I have compared in detail a Siemens QPF 2-pole GFCI breaker when put in an original Siemens PL load center bus bar versus that of generic locally made bus bar (for GE breakers). What I found out was there was no special shape in the Siemens bus bar. But they are very straight and uniform and thicker than the locally made bus bar. The latter local bus bar is a bit slant as they can't make it exactly 90% and since it is also a bit thinner.. the upper part of the Siemens breaker spring clip doesn't make full contact in that locally made bus bar. In the Siemens panel, one side of the spring clip has perfectly flat contact with the Siemens breaker while the other side is not so flat. Maybe because the breaker even needs thicker bus bar or design? Now I want to know other brand panel bus bar. Do you really see a special shape to it? Or the issue is just the thickness?

  • Welcome to Home Improvement! You could benefit a lot by taking a trip to an electrical supply outlet and physically handling and comparing some of the various name brand breakers. You likely will come away with a better understanding and answer for your question than you could get here. Also keep in mind that panel and breaker manufacturers do not have much incentive to allow cross pollination of their product lines with those from competitors.
    – Michael Karas
    Commented Nov 8, 2018 at 14:13
  • I live in a country where all our panels sold in electrical supply outlets are generic (made locally or in china). And all our breaker brands are only GE and not much. This is why I had to ordered Siemens in the US because they are not available locally. But I found the Siemens plug-in are perfect match to the GE breakers.
    – Samzun
    Commented Nov 8, 2018 at 14:19

2 Answers 2


The magic snap is not magic. Contact blades are not flat.

One thing you will notice about US breakers in matching panels is that they "Snap" in with a definite resounding snap. And when you try to remove them, the initial force needed to pull them out the first 0.1mm is considerably greater than the force needed to pull them the rest of the way.

That's because the bus bar in the service panel actually has a little "nub" shaped into it, of a specific shape. That shape engages matching curves on the breaker's spring clip. It works like a detent, creating the snap. However the good contact also creates a lot of mating surface area. As such, it runs at sane temperatures during high current flow, which is why UL approves it.

Every panel manufacturer uses a different shape of bus bar, requiring different shaping on the breaker's spring clip. They are different because of patents. Each manufacturer has patented their shape, because they think it outperforms their competitor's shape (and avoids violating their competitor's patents). Eventually patents expire, such as Square D's QO (queue oh) patent expired, permitting Murray/Siemens to manufacture its QD (queue dee) breakers for QO panels. Still, Siemens is unable to make breakers that fit both Murray and QO panels, because they are still different. They are locked into the old designs because new breakers need to fit old and new panels alike.

So when you use an alien breaker, the clips and nubs don't mate as intended by the two manufacturers, and this is not an accident, it's by design. They are not trying to keep you from using alien breakers, they are (were) trying to keep from being sued for patent infringement. Anyway, you end up with the clips only mating at 2-4 points instead of flat surface contact, and point contact like that is only good for a couple of amps before it starts melting, opening, arcing and burning.

  • 1
    This is why I still prefer the DIN-rail mounted breakers I'm used to. The snap-in US breakers certainly are more convenient to install & replace, but with DIN-rails you can more-or-less mix&match as you please and you're not locked into a particular manufacturer.
    – brhans
    Commented Nov 8, 2018 at 17:45
  • Oh no. I installed the 2 pcs Siemens 2-pole GFCI breakers yesterday into my home panel after I found out it could fit. See updated picture above of the my panel. So if I remove the Siemens breaker and try to see the bottom.. can I see burn marks in the breaker plug-in connector? And about burning.. what exactly would burn, the connector or the whole panel? Each pole of 16 2-pole breakers is 120v. There is no neutral or ground bar. So using a GFCI tester, can it work if I connect it to one pole (120v) and to the centertap of the autotransformer which also powers the Siemens GFCI breakers?
    – Samzun
    Commented Nov 8, 2018 at 21:02
  • Afraid you r right (some1 didn't gave me the technical b4). I hurriedly removed the 2 Siemens to prevent arcing and all the horrors. Then I compared the Siemens plug-in clips to the GE's see: imageshack.com/a/img923/5629/P41jSN.jpg The one on the GE (right) is flat while the one on the Siemens (left) is slant.. so you guys have a point. All the bus bars used in Philippines are flat, see pic at imagizer.imageshack.com/v2/800x600q90/921/YsAHaa.jpg... maybe this explains why all of us use GE breakers? Question: Are all GE breakers like that able to use any flat generic bus bar?
    – Samzun
    Commented Nov 8, 2018 at 23:08
  • to add to the above comment.. I'm wondering... see 2nd picture I added in the original message.. Where is the "nub" located? is it in the upper, middle or lower part of the breaker clip? I think that if 60% of contact can be made then it is as good as full contact because remember it has more surface area than a wire of similar rating. Can anyone show me picture of an actual nub in any brand of breaker clip and panel bus??
    – Samzun
    Commented Nov 9, 2018 at 0:43
  • Anyway. I just ordered this 12 space-24 circuit Siemens panel..amazon.com/gp/product/B005GLDMTY/ref=ask_ql_qh_dp_hza I think it will fix my 6 Siemens breakers perfectly with the nub aligned. Hopefully all Siemens panel and breakers have one kind of nub. In case there are many kinds in same brand.. let me know immediately so I can cancel the amazon order before it ships, lol.
    – Samzun
    Commented Nov 9, 2018 at 8:23

Let me rephrase your question. I have a Chevy why can't I put a Ford motor in it if it fits?

Some breaker panels only accept a certain breaker. Sq D type "QO" and Cutler Hammer type "CH" come to mind. Many others will accept a standard breaker if approved by UL. What I have discovered is that some types of these breakers do fit but not quite as well as original equipment.

Most breakers you are referring to are basically used in residential plug-in loadcenters (Panels). Plug-in breakers have a spring loaded slot which press against the bus and if it is not original equipment it could be misaligned. This causes a point where resistance and heat could possibly cause a failure of equipment. So consider the price of getting original equipment and replacing the Panel.

Most of what you see when using an alternate breaker is just a matter of convenience where you have easy access to one type of breaker and the original equipment breaker will take more time and money to get your hands on it.

In conclusion:

Is it approved and will it work? Yes

Is it considered good workmanship? In my opinion No.

Does it affect the electrical system? It could void your equipment warranty.

Hope this helps.

  • Do you have illustration for this "Plug-in breakers have a spring loaded slot which press against the bus and if it is not original equipment it could be misaligned.". I think it is the most critical. Do all Plug-in have them?
    – Samzun
    Commented Nov 8, 2018 at 14:00
  • They're not approved, though. GE breakers will snap into a Challenger panel (badly). But only BR breakers are cross-approved for it. Commented Nov 8, 2018 at 16:32
  • Guys. So I will need to use a separate Siemens panel now (I thought the warning of mixmatched panels and breakers are just nitpicking). I ordered 4 additional Siemens GFCI before you guys gave the reason of the incompatibility (I can't return them) so I now have 6 Siemens GFCI (2 pcs 60A, 4 pcs 30A). Question. Can I use one existing breaker bus to connect to the 6 sub breakers? What is usually the ampere capacity of one breaker bus? see picture of my panel at original message above and my breaker bus bar at imagizer.imageshack.com/v2/800x600q90/921/YsAHaa.jpg
    – Samzun
    Commented Nov 8, 2018 at 23:12
  • Say. Are all models of Siemens panels and breakers have similar nubs in the bus bar and plug in clips or do they also differ between different models even if same Siemens brand?
    – Samzun
    Commented Nov 9, 2018 at 3:30

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