WTF

[dreadnought]

this happened yesterday (Sunday) i wanted to retro fit a double power socket on the 240 v system on my nb, a socket with the usb chargers on,my plan was to locate the cable and cut it at the site for the socket,simples,so i turned off the power at the mains, the consumer unit,

then to make sure there was no power i tried a couple of sockets to make sure they were dead no probs,then i got my snips and cut through the cable, a big bang followed and a puff of smoke, i was still in one piece but well surprised, any body no why this would happen with the power off,?? many thanks

 

[WotEver]

1 minute ago, dreadnought said:

this happened yesterday (Sunday) i wanted to retro fit a double power socket on the 240 v system on my nb, a socket with the usb chargers on,my plan was to locate the cable and cut it at the site for the socket,simples,so i turned off the power at the mains, the consumer unit,

then to make sure there was no power i tried a couple of sockets to make sure they were dead no probs,then i got my snips and cut through the cable, a big bang followed and a puff of smoke, i was still in one piece but well surprised, any body no why this would happen with the power off,?? many thanks

 

Clearly the power wasn’t off. Not in the cable you cut at any rate. Do you have shore power? If so maybe you cut the shore power feed from 16A socket to consumer unit. 

[Stilllearning]

By “power off”, do you mean switched off on the consumer unit/fuse box inside the boat, or at the PowerPoint on the land?

[Machpoint005]

Shows the wisdom of switching everything off, and isolating the batteries, and unplugging the shore line.

[Robbo]

5 minutes ago, dreadnought said:

this happened yesterday (Sunday) i wanted to retro fit a double power socket on the 240 v system on my nb, a socket with the usb chargers on,my plan was to locate the cable and cut it at the site for the socket,simples,so i turned off the power at the mains, the consumer unit,

then to make sure there was no power i tried a couple of sockets to make sure they were dead no probs,then i got my snips and cut through the cable, a big bang followed and a puff of smoke, i was still in one piece but well surprised, any body no why this would happen with the power off,?? many thanks

 

I would suggest getting one of those pen voltage things as clearly it was live.   Boats can have multiple sources of power, mine has 3.

[nicknorman]

How were the sockets being powered (before you “turned everything off”)? I’m thinking that if from an inverter, perhaps the inverter has a centre tapped output and your breakers only cut the live. But with centre tapped, the “neutral” will be live too. Many breakers found in domestic Consumer Units are single pole with just the master switch being double pole. If you have centre tapped electrics then of course the breakers should all be double pole.

[WotEver]

8 minutes ago, Machpoint005 said:

Shows the wisdom of switching everything off, and isolating the batteries, and unplugging the shore line.

I never do ANY mains work without first confirming that it’s dead with something like this:

https://www.screwfix.com/p/fluke-1ac-ii-voltage-detector-pen/85949?tc=JT6&ds_kid=92700022888078525&ds_rl=1241687&ds_rl=1245250&ds_rl=1244066&ds_rl=1249796&ds_rl=1245250&ds_rl=1249484&gclid=CjwKCAjw39reBRBJEiwAO1m0OVhUZMuy2Tp8bmy_X2D7IEf8Tvsf8rra7wzxL1unTG19mjs15JlxahoCo8QQAvD_BwE&gclsrc=aw.ds

5 minutes ago, Robbo said:

I would suggest getting one of those pen voltage things as clearly it was live.   Boats can have multiple sources of power, mine has 3.

Absolutely. I missed your post prior to posting the above. 

[Robbo]

1 minute ago, WotEver said:

I never do ANY mains work without first confirming that it’s dead with something like this:

https://www.screwfix.com/p/fluke-1ac-ii-voltage-detector-pen/85949?tc=JT6&ds_kid=92700022888078525&ds_rl=1241687&ds_rl=1245250&ds_rl=1244066&ds_rl=1249796&ds_rl=1245250&ds_rl=1249484&gclid=CjwKCAjw39reBRBJEiwAO1m0OVhUZMuy2Tp8bmy_X2D7IEf8Tvsf8rra7wzxL1unTG19mjs15JlxahoCo8QQAvD_BwE&gclsrc=aw.ds

Absolutely. I missed your post prior to posting the above. 

Think I might put that on my Christmas list as well.   My consumer box is a little complex with the stuff I’ve added!

[WotEver]

4 minutes ago, Robbo said:

Think I might put that on my Christmas list as well.   My consumer box is a little complex with the stuff I’ve added!

You’ll find new uses for it too. If you have any old-fashioned Christmas lights with a blown bulb you can find out where the blown one is. If you have anything that stops working and you suspect the plug fuse you can confirm whether or not there’s mains going up the cable. 

[Robbo]

3 minutes ago, WotEver said:

You’ll find new uses for it too. If you have any old-fashioned Christmas lights with a blown bulb you can find out where the blown one is. If you have anything that stops working and you suspect the plug fuse you can confirm whether or not there’s mains going up the cable. 

Ooh, never thought of those uses.  defo on the list now.

