Faulty mains main breaker

[chipwitch]

I know this isn't quite an electronics question but I know someone here will have some ideas about this problem.

I was an electrician for 20 years or so and have never seen anything like this.  Is there ANY way one could wire something on a branch circuit that would cause a 225A main breaker to lose one leg???  I'm stumped.  Here's what happened:

I ran a circuit from the main panel to a small sub-panel for a 2HP table saw (50 ft run, 10/3).  The circuit was protected by a 2 pole 30A.  The saw, at the sub-panel was also protected by a 2 pole 30A.  Simple stuff.  Table saw is equipped with a 2 pole starter (contactor).  It had not been run for 5 years or so.  Anyway, I hit the start button and the saw started and instantly quit as if it tripped a breaker.  None of the breakers were tripped.  I pulled out my VOM and discovered I only had one hot leg and traced it all the way back to the main breaker.  The breaker is only about 17 years old, physically in great shape, a Cuttler Hammer (Eaton) and has not been abused in any way.  After removing the main breaker from the panel, I tested for continuity.  It has definitely lost a leg.  Only one pole registers continuity.  Switch feels fine, engages and disengages as expected.  I tripped it on and off many times.  No change.

I am very skeptical about coincidences... but I KNOW the breaker worked before connecting the saw (otherwise the contactor wouldn't have engaged) and I KNOW the breaker stopped working after the brief time the saw was on.  Any thoughts?  I'm mystified.

[SeanB]

Breaker not exercised for a long time, so the contact faces inside have grown an oxide layer that made it lose connection, or the flexible jumper that connects the moving contact has had a fracture that finally broke the connection with the current pulse.

Common on a older breaker that has had a lot of standing that the flex will have corroded and breaks at a current pulse.

[Armadillo]

Before you branch out, have you done your 3 phase load balancing calculation?
Better check for floating neutral also just in case.

The main breaker may had sustained a un-symmetrical short circuit exceeding its short circuit interrupting capacity before, thus crippled.
So had the prospective short circuit current been calculated before? And check the KA of your breaker installed [not the trip current].

 

 

[drussell]

Yeah, sounds like just a faulty breaker.  It would be interesting to disassemble afterwards and see what actually failed.  I've really never liked the CH stuff at all.  Everything always seems so flimsy.

I have no idea what Armadillo is going on about.  I don't think he understands North American residential power wiring. 

[chipwitch]

Thanks for the replies.  I was beginning to think I might have a blindspot with regard to being able to cause upstream damage to a main breaker. 

@drussell   As for CH... the breakers are their CH line not the home line.  I can't speak for those.  I always preferred Square D QO, but then their prices just got ridiculous.  Maybe it was our local suppliers playing games.  I never really cared for GE, Siemens and the rest for the same reason you don't like CH.  I'm with you on getting a looksee.  I'm counting on the manufacturer to feel likewise.  I'm hoping they'll make a warranty exchange without a hassle.  They're supposed to be guaranteed for life... I think.  If I have to buy a replacement, you can bet I'll open it up.  I've never had one apart.

@Armadillo... Thanks.  Single phase power here. 

[Electro Detective]

Looking forward to the sledge fest     and pictures on the clapped unit if you have to fork out for a replacement   

[Armadillo]

Yeah, sounds like just a faulty breaker.  It would be interesting to disassemble afterwards and see what actually failed.  I've really never liked the CH stuff at all.  Everything always seems so flimsy.

I have no idea what Armadillo is going on about.  I don't think he understands North American residential power wiring. 

Oops! Residential.   

[mmagin]

I once lived in an apartment where the dishwasher's motor failed short and caused a breaker to trip -- but not the 15 or 20 amp (I forget) breaker in the panel in the unit, but instead the 60 or 100 amp breaker in the main panel for the building tripped on one side of the 240.

Lessons: yes, faulty old breakers can trip too easily.  Also, multi-pole "handle-tie" breakers suck.

