I'm looking to install a Schneider surge protector at the main breaker, likely this one: https://www.amazon.com/gp/product/B00CONA1OQ/

enter image description here

The key things in the instructions which I'm trying to resolve:

  1. Install it as close to the top (main feed) of the panel as possible

  2. Use an empty 20A 240V breaker

  3. In some jurisdictions (I'm in FL) you can piggyback it onto a used breaker by wiring it in the same hole as the existing wiring, but otherwise, you can consider adding a new breaker.

My panel looks like this: enter image description here

So, my questions:

  1. The breakers at the top are 60A, will it matter if I use one of these?

  2. If I do, can I piggyback it in with the wires in that 60A breaker?

  3. It looks like there's a spare 30A breaker near the bottom. Does that look right? If so, will it matter that it's not 20A, and also that it's not closer to the feed?

  4. Is adding a new breaker at the bottom feasible?

Closeup of that empty breaker and the current space at the bottom: enter image description here


I have an older house which doesn't have grounding throughout, and I'm wanting to put some surge protection in. I've read mixed info on whether a ground is required for surge protection at each socket, and in the end decided it's just going to be easier to do it at the main breaker.

  • What type of breakers does the panel currently have in it? Double-tapping a breaker lug is a function of that breaker's UL listing, not of any rules in Code I've ever seen... Dec 3, 2017 at 18:40
  • Makes sense, and I'm assuming you're talking about which brand? I can't see this from my pic, is there a specific way to do this? Pull one of the breakers off the bus?
    – Geoff
    Dec 3, 2017 at 19:22
  • 1
    A whole-house surge protector is a good investment. Especially if you live in a lightning-prone area. But it is not a complete solution. See this IEEE presentation for why you should have layers of surge protection (ieee-sfv.org/app/download/9493392/…)
    – Stanwood
    Dec 4, 2017 at 2:52
  • 1
    Standard MOV surge protectors shunt excess voltage to ground. But there are other designs that depend only on the neutral line. The simple diagrams in the IEEE paper show how this is done. I would advise that you supplement whole-house suppression with local point-of-use suppression and if you can't do this on a grounded outlet then buy a surge suppressor that doesn't require it. Here's one company that touts this but there may be others: zerosurge.com/ungrounded-buildings-older-homes.
    – Stanwood
    Dec 4, 2017 at 2:57
  • 1
    That looks like a zinsco panel, if you are concerned about safety get a new service panel and upgrade to 3 wire. Don't put the suppressor on a breaker larger than it is listed for. When the MOV's take a very large spike out (if not properly protected) they will burst into flames.
    – Ed Beal
    Dec 4, 2017 at 15:16

2 Answers 2


First I would like to extend my sympathy for you having a ZINSCO Panel. It is without question the worst panel ever manufactured except for a Federal Panel. However I must say that it has kept many an electrician employed on the replacement of these panels. The breakers have a tendency to weaken and spread over time and that causes arcing and overheating on the bus basically destroying the panel. I would recommend replacement at you earliest convenience.

Now on to your problem. The surge arrestor is designed to be installed on a 20A/2P breaker. If you try and connect it to a larger breaker you are not protecting the Surge arrester circuit small as it may be. In Commercial installations we are required to install in line fuses if we are installing on a larger breaker.

Tapping on to another breaker is allowed but only if that lug is designed to accept two conductors. The only two residential breakers that allow this that I know of are Sq D QO style and Cutler Hammer CH style and definitely not ZINSCO. So you will have to pigtail the conductors of the Surge Arrester to another circuit, then connect it to the breaker.

Mounting the Arrester anywhere on the panel after the Main doesn't have a profound effect on the Arresters use.

Hope this helps.

  • Thanks for the panel identification - I'll put replacing that on my list! Pending that potentially very expensive job, does it look feasible to add a new 20A (2 pole) breaker at the bottom of the existing panel?
    – Geoff
    Dec 4, 2017 at 14:44
  • I agree with RME on the zinsco , not as bad as federal Pacific but should be replaced. There may be room is there a listing on the case that is ledgable for the max # of breakers? You can still get them but the aftermarket ones are quite expensive. I would pig tail and use an existing breaker and put the dollars saved into a replace the panel fund. The protector will only use power when there is a strike or bump but if the 20a circuit is heavily loaded it will trip faster.
    – Ed Beal
    Dec 4, 2017 at 15:28

In this case I wouldn't even bother fitting a whole-house-surge-suppressor here. I'd fit it in the respective subpanel(s).

When they say "put it as close as possible to the main breaker" that is simply stock advice. That doesn't necessarily fit your unique situation. You don't care about surge suppressing loads which are not surge sensitive.

*What's more, it's easy to think of "surges" as something that come only from outside the house. That is not true, and not likely, since transformers naturally suppress surges. An equal threat is your own appliances. So you want to be where appliance branch wires come together, e.g. at your subpanel.

I mean, I see three 60A breakers sending #6 cables off to faraway places; that's awfully large for anything but electric furnace heat (which doesn't need surge suppression), so I have to assume at least one of them is going to a subpanel, into which are wired all your 15/20A branch circuit loads. Put the surge suppression there.

As an aside, I note that 30A breaker is an odd duck. Normally, at first glance we assume that is a "double-stuff" breaker with both outputs on the same pole. Not on Zinsco. Zinsco builds that as a 2-pole breaker. It has 2 clips, typically on opposite poles, and they can be field-reversed so you have to check it (measure for 240V across output screws).

Regardless, the 1 wire I see on that 30A breaker is way too small for a 30A breaker. It looks like a #14. It should be pigtailed, so it shares the 15A breaker with the #12 wire already going to it. *Hey, at that point, the 30A breaker is totally free! Weren't you looking for a place to attach a surge suppressor? Regardless, I still would put the whole-house protector into the subpanel with the 15/20A branch circuits.

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