I have a brand new installed "GE A-Series" panelboard. Bolt on THQB's. after a teacher somehow got a peice of jewrey stuck in an outlet.She claimed the breaker never tripped, after looking at the plug face and the jewlrey peice it had arced pretty bad. To test the theory I directly shorted circuit. The breaker did not trip, the jumper wire melted and caught fire. I tried another breaker, same thing. Brand new go figure.

That was not 'testing a breaker', that was for lack of a better word stupid

I highly doubt you got two non-functional breakers in a row.

It is possible that the branch circuit has high impedance.

It is more likely that the jewelry and your jumper where not 'connected' to the circuit well enough to produce a magnetic trip.

That was a very bad idea, you should change your 'testing' procedures.

Ummm... Being a C-10, I hope you're kidding about the whole jumper idea... It's one thing to use some #10 and put a 28A load on a 20A breaker to see if it'll trip, but intentionally dead shorting a circuit in an uncontrolled environment is just a bad idea...

If you have doubts about your breaker(s) functioning, I can tell you 2 breaker houses in your area that'll put em on their test bench and let you know if they work.

Oooooo, you're trouble now.....

I'm not going to go on the lecture circuit of arch flash and general electrical safety, but will say that the reasons that can happen under vary quite a bit. AIC rating for tranformer to OCP - OCP to fault distance. Circuit design and impedance. The trip current/time rating of the breaker I believe is this page?: I cant see it.... But may hold several thousand amps for a small amount of time, enough to clear the molten metal out of the path, slowing reaction time.
http://www.geindustrial.com/publibrary/checkout/38652.30055.31248.24184/PDF/GES-9920.pdf

Unfortunately ilegible... But can be found here: http://www.geindustrial.com/publibr...Id=8&pubType=Time%20Current%20Curves

Either way, you may have caused significant damage to the wiring between the short, and the breaker, and may have even damaged the breaker to boot. You may have to re-do that run....

TM breakers with trip because of an overload in response to I2t or magnetically (instantaneously). The must be current maintained for a given amount of time to fall within the thermal trip curve of the breaker in order for the breaker to trip thermally. If you were tat the breaker location when the breaker tripped more often than not the breaker can not be reset, latched and closed immediately as the thermal element must cool.
The magnetic element is often calibrated 7-10x the breaker rating for residential breakers and 10x for commercial and industrial breakers +20%. This means that a common 20at breaker would be calibrated at 200a but most likely is calibrated toward the high end at 240a. This means that a 20at breaker must see an instantaneous current of over 200a for it to call for a trip.
The question is if in fact the breaker saw 200+ amperes. Since the scenario as described was most likely resulted in an arcing fault it is highly doubtful that the breaker saw enough fault current to trip.
Such a situation is common in that we expect a breaker to trip. Because the breaker doesn't have eyes to actually see when we can, the breaker can only respond to the current values that it has been designed to respond to regardless of what is or has happened down stream on the circuit it protecting.
Since arcing faults often are L-G or end up to be so within a very short time a GFI breaker will with almost all certainty would have picked up the fault and opened the breaker.

The only time I'll jump an outlet is when I need to figure out which outlet goes to which cable; when there's no power to the house; in other words no power anywhere. For what you did though:

Ohh man you're in trouble. Just looking at a few past posts proves that.

Ian A.
Edited 'cause I kant spell!

[This message has been edited by Theelectrikid (edited 10-30-2006).]

Ok I knew I was going to get a lecture or two on the way I tested it. That's not the question here.I don't use this as a general testing method, in fact I never had a breaker that refuses to trip.OK does anyone have anything useful to say? I got five reply's saying the same thing, but not one that comes close to explaining the problem.Can anyone address the breaker problem instead of my procedure problem?

Watch out for Black on Black/ Red on Red circuit 'crossovers'.

I can' speak to the residential situation but many's the time that my apprentices cross circuit 1 with circuit 7 in a three phase system.

Naturally, this permits the wire to draw across double breakers -- completely defeating their protection: #12 is now able to receive 40 continous amperes!

Could anything like that have happened to you?

This kind of circuit fault is just another reason why deliberately faulting circuits is so risky, especially troubled circuits.

BTW, After MELTING my jumper... a free air conductor...I'd consider my in-the-wall Romex TOAST. It's wearing a fur coat... the jumper was wearing Bermuda shorts.

I agree of the possability of 2 breakers feeding the same circuit.

