Mains surge suppressor teardowns

I saw a request for circuit diagram in Facebook electronics group: Hello feds. Required surge protector circuit. Working on 220v. 50hz 10amps load.

I first offered this reverse engineering of one commercial mains surge protector “Ahlstrom 23 368″.

The manufacturee component codes of the exact components used.
S20K250 is a varistor for 250V AC / 320V DC (390V varistor operating voltage) 140J 8kA
UZ470B32 is a gas discharge tube surge arrestor with voltage rating of 470V

Unfortunately it seemed that the UZ470B32 TUBE was no longer available.

Then I mentioned that some commercial surge protectors and built in protection inside some power supplies have been built with only VDR between live and neutral (and some cases between neutral and ground, and sometimes even live and ground).

I decided to make a tear-down and reverse-engineering of another commercially sold surge protector (no brand name on case). It uses three 14D471 varistors and indicator lamp (glimm lamp with 120 kohms current limiting resistor). The 14D471 varistors are 14 mm diameter 470V DC rated (300V AC). One is between live and neutral. The other two are from live to ground and neutral to ground.



  1. Tomi Engdahl says:

    Y08UZ-470B New plug-in ceramic gas discharge tube UZ470B 470V lightning pipe U-9B 2R470.

  2. Tomi Engdahl says:

    Never Use a Surge Protector with a Step-Down Transformer


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