But a bridge tap, that is open at the far end, will look like a short-circuit somewhere back toward its junction with the main line. The length of bridged line that will look like a short-circuit at the bridge tap depends on the electrical characteristics of the bridging wire and the frequencyof the signals. But if the overall circuit is close to being marginal, the extra 50 feet of wire bridged onto the main wire may very well be just enough of an impedance discontinuity to render the DSL ineffective. When we converted to DSL, I made sure that the line/wire from the telco point of presence to where the DSL signal was filtered/split off from the main telephone line was a straight shot, no splices or any dicontinuities. Once past the DSL filter, the phone line goes to several locations in both star and mesh configurations.