A UK Housing Association has installed over 200 of these devices within their larger blocks of flats to protect the means of escape and communal areas from RCTT within sockets.

I am keen to raise awareness within the fire safety sector both here in the UK and the rest of the world as RCTT is a common electrical fault which can lead to fire. I would like to start by asking members whether you have experienced fires that have started due to this type of fault or whether members are already aware of this type of problem and if so how were you made aware of RCTT?

Edited: 01 September 2012 at 10:24 PM by colinwalker

You dont actually say what the devices are?

Regards

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry

The item in question has been under test for some time in various areas, it looks like a fuse and is fitted between the live cables and the terminal and the neutral cables and the terminal at the back of the socket, we have no firm data as to their effectiveness and are unable to comment at the moment. The various fire protection agencies may have more information on the effectiveness of this product for you.

Basically a thermal switch, if the terminal reaches a temperature of around 70 degrees it will cut out, putting one on the neutral side could cause worry as one taking the socket apart may assume that it is fully dead and the live is still live.

I would just like to point out to forum members that the term RCTT is just an americanism for loose terminal, cable broken in a ring main and arcing, ineffective screw or cracked terminal etc causing it to overheat through arcing.

The item mentioned is a PRODUCT for sale so you must judge it along with all the other products that allegedly save you money, save your life etc that are on sale everywhere.

The RCD does an effective job in detecting RCTT and will operate most of the time under these conditions.

regards

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"Take nothing but a picture,
leave nothing but footprints!"
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"Oh! The drama of it all."
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"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
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Edited: 30 August 2012 at 12:19 AM by rocknroll

So that's what it is? Well I never! Sounds like legal speak by a lawyer who is a frustrated medical practitioner.

Not a new concept, but the principle is in prevalent use across the divide, but at the start of circuits. Known as AFCI's, (there we go again! ) AFCI's are primarily designed to protect against arcing and fire, whilst GFCI's and RCD's are designed to protect against electrical shock.


It's common knowledge as a cause of "trauma" by us electricians!

From the Peccater web site, it's a thermistor with an alarm, or a cricket with a chirp? : -

Quote: In normal conditions (below 80oC), the Thermiac device is in an open condition with the contacts held apart by a specially formulated compound, in fault conditions (above 80oC) the compound releases the spring loaded contact closing the circuit thereby operating an alarm or trip as required. This operation is non reversible so a positive indication is maintained showing that the installation has been subjected to a thermal event, this is particularly useful where the heating was due to a transient effect and is a very effective way of detecting elevated temperatures have occurred. A good example is vehicle axles or bearings where temperatures in excess of 80oC may be the precursor of a future failure.

Obviously anything which can detect overtemperature within equipment at an early stage, is desireable but at what cost? and consider the influence of the "Hawthorne effect" on a small sample. Councils are strapped for cash but it could be jobs for the boys, but if you're going in to fit these units, why not just leave them out and simply torque up the connections? Will the introduction of the requirements for torque screwdrivers prevent the "trauma", in any case?

Regards

Oh the Trauma! : D

Have you really considered the risk? Fires caused by fixed wiring being faulty are quite rare, and very few of these are ever isolated to loose connections in sockets. Sockets on escape paths are only used occasionally for cleaning machines, and there should not be trailing cables or fixed loads. The fault sensing connections also add lots more fixed wiring to the installation, and depending on the exact design may introduce other risks and difficulties. Do sockets on multiple phases have separate sense systems, and what are the risks of the sense devices themselves going faulty? There are obvious problems with achieving isolation of a socket for maintenance, how is compliance with 132.15.1 achieved? This device seems to introduce a whole new range of risks to fixed wiring, perhaps in response to a non-problem?

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David
CEng etc, don't ask, its a result not a question!

Here we go again, the world according to "Carp". Why does the NFPA not agree with that?

Regards

I've seen plenty of burned out connections over the years - but then our regulations seem to anticipate problems from connections and demand that they're put in an non-combustible enclosure or equivalent (reg 526.5). Personally I've not come across problems with overheated joints that have caused damage beyond their immediate enclosure.

The Americas do seem to have a particular problem with arcs initiating fires (hence the popularity of AFCIs over there) - if I recall correctly their 'high risk' areas were usually domestic bedrooms. They do have a significantly different way of doing things, which might have an influence - double the current for starters (as 115V), the flimsly pins on their plugs must surely have much more difficulty making a good reliable contact than ours. Their RCDs (GFCIs) tend to be built-in to sockets rather than at the DB, so the fixed wiring typically lacks sensitive RCD protection (which also often gives a reasonable protection from fire). Their common use of figure-8 leads rather than sheathed flex maybe makes cord grips less reliable, so more strain on terminations, and so on.

