Duke Power Zinsco Panel

[Chapin Ratte]

AllI had to do was to shut off power at the meter, disconnect both feed wires, pull off all of the breakers (allowing them to hang from their wires), pull the two mounting screws from the bonding bar assembly that also holds the bottom end of the bus bars, and slip them out. I then polished the metal a little with steel wool, put the original left bar in the right slot, right in left slot, connected the feed wires, pushed the breakers back in place and put the cover back on.

Pretty good idea you got there. Mine did the same thing. I didn't even try that. I just changed it out. My thinking at the time was If I have one 220 breaker go bad then I can cover the cost of the new panel. $80.00 at the time. I had previously lost one 15 amp breaker and when I put in my hot tub I had to get a new double pole breaker. I had scrounged them up at work so I got lucky. But the cost would have been pretty steep if I had to pay for them.

Old panels often have too few breakers for the necessart circuits. For example, since Zinsco went to the "great scrapyard in the sky," we've come to recognise a need for at least two kitchen circuits. An old house will often have problems with breakers tripping, as too many appliances are used at once.

I agree with Renosteinke, Maddog and Zak, that old places are under-wired by todays standards, but for a single woman in a 900sq foot townhouse, I think re-wiring the place to provide multiple circuits in the kitchen and additional circuits in other rooms would not be worth the cost.As for Zinsco replacements being re-conditioned, I know that they used to be, but there is at least one company making new replacement breakers for Zinsco panels.I inspected all of the breakers before putting them back in the panel and there was no sign of heat damage to cases or contacts and all of them were capable of shutting off and then restoring power to their respective circuits. Is there a safe and reliable way to test a breaker's functionality under actual overload conditions? I suppose I could plug a bobby pin into an outlet, but I don't think I want to :)BruceT

The reason that the UL listing is no longer valid on reconditioned equipment is that there is NO industry standard way to test an individual breaker, to ensure that it will trip when it is supposed to. UL tests of new breakers actually destroy the breakers; an assumption is made that identical assemblies, made under identical circumstances, will perform the same. This is validated by quality controls and the testing of random samples. It just is not possible to do this with used equipment- you have no idea where the stuff has been. Likewise, there are new breakers manufactured as replacements to obsolete ones, but virtually all of these are not UL listed. The recent floods, etc., have brought to light 'hidden damage' that may occur in electrical equipment. The fact is, everything wears out... and electrical panels are no exception. Too expensive to change out a panel? Compare the price of a proper "service change" to what you pay for a new roof, or to remodel the bathroom- both tasks routinelt done to older homes. Just because the wiring is not as visible as the new countertop does not mean it's any less important.

how fast it will fail hard to say but overloading get them pretty hot and short circuits ?? humm you are pretty much on your own because the zinsco dont trip very well at all even a overload it will not trip at all.

i have quite few service calls related to this and many time i strongly recomoned to replace the box with more modern set up because the cost of repalcement breaker is getting to the point where it not even worth [ beepped ] a thing. and many hardware store only stock very limited items and those repalcement breakers are genrally not UL listed at all

Thanks Renosteinke and Cap for your answers to the question about testing breakers. I had assumed that there wouldn't be much to go wrong with a breaker, especially since they are called upon to trip very rarely. In 35 years living in my house I have had to re-set a breaker only a handful of times, so other than turning them off and on deliberately, most of them have never had to do anything. So this brings up other questions. Renosteinke said "The fact is, everything wears out... and electrical panels are no exception." If a breaker trips once or twice in 35 years, what wears out? Should I be suspicious of the condition of breakers in my 35-year old Square-D combination meter and service panel box?CAP said, "There is a UL-listed test instrument that measures the magnetic response of a 15 or 20 amp brach circuit breaker." Should I get a licensed electrician to run this test on that Zinsco box or even on my own Square-D?Is it true that you should cycle all breakers off/on annually to keep them mechanically free to trip when needed?Thanks for taking time on this.BruceT

I have not heard of regular flipping of breakers as a practice, but see no harm in it. Breakers do contain contacts, springs, and sundry little parts. Most will trip from at least two separate causes- usually heat, and magnetism (created by current passing through). Heat can change the behavior of springs, contacts can be damaged by arcing, and everything can be affected by corrosion or grit that interferes with movement. This is where lots of folks in New Orleans are going to get "bit." After the flood, many are using breakers that look, on the surface, to be clean. Give them a few years, however, and those breakers are not going to be reliable. In a similar manner, you can be sure that lots of replaced breakers are going to turn up in the "reconditioned" market. Again, lets look at the costs involved. New breakers usually cost under $5. Obsolete ones, $20. You don't have to buy many obsolete breakers to exceed the cost of a new panel.

