I Did Something Stupid...

kwired

Electron manager
Location
NE Nebraska
I don't know what brand of breaker you were useing but it doesn't sound like it was in good condition to start with.

Normally with a 20 amp breaker you won't hear any boom and no big arc flash even when it's a short. Normally the breaker will just click off.

What brand of breakers are you dealing with? Federal Pacific may get you a good boom (can be hard to trip) but they cost more than even an expensive imported beer ( purchased at the airport).
Really depends on how much fault current flows and time til opening the circuit.

Many dwelling locations available fault current isn't high enough to create much of a boom.

get into a place where fault current can be higher and they will go boom. Once had larger dwelling with a 75 kVA transformer not to far away from house one time - a helper over tightened a cable clamp on a 30 amp 2 pole circuit, QO loadcenter. It made a pretty good boom, and also tripped 200 amp main breaker when that breaker was turned on the first time.
 

Theclash84

Member
Location
Missouri
Occupation
Estimator
Since you are going to replace the breaker anyway. Rather than throwing it away. I would be interested in what the insides look like. That may give you some idea how long the breaker "would have" lasted. Whenever I do stupid things, I like to learn from that experience. This way I could learn without having to go through the experience of an arc flash.
I tried to upload a pic, but the file size is too large for the forum to upload...tried a few different things to compress the file, but was unable. At any rate, there is no visual damage to the exterior of the breaker or the breaker contacts. Also no visible damage to the bus bar on the service panel.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I tried to upload a pic, but the file size is too large for the forum to upload...tried a few different things to compress the file, but was unable. At any rate, there is no visual damage to the exterior of the breaker or the breaker contacts. Also no visible damage to the bus bar on the service panel.
OK, but what does the breaker look like inside? An arc flash like that at the breaker is very likely to have damaged something, it seems to me.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
If there is no visible arc extinguishing product, like soot, visible on the exterior of the breaker, I would not be surprised to find your fault was on a medium level event. Most of us have never seen a breaker as it interrupts faults above a few thousand amps.

How long were the conductors between the breaker and the fault point? #12 AWG is pretty good at limiting fault current.
 

Theclash84

Member
Location
Missouri
Occupation
Estimator
If there is no visible arc extinguishing product, like soot, visible on the exterior of the breaker, I would not be surprised to find your fault was on a medium level event. Most of us have never seen a breaker as it interrupts faults above a few thousand amps.

How long were the conductors between the breaker and the fault point? #12 AWG is pretty good at limiting fault current.
Roughly 10' of romex from the breaker to a junction box where it branched out. The shorted wires ran another 10' from the junction box to a switch box in the wall, so 20' total.

I don't see any soot. I've never opened/dissected a breaker, but I'll try.
 

junkhound

Senior Member
Location
Renton, WA
Occupation
EE, power electronics specialty
It was a brand new Square D breaker.
I test power circuits with FETs and IGBTs to failure in the course of design/development.
My lab bench has about 30 feet of 12 AWG from a 15A QO breaker, short circuit current can be a bit over 1 kA when a FET shorts.
The breaker is 47 yeas old.
Tripped a few times just this last week, no problems, (those trips were likely < 100A). I suspect over lifetime number of trips is in the many hundreds at 1 kA or more, thousands of trips at 100 A level. Note: will replace is the upstream 50A breaker ever trips :sneaky:

EDIT - did see that OP later posted it was a homeline breaker.


As for BOOM! There was an arc of light about the size of my fist, op obviously has very little electrical experience and needs to get some training before stripping wires. 200 J at most from residential short circuit with a QO breaker trip, similar to small firecracker.
Perhaps OP has a homeline breaker - no experience with those, probably take longer to trip than QO. too lazy and uninterested to look up homeline trip curves.
Now, as far as boom, discharging a 6 kV, 0.4 Farad (huge, big, etc, 7MJ) is BOOM.
 

growler

Senior Member
Location
Atlanta,GA
Unusual for a QO to go boom, so if a Homeline has the same guts, should be the same. I’ve had QO and CH breakers that trip without as much as a whimper on a short, but GE and BR you know it! LOL!
I kind of wonder if this wasn't some sort of knock-off or counterfeit version of a Square D breaker. Those things do have a way of getting into the supply chain.
 

4x4dually

Member
Location
Stillwater, OK
Occupation
Electrical Engineer
Holy crap? That was from one short circuit event? I wouldn't have expected that.
Unusual for a QO to go boom, so if a Homeline has the same guts, should be the same.
I guess I've always expected the QO line to be superior internally in addition to externally. I've never researched it, but I might now. Other than trip indication and 3 pole options, I figured there would be something better about them.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
Holy crap? That was from one short circuit event? I wouldn't have expected that.

I guess I've always expected the QO line to be superior internally in addition to externally. I've never researched it, but I might now. Other than trip indication and 3 pole options, I figured there would be something better about them.
Nope. 40 years ago they were designed to use common components, the differentiator was the trip indicator and the plug on jaw.
 
Top