The protection concept consists of a combination of components that complement each other in terms of functionality:

• Surge arresters filled with noble gas as coarse protection (G1, G2)
• Inductance that limits the rise of the current (L1, L2)
• Metal-oxide varistor as surge protection (voltage-dependent resistor; R1)
• Translator for galvanic decoupling (T1)
• Suppressor diode for limiting the secondary voltage of the translator (V1)

The overvoltage protection module LTOP is available in two variants:

• LTOP 1;
  overvoltage protection module for use at the beginning or at the end of a 2-wire cable
• LTOP 2;
  overvoltage protection module for use at the beginning or at the end of a 4-wire cable or at a 2-wire grading point. At a 4-wire graded point, two LTOP2 units are needed.

Both LTOP variants feature screw-type terminals and an RJ12 Western jack. The WAN connecting cable (RJ12 - RJ12) that came with the MD2 and MD3 modems (used as dedicated line modem) can be connected directly to this RJ12 jack.