Miniture circuit breakers

[Paul2886]

Just thought it may be of interest to you know that I have just been informed of a miniture circuit breaker overheating and igniting.
The smoke produced was sufficient to require a total evacuation of the care home. The consumer unit was within a downstairs toilet that was not encased with any fire resistant materials and, as usual for these areas, no detection within.
Just wondering if any of you guys have known of this before and to make the point that it can and does happen. A consideration during your next FRA perhaps.

[slubberdegullion]

Thanks for the info

[Redone]

Cheers P

[Graeme]

i have always specified afd within cupboards etc where there is a fuseboard during the design stage.
Glad i do.

[Paul2886]

i have always specified afd within cupboards etc where there is a fuseboard during the design stage.
Glad i do.

And if a bathroom/toilet what option then. Heat detection and FD30s door perhaps

[John Webb]

Have you been able to find out the reason why this MCB failed in this way? Was it subject to an overload and failed to work or was there some other factor?

[kurnal]

And if a bathroom/toilet what option then. Heat detection and FD30s door perhaps

I note what you say and the issue of siting of consumer units of this type perhaps needs more careful consideration. However on the provision of a fire door-  many care homes and hotels have consumer units in bedroom corridors. There  is currently no guidance that says this should not be the case.

If risk is defined as the quantum of liklihood and consequence it would be interesting to know if this is a one off or if it has happened elsewhere.

[Paul2886]

And if a bathroom/toilet what option then. Heat detection and FD30s door perhaps

I note what you say and the issue of siting of consumer units of this type perhaps needs more careful consideration. However on the provision of a fire door-  many care homes and hotels have consumer units in bedroom corridors. There  is currently no guidance that says this should not be the case.

If risk is defined as the quantum of liklihood and consequence it would be interesting to know if this is a one off or if it has happened elsewhere.

Hi Kurnal,
Made some additional enquiries about the incident and it appears that it was just a very rare occurance. The attending electrician said he'd never seen it before and could give no explanation. It did incidently ignite the adjacent MCB's which caused smoke logging in the linen cupboard above as well. Shows the importance of fire stopping these little holes created by the cable entries through the above ceiling. The fuse box was also a metal clad type which may have help prevent a much worse situation. That's all I can add but to say that I am going to photgraph the MCB's that caught fire and if possible post them on this forum for viewing. If that's possible.

[wormhole]

MCB's don't normally cause problems, however if the installations PSC (prospective short curcuit current) is remotely close to the maximum PSC breaking capacity of the MCB this can cause problems - the electrictian should have measured the PSC so I would ask him what it is (it will be a value in thousands of amps) - most domestic MCB's are only rated to 6kA, however in some (although not to often) a fault level can be acheived needing higher rated MCB's to ensure they can break the circuit.

It would not normally need to be a specific consideration within the FRA beacasue ofcause you are all stating that the electrical installation must be tested & inspected at regular intervals as required by BS7671.

AFD is a slightly different matter, depending on the category of protection, now as a care home I would expect L1 anyway so should have detection.

[nearlythere]

i have always specified afd within cupboards etc where there is a fuseboard during the design stage.
Glad i do.

And if a bathroom/toilet what option then. Heat detection and FD30s door perhaps

Yes, if the bathroom/toilet contains a fire risk.

[nearlythere]

This issue is good fodder for a protracted discussion/exchange of views on what is perceived to be a significant risk. People reading this post may now decide that RCBs are a significant finding and include it in a RA. But if this is a one of, as Kurnal asks, and if it is then will we be over-reacting by assuming RCBs to be a significant finding?

Being a Firefighter I, as well as many others, can remember fires which started in an unbelievable way, even to us. Non firefighters will never have seen not heard of these instances.

One I can recall from many moons ago is a fire in a bedroom which started under a bed. After a thorough examination and discussion with the occupier the source of the fire could only put down to a battery train set stored in a box igniting. Never saw anything like this before nor since, but is a battery train set a significant risk?

Another situation was a living room fire where the cause of the fire, as backed up by a forensic scientist, was the sun shining through glazing which had bevelled areas and the bevelling acting as a magnifying lens focusing the sunlight onto fabric. Just as one used to do at school using a magnifying glass on paper.
Is bevelled glazing a significant risk?

Can we always see the unforseen?

[Underground]

Two points of interest

1) Where I am from we have been told to count light refracting through glass as a last resort for concluding how a fire started.  Many tests have been conducted that have proved that the chances of it being able to happen are so small that it is unlikely to ever happen (apparently backed up by science).  I reiterate - this is what we have been instructed.

2) I have been to a couple of instances where MCBs have overheated and melted and could have gone on to catch fire (called to smell of burning) - one was only a couple of weeks ago.

[Mike Buckley]

When people start to talk about the chances of something happening is incrediably small, I think about the National Lottery. The chances of winning it are miniscule but most of the time there is at least one lucky person.

Most tests use a small number of trials to get a statistical probability. In the real world this scenario could arise in millions of buildings, over thousands of hours. Someone somewhere is going to get unlucky.

[Underground]

You can drown in a teaspoon of water you know!

[kurnal]

I have attended two fires caused by focussed sunlight.
One was caused by a paperweight in  a window sill - the  small fire was out on arrival but the occupier called us because he could not find a cause for the small fire involving papers on a coffee table he discovered on returning to his unoccupied house. On investigation there were other burn marks on other furnishings nearby- previous near misses!
The other was caused by a make up mirror in the window that focussed on the curtain and caused significant damage.