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#71408 11/01/06 10:32 AM
Joined: Jan 2005
Posts: 5,349
Likes: 1
Cat Servant
Member
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.

#71409 11/01/06 11:41 AM
Joined: Nov 2000
Posts: 2,148
R
Member
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


Don(resqcapt19)
#71410 11/03/06 01:18 AM
Joined: Oct 2000
Posts: 2,722
Broom Pusher and
Member
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 " 35 " Thompson
Just Say NO To Green Eggs And Ham!
#71411 11/08/06 08:43 PM
Joined: Jun 2003
Posts: 681
P
Member
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.


Pierre Belarge
#71412 11/09/06 08:42 AM
Joined: Mar 2005
Posts: 1,213
S
Member
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).]

#71413 11/09/06 10:40 AM
Joined: Jul 2001
Posts: 599
J
JBD Offline
Member
Steve,
Quote
Every breaker sold has been tested and tripped at least once already, as evidenced by the "tripped" position out of the box.

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).]

#71414 11/17/06 09:11 PM
Joined: Oct 2004
Posts: 806
Member
Quote
"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. " [Linked Image] Mxslick - thats priceless..... [Linked Image]

Thanks, e57!! [Linked Image]

Quote
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.

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...


Stupid should be painful.
#71415 11/17/06 09:50 PM
Joined: Jan 2005
Posts: 5,349
Likes: 1
Cat Servant
Member
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.

#71416 11/18/06 12:06 AM
Joined: Apr 2004
Posts: 812
Member
Quote

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

Hmm, Hammer please!

Ian A.


Is there anyone on board who knows how to fly a plane?
#71417 11/20/06 10:41 PM
Joined: Jan 2005
Posts: 39
S
skipr Offline OP
Member
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.

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