- Andy.

I've just watched the video - the Peccater device seems to attempt to disconnect by causing a short to earth and so triggering ADS. I wonder if it's creating a hazard there - if there are loose connections about you presumably can't rely on Zs being low enough for prompt disconnection, even if if there is an RCD in the circuit what's its reliability? What are the shock risks to residence if the earthing system is at an elevated voltage for a significant time?

It doesn't seem to address problems in the rest of the installation (appliances, lighting, CUs, joint boxes etc) - many of which seemed to appear prominently in the gallery of burned-out equipment.

- Andy.

I think said Housing Association has been sold a complete pup by someone claiming to understand fire risk in multi res property.

perhaps said fire risk assessor should have started with the concept of sterile means of escape and defend in place policies. Since when has it been normal for tenants to evacuate due to a fire in a single residence - the fire will be behind a fire door so the means of escape is not likley to be compromised.

as for electrical faults in MoE's, personally speaking, there is more risk from lighting (failed ballasts/luminaires usually) than there is from sockets - usually because there are very few sockets in stairwells on multi res - the landlord doesn't usually like to pay for anything tenants might want to plug in on the landing - and doing so actively contributes to the fire risk anyway

So, I'd hazard a guess the evidence is slim to non existent for the benefit of such a device - the HA would be far better advised by a competent fire engineer to adopt a simple inspection and testing regime for MoE circuits, to examine means of spread of fire/smoke in MoE,s and to routinely examine the sterility of such MoE's

Regards

OMS

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Failure is always an option

magic beans anyone?

As a housing association, should you not already have suitable RCD protection for those sockets in question, public areas and unsupervised persons???????

Surely a programme of planned maintenance and inspection would serve a better purpose and represent a better use of what is essentially public money?

Emperors new clothes anyone?

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry

I dont recall any HMO's having a "free" place to plug into, as they are mostly hidden in locked cupboards that cleaners have access to.

In the sunny southwest (well sometimes) like the rest of the country we have varing sizes of HMO'S and blocks of flats, having done work for LA Idont recall any accessable outlets, even the colleges and business parks have lockable outlets that are RCD controlled.
Infact I do recall seeing "recharable hoovers etc for the use in staircases etc so they iliminate the required "tripping hazzard flex" and they are much lighter.

Seem's someone could making thier own gravy train by scaring the HA'S into beleiving there is a "Risk"


Regards

Daren

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..... Dont pee in my pocket and tell me its raining ......


www.quest-electrical-sw.co.uk

On the youtube video they were showing them installed on socket outlets in communal areas feeding pc's etc. where residents spend the day, together with a selection of sockets with burn marks they said had been removed from their housing complexes.

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lomasjs

I wonder how many of the sockets that overheated cost more than a £1 to buy. Perhaps if they checked the quality of goods quoted for at build of these premises, instead of allowing 'contract' sockets to be used, there would be less failures.

The sockets in question are on the Means of Escape. Surely a better solution would be the use of metal accessories and steel conduit or pyro?

Sounds like a solution in search of a problem to me.

Perhaps said fire risk assessor is a director of the company selling said product!

My original question was to find out from professional electricians whether any were aware of RCTT and whether you had been involved when there had been a fire. Thanks for your comments some of which have been helpful.

"I installed the devices back in November, I am interested to know who is aware of the phenomena of Resistive ConnectionThermal Trauma (RCTT). I am a qualified electrician and also fire safety officer for the housing association which installed the devices."

133.5?

Regards

BOD

I've studied the video.



I'm not impressed.
In the socket outlet shown the "peccaters" are wired from L to E and another from N to E.
When the temperature of one or both devices reaches 80 degrees C they are expected to short the live and/or neutral to earth at some time.
Thus they are totally dependant on a working RCD to disconnect the circuit.
If the earth is broken between the socket and CU the local earth terminal on the socket is likely to become live.

IMO their introduction into each socket outlet creates far more problems than they can possibly solve.
Better quality sockets, regular inspection and good fire precautions and warnings are needed.


The video states that Cottsway Housing Association has nearly 4000 properties and that the displayed sockets and burnt out CUs were all found in their properties over the last 8 months.

That suggests to me that inspection and maintenance of the properties is inadequate.

http://www.youtube.com/watch?v=bd7adHUyM-k

Interesting. I would like to see the risk assessment that suggests introducing a phase to earth short on domestic wiring is a good idea! There seems to be no data on the manufacturers website giving clues to the current rating of these devices, or the time that they can provide a short for. Surely if the fault is a loose connection on the back of a socket, introducing a deliberate short (using the same loose connection) may not be a wise idea! I will remain unconvinced by the merits of these.

Regards,

Alan.