How many Phones on one line

[DIYspanner]

What's the maximum number of corded phones usually possible on a domestic phone line ?

 

[bernardgreen]

The limiting factor is how many bells are on the line.

REN Ringer Equivalence Number

The bells were designed to be rung using AC current ( hence the capacitor in the system to allow only AC to reach the bells ). Too many bells meant too much AC current flowing and this could result in the exchange "ring tripping" ( false answer ) on the AC current instead of waiting until DC current started to flow as a result of the handset being picked up to answer the call.

The speech circuits are powered by DC from the telephone exchange, typically 50 volts when the line is not in use and between 8 to 12 volts ( at the phone ) when the handset is lifted

If one only has 4 bells ( or equivalent AC load ) there is no limit to how many phones can be connected to the line. In most cases ( except on very long lines ) two or three phones can be used at the same time on one line before speech volume and quality is noticably degraded.

Read more: //www.diynot.com/diy/threads/telephone-cable-how-many-pairs.456132/page-2#ixzz46TU07DKH

 

[DIYspanner]

I have three corded phones, all two wire, plugged into extension sockets in the rooms they're used.

All the extension cable is the proper 4 core telephone cable, with the cabling in done in series from socket to socket.

 

[bernardgreen]

That sounds OK.

 

[DIYspanner]

I'm been experimenting over the last week and all seems well until I plugged the end of line phone in last night which had been unplugged for a week. Plugged in, I got a call and the phones didn't ring.

In recent days I fitted a new socket to the end of line, the socket I got from a electrical wholesaler its its decent quality.

The phone plugged into end off line is this one -

http://www.bmstores.co.uk/products/slimline-corded-phone-257026


Its got me a tad baffled!

 

[bernardgreen]

its its decent quality.

Maybe it is.
Does it have a label stating its REN ( Ringer Equivalaence Number ) ?

Does it have 2 3 or 4 contacts in the plug ?

If it has 3 contacts ( pins 2 5 and 3 where 3 is the bell wire ) then check you have not reversed the wires to pins 2 and 5. It they are reversed and there is a capacitor in the phone connected to pin 3 then that capacitor is in series with at least one other capacitor ( the one in the master socket ) and these are connected across the line ( pins 2 and 5 ). The capacitors in series across the line will short out the AC ringing current so no bells or sounders will get any ringing current.

 

[DIYspanner]

Here's a photo of the socket wiring. Its Selectric brand.

All three sockets are wired blue with white ring to No.2, white with blue ring to no. 5

 

[bernardgreen]

As only wires 2 and 5 are connected then it is not possible for capacitors to be connected in series via wire 3.

Either the phone is defective and taking too much ring current ( while not ringing ) and starving the other phones of ring current.

Have you tried plugging just that phone in one of the other sockets ?

When you call and the bells do not ring do you still hear ringing tone ?

 

[DIYspanner]

The only problem is with three phones plugged in, there's the intermittent fault of the phones not ringing on incoming calls.

My telephone account is with Talktalk if that's relevant at all ?

As I mentioned, during the past week I've had phones plugged into points 1 and 2 with no problems. Perhaps three phones are just too much for the line.

These are the phones I have

At socket nearest the master -

At no.2 point -

At no.3 , furthest from the master -

 

[DIYspanner]

Forgot to mention, when the ringers aren't activated by an incoming call, when I pick the phone up afterwards, I have to press the plunger again to get a dial tone.

Does that identify anything ?

 

[DIYspanner]

Would poor quality telephone cable cause this kind of problem ?

Is this item genuine modern BT cable ?

http://www.ebay.co.uk/itm/5M-BT-TEL...326916?hash=item3ce56f7dc4:g:bqIAAOSwZ8ZW4b2s

 

[PBC_1966]

Forgot to mention, when the ringers aren't activated by an incoming call, when I pick the phone up afterwards, I have to press the plunger again to get a dial tone.

Just on the one phone or on any of them? What do you hear when you pick up at first - Just a quiet "tick, tick, tick" sound?

Would poor quality telephone cable cause this kind of problem ?

Unlikely, unless it was so poor that there were intermittent shorts. Damage during installation could do it as well, but that's more likely to give random issues than the consistent problem you have.

However....

Is this item genuine modern BT cable ?

Whatever the cable may be, the picture certainly isn't correct for modern CW1308, which for 2-pair has white/blue and white/orange pairs, not blue, orange, green, brown as pictured (the older internal wire used in the Post Office days was non-paired using those colors).

A lot of the cable sold on eBay is cheap Chinese stuff. It's better to go to a reputable supplier.

 

[DIYspanner]

When I have an instance of the ringers not sounding, I only know there's been someone calling because of the led call indicator.

I can pick up any of the three phones after the call and there is no sound at all. Pressing the plunger on any phone activates the line again to hear the dialing tone.

I may try a run of cable to the end of line phone as it been there for 15 years, where as the all other cable has been in service only two years.

Thanks for the advice on the ebay listing, hopefully the seller will be forced to remove the listing. I'll get some cable from the local electrical wholesaler ( an Arrow branch).

 

[Europlex]

This cable is to BT specification CW1308A high specification cable for use in wiring telephone line outlet sockets. It is also ideal for use in other low voltage, low current applications. The cable contains four solid tinned annealed copper conductors, each 0.5mm diameter, insulated with colour-coded PVC. Overall insulation is in white PVC.

 

[DIYspanner]

Why have the colours been changed from what BT have been using over the years ?