay will fit the bill.

Call the relays "A" and "B" and the respective power circuits "A" and "B"
If a signal from the "A" bell actuating power is available the "A" relay coil is energised from this power through the "B" NC contact. Once the "A" relay operates it connects, via the pair of NO contacts, that same power to ring the bell. At the same time the "A" relay opens its NC contact which is wired into the "B" relay power feed so preventing the "B" relay energising.

If both "A" and "B" circuits are powered simultaneously, whichever relay operates first will ring the bell and isolate the other circuit.

If however the bell is operated via a DC supply then a simple pair of blocking diodes will suffice.

I trust that's as clear as mud !
 
I think that's over-complicated, unless of course there isn't a permanent power supply to the bell, in which case a second bell may be a simpler option.

You just need a single pole single throw contact relay on each supply.

View media item 75383
If they both operate together the two supplies won't be commoned, they will be isolated by the relays.
 
Sponsored Links
Thanks for your quick response guys. Maybe I should explain a little better. I have installed a bell system that has 3 bells in various parts of a large building to call staff to one aria. Because of the long distance to each bell I did it with a 240v supply right up to each bell running an 8v 1 amp transformer for the bell, thus avoiding voltage drop over such a long distance for low voltage. Each of these 240v cables are plugged into a 4 bank extension lead that has a start stop red & green push button switch wired into the centre of its run. the plug of the extension being in a wall socket above a false ceiling and left switched on. I now need to control these bells from another part of the building. Hope this explains some of your queries.
 
Sounds a bodge to be :confused:

If you have a red/green start stop station, with NC stop and NO start, you could just run a three core and earth to another pair of switches.

Why a start/stop? Why not just a momentary push button?
 
What's the lengths like? I would of gone for low current 24v sounders I reckon.
 
The reason for the start stop station is as follows. I put the system in to call all staff to a designated room for an emergency & the person who activated it would need to be free handed to carry on dealing with the emergency, this being a veterinary hospital. The stop button would be pushed when the senior member of the team was satisfied they had enough of the necessary qualified staff to deal with that particular problem. I hope this sounds feasible.
If I ran another cable back to another pair of switches in different room what would happen if for some reason both green buttons were operated simultaneously?
Many thanks for your suggestions and patience.
 
The lengths vary up to 300 ft. I didn't want the transformers being on all the time, this way there is only a short 240v cable to the switch that is constantly live. Most of the24v bells I could find were fire bells that would lead to confusion. Hope these answer your Questions.
Many thanks.
 
There are loads of 24v sounders, may with dual inputs, to allow two tones, to differentiate use (we use them in industry as loud, distributed, door bells on loading bays etc).

Do you need red stops at each location too? If not, two cores and just greens.

People pressing two greens would do nothing, other than trigger the bell.
 
"emergency"colour is generally considered as being "red"

You should also use latch-in buttons to activate the sounders which will only release when twisted.

I feel you are fretting over about having the transformer permanently energised. Virtually all, if not every, domestic AC bell system operating on an 8V AC circuit uses permanently energised 230/8 transformers and they push-button switch on the LV side only.

If voltage drop over distance is a problem you could use a low voltage circuit to all locations at which there would be RED latch-in buttons only. All buttons wired in parallel with NO contact to activate a single master LV relay. Since the relay demands little current the distance problem is eliminated. Any button being pressed would latch in and this will energise the LV relay which in turn excites the alarms - at whatever voltage they operate on.
 
Thanks lads you have given me much food for thought from many different angles.
Most grateful for all your time & advice
skippy3
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top