Surge protection for data lines

A surge protector for a data transmission line including first and second data signal conductors, the surge protector comprising:

• first and second normally non-conductive "crowbar" devices each of which becomes conductive when subjected to a predetermined breakdown voltage;
• connector means for connecting each crowbar device between one of the data signal conductors and a reference potential in a circuit configuration such that, in the event of a voltage surge exceeding the breakdown voltage on the one data signal conductor to which it is connected, each crowbar device is driven conductive and establishes a very low impedance path from its associated data signal conductor to the reference potential;
• and an inductive reactance connected in series in each of the low impedance paths to materially increase the effective impedance in the path established by that crowbar device from its associated data signal conductor to the reference potential for a brief interval after the crowbar device is driven conductive;
• the surge protector including no appreciable resistance in series with either data conductor.

A secondary surge protector for a data transmission line including first and second data signal conductors, the secondary surge protector comprising:

• first and second capacitors connected to the first and second data signal conductors, respectively;
• first and second normally non-conductive threshold devices, each having a threshold voltage in a range of approximately ten to seventy volts;
• and means for connecting each threshold device in series with at least one of the capacitors in a circuit connected to a reference potential;
• the secondary surge protector including no appreciable resistance in series with either data signal conductor.

A combined primary/secondary surge protector for a data transmission line including first and second data signal conductors, the surge protector comprising:

• a blocking-diode bridge having first and second anode-cathode terminals, a third anode--anode terminal, and a fourth cathode--cathode terminal;
• two blocking diodes external to the bridge;
• each of the first and second bridge terminals being connected to one of the data signal conductors and each of the third and fourth bridge terminals being connected to a reference potential through one of the two external blocking diodes;
• a normally non-conductive threshold device connected across the third and fourth bridge terminals, the threshold device having a threshold voltage approximately in the range of ten to seventy volts;
• and
• a normal non-conductive crowbar device connected across the third and fourth bridge terminals, the crowbar device having a breakdown voltage approximately in the range of two hundred to three hundred volts;
• the surge protector including no appreciable resistance in series with either data conductor.