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I have two Square D QO main panels split from a 320A service. They make a plug-in whole house surge protector for these panels.

Question: Would a QO plug-in surge protector placed in either panel protect the whole house, including circuits in the other panel?

The panels are right next to each other, and the service is split in a gutter right next to them. The phases and neutral are joined together at the split, less than two feet of cable away. The neutrals and ground are all bonded in the panels and via metal pipes and ground straps between the three boxes.

Secondary question: Right now the loads are spread randomly between the panels. I may one day rearrange all the loads in the two panels so that one of them can be a critical-loads panel. If I do that, the surge protector should be in that panel, I believe. And then, during an outage, the other panel will remain connected to the (dead) utility and have no surge protection. Is that the way to go? Is there any sense in putting a surge protector in each panel?

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  • I don't have complete understanding, but think a surge protector should close to the feeder wires(in the main panel), but you almost have two panels with their own feeders. One protector might work, but I think you need one in each panel to be safe. Any surges will follow the split also and go to each panel together.
    – crip659
    Mar 15 at 15:59
  • I don't have a complete understanding either. Obviously. :) But I think vaguely the suppressor "absorbs" spikes, similar to a water hammer arrestor, and if you think of the suppressor and one random electronic gadget in my house being on distant leaf nodes of a tree, I don't see why it would matter if there's a little extra branching near the trunk. Hopefully someone understands this better.
    – jay613
    Mar 15 at 16:04
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    This question talks putting a surge protector in a sub panel, that might help some. diy.stackexchange.com/questions/259752/…
    – crip659
    Mar 15 at 16:46

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Answer: Not if the cables are to long.

In Germany we have surge protector in the main-panel and if the cables to the sub-distribution-panel is more than 9 meters away, then they get their own surge protector-unit. This is because of the electromagnetic field, it can induce a current into the cables of the house.

The distance to the surge protector should be very short.

There 3 types of surge protectors.

  1. The protection in the main-panel, this is made with gas tubes. The distance is low enough to create a plasma arc if the voltage is much to high. If this happens, then the fuse of the main panel drops.

  2. The protection after the energy metering device is normally a varistor with Uc = ~275V.

  3. The fine protection what you can plug into the power outlet or between the power point and the PC.

A surge protector is a varistor or a gas tube with a little thermal fuse. The fuse inside of the varistor-surge-protector is there to protect the varistor from burning if he get to hot.

https://en.wikipedia.org/wiki/Surge_protector

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  • "The distance to the surge protector should be very short" --- the distance from where to the surge protector? In the question linked by @crisp659 there are suggestions the protector should be EITHER near the outside power source OR near the device to be protected. So it seems to me that "whole house" protection is a matter of designing a compromise that protects a lot of your devices from a lot of threats a lot of the time. Perfection would dictate surge protectors everywhere.
    – jay613
    Mar 15 at 17:57
  • If you install the surge protection, then the wires go from the electricity meter to the surge protector and then to all the circuit breaker. This wiring should look like an "i" and not like a "T". The live wire and the Earth should be close together, so that you do not create a coil. The way from the incoming live wire to Ground should be the lowest resistance, so that the household devices do not get harmed.
    – MikroPower
    Mar 15 at 18:24

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