Why ? Almighty bang, huge blue flash when I unplugged an electric heater

[Wyleecoyote]

For a good few years I have used an upright electric heater in living room plugged into a 6 way extension lead.

The heater and also an electric fan are plugged into the extention lead all the time, at either end of the ext lead socket line, so theres 4 outlets in between, which are only ever used for phone chargers but wasn't plugged in at the time.

When heater not in use, I normally unplug the ext lead from the wall socket but fan and the heater remain plugged into the ext lead outlets/sockets.

The heater is controlled by its own thermostat and is normally unplugged when fan is in use, although on this occasion the fan was in use and I'd forgot to unplug the electric heater.

I only unplug the heater because it's pointless the heater being on when weather's so hot & the fan is in use.
I've never unplugged the heater for safety reasons because the fan is on.

The heater is adjacent to french doors on the first floor and when the french doors are open, the breeze is sufficient to cool the heaters thermostat and switch it on, hence why I normally unplug it.

On this occasion with upright oscillating fan on speed setting One and electric heater on setting Two, emitting heat; I unplugged the heater which created and almighty bang and intense blue and white lightening type flash...... Why ?

 

[EFLImpudence]

I suppose it depends on your definition of almighty and intense.

Presumably a live something (wire or part) touched a neutral or earth something (wire or part).


Where was the bang and lightning flash?

In the socket, in the plug or at the flex.


Did no fuse blow or circuit breaker trip?

 

[Bodgedbuild]

High current is great for creating an arc and once the air at the "switch contacts" (in your case the pins on the plug) becomes Ionised, it becomes more conductive. This is the basic principle in arc welding that you strike an arc and then the gap can be increased because of the ionisation of the air. This issue is simply the heavy load and it may be coupled with a partial inductive load too which may be out of phase with the resistive load of the heating element. In industry they use powerful springs to make switch contacts separate or join together at very high speed to reduce the time in which the arc can create heat, they even use some rather nasty gases to suppress the ionisation.
I think you would be wise to use two sockets and avoid plugging both into a multiway socket as well as being more cautious in ensure the heaters are each switched off. You are basically creating your own mini arc welder albeit a high voltage one!

 

[Wyleecoyote]

Yeah, trip switch at consumer unit tripped sockets and fuse of ext lead blew but not before the almighty bang, lightening type flash; which was very much like the flash emitted from arc welding.

The flash, bang, I assume came from the plug I was holding and the ext lead socket, the noise was immense and I could still see the flash even when I closed my eyes until the following day.

There's no damage to the ext lead cable or the ext lead sockets, nor the wall outlet that the ext lead was plugged into, other than little charring/blackness to the Live & Neutral of the Heaters plug

The UK 3 pin plugs of both the Heater and Fan, have no damage, to the plugs themselves or the installation to the pins.

The Heaters plug was maybe 6 inches away from the Fan's plug and there's no damage, blackness or charing to the fans plug.

The ext lead sockets have red plastic covers over the Live & Neutral apetures when not in use, which are operated when the plug is inserted via its Earth pin.

I kind of knew what had occurred; my why, was how did it occur, I've used all kind of extension leads in such a manner for many years, as well as unplugging plugs from wall sockets; although I do tend to switch off wall sockets at the wall before I unplug but as my ext leads don't have switches at the socket end, I tend to just unplug rather than walk the 4ft distance to the wall outlet and switch it off.

When I initially posted, I believed the issue was due to the Fan and Heater sharing the same ext lead but now I'm of the belief that the Heater plug, all by itself created the arc and it would have still occurred with or without the fan being plugged in and in use; so there must be internal wear or an issue within the ext lead socket.

Lesson learnt.... ALWAYS SWITCH OFF AT THE WALL OUTLET BEFORE UNPLUGGING !

 

[opps]

There's no damage to the ext lead cable or the ext lead sockets, nor the wall outlet that the ext lead was plugged into, other than little charring/blackness to the Live & Neutral of the Heaters plug

If the pins have carbon on them, it is probably safe to assume that whatever they were plugged in to has carbon deposits as well.

 

[Wyleecoyote]

If the pins have carbon on them, it is probably safe to assume that whatever they were plugged in to has carbon deposits as well.

May well be but I believe the blackening and charring is a result of the recent arcing incident rather than a build up over the years.
I tend to plug and unplug the heater quite often and I've never noticed charring to the plug before.

The ext lead with be rendered useless and binned and to be on the safe side, I'll buy a new heater

 

[opps]

May well be but I believe the blackening and charring is a result of the recent arcing incident rather than a build up over the years.
I tend to plug and unplug the heater quite often and I've never noticed charring to the plug before.

The ext lead with be rendered useless and binned and to be on the safe side, I'll buy a new heater

Probably a wise move. I was suggesting that the arc would have had a similar effect on both the plug and socket (simultaneously).

 

[ericmark]

Ionisation of the atmosphere. It happens once in a blue moon flash.

 

[ericmark]

I should maybe expand, the main experience we get to ionisation is the old tungsten bulb, in the main they simply failed, but every so often you would get ionisation of the gas inside the bulb when it failed, resulting in a bright flash when it failed, and often it would also trip the MCB as it failed. On rare time even the glass would break, this is why quartz lamps need to either be high enough so if the break the bits have cooled before they hit the ground, or they are retained by a secondary glass protector, also the glass stops some rays which can be dangerous if the lamp is close.

Number 8 is Arc divider/extinguisher in the MCB, again designed to try and stop ionisation. This is why we design switches to work fast, odd however for high voltage over 1000 volt AC, some times the switches seem to close on open very slowly, I have not worked out why.

The other ionisation is lighting of course.

 

[Wyleecoyote]

Update...... I took extension cable/socket enclosure apart, and the arcing was caused by the one socket.

With the socket I used solely for the electric heater; there's a hairline crack in the plastic enclosure from Live to Earth, which during normal use, it was totally un-noticeable, especially as it was also hidden by the plug; in fact, it could only be seen when the enclosure top cover was removed and held up to the light or a torch shone behind it.

The two sockets used most often, one only ever used for the electric heater, the other for phone chargers, and seperated by two sockets in-between; had weakend in the shape of a plug, one had eventually cracked, I guess due to heat generated over years.