I've been thinking for some time now that we should have a sticky thread for safety tips here in this forum.

Working with electricity can be dangerous, or even lethal, if you don't follow proper safety precautions. If you are new to working with electrical circuits and are contemplating embarking on a DIY project along these lines, there are things you MUST be aware of before you start poking your fingers into electrical circuits.


Please feel free to post any safety tips you can offer, or any links to sites that offer safety tips, here in this thread.

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Scott
--Where are we going and why am I in this handbasket?

For starters, I ran across this page recently. The safety tips are mainly aimed at people wanting to build or work on tube amps, but there are a number of excellent suggestions there that apply generally to working on electrical circuits.

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Scott
--Where are we going and why am I in this handbasket?

Good plan... One thing: in the link you posted, the author says 'be the one-armed technician'... my college lecturers (when I did a test and repair course) said 'Always use your right hand - even if you're left handed - keep your left hand in your pocket!!' That way any large electric shocks go down the right side of your body rather than the left (near your heart!).

Having said that, I did get something like a 15kv shock straight across my chest once when I was testing solenoid hydraulic valves... bare wires in each hand

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[MacBook/rev1 2.0GHz/2GB, OSX 10.6.x; Logic Express 7.2.3; Reaktor 5.6.x; too many vintage synths]
http://namke.com | http://minimism.com

The one handed approach is good -- especially if working in a rack bay where the natural tendency is often to hold on to the earthed metal bay with one hand while poking around in potentially live things with the other

The other thing I would stonrgly recommend is to remove watches and any rings before working on equipment -- especially valve gear where everything is wired between tag strips. It is surpsingly easy to foget about the rings or metal watch you might be wearing, and accidentally short something out, sometimes with very dramatic effects.

It tends not to life threatening to the wearer because being made of metal, these things conduct the electricity around the wearer rather than through him or her, but it can make one hell of a mes of the thing you were working on and turn a quick simpole job into a major rebuild!

Been there, done that, got the burn marks

hugh

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Technical Editor, Sound On Sound

I'll second the warning about wedding rings! I don't wear mine any more after seeing the state of a friend's hand after he shorted a 1000AH 24V battery with one whilst servicing an OB truck! The ring arced to a terminal, fused to it, melted, and welded itself and his finger to the battery terminal - in a pretty spectacular and very unpleasant way.

One of the best bits of safety advice I received was from an elderly college professor who said "always remember that every piece of wire has at least two ends" He went on to say that just because you can see one end, it doesn't mean that the other isn't connected to something that can kill you!

This link here not only provides an excellent on-line course in basic electronics, but also covers electrical safety and has good introductions on systems and signal which is actually more applicable to audio but is often lacking in basic electronics textbooks.

P-X

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My Home Studio Build Thread

Quote PrinceXizor:

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This link here (...)

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You've made a typo in the URL of that link, clicking it will get you a 404. This should get you there.

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Imagination is more important than knowledge - A. Einstein

Thanks Frank!

My original post got eaten and I don't have time to type another one so here's the short version.

I like this site for a few reasons:
--Very well written with clear explanations, plenty of examples and practical application.
--Written from the standpoint of an electrical technician which is beneficial for DIY'ers.
--A good part (and even a soapbox!) on electrical safety that's put right after the very basics.
--There seems to be a good ammount of information on troubleshooting (see point 2) when discussing.

Frank has the right link but here it is again. The URL is short enough to be typed out.

http://www.allaboutcircuits.com

P-X

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My Home Studio Build Thread

Quote namke:

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Good plan... One thing: in the link you posted, the author says 'be the one-armed technician'... my college lecturers (when I did a test and repair course) said 'Always use your right hand - even if you're left handed - keep your left hand in your pocket!!' That way any large electric shocks go down the right side of your body rather than the left (near your heart!).

