Arrangement for protecting telecommunications equipment from voltage transients

A circuit protection unit which comprises a pair of arrangements for protecting an electrical circuit from a voltage transient, wherein the circuit comprises telecommunications equipment comprising a pair of current carrying lines having a common ground, with a high-energy foldback device connected between each of the current-carrying lines and the common ground, each of the pair of arrangements comprising:

• (1) a voltage clamping device which has a first capacitance and which, in use, is connected between a current-carrying line of the circuit and the common ground,
• (2) a capacitor which has a second capacitance of up to 1 .mu.F and which is connected in series with the voltage clamping device, and
• (3) an inductor which has an inductance of from 1 .mu.H to 100 mH, and which, in use, is series connected in the current-carrying line,
• each of the pair of arrangements, when in use under normal operating conditions acting as an LC filter having a first high frequency break-point which
• (a) is determined by
• (i) the first capacitance,
• (ii) the capacitance of any additional capacitor optionally connected in parallel with the voltage clamping device, and
• (iii) the inductance, and
• (b) is in the range of from 1 kHz and 10 Mhz, and
• when each arrangement, while in use, is subjected to a voltage transient sufficient to cause the voltage clamping device to conduct, acting as an LC filter having a second high frequency break-point which is lower than the first high frequency break-point and which is determined by the second capacitance and the inductance.

An electrical circuit, comprising:

• a. telecommunications equipment comprising a current-carrying line and ground;
• b. a high-energy foldback device connected between the current-carrying line and ground;
• and
• c. an arrangement for protecting the electrical circuit from a voltage transient, the arrangement comprising
• (1) a voltage clamping device which has a first capacitance and which is connected between the current-carrying line of the circuit and ground,
• (2) a capacitor which has a second capacitance of up to 1 .mu.F and which is connected in series with the voltage clamping device, and
• (3) an inductor which has an inductance of from 1 .mu.H to 100 mH, and which is series connected in the current-carrying line,
• the arrangement, under normal operating conditions, acting as an LC filter having a first high frequency break-point which
• (a) is determined by
• (i) the first capacitance,
• (ii) the capacitance of any additional capacitor optionally connected in parallel with the voltage clamping device, and
• (iii) the inductance, and
• (b) is in the range of from 1 kHz to 10 Mhz, and
• the arrangement, when the arrangement is subjected to a voltage transient sufficient to cause the voltage clamping device to conduct, acting as an LC filter having a second high frequency break point which is lower than the first high frequency break point and which is determined by the second capacitance and the inductance.