[chipwitch]

Yeah, I've seen that too.  But it was an FPE panel and breakers.  Probably somewhere between the 4th and 5th time they filed bankruptcy for substandard equipment.  LOL

[IanB]

I have read somewhere that mechanical devices like breakers need to be operated from time to time to maintain good working order.

It seems to be a likely scenario where something that has sat unused for 17 years is suddenly called to action and it fails from corrosion, sticking, jamming, or something like that.

The inrush current for the motor in the table saw was probably more action than the main breaker has seen in a long time and that probably precipitated the failure.

[drussell]

I once lived in an apartment where the dishwasher's motor failed short and caused a breaker to trip

That is the expected behavior, yes...  In a short circuit condition, one of the current interrupt devices, be it fuses or breakers that is in series with the load (in this case, a short circuit) is supposed to open when extreme fault currents are present on the line...  And open safely!  This is the reason for maximum fault current ratings on things like circuit breakers and the HRC fuses you want to have installed in your multimeter when you go probing around in said low-impedance, ridiculously powerful areas.

-- but not the 15 or 20 amp (I forget) breaker in the panel in the unit, but instead the 60 or 100 amp breaker in the main panel for the building tripped on one side of the 240.

Depending on where along the chain of the potentially many-layer <sub-device fuse> - <power supply fuse> - <branch circuit breaker> - <sub-panel circuit breaker> - <main panel circuit breaker> - <distribution breaker> - <transformer fuse> area of the circuit that the actual fault occurs, there can be many different places that are likely to open.

Obviously, a dead short in a (hopefully) well connected device like a dishwasher will (at least in a good, low-impedance mains system like I'm used to here in Canada) cause a surprisingly large current to flow, even in relatively low cross-section conductors.  I meant to point that out in the recent thread about the AC or heat pump system with the 30 vs 40 A breaker on 10ga wire discusssion.

When that kind of fault current happens, any of the upstream protection devices may open depending on their total instantaneous load, long term heating, device life issues, etc. etc.  The fact that a mains type breaker opened instead of a branch type breaker is irrelevant.  It was a low impedance short... Personally, I would almost want the main breaker to be the one that opened, to take the blast since it should be rated at least as high if not higher than any downstream branch breaker as far as fault current interrupt ratings are concerned. 

In this case it seems that the mains-style breaker didn't survive opening on a reasonable downstream surge, rather than some horrendous fault current blasting it open, which is why it seems that it is a somehow flawed, faulty breaker.  They should be able to survive way more than that!

Lessons: yes, faulty old breakers can trip too easily.  Also, multi-pole "handle-tie" breakers suck.

I don't understand, you mean that a one-side overload tripped both sides (or all 3) of the upstream breaker?  That is by design.

Yeah, I've seen that too.  But it was an FPE panel and breakers.  Probably somewhere between the 4th and 5th time they filed bankruptcy for substandard equipment.  LOL

I've always liked the Federal Pioneer stuff and it is my preferred brand, though now that Schneider basically killed it off (probably mostly just strategically, of course,) as stock dries up I pretty much have been starting to have to use Square-D (my second choice) or least desirable like the CH / Eaton / Westinghouse / Siemens style.

[chipwitch]

Seriously?  You like FPE?  The only problems in panels I've ever really witnessed were a result of the stablok breakers poor contact.  Half the FPE panels I've had apart have had visible heat damage, welded contacts and melted insulation.  I'd personally go without electric before installing FPE.  To each their own.

[Gregg]

It could be a loose connection at the main breaker caused heating over the 17 years and the saw inrush finally killed it.  Is the main connected to the bus by spring tension (stab-in) or is it bolt on?  Also are the service entrance cables aluminum?
Any connection that isn't sound can cause what you experienced.  Poor connections were the norm with FPE.

[Gregg]

As an example; attached is a picture of a 60 amp 3 phase Square D breaker that failed on one pole first; the others weren't too far behind.  The breaker for a rooftop HVAC unit was in too hot of a location; an electrical room with two large transformers.   The full continuous load was 32 amps running the compressor and fans plus whatever starting inrush the compressor motor needed.  Part of the problem was running 240/208 volt motors on 208 volts, they take much longer to start and draw more current than if they are run on 240 volts.  The location had plenty of 480 volt power which would have made a lot of sense to use from the start but architects don't understand electrical power.
I did what Dave would have done; I took it apaart. 

