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Is there such a thing as a whole-house surge protector installed at or near the panel that can shield devices inside the home from surges originating on the mains, as well as shield devices inside the home from surges caused by other devices inside the home? I've tried reading about this but find conflicting info, and have spoken with a couple of electricians who say it's not possible to centrally protect all devices in the house from "intramural" surges; each device would need to be protected individually with its own surge-suppressor.

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    do not understand your dilemma. There are devices available "whole house surge protection"
    – Traveler
    Commented Mar 14 at 19:29
  • As one of the answers states Type 2 surge protectors provide some protection for surges whether they are externally or internally generated. All the hots come together in the panel. The Type 2 protector evidently prevents the voltage there from spiking. There of course may be and probably is a benefit to further protecting some delicate appliances at the receptacle or between the receptacle and the applicance. Commented Mar 15 at 15:49
  • HVAC company is trying to sell me two local device surge protectors for A/C, one for the motor up in the attic, and another for the fan outdoors, about $750 for the pair, but they said they would protect only those devices from surges, so I believe they would be type 3. So I am looking to see what can be done at the panel.
    – mr blint
    Commented Mar 15 at 16:04

2 Answers 2

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You are asking several questions, but the electricians are correct: no single central surge protector can protect all devices from surges originating both inside and outside of your house.

A whole house surge protector is also referred to as a Type 1 surge protector, mounted on the line side of a panel, and is intended to prevent surges from the supply grid from affecting your house. It cannot protect against "intramural" surges, such as one of your appliances experiencing some sort of spectacular capacitor disaster, or a lightning surge that comes in via unprotected data cables, or that one cousin eager to show off his DIY generator by plugging it into your living room.

Type 2 surge protectors are also generally placed at or near the panel, but on the load side. These aren't as common in residential applications as types 1 or 3, but may be used to isolate circuits that may generate large spikes (like HVAC systems), or for circuits that will have heavy appliances that have draw higher than the rating on most Type 3 protectors.

Individual surge suppressor such as power strips and other devices functioning at the outlet end of things are referred to as Type 3 surge protectors. They are intended to protect whatever is plugged into them from surges in the rest of the house, as well as protecting the rest of the house from surges originating from things plugged into them (as the "intramural" examples given above).

Any surge protector is a potential interruption in the web of circuits, that protects everything on one side of the interruption from everything on the other side. If you want to protect things that are on the same side of the interruption from each other, you need more interruptions. It comes down to your own evaluation of the cost of layering these levels of protection vs the probability of something going wrong and the expense if it does.

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    Surge protectors have parts, e.g., MOV's, that can short while stopping a surge. For that reason, there should be a fuse in the protector. This means that after saving devices from a fault, the protector is effectively "burnt out", no longer functioning. Even with Type 1 or 2 protection, having surge protection at outlets is worthwhile -- they've saved a computer in my house, when an unprotected lamp and a clock went up in smoke (no flames, though). Commented Mar 14 at 21:50
  • @DrMoishePippik about 15 years ago now, I experienced a nice weekend when the UPS at work decided to short and take out half our companies backoffice IT infrastructure. Servers were literally pumping out smoke. That was a relaxing weekend, for sure.
    – Moo
    Commented Mar 15 at 3:59
  • Whole house surge protectors can indeed protect virtually everything in the house, within the limits of their ability to protect anything at all. See my explanation below, which exceeds the permitted length of comments.
    – MadMonty
    Commented Mar 20 at 2:13
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**Whole house surge protectors do offer equal protection against surges originating within the house, except for devices on the branch where the surge originates and even there the risk is quite small (zero?).

A whole-house surge protector drops the voltage to a safe value (the clamping voltage) at the point it is connected, at the main panel the service line comes in and all the branch circuits come together. The voltage drops when the surge current passes through the wires to your house. (Whenever current passes through a finite impedance, the voltage drops, per Ohm's Law.) Every branch circuit has the same, safe voltage, so everything is protected.

For surges originating inside the house, the process is almost identical: the voltage surge sends current through conductors whose impedance causes the voltage to drop when the protector clamps it. That sets the maximum voltage for all the branches, preventing the surge from spreading to other branches.

The only branch where devices could conceivably be harmed is the one where the surge originated. But what device could cause such a surge? It would almost certainly have to come from a high-current inductive load. In most homes, only the HVAC compressor would qualify. But since code requires it to have a dedicated branch, there would be no other devices to damage, either on it or anywhere in the house.

The whole house surge protector a pretty wise choice to prevent damage from surges originating from either inside or outside. I have had one for my home for many years with zero surge damage and many thunderstorms. But two caveats:

  1. Surge protectors have finite limitations in how much energy they can absorb before they fail, and limited lifetimes.
  2. A lightning strike to your home may send catastrophic currents through several (or even all) the branches and damage the devices connected to them. The whole house protector mitigates but does not eliminate that risk.
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  • I am sort of in the dark about the precise meaning of certain terms, like "conductor". If I have a ground, a neutral, and a hot going to a device in the house, can a surge at that device travel back to the panel on the neutral and then proceed out to other circuits on their neutrals?
    – mr blint
    Commented Mar 15 at 10:33
  • Are any of the wires able to be a conductor?
    – mr blint
    Commented Mar 15 at 11:36
  • It is my understanding that a Type 2 surge protector installed in the panel can mitigate a spike or surge originating in that branch circuit and in all other circuits. I think some people misunderstand the nature of a "spike" by imagining the wavelength of the spike being short compared to the distance along the wire whereas in actuality the wavelength is long compared to the distance from applicance to the panel. The result is that the developing surge appears at the panel simultaneously with its origin in the appliance. Hence the Type 2 protector interrupts the development of the surge. Commented Mar 15 at 16:02
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    @mr blint, the metal of a wire is the conductor. If you define a wire as the metallic core plus any insulation, then the metal core is the conductor. Any wire can conduct a spike. Commented Mar 15 at 16:20

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