[bizzard]

Ideally. Before you touch shocking things like that rig yourself out with a complete rubber suit, plimsoles, rubber gloves and motorcycle goggles, your aspect will resemble Hannibal Lector and frighten people but don't let that bother you.  Clamp on a jump lead between your arm and a huge steel stake bashed into the ground outside, ''just in case the plimsoles prove to be no good'', and have a pretty young nurse to administer mouth to mouth resusition and fribulator machine thing standing by, Choose insulated pliers, screwdrivers ect.  You are then all ready to start work. Disconnect everything, everything, everything, pull the shoreline plug out, turn off ALL isolators, disconnect the batteries, switch off the inverter, yank it out and chuck it overboard.  Now you can safely approach the job in hand,''but with great caution though''. Don't do nervous dithering as that causes inacurate ineptnesses using the tools. Check and double triple check for electricity liveness with you meter and if it reads zero power, get at it with great deliberation and positivity until the job is done.

Edited October 29, 2018 by bizzard

[matty40s]

1 hour ago, WotEver said:

You’ll find new uses for it too. If you have any old-fashioned Christmas lights with a blown bulb you can find out where the blown one is.

I find it easier to look for the one that isn't lit.☺

[LadyG]

17 minutes ago, matty40s said:

I find it easier to look for the one that isn't lit.☺

You're not "old enough", they all went out ......................... and you had to go  round with a new bulb, testing the system till all came on again.

[Wanted]

I carry my Fluke Volt stick pretty much everywhere I go, I am always in old buildings and spaces where layer upon layer of dubious wiring can catch you out.

 

If you ever want to see 'interesting' wiring then come and look in the belly boxes of my showman's trailer, I have all but re-done it now bit but bloody hell, those guys could make things work, but they didn't care how!

The old system seemed to be, Green is Earth and or neutral, red or black is live and brown if modern is live but if old is neutral. If wire is wrapped in white tape it is probably earth unless its in the kitchen area where it is almost certainly live. If all 3 wires were black then assume all were live and don't lick anything.

 

  

[bizzard]

5 minutes ago, LadyG said:

You're not "old enough", they all went out ......................... and you had to go  round with a new bulb, testing the system till all came on again.

Candles were more reliable, you could see when one went out.

[Chewbacka]

1 hour ago, nicknorman said:

How were the sockets being powered (before you “turned everything off”)? I’m thinking that if from an inverter, perhaps the inverter has a centre tapped output and your breakers only cut the live. But with centre tapped, the “neutral” will be live too. Many breakers found in domestic Consumer Units are single pole with just the master switch being double pole. If you have centre tapped electrics then of course the breakers should all be double pole.

It’s also possible that the live and neutral wires have been swapped as they enter the consumer unit, so all the breakers are switching the neutrals and all the neutrals in the sockets are live.  Interested to know the cause of your problem.

[Momac]

3 hours ago, dreadnought said:

a big bang followed and a puff of smoke

 

Are you sure you are still alive ?

[sharpness]

5 hours ago, LadyG said:

You're not "old enough", they all went out ......................... and you had to go  round with a new bulb, testing the system till all came on again.

Which was OK till there were 2 blown bulbs

[WotEver]

5 hours ago, matty40s said:

I find it easier to look for the one that isn't lit.☺

How does that work with series wiring then...?

 

6 minutes ago, sharpness said:

Which was OK till there were 2 blown bulbs

 

Absolutely!

[Athy]

6 hours ago, Wanted said:

I carry my Fluke Volt stick pretty much everywhere I go, I am always in old buildings and spaces where layer upon layer of dubious wiring can catch you out.

 

If you ever want to see 'interesting' wiring then come and look in the belly boxes of my showman's trailer, I have all but re-done it now bit but bloody hell, those guys could make things work, but they didn't care how!

The old system seemed to be, Green is Earth and or neutral, red or black is live and brown if modern is live but if old is neutral. If wire is wrapped in white tape it is probably earth unless its in the kitchen area where it is almost certainly live. If all 3 wires were black then assume all were live and don't lick anything.

 

  

Crikey, who wired it up, Wyatt Earp?

[MtB]

31 minutes ago, Athy said:

Crikey, who wired it up, Wyatt Earp?

 

Wyat Twerp more likely....

 

 

[Sir Nibble]

First thing when working on dangerous voltages, isolate.

Second thing, confirm isolation.

[Detling]

whatever was providing the power has probably tripped or blown a fuse so you will find out when you try to get the new socket to work.

[Wanted]

On 29/10/2018 at 23:21, Athy said:

Crikey, who wired it up, Wyatt Earp?

Years of showman wiring, patching up with whatever was to hand and no real future proofing, I would almost guarantee that about twenty people have all tried to ‘improve’ over time. 

[Athy]

2 minutes ago, Wanted said:

Years of showman wiring, patching up with whatever was to hand and no real future proofing, I would almost guarantee that about twenty people have all tried to ‘improve’ over time. 

I guess that the showman's life, always on the move with schedules to adhere to, does not lend itself to sitting down peacefully and thinking the problem through - it has to work now.