The RCD tripped

[tom66]

I was unplugging a plug, and I heard a loud pop, then all the lights went out. Main 80A/30mA RCD tripped.

This is in university dorms, so I am fairly confident in the quality of wiring. But should I be concerned?

My housemates are a little confused, and I have no idea how I caused it (if I did at all?)

Could the pop I heard be related to an earthing fault?

[M. András]

small arcing in the socket? or someone on the same phase was switching something on which tripped the rcd

[Psi]

Check the cable, plug and socket in question for any signs of damage.

You could try to reproduce the fault and figure out which part is causing it,  the cable, plug or socket, but you need to be careful as there is obviously a problem somewhere.

[tom66]

I found the fuse to be blown in the extension cord I unplugged the device from, if that adds anything. It was a Nokia phone charger (genuine, early iron core transformer type), but that still works, and hasn't tripped it again. I have added the cord to my do not use list, a friend is giving me a spare.

[Zero999]

Perhaps you caught the plug with your finger when you unplugged it and the RCD tripped before you felt the shock?

[IanB]

Perhaps you caught the plug with your finger when you unplugged it and the RCD tripped before you felt the shock?

That wouldn't blow a fuse, though, as happened here.

[IanB]

I was unplugging a plug, and I heard a loud pop, then all the lights went out. Main 80A/30mA RCD tripped.

This is in university dorms, so I am fairly confident in the quality of wiring. But should I be concerned?

My housemates are a little confused, and I have no idea how I caused it (if I did at all?)

Could the pop I heard be related to an earthing fault?

I found the fuse to be blown in the extension cord I unplugged the device from, if that adds anything. It was a Nokia phone charger (genuine, early iron core transformer type), but that still works, and hasn't tripped it again. I have added the cord to my do not use list, a friend is giving me a spare.

If there was a loud pop followed by a blown fuse and an RCD trip, then all the signs point to a direct short between live and earth. The short circuit will cause the pop and blown fuse, and the earth current will trip the RCD at the same time.

It's quite possible the wiring is faulty inside the extension cord you were using. If it comes apart, unscrew the covers on the plug and socket ends and see if there are any loose wires. Also check that the strain relief at the cable entry is not loose as this can cause wires to pull out of the terminals.

[Monkeh]

This is in university dorms, so I am fairly confident in the quality of wiring.

You lost your lights because of a socket. You should not be so confident.

[tom66]

This is in university dorms, so I am fairly confident in the quality of wiring.

You lost your lights because of a socket. You should not be so confident.

There were two RCDs. One for just the sockets; one for the whole lot, including lights. They were the same device so presented with the same short one might trip before the other.

We still had the emergency exit light.

I am going to disassemble the strip and see if there's any damage.

[Monkeh]

This is in university dorms, so I am fairly confident in the quality of wiring.

You lost your lights because of a socket. You should not be so confident.

There were two RCDs. One for just the sockets; one for the whole lot, including lights. They were the same device so presented with the same short one might trip before the other.

As I said, don't be confident of the wiring. That's plain wrong.

[IanB]

You lost your lights because of a socket. You should not be so confident.

If the fuse blew in the extension cord the fault would be downstream of the fuse. Hence, unlikely to be in the building wiring.

[tom66]

I can see some dark colour in the earth pin for the particular socket that went bang. I think this must be a clue. I can also hear a rattling sound... hmm.

It is very difficult to disassemble it as it appears to be sealed, but I will try. I have succeeded before with wall warts.

I have never had a look at this extension before, but now I notice no CE marking at all. It must be at least 8 years old as I see a "2004" date partially visible and I found it in the spares pile while searching for stuff to bring when away from home. The only indication is:

13A 250V~BS1363/A
Total Load must not exceed 13A
EURO 9988

Hmm... want to bet that something has come loose and me moving the plug made the final contact? Next time I will be more vigilant.

[Monkeh]

It's very likely the cheap POS shorted internally.

[IanB]

Taking it apart may help with forensics to determine what failed, but it doesn't look like you ever want to use it again. Cut the cord off for potential re-use and throw the rest of it away after you have finished examining it.

[tom66]

I am destructively disassembling it. No chance of ever reusing this...

[Monkeh]

You lost your lights because of a socket. You should not be so confident.

If the fuse blew in the extension cord the fault would be downstream of the fuse. Hence, unlikely to be in the building wiring.

That doesn't mean having every circuit in the building on a single RCD is correct. As I said, do not be confident of such an installation.

[tom66]

If I cannot be confident in the work of professional contractors, I do not know what to be confident in. You have to draw a line...

[Monkeh]

If I cannot be confident in the work of professional contractors, I do not know what to be confident in. You have to draw a line...

I draw the line where someone puts every circuit on one RCD. It's against regs, common sense, and good workmanship.

[tom66]

If I cannot be confident in the work of professional contractors, I do not know what to be confident in. You have to draw a line...

I draw the line where someone puts every circuit on one RCD. It's against regs, common sense, and good workmanship.

Every household installation I've seen has one main RCD for all circuits, then a separate RCD for the sockets only. What's wrong with this?

[Monkeh]

If I cannot be confident in the work of professional contractors, I do not know what to be confident in. You have to draw a line...

I draw the line where someone puts every circuit on one RCD. It's against regs, common sense, and good workmanship.

Every household installation I've seen has one main RCD for all circuits, then a separate RCD for the sockets only. What's wrong with this?

Well if you put them in series, which one trips? That's right, you don't know. They must be separate.

[tom66]

But it gives you a backup for the main sockets for essentially no extra cost (which is always a consideration) -- sockets which are far likely to have a ground fault than a light bulb or cooker.

[Monkeh]

But it gives you a backup for the main sockets for essentially no extra cost (which is always a consideration) -- sockets which are far likely to have a ground fault than a light bulb or cooker.

You don't need a backup. You need lights which work so you can go and turn the power back on without breaking your neck.

[tom66]

But it gives you a backup for the main sockets for essentially no extra cost (which is always a consideration) -- sockets which are far likely to have a ground fault than a light bulb or cooker.

You don't need a backup. You need lights which work so you can go and turn the power back on without breaking your neck.

There's an emergency light positioned very close to the breaker box which makes it possible to see the switches. I would recommend a torch in case it happens to be a lighting circuit fault though. Minor inconvenience At home, power trips were common on the pay-as-you-go electric meter -- often forgetting to top it up or activate the top up. I got quite adept at navigating in the dark and locating the charge key.

[Monkeh]

Doesn't change the regs. You don't put RCDs in series.

[tom66]

Doesn't change the regs. You don't put RCDs in series.

Eh. I'm no electrician. I stop once it gets beyond wiring a plug. There must be some reason they did it like this.
Remember, I am basing this all on the labels outside, as I have not lifted the cover (nor will I), to check the actual wiring.