Having said that, I did get something like a 15kv shock straight across my chest once when I was testing solenoid hydraulic valves... bare wires in each hand

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I herd an interesting story from one of the service engineers at work. I work at a company that makes coal mining machines. These machines all run on high voltage AC power. Well one day said service engineer was on a call where a machine went down. Him and the mine electrician were working on the machine and had the breaker for the machine locked and tagged out. Well the shift ends and the machine isn't running so the service engineer stays to continue working. Unknown to him the electrician takes his tag off the breaker. Long story short, the electrician on the next shift turns the power on and the service engineer gets a 950VAC shock to his right arm. He's sitting on the ground so the current travels through his arm and out his right butt cheek. He says it acualy took a chunk out of his rump. Thankfully the engineer lived to tell the tale and has a nasty scar (so he says, I didn't care to look . Lesson learned.

Quote Radical Ans:

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the shift ends and the machine isn't running so the service engineer stays to continue working. Unknown to him the electrician takes his tag off the breaker.

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I think this goes against Health and Safety regs, and certainly against good practice. When more than one person is working on a machine, they should all place their own padlocks or tags on the isolation switch, specifically so that it can't be turned on until every engineer is happy for that to be done.

Lucky the guy is alive...

hugh

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Technical Editor, Sound On Sound

Quote Hugh Robjohns:

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Quote Radical Ans:

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the shift ends and the machine isn't running so the service engineer stays to continue working. Unknown to him the electrician takes his tag off the breaker.

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I think this goes against Health and Safety regs, and certainly against good practice. When more than one person is working on a machine, they should all place their own padlocks or tags on the isolation switch, specifically so that it can't be turned on until every engineer is happy for that to be done.

Lucky the guy is alive...

hugh

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From what I've herd safety in a coal mine can sometimes be lacking. At least in the US. In other countries it's a different story. For instance, Australian mines are so concerned with safety that they can hardly produce coal sometimes.

anyone help me out?

I'm trying to add a light and a switch to an existing lighting ring. (I did once know this about 20 years ago!)

the existing ring has one light and one switch.

can anyone provide a step by step guide to what goes where?
the existing ring is live(red) common(yellow) nuetral(blue) and earth.

Is that a DC system? Doesn't sound like any AC wiring I've ever encountered. Normal mains is live (brown) neutral (blue) and earth (green/yellow) and 3-phase used to be live red, yellow and blue connectors, with a black neutral and yellow/green earth (now, thanks to european harmonisation it's brown, black and grey lives with a blue neutral).

The closest thing your installation sounds like to me is a 3-phase AC supply and you have to be bloody careful with those, because when you short yourself across one of the phases and earth, that's just good old 230VAC, but get yourself between any two of the three phases and you'll shove over 400VAC across yourself, and you don't want that!

Apart from for powering big 3-phase items (air-handling units on top of buildings spring to mind), you should only ever have 1 of the three phases in any one room (or in one whole domestic house, for preference). This is why it's vitally important not to use a really long extension cord to steal your neighbors electricty, because you could expose yourself to much higher voltages than usual should there be a fault!

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Tesco Value Tonmeister

Edited by hughb (27/11/06 05:20 PM)

thanks hugh, I think it is just a 240 ac supply - live, nuetral, common and earth, my memeory may have failed on the colours

I have tried to attach the new switch and light with limited sucess I have somehow made the new switch dependant on the old switch being switched on, how do I bridge this?

I have tried a few variations on this theme but without much luck, and ideas before I spend £100 on a proper electrician?

thanks

as I said before I have 4 wires on the main ring,

I need to attach a dimmer to this - I need a feed to then power a switch and a light which I have added, this is standard 2 core and earth.

any ideas?

Quote Clunk:

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I have tried a few variations on this theme but without much luck, and ideas before I spend £100 on a proper electrician?

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Consulting a qualified electrician seems the absolute best thing to do - trying to 'experiment' what works without having proper knowledge of an electrical system is very hazardous and may even turn out to be lethal. Don't mess with electrics until you know what you're doing.

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Imagination is more important than knowledge - A. Einstein

Quote Clunk:

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anyone help me out?

I'm trying to add a light and a switch to an existing lighting ring. (I did once know this about 20 years ago!)

the existing ring has one light and one switch.

can anyone provide a step by step guide to what goes where?
the existing ring is live(red) common(yellow) nuetral(blue) and earth.

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I know what you mean!

Ceiling rose lighting is also very confusing if you don't understand it!

I'll draw and scan you a diagram. But if in doubt, get someone to check it or pay them to sort it!