Did you short the circuit hot to the Nutral or the equipment ground? If it was hot to EG then a question of the equipment ground integerty comes to mind. How far does the fault current need to travel to get to the incoming service? Is the EG conduit only? Could be loose connections at boxes or couplings creating resistance on the branch circuit or between a sub panel and service. You could look at the service equipment grounding.

The ideal suretest I never used myself but I believe it tests the EG for impedance.

and

Skipr, re-read iwire's post. Especially this:


I think that's the best explanation of what happened, similar situations have happened to me. (An arcing fault I though would have taken out a breaker, but other problems or a long homerun prevented the trip.)


As others have given other possible explanations here, I will also join the bandwagon of disagreeing with your test method. First, It didn't prove or disprove a bad breaker. Second, various circuit factors could have prevented the tripping of the breaker (for instance, what size was the jumper you used? Anything smaller than the branch circuit conductors would just act as a heater element anyway.) Third, you could have easily started a fire elsewhere if there were any bad/questionable connections or as mentioned, conduit fittings if the EGC was involved.

Finally, it reminded me of the worst possible troubleshooting technique I saw while in the Air Force. One of the avionics techs couldn't figure out why a system kept popping the circuit breaker in the cockpit. His solution? HOLD the breaker in until something smoked. (Aircraft breakers are NOT trip-free.)

That genius caused over $170,000 worth of damage to the aircraft and required the replacement of a wiring harness from the cockpit back to the tail. And yes, he was discharged and had to pay back the damage. (It wasn't his first time using the "smoke test.")

So you learned that a teacher was dumb enough to get her jewlery into a hot outlet. The thing to have done was replace the outlet and move on.

Even a simple bad plug on a cord can arc enough to look really bad, and those who don't know electricity tend to get overly dramatic when describing arc faults.

Nothing personal, just my 25c. (Used to be 2c, inflation, you know.)

Edit to add smiley....

I'm not going to try to be overly technical - because this is just the way I see it. Others may clarify or obfiscate at will....

Time, in the grand sceme of things AC is very short, and exceadingly long... The amount of time it takes to do a while lot of arching, and blasting of metal away opens and closes the circuit really quickly. That buzzing is about the frequencey of it... Not un-like welding.... The smaller points of contact just get expelled away - like a fuse, and then reconnects.... What you were doing was blowing away the portions of wire faster than the CB could gather the energy to trip, which takes some time.... Upwards of a second or two, but blowing away metal in micro-seconds in flashes of white light.

Common HACR breakers will hold much more than thier rating for some time - each are different - but relitively simular. About 175 for a minute or two, but will hold hundreds - thousands for a shorter time. Since the GE example was illegible, try this one: http://www.eatonelectrical.com/unsecure/cms1/TC00302001E.PDF

Note that this breaker simular to what you are using, can hold at minimum 600 - 1200% (PERCENT) of its current rating for 1 second! ~2400 amps In that amount of time you could have opened and closed the circuit 60 times - every spark of the arching.... Each not enough time to trip the breaker. Collectively, they may heat the elemants of the breaker to the trip point, but over a longer time. Look at the graphs agian and notice that the breaker can hold many thousands of times it's rating for milliseconds. Which is what the breaker saw, a whole bunch of millisecond shorts at several thousand amps a piece. Or, whatever the transormer feeding the neighborhood could supply at that distance from it.

Now if you had bolted, or wirenuted two wires together as a direct short you would be looking at a shorter reaction time, but then again you might be going to the hospital for arch-flash burns from the breaker exploding after it superheated any gas and metal in the breaker to the flash point. Because even though you may have had AIC calcs done, they are still only calculations... If that particular breaker can take it is another story. So don't do that either.

"So you learned that a teacher was dumb enough to get her jewlery into a hot outlet. The thing to have done was replace the outlet and move on. " Mxslick - thats priceless.....

I'm gonna go out on a limb here, but if there was an issue of a breaker not tripping - an EXTREMELY DANGEROUS situation - I would rather find out by testing live with a dead short then simply replacing a breaker or testing for high impedence and "assuming" or "hoping" the problem is corrected. In a situation like this, you really need to test live to make sure the electrical system functions as it was intended to. I mean really if a circuit breaker doesn't clear the fault, then what's the point?

If you're called in for this type of problem and you don't test live and a fault occurs that results in the building burning down or someone getting killed, guess who's assets are on the line? YOURS!

