Isolating electric circuits while working.

[The Medway Handyman]

Or even better, a volt stick.

[Dave Liquorice]

canal

Yeah, some canal water is pretty foul, there is a section some where that down stream of a sewage works...

Lock (or tie) the gear leaver into neutral and attach a big notice.

[Adam Funk]

100% of the survivors graduate! ;-)

[Adam Funk]

Interesting. How does that work?

[Dave Liquorice]

better

Think I much prefer testing with a volt stick first then shorting. The flash/bang on a ring can still spray molten metal about.

SIDE: Switch off, Isolate, Dump, Earth.

fuse/s on

Not so easy to do with MCBs. But you can get locking thingies.

[Dave Liquorice]

Define "switch".

The main isolator "switch" and any RCD "switches"(*) are double pole but MCB "switches" are single pole.

(*) Are RCBO's double pole? They have to monitor the relevant circuits neutral current but that doesn't mean they have to switch it.

[Dave Liquorice]

+1, test your tester before and after testing, particulary if it says "dead".

[Huge]

S'what I always do - watching that damn SIDE (*) public information film when off sick from school must have sunk in.

(* S witch off I solate D ump E arth)

[polygonum]

What if you've already had your morning dump in the earth closet?

[tony sayer]

They ought .. instead of transmitting cheap yank TV drivel during the day .. TX films like that, never forgot the message of that one;!...

[tony sayer]

In fact many years ago now when I worked at Pye TVT someone there did that, there was quite a large bang on a 415 volt buss bar IIRC..

In fact it was he who told us young 'uns to do just that!..

Used to have a bit of fun from time to time by putting the buzzer boxes we used to have for "buzzing" circuits thru the wring, inside transformer cabinets so they sounded like the were working. One very crafty apprentice wired some panel lights to a battery to make it all look as it was live;!.

Some 15 kV in those cabs at quite a few amps capacity for the Klystron's..

Indeed you can and at least a lump of wire thru it Might be sufficient to tell someone that someone's working elsewhere on that?..

[Rick Hughes]

When I worked in Hi-Voltage testing there was always the crowbar protection... once told the cct was isolated you dropped a bar across live & earth to ensure it was safe..

[tony sayer]

Thats what the SIDE system used to do in high power TV transmitters you opened the one switch and the other used to crowbar across the HT lines to discharge the capacitors huge 32 uF ones at 20 odd kV paper type they could recover a charge given a short while hence the short circuiting system.. Interlocked so that you couldn't closer them with the mains switch in the on position and it had a A and B key system so when off it released the keys needed to open all the other cabinets up ..

Unless you had a duplicate A key then you could bypass the safely systems.

Someone did that out in the wilds of Borneo many years ago, no one heard from him for a while but they found him .. bones picked clean by the local wildlife after he got into a cabinet with the power on;(...

[F Murtz]

It takes a bit of sensibility as they light up on almost everything I suppose if you trust that the driver is working a complete lack of light is an indication.

[F Murtz]

Don't you put your fingers on both wires before letting the apprentice at it?

[John Rumm]

I suspect Bob's handy tag line has bolloxed his search triggers such that any real comment he may care about is now lost in the noise of false positives ;-)

[John Rumm]

Inductive coupling I would imagine. A sensible addition to any electrical tool kit IMHO.

[John Rumm]

Bet that woke him up with a jump ;-)

[newshound]

Presumably, a tuned circuit looking for what, in the old days, we would have called "mains hum" and lighting up when it finds it. I remember tracing circuits with a transistor radio. Unlike the neon screwdriver, it works through the insulation. Like neons, you can get a "false positive" where an isolated conductor has picked up volts from a live one by induction. But neons sometimes go intermittent because of their crude construction; IME you are less likely to get a false negative from a volt stick.

[John Rumm]

Its appropriate to be cautious, and you rightly recognise that there are still risks working on a circuit with the neutral connected. One of the most common problems with modern installations is that its very easy to trip the RCD protecting a circuit with a neutral to earth short while working on it.

If you are going to do extensive work[1] on a circuit, then its safest to turn it off, and then open the CU and disconnect its neutral from the neutral bus bar. (if someone has wired it nicely, it may even be in the numbered position to match that of the MCB!). Once its disconnected, your only real risk is from a cross connection to another circuit.

Testing your tester on the working circuit first is sensible. Include tests between each pole and earth as well. Disconnect and then repeat. That will pick up most of the possible non conventional wiring issues. For complete peace of mind, then test the tester on a working circuit again.

[1] If I were just changing a lightswitch or similar, I would probably just turn off the MCB at the CU and leave the neutral connected. (I also have the advantage of having wired the CU in the first place and tested all the circuits, so I know what is connected to what!)