Speaking of arc flash accidents, there's a bad one on youtube

https://www.youtube.com/watch?v=ePiTODvl_vk

I heard that he did bot survive...

WARNING: VERY GRAPHIC CONTENT.

To all members - posting these videos is okay but must come with a content warning. This isn't for everyone. The above shows what I described in an earlier post - basically, someone being cooked alive.

Yuck ! I'm glad I did not see that! Just yuck!
Images are very stong on the mind...

GTC and Brad I take your points but I still reckon a neon is a good last check before touching something that you are not sure is definitely safe. The neon screwdriver I have is very well made, properly insulated and I use it as a test instrument not as a screwdriver so it is kept in a protective cover. I did a 'calibration' test to determine the minimum voltage, 100V, that would strike the neon but I would not attempt to use it on anything that was likely to be over 400V AC. As far as I am aware there is no non-contact tester that can detect high DC voltages or dangerous charges stored in capacitors. (If there is then I would like to know so I can buy one.) Of course I do use other instruments for measurement and a non-contact tester to check for or trace live cables but a neon screwdriver has saved me from being bitten on occasions when I had no access to anything better. Most of my paid electronics work was on computer systems in Australia and in government offices overseas.

Some of interesting things my screwdriver has detected were:

- a hardwired UPS that was still on when its power switch was off so the associated power strips in the rack and attached servers were still 'live' contrary to what it said in the manual.

- a power supply for a Cisco router that had failed in such a way that 230V AC was present on every Cat 5 UTP cable plugged into the router which then went through the network cards to the motherboards in the computer workstations.

- network cables that had been run alongside a power cable in a suspended cable tray with a clamp that had a sharp edge and had been tighten to the point that it cut through the insulation on all cables putting 230V onto the data cables and making the tray 'live' as well.

- a coax cable that had been dragged through a ceiling cavity so that it dislodged the cover on a power junction block making the sheath on the cable live when the outer insulation on the cable was scraped/cut.

- a transformer in an old power supply that had a short to the frame and therefore the chassis which in turn had a high resistance connection to the earth wire on the fitted power cable making the chassis live (but the earth leakage detector in the board didn't trip).

The last example was the closest I have to testing an old radio. I had visually checked the unit when it was unplugged and made the usual tests with a multimeter. The power cord and plug appeared to be in good condition so the next step was to apply power and check the output voltages. Yes I had the cover off but the 230V sections were totally insulated. I would have been holding the meter probes but I could have easily brushed a hand against the chassis in the process. Fortunately I decided to just tap the neon to the chassis first and was rather surprised when it glowed. As I am sure some readers are saying, I should have measured the resistance between the chassis and the earth pin while the unit was unplugged; certainly that is what I do now.

As far as I am aware there is no non-contact tester that can detect high DC voltages or dangerous charges stored in capacitors.

I use a 'chicken stick' for that -- a resistor inside a probe with an alligator clip for the earth end to discharge caps.

I don't like non-contact voltage testers either. I tried one for a while when they were a new idea and it was far too sensitive. I could not determine which wire in a bunch was hot. It was beeping at the whole bundle. As you'd be aware they operate on rather crude means of detection of the electromagnetic field, thus can easily be swamped and give false positives from other sources.

I am not aware of any non-contact voltage detector that works on DC.

There's an ancient contact type solenoid-based tester known as the Wiggy which can indicate presence of either AC or DC voltage by vibrating. I don't think they were ever sold in Oz.

This Topic reminds me of those stupid stud wall finders!!
Hopless things! They will pick up the wire ok ,but the stud is more of a guess.
I find it much easier to just use the ball of my hand.
The most expensive one I have owned was around 50 bucks so perhaps I high quality one works well I dont know.
Pete

stupid stud wall finders

I have a Stanley that works OK with metal studs, but most times I've needed to use one the house had wooden studs.

Hi Relay, just a comment re the earth wire connections to anything.

One of my pre powering up tests is earth continuity and I have the habit for years now of using a 30 volt 3 amp current limited power supply on the bench for that.

It has handy long clip leads (figure 8) coming from it and I clip one lead to the earth pin of the power plug and I then touch the other lead to the chassis of the equipment, to covers, to any bolted on metal parts and so on. I should get a good spark to every metal part and 3 amps driven through the loop circuit. I can then clip both ends firm and measure the mV potential across the points to get a rough measure of the "earth resistance". If there are volts present and metal bits get warm(!!!) then I know I have a problem.

I know its not an exact measurement and clips do have contact drop but it sorts out the obvious wrong/poor connections and its easy.

Fred.

Unable to watch that video...

"Sign in to confirm your age
This video may be inappropriate for some users."


I don't have an account, and I don't know what signing in would prove anyway.

Ohhh Robbert! Would you really want to watch it?
I would have trouble getting it out of my mind.
Like a bad horrible news story! I dodge them too for the same reason.

Pete

I am the same with those sort of video's.
They can be quite disturbing and stay with you for a long time.
I know these sort of things go on and sometimes the video's represent a warning to others but I'd rather not see them.
But I guess if it has a prior warning about content you can choose to watch or not.