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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 in the US
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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