Strange socket behavior

[DiyNutJob]

On a switched 13A socket, I tried to run a vacuum cleaner. But, it wouldn't come on. I used the non-contact test beeper on the socket and it was beeping when near the switch. The vacuum ran fine from another socket. I opened up the faulty socket while the vacuum was plugged in and used a neon testing screwdriver on it. The live terminal tested fine with the neon glowing. Then earth terminal was tested and no glowing. As soon as the test was made on the neutral terminal, the vacuum started running. This feels like a very serious fault. Can any one explain what's going on? The sockets in the flat never ever did that in the past. The wiring was touched by the builder's people recently, but everything appeared to work normally until now.

 

[EFLImpudence]

As soon as the test was made on the neutral terminal, the vacuum started running.

Do you mean you pressed the wire against the terminal?

Redo the neutral connection - and probably the others as well.


Try a new socket.

 

[DiyNutJob]

No. The test screwdriver made contact with the clamp screw of the neutral terminal in the socket. I just realised I didn't try to see if the screw was lose. I have no idea how the test screwdriver worked and assumed the "earthing" through me was what made it work again. I will double check tomorrow.

 

[oldbutnotdead]

Those neon testers are not be be relied on.
Especially with your unnecessary live working- if your neon had failed to light would you have assumed there was no power to the socket and started touching connectors?
Isolate the circuit, remake the connections- good odds a terminal screw is either loose or clamped to insulation. And buy yourself a multimeter.

 

[JohnD]

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Loose, high-resistance connection.

If you are lucky it might be in the socket you have been tinkering.

Try removing and re-inserting tbe wires and tightening the screws. Look out for any sign of heat discolouration.

If old or poor quality, it might be the switch or the grippers in tbe socket.

Might be in the next socket along, especially if a spur or radial.

 

[DiyNutJob]

Especially with your unnecessary live working- if your neon had failed to light would you have assumed there was no power to the socket and started touching connectors?

I have a beeper. So, I knew it was live. I learnt the neon trick from one of the builder guys.

 

[DiyNutJob]

If you are lucky it might be in the socket you have been tinkering.

Are you saying the problem could be caused by loose connection elsewhere? I had no reason to believe the wires in the faulted socket was worked on. Hence, I automatically assumed the screw was tight.

 

[JohnD]

assumed

Hmmmmmmm.

 

[Harry Bloomfield]

Can any one explain what's going on? The sockets in the flat never ever did that in the past. The wiring was touched by the builder's people recently, but everything appeared to work normally until now.

The problem could be loss of live, loss of neutral or even both - whilst your vac was plugged in. Where it or they were lost, could have been due to a faulty switch on the socket, a poor connection between socket and plug, between socket and it's wiring at the back, or further upstream to include the next socket on the circuit.

The trick is one of deducing, along with some luck - which of the above it is, before attempting to fix it.

Had it been me faced with my vac not working when plugged in, a trick I use with a volt-stick, is to partially shield the tip with my fingers, then run the tip along the vac's flex. On a two core - If it lights up all the way along/ all the way around, that suggests a live is present, but the neutral is absentia. A three core flex, with all OK, should light up for around 1/3 of the circumference. Just a rough guide and needs some practice to interpret.

 

[DiyNutJob]

The socket is chained to another set of wires. How do I work out which is the next socket?

I don't have a volt stick, only a beeper stick for live. There was no beep on the vac's cable. There was beep at the rocker switch.

Suppose the neutral was lost temporarily, where did it go and why would it come back? The contact using the screwdriver with the neutral clamping screw was light and I don't think there was enough of a mechanical shock to affect the clamped connection. I was surprised by the very light touch suddenly caused it to work. I thought I must have discharged some kind of a block.

 

[conny]

If the screw was loose it can have a tendency to slightly move/rock in the hole.
Your cables may have been a hairsbreadth away from making contact, (albeit a bad one), and you touching the screw caused it to bridge that hairsbreadth gap, thereby forming a circuit. Or, if the cables were not secure they could have moved just enough to have the same effect when you were holding the socket.
As you didn't check if the screws were tight I suggest you isolate the circuit, check the screws in the 'faulty' socket are tight and then try your vacuum in it again.

 

[DiyNutJob]

I went to confirm the screw was tight. My initial description was correct. I also opened the 3 nearest sockets, and they were all fine. 1 would have been worked on by the builders, 2 would not have. The flaw on the worked on socket was that the live conductors were too long, and 3-4mm of bare copper was outside of the clamping hole. This would be unrelated to the described problem.

The faulted socket refused to fail now. An interesting effect I found was: with my knee on vinyl floor, test neon screwdriver in hand on the live terminal, my knee beeped by the proximity live detector, but my thigh doesn't beep. What kind of magic is this?

 

[Harry Bloomfield]

I don't have a volt stick, only a beeper stick for live.

I suspect both are the same thing.

 

[DiyNutJob]

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