Of course, there are far more "elegant" ways of creating a dead short, like using a higher amperage breaker to create the short. For example, if you're testing a 20A circuit, you could use a 30A or even a 40A breaker for the dead short. If the test breaker trips and the panel breaker doesn't, obviously you've got a SERIOUS issue that absolutely needs to be corrected.

And if you damage a branch circuit as a result of a dead short all the better! A bad splice finally giving out, a nick in Romex now staying open, all better outcomes in the hands of someone who knows what they're doing and what to look for then failing in catastrophic way, arcing, heat buildup, open neutrals, etc.

Simply replacing an outlet that was damaged as a result of a breaker not tripping, in my opinion, would be negligence in the worst way in my opinion. That breaker should've tripped, what's the sense of a breaker panel then?

Liability is a REAL issue here.

Joe

Joe, after you have shorted this circuit how do you know what insulation or conductor damage is now concealed inside the walls?

It is very easy to use heating elements to make an adjustable load bank that can be monitored as you increase the load to a set point.

Roger

Was his name Norm?

I worked with a guy once whose troubleshooting procedure was to put bigger fuse elements in a fuse, and see what smoked. And then he would know what was causing the fuse to blow.

Thank goodness they did away with those type fuses.

Well, that's what meggars are for. Wouldn't leave after that kind of stress testing without meg testing the circuit.

Load testing with a heating element and a rheostat will often require going over the CB rating, which also has the potential of damaging wire too. DaveT also made some excellent points about magnetic versus thermal tripping. The heating element test might cause the breker to trip thermally but not magnetically, which still leaves potential danger.

Seriously, can you imagine a lawyer having you on the stand, asking you if you actually TESTED to see if the circuit breaker tripped like it should, and then you go on about how electrocution, fire or explosion could result? Guaranteed that lawyer gets a big paycheck, and you joinh the guy on the corner with the tin cup.

Breakers trip all the time. How many times have you troubleshooted a live circuit and accidentally caused a breaker to trip? Did an fire or explosion occur? Of course not! You saw and heard a little spark for a moment, and that was it. What about job sites where part of a building is energized and someone cuts into something? We're not talking testing a 1000A main breaker, we're talking about 15, 20 and 30A branch circuits.

Sure some nasty things have happened with small branch circuits, but those are exceedingly rare.

Over the weekend, I was working in the garage, when an extension cord similar to the one below made that short circuit "pop" after being pulled too tightly around an obstruction:



The circuit breaker tripped uneventfully, and since my cord was pretty well beat, it went in the trash. Branch circuit wiring wasn't even a consideration, despite the fact the extension cord clearly shorted.

How many times do you go on a troubleshooting call, reset a tripped breaker, and then it snaps right back? No explosion, fire, extensive wire damage, right? Ok, if you're gonna bring up FPE you got me, call the fire dept, otherwise it's essentially a non-event.

I'm not saying this should be a standard troubleshooting "technique" and totally discounting the potential dangers involved, but if you're on a call for a CB that didn't trip, you'd BETTER make absolutely sure it trips next time a fault occurs others.

Joe


[This message has been edited by JJM (edited 10-31-2006).]

Joe, a megger is far from a reliable method of checking non metalic cable. A megger is not fool proof even when checking conductors inside metallic conduit .

Roger

[This message has been edited by Roger (edited 10-31-2006).]

If both faults were L-G then I would suspect high impedance ground fault path. I wouldn't worry too much about conductor damage if that was the case because the conductor probably never saw enough amperage. Did the jumper melt because along the whole conductor, or from the contact point back?


skipr, I thought at least 3 explained it pretty well. Lose the defensiveness and reread.

[This message has been edited by Jps1006 (edited 10-31-2006).]

JJM, if a lawyer got you on the stand and asks how you tested the breaker - take the fifth... Testing a breaker in the field like that will cause more damage than good if they have the industry expert from the factory on right after you. Not to mention dangerous. There are places to take breakers for testing, there is one in my area (SF Switchgear - I sell my larger breakers to them... They test and re-sell.), and Randy knows of some in the So. Cal area that are closer to the OP's area that will test in a controled enviornment against UL standard 489. Load banking for thermal, and bolted short for magnetic against the parameters of the breaker with a limited AIC control board. It is not expensive, and if friendly enough, they may not even charge you for a single breaker.

