3. Low-Voltage Power System Basics · Page 3 of 6
MDB, SDB and Final Circuits
Map protection stages to the physical board hierarchy.
Main distribution board
Highest energy exposure. Often the home of Type 1 or Type 1+2 SPDs when an external LPS or overhead line is present.
Sub-distribution
Type 2 SPDs reduce residual surges before they fan out to many final circuits.
Final / equipment level
Type 3 or point-of-use protection tightens voltage for PLCs, servers, medical devices, and access controllers.