[chipwitch]

Connections were all good.  They were tight.  Main breaker IS a bolt-on.  Nothin' but copper man!  I installed the panel myself.

All the responses that people were kind enough to post more or less mimic my own thought process.  That's reassuring because my confidence is a little shaken in the absence of a positive, definitive answer to the question: "Can something on a branch circuit  cause a 225A main breaker to lose one leg?"  A definitive "no" is what I was searching for in my own mind and here on the forum I suppose.  But, that's asking that something does not exist... essentially proving a negative, which is impossible.  For that reason, it was a poorly worded original question. 

Nevertheless, I appreciate you all for loaning me your fresh eyes and brain power.  It's disconcerting getting old and wondering if you're "missing something" you SHOULD know.  I found a local supply house with a replacement breaker in stock for $80.  Getting that today.  Internet search has prices on the same item from about $160 up to $600 or more!     How does THAT business model work?  Do people actually pay those prices?  *rhetorical*

Thanks again everybody.  I'll probably be taking that breaker apart tomorrow and will post pictures afterward.

[Electro Detective]

Some breaker p0rn pics might motivate people to test and mechanically exercise them twice or at least once a year, or risk failure when you need them the most. 

Breakers in external panels subject to heat, cold, fine dust particles, moist air etc WILL FAIL any time within a 10 year period or at best become unreliable, 'trippy', seize up,
develop internal lube/contact issues, rain water ingress, homeless insect housing, choose your poison...
seen it too many times. so has my bench vice and sledge

They look simple enough and many/some are built well, but the forces of nature and time can't be ignored,
nor can the  -CHEAPSKATE-  factor, filling up ones panel with 'TuHungLo Specail MBC' $4.99 knockoffs  (fortee dollar for 10)  


FWIW: A power outage is the best time to test and exercise breakers and RCD/GFCI units, if other times are sort of 'inconvenient'... LOL   

[chipwitch]

I only tore down the breaker to a point.  I'm not sure how to proceed.  But the pictures I took say a lot.  The breaker switch operates smoothly.  However, it looks like a manufacturing defect.  I find that incredible though as I'll explain later.  Note two things... arcing on one set of contacts (please forgive the orientation inconsistency as the bad contact may appear on the left or the right depending on camera angle).  The other is the cause of the arcing.  One contact set mates perfectly, the other set only contacts on the edge.  Well, now it no longer contacts at all as they've been burned away.  While the breaker has never been tested to its 225A limit, it has been used for operating a 3 phase converter with a 25 HP 3 phase motor generating the 3rd leg.  Twice, those motors burned up.  I eventually replaced them with a capacitive (not the cheap ones, but a clean signal Phase Perfect) 3 phase generator which has happily operated a 10 HP CNC mill.  I find it hard to believe that an edge contact would be sufficient to provide the necessary current for that load.  But, I'll be damned if I can see anything that could be causing the poor mating contacts.

I would describe the bad contacts as being the "driven" contacts (because they are driven by the switch) while the good contacts are the "floating" or "slave" contacts.  The latter follow the former.  Pushing down on the driven contact while open, will snap cleanly closed (but with the poor edge contact) once the over-center point is reached simultaneously dragging with it the slave contact.  Pushing down on the slave while open is springy and won't drag the driven down.  This is by design.  All mechanical connection between the switch and contacts is made on only one set of contacts.  There is a minute amount of play in the drive contact, meaning it is not quite a weldment of the switch, but close.  I tried prying it with a screwdriver close to the fulcrum back inside the breaker thinking that a disconnection from the contacts fulcrum or hinge point might account for the angular mismatch of the bad contacts, but I could discern no play.  Without further disassembly, it appears the arm of the contact was always misaligned.

Enjoy!

[duak]

From the pictures it looks like the damaged arm is either bent, the pivot is worn or mislocated or maybe it's just not being pushed to the right position. 