Laurence

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P.I.G.L.E.T - where is polly?

Not exactly OT but worth a mention.
Threee very dear friends of mine *almost* shuffled off the mortal coil last week.
Playing at an outdoor "do" and the 3 phase had been wired up wrong. Amps lasted for the first set & then all three blew - one guys lethally frying the mains tfr down to the chassis ground and sending a swift 400-odd volts to the earthy side of his guitar jack.
Fortunately he wasn`t grabbing anything & simply got hurled across the stage. And he already had curly hair....

Let`s be CAREFUL out there!
RDF`s and mains testers at all times, chaps!

P.S. Can all you techie types refrain from correcting me as to how many volts, where the earth potential lies, etc. this time?
Regardless of my technical coherence or lack thereof, the message needs to get across.

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Me? But I`m such a loveable old bugger!

You're right. The important message is what can happen, not the detail of voltages.

But who on earth managed to mis-wire the mains supplies so utterly incompetently, and are they still in business, or banged up in prison for attempted manslaughter?

Hugh

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Technical Editor, Sound On Sound

excellent thread, well worth a sticky. i, too, have long heard the 'one-armed electrician' rule from a friend who studied electrical engineering at one of the top research unis in the states. they taught it to freshman in their first circuit class and the lesson stuck. electricity is one of those topics, along with exotic foods and problem women, that merit an entire chapter in the 'big book of famous last words' ;-)

cheers,

d

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"Patsy had the drug tolerance of Keith Richards and the moral rectitude of Brian Jones." - Dr. Walter Bishop, "Fringe"

Quote Hugh Robjohns:

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You're right. The important message is what can happen, not the detail of voltages.

But who on earth managed to mis-wire the mains supplies so utterly incompetently, and are they still in business, or banged up in prison for attempted manslaughter?

Hugh

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Have`nt managed to contact any of them yet, but apparently it was a smallish private "do" so who knows WHO was allowed to do the wiring.
I agree with you 100% - hopefully the survivors are now carrying their OWN safety kit, like I have for years!

The only thing I can think of here is that somehow they wound up being on 2 different phases at the same time, but surely an RDF would have seen this immediately and killed the power? The idea that anyone would hook up a temporary 3 phase supply without automatically fitting some sort of safety devices (particularly with the weeather we have been having recently) makes me shudder.

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Me? But I`m such a loveable old bugger!

Might have been a faulty neutral. Get this happen quite a lot on 3 phase machinery. As long as the phases remain in balance nobody notices, but as soon as someone puts a significant load from one phase to the (faulty) neutral all bets are off.

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It wasn't me!
(Well, actually, it probably was)

Not really a safety problem as such, well, for the lashup perhaps...

Always fit an on off switch in the supply line(s)even for the most crude of rats nests so you can bang it off at the first sign of smoke.

Also worth having a couple of LEDs setup with a few K in the positive leg to tack in to show various operations, e.g. small 5V relays cannot be seen or heard to operate.

Dave.

(Yikes.

The mains tester I carry just tells me that there is an actual earth (not waving its leg in the air) and that active and neutral are the correct way round.

Its just got three bulbs on it. There's a placard with expected "correct" display (two ambers) and the various faults. None of them say "you are across two phases of a three phase".

I wonder what that would display. Especially if, as well as being across the phases, it was miswired as well - anybody who can get it that wrong can't even be trusted to get the earth right.

Maybe it indicates this condition by emitting smoke?

Were they running through surge protectors? Be useful to know if they were and they failed to give protection.

Quote damoore:

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None of them say "you are across two phases of a three phase".

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Remember that standard practice is totally different in your part of the world and (as I understand it) things like tumble driers are commonly wired across two phases of a three phase supply in the US.

If you don't have a good knowledge of the standard wiring practices of the country that you are in then leave all mains wiring to someone who does. There are massive differences between the US and UK.

James.

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JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net

Howabout the Newbury Races horse deaths recently?
What happened there?

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I am the Walrus.

Quote ROLO46:

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Howabout the Newbury Races horse deaths recently?
What happened there?

