Electric heater plug just exploded - what would have caused that?

[AVR2]

For the last 4 years or so, we've been regularly using an electric heater given to us by relatives who were decluttering. Not sure how old it is, but it's got a moulded plug (and it was apparently PAT tested before it came to us). About 10 minutes ago, I heard a sudden hissing, spluttering noise and saw flickering flashes from behind the cabinet where the fire is plugged in (to its own socket, it wasn't on an extension cable or multi-plug). The heater shut down, and for a moment I thought we were going to have an actual house fire on our hands.

Anyway, the plug clearly exploded through its rear casing, and from the position of the hole it looks like it's from roughly where the neutral terminal is, as can be seen from the pictures. I've pulled the fuse out and it's got surface burns, but its outer casing is still completely physically intact and the metal fuse contacts inside the plug haven't melted. What the hell could have caused that? And will the socket be OK? (edit - I hadn't previously looked close enough to see the crack across the face of it).

 

[pete01]

Doubt it it's got a big crack in it.

 

[AVR2]

Doubt it it's got a big crack in it.

Yeah, only just noticed that, I hadn't looked that closely. Any ideas as to what the hell happened?

 

[pete01]

Believe it or not 13 amp sockets dont like running close to 13 amps for long periods.


If it were me I'd replace the socket with a decent make MK or similar not a cheap one, and get a new heater.

 

[SUNRAY]

Believe it or not 13 amp sockets dont like running close to 13 amps for long periods.

Wow! I've been saying that for years, no make that decades and just about everone esle ridiculed me.

Thank you Pete.

 

[SUNRAY]

Personally I don't find MK sockets are as good as their reputation anymore

 

[ericmark]

Wow! I've been saying that for years, no make that decades and just about everone esle ridiculed me.

I would assume there is a reason why EV granny chargers don't run at 3 kW. Seems only considered as safe for a long time with 10 amps, and even then the socket should be marked for EV charging.

Even in the early days of the 13 amp socket, immersion heaters still used the old 15 amp round pin.

 

[AndyPRK]

Plastic around fuse melted and live has touched another terminal.

Would have thought your consumer unit would have tripped. Any pics of that please?

 

[SUNRAY]

I would assume there is a reason why EV granny chargers don't run at 3 kW. Seems only considered as safe for a long time with 10 amps, and even then the socket should be marked for EV charging.

Even in the early days of the 13 amp socket, immersion heaters still used the old 15 amp round pin.

Which I whole heartedly agree with.

However the rules for immersion heater were it's own circuit so it was perfectly correct to run a 15A radial to a single BS546 which effectively prevented it being plugged into a different circuit. As it turned out that proved to have been a far better/safer solution.

 

[Harry Bloomfield]

Not sure how old it is, but it's got a moulded plug (and it was apparently PAT tested before it came to us).

I don't understand how it passed PAT, it appears to have unsleeved pins on the plug. Sleeved pins rule, predates the PAT.

What seems to have happened, is a flash-over between live and neutral pins, internally. The socket, needs to be replaced, and the heater recycled - likely it would pass a PAT, even with a new plug fitted.

 

[AndyPRK]

I think I can see sleeving on the left pin.
maybe part of the problem!
Unless it’s charring!

 

[flameport]

it was apparently PAT tested before it came to us

That means nothing. Most 'PAT Testing' comprises sticking a label on it. Sometimes it might have been near a machine that passes a few milliamps through the wiring for some purpose or other.

Many plugs are cheap poorly made junk. Silver coloured pins are the usual giveaway.
Using such a plug with a high power load will cause it to get hot. Very hot for some of them.
Over time, things melt, smoke, conductive paths form, excessive current flows between the pins until something fails.

And will the socket be OK?

No. Even if it wasn't cracked, a socket that as been used with an overheating plug will need to be replaced.

 

[endecotp]

I don't understand how it passed PAT, it appears to have unsleeved pins on the plug.

No, they are sleeved.

 

[SUNRAY]

That means nothing. Most 'PAT Testing' comprises sticking a label on it. Sometimes it might have been near a machine that passes a few milliamps through the wiring for some purpose or other.

Many plugs are cheap poorly made junk. Silver coloured pins are the usual giveaway.
Using such a plug with a high power load will cause it to get hot. Very hot for some of them.
Over time, things melt, smoke, conductive paths form, excessive current flows between the pins until something fails.


No. Even if it wasn't cracked, a socket that as been used with an overheating plug will need to be replaced.

Let's face it: A majority (verging on most) 13A plugs and sockets are poorly made junk now.