I can't see from the picture if the arm has been overheated.  Are there any signs of it ever being hot?  I could imagine it working well enough for years until a small misalignment that caused high series resistance leading to heating and softening of the copper alloy.  At some point, the arm bent and pulled back enough to strike an arc and the rest is history.

I agree that the original cause is a manufacturing defect.  I'm amazed that these things work as well as they do for being as simple as they are.

I was helping a friend try to figure out why his new compressor was sometime tripping the load center breaker.  I pulled the breaker and noticed what looked like rust coming out of the arc chutes.  "Where's this from?  "From this here panel"  I go over to another panel and see a rusty high water mark on the breakers, the bus bars and inside walls.  I'm surprised it worked at all.

Cheers,

[james_s]

I've always liked the Federal Pioneer stuff and it is my preferred brand, though now that Schneider basically killed it off (probably mostly just strategically, of course,) as stock dries up I pretty much have been starting to have to use Square-D (my second choice) or least desirable like the CH / Eaton / Westinghouse / Siemens style.

Several years ago I put a new Siemens panel in a friend's house and I was impressed by the quality, didn't have any issues with it. It had nice copper bus bars while most of the other panels I looked at used aluminum. I should have put one in my own house back before the code got so draconian that I'd have to update all sorts of stuff if I mess with the panel so the original 1970s panel stays.

[chipwitch]

@james are you sure the bus bars are aluminum?  I know some are, but Cutler Hammer for instance is silver plated copper.

[Gregg]

@james are you sure the bus bars are aluminum?  I know some are, but Cutler Hammer for instance is silver plated copper.

Most of the cheaper breaker panels that use stab in breakers in the US have aluminum bus bars (like Bryant brand, for instance).  Many of the big box stores don't stock anything but the cheapest options because that's what sells the most; sometimes you can get better quality if you pay more.  Many of the aluminum bus bars are tin plated; also some of the ones with copper bus bars have tin plating.  Silver plated bus bars in residential breaker panels is very rare these days.  My home Cutler Hammer has tin plated copper bus bars and uses bolt in breakers. 

[james_s]

I wouldn't have thought silver plating would be great for that application, true it has excellent conductivity but it also tarnishes extremely readily. Copper and aluminum seem to hold up reasonably well although I lived in a rental for a bit where the breaker developed a bad connection and the arcing burned a chunk out of the aluminum bus bar. Fortunately I got home and saw the lights flickering before any more serious damage occurred.

[Electro Detective]

Breaker manufacturers should offer clear plastic housings so clued consumers can visibly check for such flaws, monitor wear and tear on the unit, breaking performance, arcing effects etc

Instead they keep producing the same sealed units,  nowadays  -Made In WHERE?-     

leaving the installer and trusting end user to take their chances   or ask a drinking buddy to use The Force

I would prefer to spot a dud breaker performing poorly in a transparent housing, 

rather than prying the sucker open to see how and why it eventually died,

and whether it was the cause of other previous unexplained issues as well 

[james_s]

I think it might be tricky to see what's actually happening, especially if arc flash darkens the housing around the contacts. Also I don't know what breaker housings are made of but it's possible that transparent materials would not have the strength or resistance to heat or fire that the stuff they use has. While I agree it would be cool because I like to see inside things, I think most people would just replace a malfunctioning breaker and toss the old one in the garbage without any attempt at a postmortem.

[Electro Detective]

A transparent breaker upstream to expensive equipment would be a wise investment, rather than waiting for one to fail or cause issues during its operating life span

One could video record its operation during a test, and play it back in slow motion to ensure the device is doing the job properly

Surely there are tough enough transparent materials out there that can be used, and someone must have had a go at making them in the last 20 years and it either never took off or victim of slack marketing,
 or the idea shelved/trashed and company taken over by asset liquidating cash grabbing corporat meatheads   

If you've got expensive gear and or time is money,  transparent breakers would be a better investment than crossed fingers on a generic sealed one that either works as it should (for a time) , becomes intermittent, or a factory defect screwing with your equipment and pocket and eventually going BANG! CRACK! or POP! etc