This was an arc fault, right?

[mbrooke]

I came across what IMO is a good example of resistive heating/installer error being relabeled as arcing or in this case "spark".


http://www.dailymail.co.uk/news/art...laze-caused-spark-dodgy-electrical-board.html

A professional analysis was done revealing otherwise:

https://www.surreycc.gov.uk/__data/...2/Fire-investigation-report-Clandon-Park-.pdf

It is theorized an over-tightened connection resulted in joule heating and a fire ensued from this condition:

In conclusion, the probable cause was a resistance heating fault on a neutral
bar in the electrical distribution board in the basement catching fire which was
not contained through adequate fire compartmentation, spreading quickly
throughout the entire building.

What do you think, can an arc fault take the blame?

 

[ptonsparky]

I came across what IMO is a good example of resistive heating/installer error being relabeled as arcing or in this case "spark".


http://www.dailymail.co.uk/news/art...laze-caused-spark-dodgy-electrical-board.html

A professional analysis was done revealing otherwise:

https://www.surreycc.gov.uk/__data/...2/Fire-investigation-report-Clandon-Park-.pdf

It is theorized an over-tightened connection resulted in joule heating and a fire ensued from this condition:




What do you think, can an arc fault take the blame?

Would this be what is called a glowing connection, even though they called it a spark? I don't believe our stateside AFCIs are intended to sense these faults. Those in the UK, don't know.

 

[mbrooke]

Would this be what is called a glowing connection, even though they called it a spark? I don't believe our stateside AFCIs are intended to sense these faults. Those in the UK, don't know.

Yup, glowing connection. Our AFCI will not catch those but will supposedly catch a series arc fault.

 

[JFletcher]

"is believed to have been caused by an electrical fault"
"which is believed to have been caused by a fault in an electrical board"

"Surrey Fire and Rescue Service today published a report concluding the fire was probably caused by a defect in an electrical board in a basement cupboard. It 'could be assumed' that the board, made by Midland Electrical Manufacturing, was 'delivered from the manufacturer with this fault'

since when do fire investigators anywhere assume or believe? Nothing said of the point of origin, tho if it were the panel, there are at least 5 ways one can fail that come to mind, and which way it failed will determine who's liable.

 

[al hildenbrand]

Nothing said of the point of origin, tho if it were the panel, . . .

Take a look at the last pictures at the end of the formal forensic report (mbrooke's second link)

The investigator says the bottom of the lower left neutral bus, and shows several pictures, and explains over-tightening as the probable primary error. The very last image in the report shows the "frozen" near-drop of molten bus metal that likely occurred in the last moments before the staff person that discovered the electrical panel ablaze turned off the panel feeder disconnect and called 999.

Interesting forensics.

 

[JFletcher]

Take a look at the last pictures at the end of the formal forensic report (mbrooke's second link)

The investigator says the bottom of the lower left neutral bus, and shows several pictures, and explains over-tightening as the probable primary error. The very last image in the report shows the "frozen" near-drop of molten bus metal that likely occurred in the last moments before the staff person that discovered the electrical panel ablaze turned off the panel feeder disconnect and called 999.

Interesting forensics.

Ah, I just read the news story. Read the second link now; much more informative.

 

[growler]

Take a look at the last pictures at the end of the formal forensic report (mbrooke's second link)

The investigator says the bottom of the lower left neutral bus, and shows several pictures, and explains over-tightening as the probable primary error. The very last image in the report shows the "frozen" near-drop of molten bus metal that likely occurred in the last moments before the staff person that discovered the electrical panel ablaze turned off the panel feeder disconnect and called 999.

Interesting forensics.

I can believe that the neutral got hot and melted and maybe even provided a spark.

MY question would be, just what was used for fuel after the initial spark, blaze . I'm guessing but I would think there were combustable materials stored in close proximity to the panel.

Here in the US we have a big problem with people useing the electrical rooms as storage closets and storeing all sorts of combustables near the electrical panels.

 

[ggunn]

Here in the US we have a big problem with people useing the electrical rooms as storage closets and storeing all sorts of combustables near the electrical panels.

You got that right. I used to work for a company that installed EMS (energy management systems) in restaurants, which involved the installation of CT's in the MDP's of these establishments. Their electrical rooms were nearly always used for storage of old office furniture, paper goods, cleaning supplies, etc. I can remember one installation where it took us nearly an hour to move enough of that crapola out of the room so that we could get to the MDP. They had cardboard boxes full of flammable paper goods stacked to the ceiling jammed right up against the deadfront of the panel. I guess they never had to reset a breaker.

 

[growler]

I can remember one installation where it took us nearly an hour to move enough of that crapola out of the room so that we could get to the MDP. They had cardboard boxes full of flammable paper goods stacked to the ceiling jammed right up against the deadfront of the panel. I guess they never had to reset a breaker.

I have seen the same thing at the local schools.

I ask if the Fire Marshal doesn't write them up for this violation . They say that he does, every year.

If they are written up for a violation and the Fire Marshal is aware of the problem then what can be done about the problem? If there is a fire do they blame the electrical system or the idiot that decided to use the electrical room as a storage closet?

 

[Jraef]

I'm not buying the over tightening part of that conclusion though. That type of connection, a round hole with a set screw, isn't going to allow a significant amount of deformation that would result in heating of the connection. To me, it's more likely that they added a bunch of HID, CFL and LED lighting recently, which along with the computers mentioned already, increased the harmonic heating of the neutral circuits. That panel was installed 25 years ago, if that connection was bad, this would have happened a long time ago.

