Electrical Safety

[chilly1]

Everyone needs to take a little refresher in electrical saftey.
1, don't touch unless you know
2, never work on "live" circuits
3, always disconnect the equipment before working on it
4, when working on a phase change rig that has capacitors treat the system as live even if it is disconnected from the supply as capacitors will store a charge for a long period of time
5, use a meter if you done have one get one
6, Pay attention you life depends upon it
7 always use a ground when running a compressor, compressors can short internally to groungd and without a ground path the electricity will use you or your computer to make the connection killing you and the computer...

[eagle101]

chilly1....very correct about electrical safety!
question chilly1.........
when a promi m1 is running and your just sitting there mousing around can the compressor blow up like a bomb or so shooting out parts threw the m1 case?????
thanks

[100]

( [thread title]
*safety )

Refreshingly important notice. Good post.

[kayl]

yes electricity can kill, even the electricians are dieing and they know what they are doing. if you eva receive an electrical shock you should see a doctor even if you feel ok as they check your heart rate to see if its ok.
when ppl are connection wires its best to solder them together or use screw terminals.
never just twist them together as they can come apart and cover them with electrical wire.

[JSU]

and cover them with electrical wire.

electrical tape :), silicone inside the twisty connectors is also nice if its in a wet area/condensation around it.

[masterofpuppets]

Some good tips there chilly1. Electricity can KILL! I know someone who died from electrocution while working on a 30amp circuit.

[chilly1]

All it takes is 3 miliamp to stop your heart. You can get that from a 9V battery. A capacitor that is capable of dumping 10000A / sec
THE UNFORTUNATE PERSON WHO COMPLETES THE CIRCUIT WILL BE DEAD.
So dont ever play with capacitors, getting a shock is never funny it is always serious, watch your step around circuits and if you do recieve a shock and notice dry mouth,nerviosness, chestpain, lightheadness, blurred vision seek immediate medical attention, it is always a good idea to go to a medical facility after a shock. Shocks can kill hours even days after.

Short story.
I used to ride home from work with a neighbor. We were both electricians at a paper mill. He had gotten a shock off a 120V lighting circuit changing a light bulb. This was 10 AM he felt fine small shock not like it had never happened before a hundred times. He had a weird day he was thirsty and coldn't stop urinating. He thought it was due to the flu or something He went home, I rode with him he seemed normal. Dropped me off and I rode into work with my dad the next day. At the gate they told me he had died of heart failure, his heart had simply stopped, it seems that his potassium levels had dropped due to hids body's reaction to the shock, when he arrived home he took a shower laid on the livingroom couch to watch the news and expired quietly, his wife found him. He had passed when she was cooking dinner and had made not a sound.

Keep this in mind when you say I feel fine, Pay attention to yourself. Always seek medical attention after any electrical injury.

[masterofpuppets]

The only time I got a shock was when I changed a dead light without knowing the switch was on. Luckily I only got one spark from it and I was fine. Evil light bulbs!

[kayl]

anther thing for ppl to consider
check that you house has earth leakage protection circuit fitted, if not may consider working off a RCD box that plugs into the mains, (ie cutting say with a grinder and cut the electrical cord, mains trips and could save ya life)
and other tools when working with electricity.

[Revv23]

wow, im glad i read this, i had no idea tat a shock can kill after the fact, luckily only time ive ever gotten shockedwas when i stuck my finger in a light socket as a kid, and i work with open PSU's all the time.

Thanks for the heads up chilly, ill be passing this on to others.

[JohnFish]

All it takes is 3 miliamp to stop your heart. You can get that from a 9V battery. A capacitor that is capable of dumping 10000A / sec


Oh my god. 9v is nothing and still they can kill you. i remember being really young (~10 years old) and touching batteries (from small to 12v ones) to my tongue to check if they work. I never knew i suppose. Thats one of the most useful guides i have ever read and thank you chilly for reminding us

[Unknown_road]

only when you put a 9v battery to the sinus nerve in your heart will kill you. your body has a huge electrical resistance so only a few nanoamp/picoamp will cross your body. And moreover the most of the current will choose the fastest way across your body which is along the skin. and a battery is DC which is half as dangerous as AC. You should be very carefull with electricity but 9 volt is just not enough to make damage.
But I agree on the rest with you chilly.

capacitors charge up to the voltage you put on it. So if you put 120 volts on it and then onhook it, the voltage between the nodes is still 120 volts. people don't realize this and that is indeed very dangerous.

[Newb101]

Remember this kids... the one hand rule!

