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Topic Title: Clandon Park House - Fire Report
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Created On: 26 November 2015 04:10 pm
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 26 November 2015 04:10 pm
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colingwalker

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This may seem a bit off topic and i'd also declare that i have an interest in a possible solution to prevent this type of incident.

National Trust - Clandon Fire Report Published

Clandon Park House - Fire Investigation Report

The Fire Report for the devastating fire that destroyed 95% of the Grade 1 listed building - Clandon Park House has been prepared by Group Manager Bryn Strudwick and published by Surrey Fire and Rescue Service. According to the report the probable cause was a resistive heating fault on a neutral bar in a metal distribution board.

As a Fire safety Professional my interest is that one of the comments within the report states that a 20 - 25 year old MEM Distribution Board was the source of ignition and the fault was probably there since it was installed from new. The source of ignition was pinpointed to a connection on the neutral bar and over the years the fault had not been detected by professional electricians.

I am aware that there is a wiring regulation change which comes into effect from 1 January 2016 which requires consumer units to be of metal construction. From the report I also see that over time heat was generated from the fault causing combustible material to ignite.

Recently I listened to a presentation from a Part P certification body that stated because all the combustible material had now been removed by using metal boards within dwellings there was no chance of a fire.

I made comments during this presentation and was told that everyone was entitled to have an opinion but that the fact manufactures had used hot wire testing within a domestic non-combustible consumer unit showed that it adequately prevented a fire.

My own views are slightly different, using radiated heat to prove that a direct contact with a high temperature contact is not sufficient to prove that the introduction of metal boards is a solution to reduce the risk of fire spread.

This report and those of other fires where metal boards have been involved in fire demonstrate that trying to contain and restrict a fire is not a solution.

Can a manufacture be responsible for a connection 20-25 years after a board is installed even when its been installed and maintained by professional electricians?
 26 November 2015 04:44 pm
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AJJewsbury

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I agree with your misgivings...

Recently I listened to a presentation from a Part P certification body that stated because all the combustible material had now been removed by using metal boards within dwellings there was no chance of a fire.

But the plastic casings of all the internal components & wiring insulation is still in there?

the fact manufactures had used hot wire testing within a domestic non-combustible consumer unit showed that it adequately prevented a fire.

These will be the same manufacturers who until recently were similarly testing their plastic CUs to show compliance with the fire resisting requirements of BS EN 61439 (and before that BS EN 60439) ... and were subsequently show to burst into flames in an independent lab test?

i have an interest in a possible solution to prevent this type of incident.

Ah, that wouldn't be the thermarestor devices that we discussed before? - the ones that create a N-PE fault and may permanently disconnect themselves after activation by an internal overcurrent device and so defeat themselves? http://www.theiet.org/Forums/f...R_FORUMVIEWTMP=Linear

- Andy.
 26 November 2015 05:15 pm
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colingwalker

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The point you make about the internal components is absolutely correct and that was my point about using radiated heat to try and replicate a high temp resistive fault in a device, it's just not subjected to the same temp or conditions.

With regards to the N-PE there has been a change to the type of device and connection on RCBO's.

Colin
 26 November 2015 06:18 pm
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leckie

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Here is an example of what heat inside a metal enclosure can do.

Two weeks ago I called to a building where the ballast of a very old fluorescent batten fitting had overheated to the point where the fitting was glowing red. It been left switched on all day along with other fittings, but with there were no lamps fitted in faulty fitting. It was fitted to a plasterboard ceiling but the joists above were charred and black. I assume the internal wiring caught fire and a flame went through the cable entry hole, but I'm not certain, it might just gave been heat transfer. So even inside the metal case, a near disaster was caused, only prevented because the owners popped back into the building to do something and could smell burning, found the fitting and turned of the supply. This year I have seen two law bays and one other fluorescent in that condition, dangerous stuff this lectric!
 26 November 2015 08:38 pm
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sparkingchip

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I have passed comment in the past on this forum that electrical testing and certification concentrates on the live and earth, neglecting the neutral.

We test R1 + R2 as a dead test then carry out a loop test as a live test carefully recording the results.

However the neutral gets little attention when testing is undertaken and doesn't get a mention on the certification.

A couple of Twitter links.

A storage heater circuit from a job last week, installed 10-20 years ago and "tested & inspected" several times.

Domestic consumer unit busbar installed, tested and inspected about three years ago.

Andy
 26 November 2015 09:27 pm
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sparkingchip

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So the conclusion is that a termination made by MEM in the factory was over tightened resulting in the termination failing many years later.

The point is made that in the intervening years this was not found by professional electricians.

Without stripping out and remaking all the terminations how would an electrician detect this fault?

