If you have a type-2 surge protector installed in your main breaker panel, does that render redundant any type-3 protectors plugged in to various outlets throughout the house? The only way I can think of that type-3 surge protectors might still be useful is if they are more sensitive than the type-2 surge protector in the main breaker panel. Otherwise, they would seem to be pretty useless, though not harmful. (I am not considering RF filtering in this question, which I think is a separate subject.)

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The real answer is in the specific brand and model of both types you have or plan to use. Some models break down at 400 volts some as high as 800-1000 with a Courdinated system there could be Benefits to having both on sensitive / critical systems. Most homes will be fine with a type 2 but these do fail and a redundant could save that very expensive device that has the type 3 protection in addition to the type 2.

  • Good points. And unless you open your breaker panel door on a regular basis, you may not even know your type 2 SPD has done its job, so your house may be without surge protection.
    – BillDOe
    Commented Oct 26, 2016 at 17:26

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