Being cautious re electrics ?

On Tue, 17 Nov 2015 16:17:42 +0000, ss wrote:

20switch_zps757al8ux.jpg
Going by that picture, it'll be the big red switch at the left hand end. Fuck knows why that double width black switch with what appears to be an earth leakage reset button has been marked as "MAIN SW" in black marker pen is supposed to do. Feed another consumer unit perhaps?
Each consumer unit only has a single double pole isolating switch to shut off the feed coming from the meter. Once that's shut off, everything is then isolated and safe to work on.
You can normally assume that it's safe to work on if pulling the big switch kills the supply to every electrical circuit in the house.
Obviously, if you have *any* lingering doubts as to how the unit has been wired up, you need to test with a meter or mains voltage probe[1] to verify that the "BIG SWITCH"(tm) has indeed isolated everything from the mains supply and hasn't been bypassed in some 'cunning' way from an alternative link to mains voltage via some other route. Normally, the meter tails going into the terminals of the "BIG SWITCH"(tm) are the only available access to the incoming fused supply cable in a domestic property.
[1] Whatever measuring device you're using to test for mains voltage, it's important to verify that it will give an indication of mains voltage before you start testing. You can use a multimeter set on a suitable AC volts range, (you have to set it on a range that exceeds the mains supply voltage, typically the 300vac or next higher ac voltage range on the meter) to probe for mains voltage on the PC end of its mains lead with reasonable safety.
You can usually push the meter probe tips into the IEC Live and Neutral socket holes where they'll normally stay wedged in without risk of shorting out before plugging the 13A plugtop end into a switched 13A socket so that you can switch on without actually having to handle the test leads. Once you've established that your measuring device is working as advertised, you can then use it to verify that the CU is indeed free of any nasty surprises before physically handling its wiring.
Incidentally, the best way to probe for (in this case unwanted) mains voltages is to clip the common test lead onto an earth terminal so you only have to hold onto the other test probe's insulated handle whilst carefully poking around inside the CU making sure to keep the rest of your body isolated from earthing (or even other possible sources of live mains) contact. It's best to let the meter do the work rather use yourself as a test probe. :-)
Unless a crazed lunatic installed the CU (or reconfigured it into some unsafe state), pulling the "BIG SWITCH"(tm) (in this case, rather conveniently coloured red), is more than sufficient to render the typical domestic CU and all the fixed wiring it serves (ring main(s), lighting circuit(s), Electric shower, cooker point and immersion circuits, perhaps even another CU) entirely safe to work upon.
If this all seems too complicated and you have any doubts, there's no shame in letting discretion be the better part of valour and employ a professional electrician to do the work for you.
--
Johnny B Good

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On Wednesday, 18 November 2015 02:31:49 UTC, Johnny B Good wrote:

I always thought paraffin was the better part of valor.
NT
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On Tue, 17 Nov 2015 18:47:11 -0800 (PST), snipped-for-privacy@gmail.com wrote:

Jokes like that give me the blues.
G.Harman
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On Wed, 18 Nov 2015 09:11:14 +0000, snipped-for-privacy@yahoo.co.uk wrote:

You must have been a bit of a ladd in those days!
--

Chris

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On Wed, 18 Nov 2015 09:11:14 +0000, damduck-egg wrote:

It was more a non sequitur than a bad joke (besides which, I think you're confusing valor with Esso Blue).
--
Johnny B Good

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On Wednesday, 18 November 2015 20:45:14 UTC, Johnny B Good wrote:

No, it was a joke. And I doubt he's confusing anything either.
NT
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On Wed, 18 Nov 2015 19:12:55 -0800 (PST), snipped-for-privacy@gmail.com wrote:

I wasn't , but thought that to continue would get on his Wick.
G.Harman
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snipped-for-privacy@yahoo.co.uk writes

They keep me in the pink
--
bert

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On Tue, 17 Nov 2015 18:47:11 -0800, tabbypurr wrote:

Read it again! I made absolutely no mention of valor. :-)
--
Johnny B Good

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On Wednesday, 18 November 2015 20:41:02 UTC, Johnny B Good wrote:

Why would I read it again, to come up with a better joke? Your turn.
NT
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On 18/11/15 02:31, Johnny B Good wrote:

