whole house surge protector

I installed in Siemens electrical panel two Siemens 60kA BoltShield protectors.  They are in the form of dual circuit breaker and just plug-in into empty spaces in the panel.   You can as well install Siemens FS140 that will work with any panel.  Yes, most of MOV based protectors clamp at 400V or higher, but voltage spike produced by lightning or broken power lines (like during icestorm) is very short, reduced further by filtering effects of wire inductance, limited transformer frequency response etc.  This is first necessary step.   In addidion my system is plugged into Furman Elite 20PFI power conditioner with tight non-sacrificial over/undervoltage protection.  Still, during thundersorms, or when away, I unplug.

As for negative effects - Parallel protection like MOV based surge protectors have none, while my Furman has high current outputs for the power amp.  I believe there was slight difference with my previous amp but none with the current Benchmark AHB2.  It is likely because AHB2 has line/load regulated SMPS.

The issue might be inductive reactance.  Inductance is likely in order of 300nH/ft.  It is not a lot but even the smallest reactance with thousands of amperes clamped (my Boltshields are rated 60kA each) will produce big voltage drop.  Sensitive circuitry powered closer to the power entry will see this as additional voltage on the top of already high clamping voltage.   Same goes for plain resistance of the copper bar in the panel.  Even if total resistance is in order of 10mohm it will produce 100V drop at 10kA current.  We're talking extremely short spikes (1-30us) of huge energy.  It is always good practice to place clamping device like MOV or TVS close to power entry.