If you check the torque on the terminations with a torque screwdriver it will not tell you that one is over tightened. It will merely click to tell you that it is at least equal to the recommended torque. So you would only know it is the actual required torque if you loosened the screw then retighted it.

So if you are going to loosen all the terminations then really you need to completely remake the terminations as the conductor may already be damaged from over tightening.

That is assuming the manufacturer's recommended torque is actually appropriate.

Installed to the manufacturer instructions.

Andy
 26 November 2015 10:34 pm
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leckie

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What were those conductors in the picture connected to Andy? Not MCB cage clamps, maybe neutral bar or earth bar terminals in a consumer unit?

I have bought a torque screwdriver but I think my own arm can judge much better. Mind you, I'm sure lots of think that and we can't all be right! I was checking the tightness of terminations in a very old DB today. I didn't have torque setting data so I used my calibrated arm. Most of the connections were loose. The main earth connection was almost falling out. So I suppose that as our arms appear to be calibrated to different levels, we will have to use the torque drivers!
 26 November 2015 10:56 pm
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sparkingchip

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1.0mm lightingCPC in a H???r consumer unit neutral bar.

The instructions state

"Earth and neutral bar connections : 2.0Nm.

Single conductors below 1.5mm2 need to be doubled back in the terminal bar."

Andy
 26 November 2015 11:57 pm
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alancapon

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Originally posted by: sparkingchip
. . . So the conclusion is that a termination made by MEM in the factory was over tightened resulting in the termination failing many years later.

The point is made that in the intervening years this was not found by professional electricians. . .

Having read the report in full, these points are statements by the expert investigator, not necessarily accusations.

Personally, I would be more concerned about the missing fire break being commented on and either not given the importance it needed, or not reinstated.

Regards,

Alan.
 27 November 2015 12:00 am
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mapj1

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The other problem is that as E and N are at nearly the same voltage, even if the insulation melts away, unless you get a jolly convincing contact, an RCD may not trip either, and an MCB certainly won't.

This fire is a salutory reminder that a metal fuse board is no cure-all and certainly can be a seat of fire, and a big one at that. Pics in the fire report are quite sobering.
perhaps a wago style connector would have been better, or may fail over time in another way.

-------------------------
regards Mike
 27 November 2015 12:11 am
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sparkingchip

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Originally posted by: alancapon

Originally posted by: sparkingchip

. . . So the conclusion is that a termination made by MEM in the factory was over tightened resulting in the termination failing many years later.



The point is made that in the intervening years this was not found by professional electricians. . .


Having read the report in full, these points are statements by the expert investigator, not necessarily accusations.



Personally, I would be more concerned about the missing fire break being commented on and either not given the importance it needed, or not reinstated.



Regards,



Alan.


I agree with your comments Alan, I was trying to point out that identifying a over tightened connection actually requires the terminations to be remade.

So are electricans going to strip and reterminate consumer units and distribution boards at every EICR inspection and test or just confirm that the termination are at least tightened to the minimum torque without confirming they are not over tightened?

Andy
 27 November 2015 06:53 am
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normcall

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Would not a proper visual inspection raise suspicions regarding overheating as the problem would have got worse over a period before 'real' damage caused? I'm sure all of us have spotted a 'blueing' around the odd connection/termination over the years and making us investigate further.
Extending inspection periods has missed the real point about prevention by concentrating on measurements and results.

-------------------------
Norman
 27 November 2015 08:22 am
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Bhilly

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Agree with Norman - but how many customers are willing to pay for a proper test and inspection as opposed to cheap n' cheerful tick box exercise that has become the norm? Other question is - must have been a fair neutral current. Discounting harmonic distortion this means an unbalanced load. No surprises there given the age of the installation and all the additions throughout the years - does anyone assess load balance when they carry out an EICR?
 27 November 2015 09:15 am
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normcall

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A couple of days ago I was looking at a MEM metal fusebox with rewirable fuses in a garage circa 1962. Nice and clean, no sign of overheating etc and no sign of any 'blown' fuse wire over the years. Sweated on earth in tinned copper about 7/064 and no RCD. Simple addition of front end RCD will solve the fire risk - or will it?

Talking to a family friend in the pub yesterday, her mother had warm water coming out of the cold water main complete with shocks from the washing machine and taps a few years ago. This electrical stuff can be really dangerous, can't it?

Remind me where the perfect world is, that involves humans.

-------------------------
Norman
 27 November 2015 09:18 am
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sparkingchip

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Originally posted by: normcall

Would not a proper visual inspection raise suspicions regarding overheating as the problem would have got worse over a period before 'real' damage caused? I'm sure all of us have spotted a 'blueing' around the odd connection/termination over the years and making us investigate further.

Extending inspection periods has missed the real point about prevention by concentrating on measurements and results.