It's a very common maintenance practice; cycle each breaker two or three times once a year to exercise the mechanical linkage and redistribute the grease on the piviot points. Have spare breakers handy (or be prepared to go get 'em) if a breaker won't close and hold. I've learned this the hard way...

Keep in mind that when a breaker trips under a short circuit type fault, the arcing takes a toll on the contact points. And when there's an overload that causes a trip, there's wear on the breaker too--the bimetallic strip that overheats, bends, and causes the breaker to open is designed for only so many cycles. The point is, if a breaker trips more than a few times (on either short or overload conditions), it ought to be replaced.

Unfortunately, in a lot of instances where a breaker trips, the resident or occupant will try to reset the breaker several times without addressing the cause of the trip. With an overload, they may get it to close (for a while). It's only when the breaker fails open, that an electrician is called. If it fails closed, the fire department usually gets the first call, then the electrician.

There are only a couple of brands of breakers (FPE two-pole in particular) that have a documented fail-secure problem. Most of the time, if a breaker fails, it fails safe--i.e., open and can't be closed.

Actually, there's little need for concern with a Square-D panel that has Square-D breakers in it. Square-D breakers have an excellent reputation for reliability, and their short circuit response is one of the best (quickest). Square-D (the QO line) is expensive, and you get what you pay for.

Based on my experience, on a Zinsco panel with 30-year-old breakers, I'd expect at least one breaker in 20 will fail the test. Does this make the building unsafe? Not necessarily, if the fixed wiring is all properly installed and maintained.

As far as the safety of the electrical system, if the branch circuit wiring is questionable, the best thing to do is to evaluate it with a voltge drop tester, fix it up, and add circuits as needed to alleviate overloads. That may necessitate replacing the panel to accomodate more circuits.

This brings up the whole topic of the safe working life of fixed building wiring. People generally assume that building wiring lasts forever. For instance, knob and tube wiring can continue to serve 70 years on, if installed correctly, not improperly modified, and never overstressed. Those three conditions are rarely met.

The NFPA (the folks who publish the NEC and other Codes) is conducting a study on how building wiring ages. They've actually cut sections of walls out of buildings and taken them back to the lab to dissect and test them. I'll visit the website and report back what the status and findings are to date. The website is , but be advised that the full results of most studies are are generally accessible to members only.

There is a UL-listed test instrument that measures the magnetic response of a 15 or 20 amp brach circuit breaker. It drops a dead short across the circuit and measures trip current and time to trip. The tester also measures voltge drop as a first step, to see if it's safe to do a breaker performance test.

I've found that about 5-7 percent of vintage zinsco breakers fail the magnetic response test. These are breakers that will manually cycle and otherwise appear O.K. Makes it pretty easy to make the case for a panel replacement.

Is there any test of the thermo trip on the breaker?IIRC it is not untill you get to around 6-9 times rated current until the magnetic trip controls.I don't have any statistcal information about the details of electrical problems that cause fires, but you often here "caused by overload spacing heaters". Now I would suspect that they are more typically overloaded by much less than would take for the magnetic trip to activate.

It's interesting using the KO breaker tester--seeing a current of 250 to 300 amps for 100 to 200 milliseconds--on a 20 amp breaker that's functioning properly. The tester is programmed to stop the test if the current goes too high or for too long.

When I test breakers, I advise the client that there's a small but real risk of blowing apart a weak splice in the circuit. Not that that's a bad thing, it exposes a weak point, but it's gonna cost money to find and fix it, and they need to know that.

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