can you advise please? we have had security gates fitted 200mtrs from the farm house, 4 core amoured cable plus a bt wire for the phone, the quote for the work done was for integral phones, plus an external bell to enable us to hear people at the entrance!when we are about the farm,so far the fitters have been unable to get a bell to work due to the fact they tell me its 12 volts from the bt line and the distance away won\\\'t power a bell?? can you help me please.

They will need to power a relay over that distance.

ie fit a realy and a power supply at the house to run the bell. Then just use the bt cable to power the relay. Id use a t-relay personaally then there will be minimal if any voltdrop.