# How to compute panel bus bar stab and breaker spring clip electrical contacts area

This is zoom of the image below showing the gaps and seeimingly insufficient electrical contacts between bus bar and breaker spring clips. Siemens seems to treat it as normal. So let's compute instead.

An electrical engineer told me:

"Compute the area as you would any rectangle. Remember that there is still a gap for a short distance below the edge of the feeler gauge.

I've never investigated that. But it would seem the contact area would have to be no less than the cross sectional area of the maximum wire size for the breaker... and probably a little more because of the added resistance due to the pressure contact versus the continuous metal of a wire."

To compute it, must I use the table for 60c, or 75c or 90c in the following?

https://images.homedepot-static.com/catalog/pdfImages/a7/a767224b-82d0-41a6-a02f-316c94392ce1.pdf

Original message:

Does anyone know where I can get thin copper conductor sheet. The spring clip and bus bar of original Siemens breaker and Siemens original listed enclosure panel is not making full contact (only at bottom) and Siemens won't admit they are incompatible.

So if I can insert thin copper sheet cut to the bus bar size.. then it can make spring clip and bus bar establish full contact. The bus bar thickness is short by 0.5mm or 1mm.

All Siemens load center bus systems are exactly the same and have been for decades, going back to when they were ITE brand before Siemens bought them in the 1980s. Nothing has changed. If this were a design issue, there would be countless fires, lawsuits etc. Siemens is the world's largets electrical company, something that lawyers drool over. So they would be all over this like stink on a pile of poo.

So there are three possibilities here;

1) You have a COUNTERFEIT breaker, which has been happening a lot with breakers being sold over the internet, even through big outlets like Amazon.

2) You bought a used / "refurbished" (no such thing) breaker and it had been subjected to a lot of heat, likely due to overloading, to where the springs have lost their tension.

3) You have a defective breaker. It happens, but generally Siemens catches it and issues a recall. Now, as it so happens, there WAS a recall of this series of breakers by Siemens back in 2010 for this EXACT reason! So whomever you bought this from either failed to notice that, or pulled them out of a garbage can back in 2010 and is selling them at 100% profit. If you can prove that you bought this from an AUTHORIZED dealer of Siemens equipment, they will likely replace it for you. If you bought it from FleaBay or Amazon or some surplus site, good luck with that... When the price looks too good to be true, it is.

https://www.cpsc.gov/Recalls/1998/cpsc-siemens-energy-automation-inc-announce-recall-of-gfci-circuit-breakers-used-with

• No. It's not a counterfeit breaker nor a refurbished nor defective. Are you saying that if it's real original Siemens Breaker, then something is wrong and they need to recall it?? The springs are in original tension.. this is the reason it's not straight because when you insert it to the bus bar.. then the clip opens up from below.. please see picture of the spring clip of this Siemens QF260A here imageshack.com/a/img921/5351/9r36c6.jpg Nov 19, 2018 at 23:31
• I'm saying they DID already recall that series of breaker in 2010. So if you ended up getting one that should have been recalled through a legitimate channel for Siemns products, you should be able to get it replaced. Nov 20, 2018 at 2:44
• I checked the issue number.. my GFCI is current. Say. If Siemens would say it's normal for the spring clip and bus bar to have a gap with only bottom touching. You mean this shouldn't happen and they are due for another recall of the current batch? Or is the contacts at bottom only still allowable? Nov 20, 2018 at 3:48
• The amount of surface area making contact is important in any electrical connection like that. I doubt it is supposed to be like that but I can't say if that is a sufficient amount of contact or not. What can happen with mfrs is that they don't need to re-test everything to UL once it has already passed, but over time, tolerances can "drift" as machinery wears out etc. You may have discovered a new problem for them, but maybe not. If you use it, get an IR thermal scanner and watch the temperature of that connection periodically. Nov 20, 2018 at 20:47
• J. Raefield. Siemens seems to say the gap is normal. Please see my measurement and computations of the electrical contacts area in the Answer below and comment how to compute for the resistance of the pressure contact and factor in the area of the electrical contacts. Thank you. Nov 22, 2018 at 8:38

I want to partially answer my own question. This will be my last inquiry so please bear with me one last time.

I will attempt to measure the electrical contact area between the bus bar stab and spring clip. If it is ballpark, then it's acceptable. If not, then Siemens will need to recall hundreds of thousands of GFCI 2-pole breakers which they did in 1998 as J.Raefield detailed above.

Now for my measurements:

from bottom view, the width of the spring clip is 7mm.

This is the front showing only 2mm of electrical contact between the stab and spring clip.

so the area is 7mmx2mm = 14mm

Now in the AWG size and cross section conversion...

https://www.rapidtables.com/calc/wire/awg-to-mm.html

14mm corresponds to AWG 6. And in this amperage and insulation temperature table... https://images.homedepot-static.com/catalog/pdfImages/a7/a767224b-82d0-41a6-a02f-316c94392ce1.pdf

You get 65A for the 75c column (75c because this is the terminal temperature rating of the breaker). And this is only for one side of spring clip. For 2 sides, the capacity is 65A x 2 = 130A!

So even with the partial electrical contact, there is already 130A.

What is wrong with my computations? I know we need to factor in the resistance of the pressure contacts, how do you do that?

If it is ballpark. Then it is allowable. But if not, then Siemens would need to recall all the GFCI 2-pole ever sold that uses the spring clips.