The voltage limiting devices were introduced to avoid that, due to leakage currents through the insulators, the pole itself leads to voltages towards the local earth so high to constitute a danger.
A "bidirectional" version was also introduced, the additional purpose of this device was to prevent the tracks from reaching too high voltages that could be dangerous or induce damage (corrosion).
|CAT FS 779/005 categorical||SECOM code 110470R228|
|Unidirectional device||From the rail to the pole||Direct current||160A||Direct current T=60s||500A||Maximum reverse voltage||2800V||Maximum direct voltage drop||5Vdc||Trigger treshold||150Vdc||Protection (against atmospheric discharges)||Varistor|
|CAT FS 779/006 categorical||SECOM code 110470R128|
|Bidirectional device||same characteristics of the unidirectional device, adding||From the rail to the pole||Direct current||400A||Voltage drop||2Vdc|
|CAT FS 779/007 categorical||SECOM code 110785R1002|
|Bidirectional device with redundancy three of the trigger circuit and diode fault signal||Diode direct current||600A||Reverse voltage||2kV||Scr direct current||300A||Scr current for 10s||2500A||Trigger treshold||120V||Varistor protection with short circuit breakage and current not less than||50kA|