Late last summer my 4 year old AC unit fried its mainboard and the company which installed it originally came to service it. They suggested that the reason could be a surge, as they had a rash of calls in my area.

This season I wanted to install a surge protector and did some googling to find a few, which install into the breaker slot on the loadcenter. Do they replace a breaker? Or, if they do not, where should the breaker be then?

  • How a surge protector works is probably outside the scope of this stack, perhaps Elecrical Engineering would be better.
    – Solar Mike
    May 5, 2019 at 13:54
  • Not really interested in how it works conceptually, and removed this part as the only question I really have is where does the breaker go if a surge protector is installed.
    – user101251
    May 5, 2019 at 13:59
  • See diy.stackexchange.com/questions/51897/… for some discussion. The particular devices I use are wired into the circuit you want to protect without taking up an addtional breaker space. They provide some protecton for other circuits, so if you need to provide some whole-house protection but devices of interest are larger ampacity than the surge device, you put the surge device on a circuit that's fed by a breaker equal to or less than its rating - or get a larger capacity surge device.
    – Ecnerwal
    May 5, 2019 at 15:53

4 Answers 4


Surge protectors come in a wide variety of form-factors, and you don't even need to protect your whole house, you can protect particular circuits. That is decided by where you place the protector.

The problem with "surge protectors in a circuit-breaker form factor" is that breakers do not interchange across brands. You cannot put Brand X breaker in Brand Y panel, unless Brand X has specifically built that breaker for Brand Y panels and UL has tested and classified it for that use.

So you are probably better off using a "goes in a knockout" type suppressor. This will let you use anyone's brand and a common $10 breaker, instead of paying a big premium for one specifically for your panel. You can install this anywhere - it can go on its very own 2-pole breaker, where it'll protect the whole house. Or you can install it out at the air conditioner shutoff switch (if it's wet rated).

If you install it at the air conditioner, it will better protect the air conditioner (and the house from the air conditioner's own spikes) and less well protect the rest of the house from external spikes.

That's because long wire runs tend to weaken spikes also. By putting the spike suppressor at the air conditioner, the suppressor spends less of its bandwidth/capacity fighting surges that wouldn't make it to the A/C anyway, and 100% of its capacity on ones likely to affect the A/C.

Internal spikes are a thing. You can have one of your appliances damaging another, and large motor-driven appliances are a major culprit. Putting the spike suppressor near the air conditioner means it will "catch" any spikes from the A/C unit before they get near the rest of the house. It will also do a better job protecting A/C electronics from A/C motor spikes!

However a suppressor at the A/C unit will do a lesser job of protecting your computer from external power spikes, obviously, since the long cable run will dampen its ability to neutralize those spikes.

Nothing says you can't install as many surge suppressors as you please, so you can fit 1 at the A/C unit and 1 in the main panel.


In answer to your question Eaton makes a surge protector that fits into 2 full slots in your loadcenter. It can either replace two breakers or it can fit into slots that are currently just spaces. They also make a combination surge protector which allows you not to lose any breaker spaces. See below for specification.


Good luck


I don't know that I would want a surge protector inside my load center. Most of the ones I have installed have a feed from a double pole breaker and are housed in there own enclosure. The reason I would not recommend a surge protector inside the load center because almost all of them are metal oxide varistors , These break down and dump over voltage spikes to ground. I have seen the modules actually catch fire with large spikes, this is the reason I would not want to see them inside the load center. Since you have had large spikes I would recommend a large unit outside the breaker panel.

  • Could you share a few brand names/models of "outside the load center" protectors for further googling?
    – user101251
    May 5, 2019 at 16:10
  • I have had good results with both square D and leviton whole house surge protectors, the smaller ones less than 20 amps are the ones I have seen catch fire the ones that are 30 amp have lasted and not required module replacement, there is an area close to here that a cedar mill is on the same feed as close to 100 homes and when they start up and shut down there are huge spikes on the line, I started out with the smaller units but after several failures move to the larger units and they have held up going on 8-10 years where the smaller ones all failed within 3-4 years so the higher cost is ok.
    – Ed Beal
    May 5, 2019 at 19:28

Install a whole house surge suppressor in the main panel and then add additional protection for sensitive electronics with uninterruptible power supply which acts as a gap between the incoming power and the sensitive electronics.

The problem is that there's a loss in these devices because you're converting the power basically across a series of transformers and that actual loss cost real money. You need to decide if that cost is recuperated with the purchase of the additional equipment or the random voltage/current spikes are worth dealing with.

  • 1
    Um, you can't really put an air conditioner on a UPS.... May 6, 2019 at 4:32
  • A double-conversion always-online UPS has a series of transformers and therefore "costs real money". But a surge protector doesn't normally work that way, and a typical consumer-grade UPS is running as a surge protector (plus trickle charge the battery) except when power goes out. May 6, 2019 at 5:17

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