Keep one hand in your pocket while connecting or touching anything that carries electricity. Even if you are sure you disconnected it. Because if you happen to become the circuit through both your arms, you guessed it, it passes through your chest.

You can pretty much guess what happens next.

[Aphex_Tom_9]

Remember this kids... the one hand rule!

Keep one hand in your pocket while connecting or touching anything that carries electricity. Even if you are sure you disconnected it. Because if you happen to become the circuit through both your arms, you guessed it, it passes through your chest.

You can pretty much guess what happens next.
ooh boy...i came close to that once...open PSU + both hands :shakes:
i was scared for like an hour after i felt the shock, im fine though (it was 2 weeks ago). That's some good advice.

[Scout255]

It's also recomended that you use only your right hand, as that way if you get electrocuted, the shock travels through your right arm and down your right leg into the ground. If it were your left hand it would go through your heart and then your left leg.

[FallenAngel]

I just told my wife to not let my kids play anymore with any kinds of battery, wow didn't know it too

[Unknown_road]

I just told my wife to not let my kids play anymore with any kinds of battery, wow didn't know it too

You let your kids play with batteries? Those things contain very harmfull chemicals.

[FallenAngel]

I never let them play with that, but you know how kids are, they found things we lost some months before, sometimes they pick the TV control and just take those batteries, if we don't see them they simply put in their mouth any kind of stuff, until we see them, kids don't know how dangerous life can be. It's why we are always near... btw my english sometimes sucks and now I see that phrase and noticed that someone could think I was a bad father letting my kids play with batt. I will rephrase it "I just told my wife to never let them play with any kind of battery" and I was refering to TV controls batterys anyway...

[Revv23]

i doubt a AAA battery will be a health risk, even to a small child.

[chilly1]

Remember 3 millaamps of current can stop your heart, how your body becomes conductive enough to conduct that current through you heart is what matters so it is best not to play around with electricity. Higher voltages need less resistance to move 3 ma so you guys in europe and 220V house current be careful......

[Unknown_road]

I study electrical engeneering and I daily have connectors in my hand with up to 30Volt DC and 15 VoltAC. It is even impossible to do my work without touching the bare connectors. A 1.5Volt battery is only a health risk because it contains dangerous chemicals. You should be very carefull nontheless but mainly you should know what your doing! Btw every shock is different, I survived many 230Volt shocks but some people die from much less.

[Pandrone]

I too have made the fault not disconnecting/discharging the capacitor in a rig. This capacitor was cracked open due to unknown reason. So you could se inside it, i didn't notice this and the compressor worked fine, so i was just about to cut the compressor out when i touched the capacitor, damn, it's not a nice feeling having that current passing through your arm...

I was lucky to just touch it with one hand, could have been much worse i belive.

[Adasi]

Higher voltages need less resistance to move 3 ma so you guys in europe and 220V house current be careful......
I really try to be careful, but you know - accidents are difficult to avoid. About a month ago my dad decided (don't know why) to change the switch which puts on the light in the bathroom and of course he didn't tell me. During the night I decided to go to the toilet and guess on happened... I put my hand on bare cables i got a shock of 230V (now in Poland we have 230, not 220). As a result i've fallen on my knees and couldn't stand up for few seconds, i was standing before of course ;)
Thankfully nothing happend to me, I think that was the worst (longest) electric shock i've ever had.

So be careful guys ;)

[hatemi]

Last night I was once again fidling with compressors and was filling the system with R290 and touched the service port when the damn thing was running...I felt like something hit me real bad and took 2 steps back. It took me quite some time to realize I had got an shock! The thing wasnt plugged to a properly grounded plug(well the plug is grounded but the damn extension cord wasnt) si I guess it was the reason but tonight I'm gonna take seome measurements with DMM and try to find out what realy was the reason.

You can be I was scared and my heart was beating like crazy!

[hatemi]

Well it seems it's running a 230v current between the ground and the blue wire...I have no idea of whats wrong with it but I'm pretty sure It shouldnt be like that. The compressor is Danfoss SC10D with start capasitor if that helps.

It seems to have some funky internal connections... Do you suppose I could still use it or do I have to just get rid of it?

[Pandrone]

If the compressor is grounded and it shorts internally, shouldn't that trip the fuse? (or that other thing, dunno what it is called in english, in swedish= jordfelsbrytare)

[chilly1]

Actually for a grounded compressor to trip the fuse it would need to be comnnsected to the buildings ground this is why it is important to never remove the third prong and always use grounded equipment, if say a vapo shoted and did not have a ground connected and it only was near the supply side of the incomming power if you were to get your hand on that and another on the system ground (water pipe, faucet, a computer case that was grounded) the potential would be 120V in the us and 220 in europe and higher in some other countries. So be careful and safe never use a cooling rig with no ground. It will kill you.