Quite possible these to papers were written by the same person????? http://www.e-t-a.com/fileadmin/user_upload/USA/PDF-files/White_Papers/wp_standards.pdf
http://www.maintenanceresources.com/referencelibrary/ezine/eleccircbreak2.html

OK, reality check here. Assume a short run from the box- 25' of 12-2 cable, 50' electrical round-trip to the box. That #12 cable has a resistance of about 2.0 Ohms/1000' and a reactance of about 0.177 Ohms/1000'. Since the PF is close to 1, the overall impedance rounds to 2.0 Ohms/1000'.

50' of #12 wire would have an impedance of 0.1 Ohms. At 120V, that's 1200A (6000% breaker rating) for a dead-short. 1200A is going to cause significant voltage drop, though! If the poco ran 100' of 4/0 Al to the pole pig, voltage drop would be about 40V, and voltage/current through the #12 wires would actually be 80V and 800A (4000% breaker rating).

Approximately 64kW will be dissipated over the length of the wire. The specific heat of copper is 385 J/kg/K. 50' of #12 contains about of copper. It would take 2 tenths of a second for 64kW of power to heat up 1.06kg of copper from 25C to 60C. If the breaker trips within those 2 tenths of a second, there will be absolutely no cable damage whatsoever. And this is conservative- if the cables in the house were longer, current would be lower and they would heat up slower. If a 50 Amp load was connected (2.4 Ohms), and that breaker trips within 5 seconds, there would be no chance of cable damage. Cross referencing the breaker trip curves- surprise! All the numbers you can run very closely match the upper curves for residential breakers.

...but if the breaker doesn't function correctly, any fault capable of tripping the thermal overload of the breaker MAY begin to damage the cable if the temperature rises much past 60C before the breaker finally trips.

[This message has been edited by SteveFehr (edited 11-01-2006).]

Isn't someone out there marketing a $1000 tester for this purpose?

I am not aware of a method to check circuit breaker function with any reliability. The possibility of impedance, especially for lightly loaded, long wire runs, does present issues not covered by either practice or code.

Right now, we have to pretty much take breakers on faith. Creating a dead short for testing is like... checking for broken legs by jumping out of an airplane. Not much use if the test itself causes the failure.

One problem here is the instantaneous trip point of GE breakers. It is set at ~40 times the handle rating. Most other breakers are set at ~11 times the handle rating. You would have to have 800 amps of current flowing to trip a 20 amp GE breaker in its instantaneous range. If you can’t flow that much, then you are in the inverse time trip curve and the time to trip will be based on the amount of current flowing. Note that circuits that have 800 amps of short circuit current available at a receptacle are rare.
Don

I will stay away from the "You Should Never Do That" stuff, as it's been mentioned and understood (plus is not very relavent to explain what may have occured to keep the OCPD from tripping).

I have seen quite a few faults which had odd results.
Many of these faults took out the OCPD _AHEAD OF_ the Branch Circuit involved.
When no OCPD was activated, the reason was from one of two culprites: Inadequate Fault Path, or Frames known to have issues with "low level trip".

The GE THQB Series is "Trippable" (IMO), as I have not yet experienced these Frames to exibit the "No-Blow Zinsco" and similar non-trip hazards.

Here are my ideas per this thread's scenario:

1: The original "Fault Via Jewelry" most likely consisted of conduction paths through Gold with high impurities (like 10 Carat Gold). The lower Gold content is to obtain a higher strength alloy, which stands up better to normal wear.

Conductivity of "Pure Gold" ranks something like 24% of Copper, so right off the start we have a low Conductivity material.
Include the Alloys doped into the material, and the Conductivity drops even lower.

2: Next, let's look at the _Overall Conductivity_ of the Equipment Grounding, between the Outlet and the Panelboard.

If the Jewelry Fault _AND_ the Intentional "Jumper Fault" were done between the Ungrounded Blade of a Receptacle and something connected to the Metallic Equipment of that Outlet's Box (be it the plate screw, Ground Pin, etc.), and the connections of the raceway are loose, this will not allow a solid connection to be established.

3: The internal connection points of the Receptacle may have become "Plated" with low conductivity Gold, during the "Jewelry Fault", resulting in an internal low conductivity situation.

If the Equipment Grounding "Path" via Conduit has loose Locknuts, loose Couplings, and similar, than the Ground Faults experienced will be really noisy + sparky, yet fall short of sustaining a steady fault current level, which would allow the OCPD to trip.

The "Jumper Wire" burned up, due to the Arcing and instantanious heat generated at the terminations.

The "Jumper Wire" may have been a short piece of #12 cu, and when thrown in an L-G conduction path, could have easilly drawn 100 Amps for 1-2 Seconds, dropping to 50 Amps for an additional 2 Seconds, and tapering down as the contact resistance increases (due to the heat created).