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There doesn't appear to have been much further news after the incident, perhaps because of the possible big bucks involved and concerns about liability. From what was reported it sounded like the insulation had broken on a disused underground mains cable that hadn't been isolated, and current to earth created a large enough potential difference at ground level to kill the two horses. All the stuff in the reports about the other horses being saved because they were wearing aluminium shoes couldn't have been right though - the danger zone was probably very localised and they missed it, or got away sufficiently quickly.

Evidently the fault current was insufficient to blow a fuse or trip a circuit breaker, which is strange considering that the cable should have been armoured and the metal armour strands connected to earth at both ends and, probably, to neutral at the supply end. But then again, the cable shouldn't have been live in the first place so it might not have been intentionally connected via a protection device.

Chris

Horses and cattle are notoriously prone to electrocution from ground voltage differences simply because the 4 legs are a reasonable distance apart.

There is actually considerable guidance in the 'special locations' section of the wiring regs dealing with stables and similar locations for exactly this reason.

Regards, Dan.

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Audiophiles use phono leads because they are unbalanced people!

More for protecting what you're working on than for yourself...

Make a pair of needle probes.

To do this solder a conventional sewing needle to a test lead in place of the normal probe (it is surprisingly easy to solder to the eye of a new needle). Try and make this joint as small and smooth as possible.

Then use the insulation from a thin wire to make a sleeve that goes over the needle itself right up to the joint and only leaving 2-3mm of the point exposed. Hold this in place with heatshrink tubing going over the joint and about 10mm either side. Put another piece of heatshrink on top of this going about 15mm either side, so you have a small firm 'probe' that's reasonably well insulated - not suitable for high voltage work!

Your new probes are ideal for testing chips and surface mount stuff as they are small enough for you to actually see what you're hitting and far less likely to accidentally bridge across two legs. Also, the very sharp points will easily punch through dirt and oxides, and even most PCB varnishes.

With care, you can also use them to spike through the insulation of ribbon cables etc. when you have possible faulty connectors.

P.S.
After you've stabbed yourself with them a few times, you'll learn to respect them

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It wasn't me!
(Well, actually, it probably was)

Edited by Folderol (18/06/11 06:54 PM)

Quote Folderol:

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More for protecting what you're working on than for yourself...

Make a pair of needle probes.

To do this solder a conventional sewing needle to a test lead in place of the normal probe (it is surprisingly easy to solder to the eye of a new needle). Try and make this joint as small and smooth as possible.

Then use the insulation from a thin wire to make a sleeve that goes over the needle itself right up to the joint and only leaving 2-3mm of the point exposed. Hold this in place with heatshrink tubing going over the joint and about 10mm either side. Put another piece of heatshrink on top of this going about 15mm either side, so you have a small firm 'probe' that's reasonably well insulated - not suitable for high voltage work!

Your new probes are ideal for testing chips and surface mount stuff as they are small enough for you to actually see what you're hitting and far less likely to accidentally bridge across two legs. Also, the very sharp points will easily punch through dirt and oxides, and even most PCB varnishes.

With care, you can also use them to spike through the insulation of ribbon cables etc. when you have possible faulty connectors.

P.S.
After you've stabbed yourself with them a few times, you'll learn to respect them

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Lot of work Will?
I just used to get something like this: http://www.maplin.co.uk/moulded-4mm-test-probe-leads-5665

and tickle the ends up on a grinding wheel (now I have to do it laboriously with a file!).

Also a good idea to makeup a jack plug and jack socket to 4mm conns, saves a lot of bad language when interfacing with amps, AI's and such.

Dave.

Not at all Dave, I've attached a piccy of the probes I made quite a few years ago. I used the leads from a pair crappy probes - just cut them off. Must have taken me all of 15 minutes.

The points have never needed sharpening, and will poke through just about anything, unlike ordinary brass ones. They also don't have the ridiculously long exposed metal that standard probes have.

I have to watch the other engineers as they are inclined to attempt to 'borrow' them, and our apprentice is very pleased with himself have recently made a pair of his own, only he stuck to the 2mm exposed length (having recently experienced the death of a chip).

P.S.
These probes are used every day!


By the_real_folderol at 2011-06-18

Edited by Folderol (18/06/11 09:38 PM)

Just want to say...
If in doubt - don't!

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It wasn't me!
(Well, actually, it probably was)