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Essential Safety Tips for Working with Electrical Circuits

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Essential Safety Tips for Working with Electrical Circuits

Postby Scottdru » Thu May 12, 2005 1:53 pm

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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Re: Essential Safety Tips for Working with Electrical Circuits

Postby Scottdru » Thu May 12, 2005 1:56 pm

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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Re: Essential Safety Tips for Working with Electrical Circuits

Postby namke » Thu May 12, 2005 5:41 pm

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... :shock: bare wires in each hand :headbang:
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Re: Essential Safety Tips for Working with Electrical Circuits

Postby Hugh Robjohns » Thu May 12, 2005 6:15 pm

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 :shock:

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 ;)

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Re: Essential Safety Tips for Working with Electrical Circuits

Postby Guest » Thu May 12, 2005 9:38 pm

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. :shock:

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!
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Re: Essential Safety Tips for Working with Electrical Circuits

Postby PrinceXizor » Thu Apr 06, 2006 3:13 am

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.

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Re: Essential Safety Tips for Working with Electrical Circuits

Postby Frank Eleveld » Thu Apr 06, 2006 6:34 am

PrinceXizor wrote:This link here (...)

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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Re: Essential Safety Tips for Working with Electrical Circuits

Postby PrinceXizor » Thu Apr 06, 2006 4:02 pm

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

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Re: Essential Safety Tips for Working with Electrical Circuits

Postby Radical Ans » Fri Apr 07, 2006 3:57 pm

namke wrote: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... :shock: bare wires in each hand :headbang:

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.
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Re: Essential Safety Tips for Working with Electrical Circuits

Postby Hugh Robjohns » Sun Apr 09, 2006 2:07 pm

Radical Ans wrote: 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.

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...

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Re: Essential Safety Tips for Working with Electrical Circuits

Postby Radical Ans » Sun Apr 09, 2006 5:11 pm

Hugh Robjohns wrote:
Radical Ans wrote: 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.

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
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.
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Re: Essential Safety Tips for Working with Electrical Circuits

Postby Clunk » Mon Nov 27, 2006 2:14 pm

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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Re: Essential Safety Tips for Working with Electrical Circuits

Postby hughb » Mon Nov 27, 2006 6:17 pm

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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Re: Essential Safety Tips for Working with Electrical Circuits

Postby Clunk » Mon Nov 27, 2006 9:09 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 :tongue:

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
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Re: Essential Safety Tips for Working with Electrical Circuits

Postby Clunk » Mon Nov 27, 2006 9:12 pm

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?
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Re: Essential Safety Tips for Working with Electrical Circuits

Postby Frank Eleveld » Mon Nov 27, 2006 11:28 pm

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

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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Re: Essential Safety Tips for Working with Electrical Circuits

Postby PWGLE » Tue Nov 28, 2006 1:49 am

Clunk wrote: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.

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! ;)

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Re: Essential Safety Tips for Working with Electrical Circuits

Postby IvanSC » Mon Sep 08, 2008 5:08 pm

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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Re: Essential Safety Tips for Working with Electrical Circuits

Postby Hugh Robjohns » Tue Sep 09, 2008 12:47 am

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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Re: Essential Safety Tips for Working with Electrical Circuits

Postby dubbmann » Tue Sep 09, 2008 2:02 am

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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