Anecdote of weird electrics

[bankruatsteve]

I have an under stair storage that I ran power to as extension of a light circuit.  That provides power to a light, aquarium pumps, and garden lights.  While I was standing in the patio where these things are this morning, the aquarium pumps suddenly stopped.  The under stair light doesn't work either.  All the other lights on the circuit work fine.  All this in place for about 10 years now.

 

I used my voltage sensor and got nothing on the feed cable.  All the routing and connections for that are above ceiling and there's no way I'm going to start cutting into that.  So dammit, I string in another cable and connect to nearby power point.  It's now on the surface but with conduit, not so bad  Everything good again.

 

So, I think I should cut and tape the old cable "just in case".  I test with my voltage sensor again - nothing.  I start cutting the cable and BANG.  Scared the <deleted> out of me but no damage.  It tripped the breaker though.  With the breaker off, I finished the cut and taped it.  Turned the breaker back on.  All is good with the lights.  But NOW the cable that was dead a few minutes ago lights up my sensor.

 

'splain that one Crossy.  ????

 

 

[Crossy]

7 minutes ago, bankruatsteve said:

'splain that one Crossy.

 

Crappy joint up in the ceiling somewhere went high-resistance causing your pumps etc. to stop.

 

Whilst cutting you shorted the (sort of dead) L to the N which was enough to "fix" the joint, resulting an a nice pop.

 

Should have turned the breaker off anyway.

[bankruatsteve]

7 minutes ago, Crossy said:

 

Crappy joint up in the ceiling somewhere went high-resistance causing your pumps etc. to stop.

 

Whilst cutting you shorted the (sort of dead) L to the N which was enough to "fix" the joint, resulting an a nice pop.

 

Should have turned the breaker off anyway.

That makes sense as usual.  My sensor is pretty sensitive and when I get nothing, that always has indicated dead-dead before.  Yup, should have turned the breaker off but then I wouldn't have an anecdote to tell.  ????

 

And, if the 10-year old joint suddenly got crappy, it's probably due to those terrible twist on connectors sold here.  I refuse to use those any more.  

 

BTW:  How come "crappy" is OK but c_r_a_p gets <deleted>?

[OneMoreFarang]

18 minutes ago, bankruatsteve said:

I start cutting the cable and BANG.  Scared the <deleted> out of me but no damage.  It tripped the breaker though.  With the breaker off, I finished the cut and taped it.

"DIY & Electrical Forum Expert"

So you think you are the expert and you cut a cable without disconnecting the breaker and then you are surprised that there is a bang.

Yeah, sure.

 

[Crossy]

Your tester might have shown "hot" if you'd unplugged everything.

 

I had a similar issue (no bang) with a shower in the UK many years back.

With the shower off the incoming supply terminals read 230V as expected, but when the shower was turned on it collapsed to as close to zero as makes no odds.

Checking at the other end of the supply cable showed a nice steady 230V.

Evidently high resistance somewhere.

Turned out that the previous owner had installed the shower himself and taken a feed off the cooker cable by pulling the cooker cable back into the attic and re-routing to the shower.

Unfortunately the cable wasn't quite long enough so he'd used about a metre of 1.5mm² flex,  which was nicely hidden under the loft insulation where it had overheated and finally burned through leaving a trace of carbonised PVC enough to light up my meter.

 

I have no idea how long the 9kW (40A) shower had been fizzing away on that 16A cable.

 

 

 

[bankruatsteve]

19 minutes ago, Crossy said:

Your tester might have shown "hot" if you'd unplugged everything.

The incoming feed was connected to cables for the light and another cable feeding the aquarium.  It showed dead connected AND after disconnecting as I had tested just prior to trying to cut the now exposed wires off.  Whatever - lesson learned.

 

In recollection... I think I moved the cable to get a better position for cutting.  Hmmm.

[bankruatsteve]

Just to add... my sensor even blinks on 1-1/2 v DC battery if I wave it across. 

[Crossy]

One of the single most difficult things to do in the 'lectrical world is to "prove dead".

 

It's easy to show that something is there, but amazingly difficult to show that it isn't.

 

 

[Daffy D]

If you tested with a meter across the pos and neg it could have been a broken negative giving a not hot reading.

That is where those little neon screwdriver testers come in handy, they will tell what is hot regardless.

  

[bankruatsteve]

1 hour ago, Daffy D said:

If you tested with a meter across the pos and neg it could have been a broken negative giving a not hot reading.

That is where those little neon screwdriver testers come in handy, they will tell what is hot regardless.

  

Oooh Kay. 

[Daffy D]

An additional point about those little neon testers. I find they only work properly if standing barefoot on concrete or tile floor, not making "earth" contact by wearing flip-flops will not light up the neon and give a false reading.

 

Don't know why this is, perhaps it's only me as I never had this problem back in the real word where I would always get a neon to light up even in my upstairs apartment wearing shoes on fitted carpet. 

 

Perhaps Thai electricity is different after all