Bell wire: Difference between revisions

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Telephones designed for the UK will use 3 wires - 'A', 'B', and 'bell'. Their bells will be connected between the bell wire and the 'A' wire. If used in an installation without a bell capacitor or without a bell wire, such telephones won't ring their bells. A good example is a plug-in electronic ringer I have - the BT phone plug has only 2 pins - for the bell wire and the 'A' wire.

The US telephone system is different, and each telephone provides its own bell capacitor - but the US ~~doesn't use~~ pulse dialling ~~any~~ ~~more~~. Telephones designed for ~~that~~ market will ring without a bell capacitor or without a bell wire.

The US telephone system is different, and each telephone provides its own bell capacitor - but in the US pulse dialling is rare (although exchanges still support it). They tackled bell tinkle mechanically. Telephones designed for the US market will ring without a bell capacitor or without a bell wire.

The bell wire complicates DSL filtering. The best solution is a filtered master socket (e.g. NTE5c with VDSL SSFP). If using microfilters on each telephone, some microfilters include a bell capacitor, but some others don't - I've not seen any which properly support the bell wire.

The bell wire complicates DSL filtering - it's difficult having a twisted pair with only one wire. The best solution is a filtered master socket (e.g. NTE5c with VDSL SSFP), with the bell wire connected to all other sockets, and no microfilters. If using microfilters on each telephone, some microfilters include a bell capacitor, but some others don't - I've not seen any which properly support the bell wire.

= BT plug/socket numbering =

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{| class="wikitable"

|-

! ~~Function~~ !! ~~Pin~~ ~~number ||~~ Notes

! Pin number !! Function !! Notes

|-

| 1 || ||

| 1 || || ''For non-telephone facility'' ??

|-

| 2 || 'B' wire || Used to be guaranteed more negative voltage than 'A' wire

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| 4 || Local earth || ''Needed for 'C' wire signalling, which is obsolete''

|-

| 5 || 'A' wire ||

|-

| 6 || 'C' wire || '' 'C' wire signalling is obsolete''

|-

|}

[[Category:Technical Documents]]

= So, can I disconnect my bell wire ? =

Several people have reported an improvement in DSL speed by disconnecting the bell wire. It presumably picks up interference and feeds it into the other telephone wiring.

If you have no pulse dialling telephones, or you have one or more pulse dialling telephones but aren't worried by bell tinkling, then you could consider disconnecting the bell wire. But disconnecting the bell wire could result in some telephones not ringing. You would have to test each phone, perhaps trying with a microfilter if a phone fails to ring.