To a "Commonly Used" Low Power Frame, this scenario looks very much like a hard start Motor, or some kind of Inductive Load (even a Tungsten Load).
The Time-Current characteristics of this frame will allow such a Load Characteristic to operate as normal (hopefully!!!), without initiating an automatic trip.

The "Jewelry Fault" may have eventually tripped the Branch Circuit Breaker, had the conduction state remained steady.
Likely, the melting of the material resulted in less current flowing over time, to the point where the material separated and the circuit became open.

If the Jewelry Fault was able to Increase the current level, at some point an OCPD somewhere would have been tripped.

If the Branch Circuit Breaker was not able to react, then the OCPD protecting the Panelboard which contained that Branch Breaker, would have tripped.

If that could not trip - and the fault level continued to rise (or remained above the rating of the largest OCPD for this Customer), then the Main OCPD would eventually trip.

So, in conclusion, if nothing tripped, it is (almost) safe to say the fault levels experienced with the Jewelry Fault and the Jumper Fault, were, in actuality, low intensity fault levels, due to one or several reasons.

These are EXTREMELY DANGEROUS faults in themselves!
They do not pack the punch of Medium and High level faults, but instead, leave fire and shock hazards lingering around!

Scott35

Scott
I like how you explained this here, very good.

As I was reading this thread, I was wondering if I would see this written. I agree that there may be a very poor ground fault current path here, if the fault was between phase to ground.

If this was phase to phase, without any other info, I would think this may have been a very long circuit, then Don's scenario is very likely the culprit.

I talked to an engineer at Square D about their failure rate once, while trying to do some reliability calculations for an emergency power system. The company line is that their breakers are 100% reliable with absolutely no failures EVER up to the limit of the UL listing, which requires a certain number of cycles. He wouldn't give me any numbers about their in-house failures. I imagine you'd get pretty much the same story from every supplier. (Well, maybe not FPE)

Every breaker sold has been tested and tripped at least once already, as evidenced by the "tripped" position out of the box. No need to test it again! I look at breakers the same way I look at hard drives- if I have ANY reason, ANY at all to suspect the slightest chance of failure, it goes in the garbage and a new one takes its place. There are some things you just don't dick with.

[This message has been edited by SteveFehr (edited 11-09-2006).]

Steve,

I will not debate if every breaker is "trip tested". However, they can come out of the box tripped due to bouncing during shipment. Take any standard 1 pole breaker an give it a sharp smack with you hand, it will probably trip.

edit: quote

[This message has been edited by JBD (edited 11-09-2006).]

Thanks, e57!!


Yes, it MAY be possible that they were tripped during shipment, but not likely. I think it was reno who pointed out in another thread that most circuit breaker makers have a final QC test that trips the breakers right before packaging and if it doesn't trip it's considered defective. So I would think that if you open a box of breakers and any aren't tripped, I would consider the non-tripped one(s) suspect.

You are also right that some breakers can be tripped with a sharp impact.

Of course who knows if they've been played with in the meantime...

Good memory, MX! As the breakers move down the conveyor, they pass through a magnetic field that 'trips' them just prior to packaging.

It's rather inpressive... the breakers go by so fast, all you hear is a 'buzz' of tripping handles.

Hmm, Hammer please!

Ian A.

Thanks, I stayed away from this thread until today. I feared everyone was going to attack me for getting upset for the saftey lectures. I imagine everyone has accidently hit a live circuit with a screwdriver or such. Doesn't the breaker usally trip quickly? In conclusion I recommended that the school district have there electrician look into it and pull in new wires from panel to recep. He did and must have nicked the wire in one of the j-boxes. When the circuit was turned back on there was a direct short buzzing in the cieling. It melted the wires in the last j-box. In fact the wirenut was still on fire dripping molten plastic. The breaker again never tripped. It's their problem now, but I still wonder why.

Kind of a late reply here, but this topic was brought to life recently and I wanted to address something - in particular, a reply from Pierre Belarge.

Here we go!



Thanks! I hope it made sense to the O.P. and others too



You would definitely see segments written in many tech. documents. I am unsure which ones or where to look! (possibly some on-line sources, definitely in EE Manuals and such).

If you are asking about printing the data I posted (for personal use or personal references), feel free!
It's really basic and lacks verification data (experiments, text references, etc.), but it sure looks impressive!


Scott