Get paid faster with card payments | Go Paper Free - Save Hours | Offer Finance to Customers
This official sponsor may provide discounts for members

Discuss Could this stuck hallway switch cause a fire ? in the Electrical Forum area at ElectriciansForums.net

James

-
Mentor
Esteemed
Arms
Supporter
Patron
It is almost impossible for that switch to have caused a fire in the area you have pictured.

Have the fire brigade not given you any clue as to where they think the fire started?
 

Lucien Nunes

-
Mentor
Esteemed
Arms
It looks like the output terminal in the 2nd cutout (company fuse) has overheated and scorched the meterboard, and perhaps through conducted heat melted the disc out of the seal on the end of the left hand mineral insulated cable, from which the compound has run out. If it is still connected, it should be rectified without delay, as it could continue overheating and live parts are probably accessible that cannot easily be isolated, and which pose a risk of arc flash injury. It appears to have been incorrectly installed in the first place. What has been done about it so far? If nothing, the building network operator or DNO needs to be called and as it is an emergency situation they will at least turn up to isolate it for safety.

In any case the air delay push switch for the hall light is not related to this incident. If the timing screw on those Columbus switches is wound right in, the button will never pop out and the light will stay on. This is not dangerous, and I have to say they could be a bit fiddly to get right if you wanted a long delay.
 
Last edited:
Thanks for your replies. That box served the communal hallway and the upstairs flat, it did catch fire but was quickly put out, The fire brigade suggested it was caused by a surge from upstairs however nothing was damaged upstairs and no one was in.
This the installation which is as you can see was quite old and has been replaced.

If the upstairs flats electrics were not damaged how could a surge cause this ?
The main fuse was 60amps on that upstairs installation.
consumer unit1.jpg
consumer unit2.jpg
This second one did have a cover, that's the only picture I have of it, just how old was that ?
 

Lucien Nunes

-
Mentor
Esteemed
Arms
It's not so much a case of age, there are 100-year-old electrical components that are still safe; more a case of faulty installation. The MI cable gland should not have been left floating in mid-air (although it wouldn't be the first one that was) with no support and exposed basic insulation. I suspect the solid conductor was too small to be securely clamped in the cutout terminal. It's a known issue with MI cables, which have a very high current carrying capacity for a given size, and therefore sometimes require specific termination methods to make a sound connection in larger terminals of similar rating. I doubt any kind of 'surge' was involved, more likely a steady heating load that slowly overheated the bad connection.

The Mem splitter and Revo switchfuse in the grey pressed steel casings are typical 1960s. In themselves they are reliable and would survive another century. They normally get replaced when RCD protection is needed or requested either following an EICR or for additions.
 
The MI cable gland should not have been left floating in mid-air (although it wouldn't be the first one that was) with no support and exposed basic insulation. I suspect the solid conductor was too small to be securely clamped in the cutout terminal. It's a known issue with MI cables, which have a very high current carrying capacity for a given size, and therefore sometimes require specific termination methods to make a sound connection in larger terminals of similar rating. I doubt any kind of 'surge' was involved, more likely a steady heating load that slowly overheated the bad connection.
Thanks again for your detailed reply, are you referring to the big grey consumer unit or the junction box that caught fire ?
One other point I just remembered; the landlord's electrician said the continuity of the ring mains throughout both flats was poor. He thought this might be down to the installed ring mains having been in place for over 30 years. Could that have contributed to the black junction box feeds working loose and arcing ?

And lastly a new meter was put in near that black junction box by the electricity suppliers about five years ago, is it possible the black junction box was disconnected to install that new meter and added to the issue?
 

Reply to Could this stuck hallway switch cause a fire ? in the Electrical Forum area at ElectriciansForums.net

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
Top