 

[ggunn]

I'm not buying the over tightening part of that conclusion though. That type of connection, a round hole with a set screw, isn't going to allow a significant amount of deformation that would result in heating of the connection. To me, it's more likely that they added a bunch of HID, CFL and LED lighting recently, which along with the computers mentioned already, increased the harmonic heating of the neutral circuits. That panel was installed 25 years ago, if that connection was bad, this would have happened a long time ago.

What I figured they meant with the "overtightening" analysis was that it resulted in the threads being stripped out which resulted in the conductors being loose in the terminal.

 

[romex jockey]

I believe this is the fire report

Although i'm unclear as to this 'loose neutral buss' being some factory defect on recall, or something which was over torqued as a result of installation and/or annual inspection?

In any case, this conclusion , viewing photo's 5 & 7....seems a stretch....

8.3 The most probable cause for this fire was an accidental fire caused by a
resistance heating fault on a neutral bar in the electrical distribution board.
8.4 This electrical connection would have repeatedly overheated, when subject to
sufficient electrical load, ever since the distribution board was fitted. On the
day of the fire this connection and the surrounding area has degraded to the
point where it has caught fire.

~RJ~

 

[gar]

151127-1702 EDT

I agree with ggunn on how the information was presented.

The word "overtightening" used alone without further comment does not correlate with the end result. Simple overtightening, in other words greater compressive force, would not increase resistance, but might lower resistance of the joint.

I would vote for there being virtually no compressive force on the joint. This in turn resulted in an air gap, an arc, and lots of power dissipation. Note: an arc is not a linear resistance, but much more of a constant voltage load.

There was no mention of whether wiring or bus bars were aluminum.

On the original question of the thread was this an arc. I would say probably yes. Arc flash probably no. Flash implies a short time event.

Just resistive heating alone does not produce an arc. An arc is a current flow thru ionized gases. The typical voltage across an arc at atmospheric pressure is generally in the range of 5 to 100 V. A 100 A current at these voltages can produce a lot of heat (an arc welder for example). 50 V at 100 A is 5000 W in a very concentrated location.

Spot welding is not an arc. It is simply resistance welding. Thousands of amps at an ohm or less. Prior to the mid 1950s a very uncontrolled process because of the variation in resistance at the weld spot. In the late 50s voltage measurement across the welding electrodes allowed compensation to produce more consistent welds.

Another interesting welding method is "drawn arc stud welding". one can weld studs with resistance welding, but this requires high currents and without compensation weld quality is quite variable. In drawn arc stud welding the stud is placed in contact with the material to which it will be welded. A current of a few amperes is run thru the joint, not anything close to producing any great amount of heating in the joint. The stud is retracted a fixed amount from the work piece drawing a low current arc. Next a higher current source is connected to the stud and work piece producing a larger arc and enough heat to melt the stud and work piece. After a short time the stud is plunged into the work piece and the weld is completed.

I did some work for Warren Fastener on a multiplexed drawn arc stud welding system that was used to install about 12 10-32 studs on the backside of a Pontiac instrument panel at the rate of one panel every 6 seconds in the late 1960s.

.

 

[romex jockey]

On the original question of the thread was this an arc. I would say probably yes. Arc flash probably no. Flash implies a short time event.

Just resistive heating alone does not produce an arc. An arc is a current flow thru ionized gases. The typical voltage across an arc at atmospheric pressure is generally in the range of 5 to 100 V. A 100 A current at these voltages can produce a lot of heat (an arc welder for example). 50 V at 100 A is 5000 W in a very concentrated location.

.

Ionization , to my knowledge, occurs with DC far better than AC
https://www.youtube.com/watch?v=Zez2r1RPpWY

~RJ~

 

[GoldDigger]

Ionization , to my knowledge, occurs with DC far better than AC
https://www.youtube.com/watch?v=Zez2r1RPpWY

~RJ~

I would not so much say that ionization us better (more effective?) with DC but rather that you avoid the natural opportunity for the ionization to neutralize while the current is going through zero 120 times each second, extinguishing the arc and preventing it from restarting.

 

[romex jockey]

I would not so much say that ionization us better (more effective?) with DC but rather that you avoid the natural opportunity for the ionization to neutralize while the current is going through zero 120 times each second, extinguishing the arc and preventing it from restarting.

I would agree GoldOne

Most of what i read about arcs, arcing allude to what are improbable within the physics of electricity we would normally deal with

The chicken/egg scenario also playing a part.

Other than by mechanical means (switch) , any arcing is usually the end degrade of a GC, not the other way 'round

~RJ~

 

[mbrooke]

This picture has me particularly puzzled. One the neutral bar on the left appears to have melted at the end, second we have what looks like a wire that was in an overheated terminal but originates out of anther neutral bar. Was this a jumper?

 

[al hildenbrand]

This picture has me particularly puzzled. One the neutral bar on the left appears to have melted at the end, second we have what looks like a wire that was in an overheated terminal but originates out of anther neutral bar. Was this a jumper?

The picture, Photo 8, in the report immediately before this one (that you have marked up) shows the conductor you question continuing on from the second (right hand) terminal bar which leads me to believe it is a Branch Circuit Conductor. . . I think we need someone to identify the make and model, someone that can speak to the complete neutral bus assembly as seen in the two color photos labeled Photo 6.

I, for one, expect that the terminal bars are bonded to a bus assembly that ties the terminal bars to each other and to the main LINE neutral lug shown to the left of the Main Breaker at the bottom of the panel, and between the two sets of twin neutral bars. In Photo 7 one can see the bonding bus connected to the top neutral terminal bar near its middle. . . the bonding bus appears to go behind the Main Breaker.

Why the current at this melted terminal at the end of the neutral bar wouldn't have simply shifted to the other neutral bar implies to me that there are facts about this box's construction that elude this State-side electrician.