Whole-house surge protection: "intramural" surges

Question

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.

Answer 1

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.

Answer 2

**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.