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I’m just learning about whole home surge protection devices (SPDs). I recently upgraded my electrical panel and decided to add the panel brand’s latest model of in-panel SPD.

The data sheet for the SPD is here.

In the data sheet it says that I can install multiple SPDs in the panel for an increase in modes of protection. Where I am confused is connecting one SPD to the N bus and one SPD to the G bus, since in a main panel the N and G bars are bonded.

Question: if I have one SPD installed L-N and I want to get all 6 modes of protection, do I need to add an L-G connected SPD? Or are all 6 modes already covered in the main panel just by connecting the SPD L-N?

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  • You are not getting an additional mode of protection unless it's a sub-panel. You are getting Marketing Male Bovine Organic Fertilizer to sell you more devices. See also: diy.stackexchange.com/a/51903/18078 (nothing specific to "plug into the panel" devices, just surge protection in general.)
    – Ecnerwal
    Apr 10, 2022 at 13:06
  • Thanks for the responses.
    – RibaldEddie
    Apr 10, 2022 at 18:04
  • I don't know why anyone would buy a SPD that has a 10 year warranty when you can get the Eaton Cutler Hammer that can install into any panel with a lifetime limited warranty.
    – Fresh Codemonger
    Apr 11, 2022 at 16:41

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As with anything, the device must be UL-approved (NEC 110.2) and you must install it according to the instructions which UL approved (NEC 110.3). Googling QSPD-2-A-065 instructions brought them up. Page 2 says

Note: If the user is connecting the WYE SPD unit to the ground bus bar in order to change/increase the modes of protection or increase the surge current capacity, wrap the white wire with green electrical tape as per code.

So yes, it is approved to do this. However, since neutral and ground are already bonded in a main panel, I don't think this would provide any additional "modes of protection" - it would only increase the surge current capacity.

However if my goal was to do the latter, I don't think I'd be using the "fits inside a breaker space" type of surge. They are inherently limited due to the limited volume of space. A wire-up type will not be so constrained. But look at the specs and see for yourself.

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