Seven-Delta-FortyOne
Goin’ Down In Flames........
- Location
- Humboldt
- Occupation
- EC and GC
Because I don’t understand completely how they work, I have this question
SPDs are wired in parallel, but is it required that power “pass” the SPD in order for it to function?
What got me thinking about this is an install on a system with an ATS that feeds several downstream panels.
If in place it at the main, obviously it will be offline when on gen power.
If I put it on the “load“ terminals of the ATS, will it protect the ATS itself, both on utility and gen power? Or would this require 2 SPDs, one on the main breaker, and one on the generator breaker?
Its a type 1 SPD any the way, so it can go on a 200A main.

SPDs are wired in parallel, but is it required that power “pass” the SPD in order for it to function?
What got me thinking about this is an install on a system with an ATS that feeds several downstream panels.
If in place it at the main, obviously it will be offline when on gen power.
If I put it on the “load“ terminals of the ATS, will it protect the ATS itself, both on utility and gen power? Or would this require 2 SPDs, one on the main breaker, and one on the generator breaker?
Its a type 1 SPD any the way, so it can go on a 200A main.
