I see a lot of that in my area. SD HL, Siemens/ITE, CH/BR, GE, a few Challenger and old T & B. I try to keep enough breakers not to mix them, but I don't swap them if already there. Though not UL approved, I haven't seen any more trouble from mixed brands than those kept "pure". I don't see UL as that great of a quality symbol anyway. They approved backstabbing, Federal Pacific and Zinsco. I rest my case.
UL is not necessarily a guarantee of longterm quality or performance. Many product performance issues are directly related to the level of workmanship or application. However, any NRTL will "pull the listing" as soon as they validate that the product does not meet standards. The key word is "validate" and this could take a long time depending on the severity and consistency of the problem. They did this with Zinsco in the early 70's and Federal Pacific more recently.
A panel manufacturer is not required to have an NRTL evaluate competitor brands breakers in their panel. (maybe they should..). Some panel mfr's have purposely "keyed" their breakers to their panels so that their breakers cannot be used in any other panel except their own. However, there are other possible performance issues that could cause safety and reliability issues (i.e. slightly different busbar tolerances/designs, different breaker contact designs, etc.).
In Zinsco's case, the failure was primarily at the aluminum busbar / breaker interface and high contact resistance. The failures increased over time which would indicate a possible relation to oxidation or loss of contact pressure. When these breakers failed to trip or encountered a short circuit situation, they blew up or caused the conductors to heat up and melt. Because of the relatively cheap design and price point, better materials were not used. They were sufficient to pass the initial UL testing at the time.
With regards to FPE, not only were the panel/breakers substandard, the test results at UL were misrepresented.
In a class-action lawsuit against FPE/Reliance in New Jersey, the Court found that Federal Pacific Electric Co. (FPE) committed fraud by representing that their FPE Stab-Lok(R) circuit breakers met the applicable (UL) standard test requirements when in fact they did not. The Court's finding of fraud, published in 2005, indicates that FPE cheated on the tests that were required to obtain UL listings. The company improperly applied UL labels to circuit breakers that could not and did not meet the UL requirements. FPE covered up the defective performance of the circuit breakers by a long-standing practice of fraudulent testing. The Court's finding helps resolve the question as to how the defective breakers got into the marketplace and into homes." -- 2007 FPE Stab-Lok TECHNICAL REPORT, p.1, Dr. Jess Aronstein
http://www.inspectapedia.com/fpe/FPE_IAEI.htm
http://www.inspectapedia.com/fpe/FPESummary.htm
I am sure more stringent oversight and testing of overcurrent protection devices have been put in place at all NRTL's since FPE, and more recently, with SquareD counterfeit CB's.
The bottom line, is that while *most* manufacturers follow the proper protocol and procedures, there are some that cut corners in order to gain a price edge. We all know where that leads...:roll:
