The author proposed article in one of thunderstorms exploded electronic telephone with caller ID of the caller (caller ID). The same happened at the neighbors. Had to buy a new phone and engage in the manufacture protective device for simultaneously solving the problem of noise suppression television receiving, created by the handset with caller ID.
In wired communication lines often occur surge caused the influence of atmospheric electricity and lightning. Especially in rural the area where the connection is by wire, suspended on poles. Voltage as between the wires and between the wires and the ground can reach hundreds and even thousands of volts.
Of course, landline phone, well insulated from the ground, dangerous only direct lightning strikes in the wires. Some elements of the apparatus, not provided no protection, can be simply destroyed flowing at the moment discharge current. But the electronic "stuffing" modern phone much less hour, it can damage even a relatively weak pulses induced in telephone line distant lightning.
For the device, powered from the network, the danger is, and the difference potentials occurring between the earth and a telephone line under the action of atmospheric electricity. Applied between the secondary and primary (usually grounded via the network) windings of the power transformer, it" may cause the breakdown of the winding insulation.
Circuit protection device installed in a village house telephone is shown in Fig. 1. Resistors R1-R4 and capacitors C1, C2 are mounted on the Board from foiled fiberglass.
In foil cut pad for soldering parts (Fig. 2). The function of fuses F1 and F2 perform free from metal, the gap width of 0.3...0.5 mm. Cost a metal screen (the author has used the body of an automotive relay control) mounted on the wall at the entry of the telephone line and connect a cable with a standard the phone Jack X1, installed indoors. The screen and the main part foil on the circuit Board ground, connecting them with a wire 2.5 mm2 or more with hammered into the ground near the metal probe length of at least 1.5 m.
When a direct lightning stroke to the line break dischargers F1 and F2, closing the current the earth. The limiting resistors R1 and R2 in this case, as a rule, burn up, so mount them so that the replacement of trouble. Chain R3C1 and R4C2 give additional protection. In a short thunderstorm pulse the voltage on the capacitor does not have time to rise to a dangerous value.
The described node is sufficient for normal not having electronic components phone that can be connected directly to the socket X1. But electronic apparatus requires additional protection. Two pairs of connected counter-consistently diodes VD1VD2 and VD3VD4 in normal conditions do not conduct current. But if the voltage between one or both wires of the line and the earth will exceed the allowable return for diodes, they will breakdown and accumulated line static charge "flows" into the ground. Typically, the breakdown is reversible, but the diodes are still needed periodically check and replace if necessary. The last step protection (Zener diodes VD5 and VD6) limits the voltage at the input of the device safe his value. Not to create a burden on telephone station, the voltage stabilization has some margin to exceed 60 V for domestic or 48 for the import In the PBX.
Inductors L5 and L6 preventing the flow in the telephone line interference generated by the electronic units of the phone with the caller ID and inductors L1 - L4, together with capacitors C3 and C4 form a low pass filter, a second level interference penetrating the lighting network.
Capacitors C1, C2 - K15-5. Diodes VD1-VD4 must be the same type with iobr more 100 V. to Use diodes with Uo6p above 500 In inappropriate, it will not give protective effect.
The device was operated with telephones "RUS classic version 27 PRO" and "Range-315" separately and connected in parallel. In over the summer there were three severe thunderstorms. As a result one of them out of order resistors R1 and R2. Other elements, including diodes VD1-VD4, left whole.- Damage to telephones was not.
Do not operate a ground device without connecting it to the grounding in Any case do not use "surrogate" ground, the number of zero wire outlet. Do not perform the installation or replacement of elements in the approach of or during a thunderstorm. It is dangerous for life!
Author: A. Ekimov, c.Omutinskoe Tyumen region.