Careful...
That is NOT always true.
2 counter examples: Economy 7 type split tariff with dual meter feeds;
CU with UPS integration feeding a separate busbar.
Everyone's correct in that it is *usual* for the big red switch to cut off the whole box, but it is impossible to be sure that is the case here as someone could have done something exceptional.
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On Wed, 18 Nov 2015 07:49:24 +0000, Tim Watts wrote:

Thanks for the 'Heads Up' but I think I managed to cover my arse ("Ass" for the benefit of our American cousins) on this one quite nicely by using the weasel phrase, "Unless a crazed lunatic installed the CU (or reconfigured it into some unsafe state)". :-)
--
Johnny B Good

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On 18/11/2015 20:57, Johnny B Good wrote:

I recall one new CU[1] I bought came complete with "inspected" and "passed" stickers all over it, but was wired such that turning on the RCD would have shorted the incoming supply! So a sanity check of the interconnects (not to mention tightening the screws) is always a good investment of 5 mins.
[1] Can't remember if it was a Contactum or a Hager now....
--
Cheers,

John.
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On 18/11/2015 02:31, Johnny B Good wrote:

If I dont understand the wiring when I open it I wont touch it, already done that with trying to change a thermostat/timer for the gas heating, the wiring was altered and didnt make sense so got an electrician in. Even when I change a plug socket or light switch I use insulated screwdriver and thin nose plyers to handle the cable even though the CU is turned off, I wont touch the metal. I learned my lesson as a 7 year old when I took a bulb out a table lamp and stuck my fingers in. Dont ask cause I dont know why :-)
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As I said before it should be easy to establish what isolates what simply b y switching each switch and seeing which circuits are dead. The scenario th at is the main concern as implied by the sticker on the top is that the RCD has been incorrectly wired as a main switch in other words to the input si de of the main switch. If that is the case then switching off the main swit ch will not isolate all the circuits. A main switch should just be that and all circuits should be isolated using it, I think the CU needs looking at to check that the main switch does isolate all circuits and at the same tim e to place the shower MCBs so that they are protected by the RCD leaving ju st the lighting circuits unprotected by the RCD. If the main switch does is olate all circuits than the only dangerous area not to poke around in is wh ere the meter tails connect to the main switch, although depending on the C U those terminals may have an additional cover as protection.
Richard
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On Wed, 18 Nov 2015 10:51:01 +0000, ss wrote:

Quite understandable, the phrase, "Once bitten, twice shy." applies here. At that tender young age, I could imagine it must have been quite a strong bite!
As for not asking why you removed the lamp and poked your fingers into the empty socket in the first place, I've no need to. It's just the sort of thing any child with an enquiring mind would do. It's the way we gain experience as juveniles to learn how to survive in the wider world around ourselves.
I didn't suffer my own "Light Socket Moment" until I had developed a much greater resilience to such electrical 'insults' as a teenager. Mind you, I did a similar thing with my homebrewed 2 valve Top Band 10 watt transmitter's power supply when I bridged the HT smoothing cap terminals with my thumb when examining it whilst it was unplugged from the mains supply, thus learning the value of including HT smoothing capacitor bleed resistors in the circuit and the hazards of such stored potentials in the HT modules of SMPSUs when they don't (or the resistor has blown open circuit).
In my particular case, the residual voltage was the no load 500vDC peak from the fullwave rectified 350vAC secondary windings which had blown two rather neat looking pin head sized holes in the pad of my thumb. And, it still had some 300 odd volts left over which I thought, considering the capacitor was only 16 microfarads, was quite an impressive result! All that pain and I *still* hadn't properly discharged the cap!).
--
Johnny B Good

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On 18/11/2015 02:31, Johnny B Good wrote:

Agreed. FWIW *I* would pull the fuse. The other gadget which I am very fond of is the "volt stick" which is like a neon screwdriver that works through insulation. Same rule applies as with a neon or any other indicator, be *really* sure it is working before you rely on it, but very handy when poking around in rats nests of wiring where it might be possible that you have only isolated some of it.
They are also very handy for a quick check on whether a plug fuse has failed, or the wire, or the switch in the appliance, etc. They let you do a lot of diagnosis without opening anything up.
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On 18/11/2015 11:10, newshound wrote:

Yes I have one of those, I tend to use it for double checking and sometimes useful for tracking live hidden wires doesnt always work for that though.
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