Another issue that I would like opinions on is, if copper wire is heated it hardens, I have a loop of copper cable that had been subjected to heating and it is now a hard wire spring.

So if you see a termination that has a resistance fault and tighten it to the prescribed torque is it a good joint given the changed physical nature of the copper conductor?

Twitter link to photograph with neat hardened copper cable.

Andy
 27 November 2015 09:31 am
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mapj1

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The big problems are that the environment has a huge role. Copper wire in a slightly damp area (which that garage obviously was not, but it could have been) will dull, as will brass, as a thin oxide layer forms. Surfaces that my be called on to move quickly, like the pivot bearings in an MCB may also develop corrosion that makes them less responsive. This is more likely in damp and cold
Regular vibration if perhaps mounted on a stud wall with a door that slams, can loosen screws.
Lubricants in MCBs and RCDs can go stiff, as the lighter molecules evaporate off, leaving only the heavier ones behind. This is more likely in warmer situations.
Copper is a soft metal and will slowly flow under pressure, so a terminal that was tight last year, after a bit of themal cycling is likely not to be.
Predicting if this will happen or not, is very hard, especially the stuff that happens inside MCBs and RCBOs.
If the consumer unit was gas tight and full of CO2, we would be able to predict better, but even then vagaries of the wiring fill and the loading profile would conspire to mean that quite a lot would be missed.

Also contact burn is a runaway condition - it may be fine for ages - but once it starts to darken and burn away, either it welds up and self repairs, or the resistance tends to rise, increasing the dissipation. So it may really look fine inspecting one year, and yet be gone in a puff of smoke before the next inspection is due.
In some really pricy kit one might build in a fire detector, or for certain types of high voltage gear a UV light detector to see corona, but you are in an industry where an MCB has to be produced to be price competitive with a BS3036 fuse holder, and in that world the built in detector is prohibitively costly.

-------------------------
regards Mike
 27 November 2015 03:18 pm
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Angram

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Is metal a fire shield?
Fire training I did, some time ago, said very clearly that a fire at one end of an RSJ could start a second fire
at the other end, in a separate room. So we had to check the other room.

So why do metal CUs not transmit heat? The fire risk can only be mitigated if the metal CU does not come into contact
with combustible material. Cleaning materials in a cupboard?

I try not to think about what happened at Clandon.

terence
 27 November 2015 04:08 pm
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sparkingchip

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Plastic consumer unit enclosures have been adding fuel to the fire making a small fire much larger, as well as producing thick black smoke adding to the danger for those who need to evacuate the area also creating smoke damage to the fabric of the building and its contents.

So the use of metal enclosures addressees the issues of plastic enclosures that we are told cannot be resolved by reformulating the composition of the plastic.

As shown at Clandon House steel enclosures do not prevent the spread of fire from within it. Which we already knew.

The lack of fire stopping would be a major concern once the fire had spread from the enclosure.

Andy
 27 November 2015 05:09 pm
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mapj1

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Perhaps a similar remove the fuel argument for metal boards to be mounted on Hardibacker or similar, rather than on wooden board, if a flat brick wall is not available.
It also suggests that the small cupboard inside bigger cupboard idea is a good one, as you can't sensibly store a dangerous volume of potential fuel in a containment that is a tight fit around the consumer unit or dis board, and it limits air supply. (unlike the average cupboard under the stairs that may be home to deckchairs, ironing boards, various aerosol cans, bottles of lighter fluid, cleaning solvents and a gas meter - and that's just mine, I'm sure others are worse.)

In terms of the weight of plastic removed, this factor may be overplayed, in many cases the various circuit breakers and the PVC insulation on the wires is considerably more weight of hydrocarbon than the plastic box around it.
This I think is recognised by the regs suggesting that a plastic box in a fire resistant enclosure is quite acceptable.

however, I think I agree with the OP, metal boxes alone are no guarantee of 'no fires'. Detection and rapid isolation are preferable, and ideally using methods that will last a lot longer than 25 years. (like HV fuses on poles, many of which are older then me. However old that may be..)

-------------------------
regards Mike


Edited: 27 November 2015 at 05:19 pm by mapj1
 27 November 2015 05:37 pm
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sparkingchip

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Generally the one of the problems stated as causing fire in consumer units and distribution boards has been electricians leaving under tightened terminations, this time the problem appears to be the reverse, a over tightened connection.

So when peparing the two EICR'S I have been instructed to undertake next week I will visually inspect the busbars and looking to see sufficent indulation is stripped back on the conductors then check the screws are tightalong with tugging conductors with my longoing nosed plies to check they are gripped and nother broken off in the termination . What I won't be doing is releasing the terminations and completely remaking all the terminations.

Have a look at what the bikers say about checking torque.

Andy
IET » Wiring and the regulations » Clandon Park House - Fire Report

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