Screwdriver with neon electricity tester

[Lieutenant Scott]

I doubt he's ever asked you about wiring a house.

[Lieutenant Scott]

Has a bookie ever gone bankrupt?

[Lieutenant Scott]

As I said before, it all landed on my hand the only time it happened. Only one layer of skin too.

[dennis]

What has that got to do with it?

[Lieutenant Scott]

I just wanted to know if it was possible for them to get the odds all wrong.

[Tim Streater]

Exactly. So they have to calculate that, one way or another.

[Tim Streater]

The answer you know after doing the calculations, assuming you know how to, is the *probability* of the event happening. That's what insurance premiums are based on, plus a bit for admin and profit.

And if the insurance company doesn't do the calculation right, good chance it'll go bust in the long run.

But you still don't know whether it's going to happen or not.

You're always sure what might happen. My house might burn down or it might not. I'm 100% sure it'll be one or the other, I just don't know which. It's still a risk though. What I do is minimise the risk by, f'rinstance, not employing Mr O'Reilly to work on it, or, it would appear, you.

[dennis]

They don't have to get the odds wrong to go bust, they could just have too many staff, too much rent, etc.

[Lieutenant Scott]

And the risks I take also have known probabilities. But Mr Wadsworth seems to think I shouldn't be taking the slightest of risks with electricity, yet he states he does so himself.

I take issue with "a bit".

I know that either it won't happen, or the insurance company will make up an excuse as to why they don't have to pay out.

What about the whole thing vanishing in a cloud of dust when a mine shaft you didn't know about sucks it in?

I'm only likely to set fire to myself.

[brass monkey]

How likely?

[Tim Streater]

So you've done a calculation then. Make your mind up then, if you've got one.

Well, I'd use the neon screwdriver job, and prolly get away with it, because I'd be doing it so infrequently:

slightly-high-risk x not-done-too-often = acceptable-risk

whereas

slightly-high-risk x done-a-lot = unacceptable-risk

I imagine that Adam and the others who don't like the neon jobby calculate as follows, using their sonic screwdriver to look for volts:

low-risk x done-a-lot = acceptable-risk

A bit, a lot, who cares. Doesn't alter the argument.

Now you're wriggling.

That's another risk, separate to the fire risk. And that can be calculated too, depending on where your house is.

No comment.

[Lieutenant Scott]

That depends on whether you want me to and how much you're paying me.

[Lieutenant Scott]

No calculation, just prior experience and observation.

I dispute that a neon screwdriver is a high risk.

No, it's what they do.

You can't tell exactly how risky it is unless you go into the mine shaft and inspect it.

[John Rumm]

Better off not creating a short if you can avoid it... unless well earthed yourself, touching just live will only likely result in a tingle... (obviously L & N or L & E are not going to be such good outcomes).

[brass monkey]

Before you commit[1], have a word[2] with Mr Wadsworth[3] and he'll video[4] it. [1] do it, execute (for micro graduates). [2] speak with, as in using the vocal cords -

a persons name. [4]

[John Rumm]

No, I mean they have a lower breaking capacity. The breaking capacity is a measure of the maximum fault current they can interrupt, not the fusing current.

Since under short circuit conditions the current that flows is limited only by the (very low) resistance through the short circuit (and fuses don't limit current as such, they only limit the time a current over a certain threshold can flow). You need to make a sensible estimate of what the prospective fault current will be in the worst case scenario, and chose a fuse that is capable of interrupting that current. If the actual fault current is more than that which the fuse is capable of interrupting then the fuse will likely cause an arc fault that may result in an explosion (as demonstrated in that video I posted earlier), or simply a failure to interrupt the circuit, and cable damage to the circuit is likely, and hopefully operation of the next protective device upstream.

Things like 20mm glass cartridge fuses may have a breaking capacity as low as 35A and probably at most 100A.

BS 3036 rewireable fuses can interrupt 1, 2, or 4kA depending on type.

The BS 1362 fuse as used in plug should be able to interrupt 6kA

Those plug in MCBs for use in old Wylex BS3036 style consumer units usually do 3kA.

A typical MCB in a consumer unit 6kA, and some that can do 10kA are also available.

HRC Fuses (they type often used by your supplier as your main supply fuse), have a range of capabilities depending on their class, however they start at over 16kA.

Much the same logic as saying I ran across a busy road and did not get hit by a car, therefore I can do it any number of times and be at no risk.

[brass monkey]

I had a bit of a nasty one ~50 years back. Testing boiler (as in 20' long,

10' dia) control panel out of hours, only 2 of us in the building. Loads of test switches hanging on wires, crouching down holding metal light sensor near to candle (ignition simulation :D) started to overbalance so grabbed the first thing I could, happened to be a switch. I could'nt loose it and things started to go black whereupon I must've fallen backwards and it ripped the switch out of my hand. Wouldn't recommend it.

[John Rumm]

When I was 14 I used one to test if I had pulled the right fuse... no light, must be good. Took cover off a junction box and wired in a new cable, Replaced cover, went to other end and was about to strip it down, when I noticed that there was already enough of a nick in the sleeve to get hold of the earth and rip it through the sleeve. Just needed to prize it up a tad. Inserted blade of aforementioned neon screwdriver to do so, and bang! Created a L to E short on the still live cable. Blackened the end of the cable, blew the end of the screwdriver clean off (at least it solved the problem of what to do with that!). Did not blow the circuit fuse (30A BS 3036 rewireable)

(upstairs, carpet, apparently (and luckily) did not touch anything live and earthed at the same time and hence did not realise).

[John Rumm]

They would typically fail to meet the HSE guidance on suitable test equipment for electricians etc, mostly due to lack of finger guarding, and having to much exposed metalwork, and lack of a High Breaking Capacity fuse. See section 9:

[Tim Streater]

Which is a calculation.

Calculation again.