To ensure that the cost of installing surge protection devices for signal lines (for the protection of data, signal, and control circuits, etc.) is used effectively, there are 2 issues to:
Where should surge arresters be installed?
+ What type of surge arrester is suitable for each type of circuit and protection location?
+ Where should the surge protection device be installed?
Communication devices are often at risk of damage due to induced pulses on the signal lines connecting these devices. The use of surge protection barriers installed at both ends of the line is a cost-effective method of reducing this risk. The highest risk is present on communication lines and signal lines in and out of the building. In these cases, surge arresters should be installed at the entry point to the building or at the top of the equipment. Building conductors longer than 30' or 50' should also be protected. Twisting and/or wrapping the wire provides only a limited amount of protection, which should not be considered adequate protection for today's modern sensitive communication devices.
How to select the device for a specified location?
Five parameters must be considered to ensure surge arresters used in signal, data, or control circuits operate efficiently and do not adversely affect the operation of the circuit.
1. The surge arrester is designed to clamp the overvoltage surge down to a level that is safe for the device and does not affect the normal signal voltage. The clamping voltage of the surge arrester is selected in accordance with the maximum working voltage of the circuit.
2. The surge arrester must withstand the maximum signal current.
3. The bandwidth of the surge arrester must be enough for the system to operate smoothly without any signal degradation, that is, to ensure the loss of the surge arrester at the system's rated operating frequency. must not exceed certain limits. With most surge arresters, the maximum allowable frequency loss or baud rate data is usually specified.
4. Connection terminals, installation method, number of protection lines, and other physical characteristics must be evaluated.
5. The overvoltage protection level of the surge arrester must correspond to the installation location. For circuits inside the building, the minimum protection level is 0.25 KA. For circuits connected to the in/out lines outside the building, the recommended protection level is 10–20 kA.
Alternatively, a protocol or standard can define these five parameters. For example, CRITEC DEP-RS232/9/9 is designed to protect circuits that meet the V. 24 EIA-232 standard. Meanwhile, parameters 1-3 defined by the standard DEP-RS232/9/9 can be used in the RS-233 signaling protocol.