Basic door intercom wiring

Associate
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21 Nov 2008
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I need some help with wiring a 2 handset intercom (Bell 902).

I've got a cat5e from each handset to the outside speech unit and a further cat5e from the power supply to the speech unit.

So I am connecting green to T, blue to O, orange to R and brown to I at the handsets and then to the correspondng letters at the speech unit.

What I am confused about is H and C. I have a cat 5e from the power supply so I need only 1 core for each. Assuming I use white-brown for H and white-blue for C, how do I then connect the white blue for C into the bottom of I for each handset at the speech unit?

This is the wiring diagram:

v2uzEw9.jpg
 
Soldato
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13 Jun 2011
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Why do you need to connect to c. It looks like power comes thru the brown (labelled strap) on that schematic altho part of it is missing

it prob has a constant + at the handset and one of the other terninals sends the missing - to the phone when its called to power the handset.
 
Soldato
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C to 1/2/3 is internal wiring in the door station and you do not need to do this. You only need cat5 running from each handset to the door station and a two core cable running from the 12v supply to the door station.

I personally wouldn't run it in cat5 as it isn't shielded but depending on the distance you might be ok.

Edit: been a while since I done any bell kit. If it isn't internal then you just take a link from H to 1 as shown in the diagram and daisy chain it to 2.
 
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Soldato
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C to 1/2/3 is internal wiring in the door station and you do not need to do this. You only need cat5 running from each handset to the door station and a two core cable running from the 12v supply to the door station.

I personally wouldn't run it in cat5 as it isn't shielded but depending on the distance you might be ok.

Edit: been a while since I done any bell kit. If it isn't internal then you just take a link from H to 1 as shown in the diagram and daisy chain it to 2.

Don't mean to correct you but he needs to link from c to 1 but it looks like it should be internal.
 
Soldato
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Then you have done something wrong.

Would be very suprised if a 12v transformer would trip mains unless you have it
Connected the wrong way round, i.e 240v on 12v side.
 
Soldato
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Probably a short somewhere. Is this already plumbed in or are you bench testing pre-installation?

Either way, i'd start with the PSU and make sure that it's giving you 12VAC (use a DVM) as well as not tripping the breaker with it not connected to the rest of the system (disconnect from the 'Speech Unit' and buttons).

Then disconnect the rest of the system and using a DVM, go hunting for shorts in the cabling (if you can).

Failing that, and this isn't the correct procedure by any means (as something may go 'pop'), slowly reintroduce the system, eg - connect power to the 'Speech Unit' (only), see if the breaker trips; then connect pin 'O' (common ground maybe), see if it trips; then connect 'T' (transmit?), see if it trips...etc etc.

Alternatively, get someone in that fits them as it'll save you some hair!
 
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