Being cautious re electrics ?

[Chris French]

Yup, we have a sticker just like that on our MK plastic sentry CU, about 7 yo I guess.

[dennis]

Wuss, you can just snap the wire when you pull the fuse with one finger and thumb.

You can do it another way without breaking the seals but neither I nor ARW will tell you how.

[Andy Burns]

I don't know if that's a standard MK sticker, but the standard wording on newer MK Sentry units *does* say

"ALL MAIN SWITCHES MUST BE SWITCHED OFF ..."

[Tough Guy no. 1265]

I doubt it, the wire was quite tough to cut through with the first pair of snips I picked up. I had to use a decent pair to cut it. I can't see the seal part breaking either. The first thing to go would be the plastic loop on the fuse or holder, which would require a lot of force to break and is more likely to end up yanking the screws out of the wall. It's not a little plastic thing like on a fire extinguisher.

There's no point in withholding it from me. I've already done it and replaced the wire with the Ebay one. Or I might have left it without one for easier removal later I can't remember.

[Tricky Dicky]

According to a sparky, the way to remove the seal is to unwind the thin wir es snip one at the point it goes in the seal. When reassembling drill a sma ll hole in the seal and super glue the snipped end in the hole before re-tw isting the wires.

I cannot see the point of having a seal on the service fuse except it might be an indicator of attempting to bypass the meter. I believe most network providers would prefer the fuse is removed rather than working live on the connections this side of the CU.

Richard

[tabbypurr]

There are often 2, sometimes many more. There should really be one, but often isn't.

NT

[John Rumm]

Why do you say that?

[John Rumm]

Depending on how they have wired the box I would expect the big red switch along to turn off everything including the feed to the RCD (i.e. the bigger grey "switch")

With the MCB off, you should be able to safely disconnect the live of the shower cable from the top contact of the MCB.

Just keep in mind there are still live bits in the box even if you turn off the main switch (the contacts at one end of it). If you leave the main switch on, and just turn off the MCB then the bus bar feeding into the bottom of it will also be live - so keep well away from that.

[John Rumm]

Only if you consider a RCD to be a "main switch" which its not (in this circumstance anyway). You will note the set of stickers only includes one main switch sticker.

[Johnny B Good]

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.

[tabbypurr]

I always thought paraffin was the better part of valor.

NT

[Tim Watts]

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.

[damduck-egg]

Jokes like that give me the blues.

G.Harman

[Chris Hogg]

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

[ss]

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 :-)

[newshound]

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.

[Tricky Dicky]

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

[ss]

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.

[ARW]

How many main switches are there on that photo?

The OPs CU does not have an MK sticker on it.

[charles]

Mine doesn't either. MK is moulded on the cover, on the side which can't be seen in the photo