Electrician Help Please.

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Hugh Manatee

Veteran
A strange thing just happened. Our shower has broken. The pull switch doesn't pull. I isolated the shower circuit via the fuse box and had a look inside the thing. A small plastic component had failed so I went out just now and got a similar switch rated at 50A.

I am not a spark but figured if I drew the wiring and took photos I should be able to cope. It all looks fairly logical with a L and N In and Out and an Earth clamp taking a wire from each. Checking no fool had flipped the switch back on in an attempt to claim on my life policy (no they hadn't) I undid the five screws holding the cables into the switch. I then removed the old switch and was just putting the cables through the base plate of the new switch when, out went the lights!

Not mine thankfully, it just went a bit darker. The main breaker had flipped to OFF. I should add nothing happened at my end. No bang or flash or smoke or anything at all.

What do you think might have happened? Was the power outage a coincidence? What else might have caused it?

I have decided to down tools anyway and get a spark in to have a look. I really hate electrickery and don't want to take any chances with it. To repeat, the shower was isolated. The main L and N wires look fine to me with no sign of heating. The earth wires look to me a bit weird and felt as I undid them as if they were much shorter lengths?

I am curious and just want to know what happened.

Thanks in advance.
 

twentysix by twentyfive

Clinging on tightly
Location
Over the Hill
Probably the earth leakage tripped out. If the N touches the E that can happen (normally the switch only isolates the L). Hardly any volts or current but these trips are very sensitive.
 

swansonj

Guru
At a guess: you brushed the "in" neutral against something earthed. Although in theory the neutral is at earth potential, in practice, neutrals almost always have impressed voltages, so a current can flow from neutral to earth. That current then means that, for the house as a whole, the live and neutral currents are no longer exactly balanced, and that "residual current" would trip a residual current circuit breaker (RCD). RCDs only need a small current to trip, often 30 mA, and that wouldn't cause any flashes or arcing.

An impressed voltage on the neutral is less likely if your house has pme but possible with or without pme.

Edit: cos I'm a slow typer two other people have beaten me to it but I'm still going to press "post"...
 
OP
OP
Hugh Manatee

Hugh Manatee

Veteran
Thanks all. Sounds like it wasn't trying to hurry me towards the afterlife after all. I really should learn about this sort of thing I suppose. It'll have to wait, I'm building a new forge at the weekend!
 

midlife

Guru
Whenever I do any electric stuff in our house I turn off the big grey switch and then go around the house testing to see that the whole house is dead .....then I change the switch much gas stopped working.

I hate electric as you can't smell it or see it......

Shaun
 

ColinJ

Puzzle game procrastinator!
Whenever I do any electric stuff in our house I turn off the big grey switch and then go around the house testing to see that the whole house is dead .....then I change the switch much gas stopped working.

I hate electric as you can't smell it or see it......

Shaun
You can detect it with your sense of touch though! :okay:

(You can often hear a BANG! too if you make a major mistake. You can even taste it, if you are daft enough to apply it to your tongue. I know someone who did that as a young man ... :whistle:)
 

midlife

Guru
You can detect it with your sense of touch though! :okay:

(You can often hear a BANG! too if you make a major mistake. You can even taste it, if you are daft enough to apply it to your tongue. I know someone who did that as a young man ... :whistle:)

It's a throwback from the 70's, my dad never saw the point in buying plugs so it was a screwdriver in the top hole and the bare wires in the bottom two holes......thrown across the room a couple of times :sad:

Shaun
 

ColinJ

Puzzle game procrastinator!
It's a throwback from the 70's, my dad never saw the point in buying plugs so it was a screwdriver in the top hole and the bare wires in the bottom two holes......thrown across the room a couple of times :sad:

Shaun
Blimey - how much do plugs cost? That is taking frugality a bit TOO far! :eek:

I have done the 'cross the room without touching the floor, and then sit there quivering' thing a few times myself! :laugh:
 

slowmotion

Quite dreadful
Location
lost somewhere
[QUOTE 4333827, member: 9609"]what causes these ghost voltages. Is it just magnetic fields from adjacent live wires on another circuit. And if you had a ghost voltage of lets say 5v, could you power something with it or is it just a handfull of electrons (or whatever they're called) that you would never get enough current ?[/QUOTE]
I think it's this (but I could be wrong)..... The neutral is actually earthed at the substation, or somewhere distant from your house. The neutral cable between your house and the distant earth point has a finite resistance. It also has a current flowing through it...maybe up to 80 or 100 amps. This means that the voltage on the neutral cable where it leaves your house could be several volts above earth due to the V=IR voltage drop rule. If the neutral cable touches a local earth in the house, the RCD detects a current imbalance between live and neutral and it trips out.

I think.
 

subaqua

What’s the point
Location
Leytonstone
I think it's this (but I could be wrong)..... The neutral is actually earthed at the substation, or somewhere distant from your house. The neutral cable between your house and the distant earth point has a finite resistance. It also has a current flowing through it...maybe up to 80 or 100 amps. This means that the voltage on the neutral cable where it leaves your house could be several volts above earth due to the V=IR voltage drop rule. If the neutral cable touches a local earth in the house, the RCD detects a current imbalance between live and neutral and it trips out.

I think.


close . dependent on system type. you don't need a low earth path for a 30mA to trip. for safety sake we use 1667 Ohm as that won't lead to a touch voltage higher than 50V which is deemed ELV and "safe" .

out in the sticks on an overhead service from a pole Transformer the service is very likely to be TT .

in towns before 1980* the service would be TN-S and after 1980 would be TN-C-S PME (Protective Multiple Earthing) . there are other flavours of TN-C-S but these are generally not used for domestic supplies . * approx - PME was about before then but thats when most REC went to PME fully.

on a PME system the neutralk is easrthed at MULTIPLE points on its journey from the transformer at the substation. the star point at the Trans will always be referenced to earth as it keeps them at almost the same potential 0 V .

when the N-E are touched together at the switch there is another path back to the star point for a very very small amount of electricity to flow Milli Volts and milli amps ( resistors in parallel)and the RCD "sees" the imbalance on the sensing coil inside then operates the trip mechanism .

I may tidy up the post later when i am more awake. fecking electrical storms last night!
 
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