Multi meter ?

[meow2222]

2A fused/mcb circuits is a very different ballgame to exploding them with 2 5,000A. Its when you're probing about inside a live CU that you really need that CAT certification. Most diyers are never going to do that.

so we agree that a diyer could do that, but most never do.

nonsense

properly designed voltsticks and properly designed multimeters are better t han crap designed both. Not news.

not really. Cable resistance won't reduce i squared t to a safe value, the CU MCB is what reduces the user's risk.

yes, it happens. A milllion to one multiplied by a thousand to one is... a very small risk indeed. That's why there isnt just one category. When you w ork north of the CU protective devices then you do need a suitably rated me ter, but about 99% of diyers never do that. The ones that do need to know n ot to use cheapo meters _there_.

In the sad death you repeatedly refer to, a totally unrated untested meter was used in a 3phase 480v breaker panel supplying an entire shopping mall. I think we all agree cheapie meters should not be used in such a place. Dow nwind of a 5A fuse is a very different matter, something the cat system rec ognises.

NT

[meow2222]

though any 50kohm/v analogue meter would give the same readings.

NT

[whisky-dave]

Years ago that was true but at school in the mids 70s we called then smiley meters, because when an AVO 7, 8 or 9 was upside down, the two knobs looked like eyes and the scale was a smiley mouth.

We use scopes for varying values much more useful than an AVO or any digital meter but each instruments has it's advantages/disadvantages, the biggest disadvantage with our AVOs is teh 22V battery I don't think we have any.

[John Rumm]

Keep in mind you are posting in a group where many more are likely to than would be expected in the general DIY population.

Have potential to be lethal may be more accurate.

Cable resistance has a big impact on the PSCC. By the time you are approaching a resistance that will drop the fault current to a few hundred amps (then in the absence of an arc) you are unlikely to get any particularly dramatic showers of sparks or hot metal.

[meow2222]

Yup. Initially my suggestion was directed tot he OP, but it holds good for folk that arent doing distribution board work.

Almost everything has. Its the combination of unrated meter plus massive i squared t that's the big hazard combo. Remove either of those factors and t he risk drops into the long tail of risks we take daily without blinking an eye.

1 ohm from 1mm cable: 23m 1.5mm cable: 34.5m 2.5mm cable: 55m

Explosive force comes from heating, which depends on i & t. Cables can limi t i to a very variable value, the CU's mcb/fuse will limit t accordingly. I have once encountered arc from dead short on a thick cable feed, it was a total non-event. Arcing at the incomer is another matter.

NT

[ARW]

Yup. Initially my suggestion was directed tot he OP, but it holds good for folk that arent doing distribution board work.

Almost everything has. Its the combination of unrated meter plus massive i squared t that's the big hazard combo. Remove either of those factors and the risk drops into the long tail of risks we take daily without blinking an eye.

1 ohm from 1mm cable: 23m 1.5mm cable: 34.5m 2.5mm cable: 55m

Explosive force comes from heating, which depends on i & t. Cables can limit i to a very variable value, the CU's mcb/fuse will limit t accordingly. I have once encountered arc from dead short on a thick cable feed, it was a total non-event. Arcing at the incomer is another matter.

And is also limited by the Ze value.

[meow2222]

Yes, when its to earth.

The death referred to was from a 3 phase 480v panel serving a shopping mall. So I'll make a very rough estimate of the energy compared to a 6 or 32A domestic circuit:

480v: x2 3 phase: x3 mcb rating unknwon, as a starting point lets guess 320A: x10 or x53 So for those figures, the available power for an arc is around 2x3x10-53 = 60-320x as high as a domestic ciruit.

NT

[Capitol]

and it's always interesting when the wire vaporises in your hand! 415V mutiple substations ring connected feed. Just doing 10KA device testing.

[Cursitor Doom]

Yeah, it's a real scandal. I can't understand why nothing's been done about this false self-certification. When you look inside these cheap meters the build quality and layout is pretty scary.

[alan_m]

You can get DMMs with an additional bar graph type display so you can easily see the equivalent of the moving needle pointer.

[alan_m]

In my younger days I used to work for a company repairing and calibrating test equipment. At the time, AVO seemed to be a company still stuck 50 years in the past. When other companies were starting to produce hand-held DMMs (albeit costing £100s) AVO were still producing something the size and weight of a couple of house bricks. Even when they caught up they still used the same cases for their product making them seem very dated.

Possibly AVO did produce some of the better analogue meters but there was a period 40 years ago when many more companies entered the test equipment market and most(1) of the DMMs well out-performed AVO's offerings.

(1)There were some equipments from companies such as Philips that required a 'select on test' resistor adjustment every 3 months to keep it within in specification limits, indicating that the equipment was unsuitable for any accurate measurement.

[alan_m]

The last one I purchased had a nice silver coloured bit but after doing up one screw it was a different colour. A lot of conductive swarf was left in the fitting (the plating had flaked off).