[total_assault]

If the compressor is grounded and it shorts internally, shouldn't that trip the fuse? (or that other thing, dunno what it is called in english, in swedish= jordfelsbrytare)
Do you mean Circut Breaker? If thats what you mean it matters if the compressor is by it self on a 120volt 15 amp breaker it might catch fire before the breaker flips!

[chilly1]

If it shorts to equipment ground and the equipment is not grounded to the panel it probably would not trip the circuit breaker or blow the fuse so this is the real danger of unground equipment.

[froudeg]

As pointed out it's the body's path to ground that's the killer.

You could hold a 220v live wire, and if you were standing on styrofoam - you wouldnt even be aware it was live. The national grid pilons have bare metal cables btwn each pilon carrying 10,000+ volts, but birds can sit on em quite happily and feel nowt.

The one hand rule is something everyone should follow, without your other hand touching anything thats even remotely grounded, you reduce the risk of a current flowing across your chest.

As always, you should never work on any electrical equipment when wet - wet clothing will reduce your bodies electrical resistance by a factor of a 1000+ - which increases the current flowing by the same factor. Wet shoes will radically reduce the resistance path from your body to ground and can turn a minor shock into something lethal.

Btw - batteries pose almost no electrical shock risk..the main reason being is that they have no path to ground themselves, unlike mains electricity - so it would take you touching both terminals of the battery, one in each hand, be completely soaking wet and have about 30 volts worth for you to start approaching dangerous currents flowing across your chest.

[Da_Priest]

30mA can shut down ur heart.
So we once saw in school when I was like... 16 or something :)
teacher was a 'stupid' '****' but could me true...

[Butcher_]

I really try to be careful, but you know - accidents are difficult to avoid. About a month ago my dad decided (don't know why) to change the switch which puts on the light in the bathroom and of course he didn't tell me. During the night I decided to go to the toilet and guess on happened... I put my hand on bare cables i got a shock of 230V (now in Poland we have 230, not 220). As a result i've fallen on my knees and couldn't stand up for few seconds, i was standing before of course ;)
Thankfully nothing happend to me, I think that was the worst (longest) electric shock i've ever had.

So be careful guys ;)
Please please tell your dad to stop working around household electrical circuits if that's his idea of safety. I dread to think who he's going to kill with that sort of behaviour. If working on a light switch for instance the power to the lighting circuit should be off at the fuseboard for the entire diration of the work. If you can't get it done in one go, you'll have to do without lights or fit an insulating safety cover of some sort (I find not removing the old light switch till I have a new one to hand works well).

Also with regards to ground, in my opinion you should have everything grounded, extension cords especially. Luckily plugs here are designed so they don't work without an earth pin in, though I guess you can leave it disconnected (though it's illegal to do so for most equipment).

[Stewie007]

All it takes is 3 miliamp to stop your heart.

6 Milliamps across the heart will kill you. Not 3. Not that I'd wanna feel 3 :p

30 milliamps will kill you without any possibility of recussitation.

Edit: Oops, sorry for the necropost :p I saw it in the sticky and didn't really notice. Its only a month tho hehe.

[saratoga]

There is no one universally accepted value for Fibrillation current. It depends on frequency, fitness, gender and more. Women are easier to electrocute, and mid frequency AC is most dangerous because its close to the frequency your heart naturally repolarizes at. Its just plain bad luck that the 60Hz power almost exactly matches the heart rate of the average person.

Generally the clinically accepted value is 75 to 200mA through the chest for macroshock fibrillation. As an engineering rule of thumb, you design so that theres no chance of going with 2 orders of magnitude of that value. That way from a legal perspective you're in good shape if a patient using your device drops a hair drier in the bath tub and kills themselves. Otherwise you're potientially liable for that hair drier because the patient had your ECG or pacemaker or whatever.

For microshock (current applied to the inside of the chest), the value is 20 to 200 microamps. For this reason you have to be insanely careful when you put a wire inside someone. There are people who have been electrocuted licking 9v batteries, and you sure as hell don't want to catch the tab the next time that happens.

Of course none of that really matters, since IMO any current is too much.

Fortunately, theres really no limit on how high you can be defribulated from, at least as long as you don't burn yourself to death. A defribulator will repolarize your pacemaker, and unless you're burnt to ash, it'll generally restart.

[endo]

Refreshingly important notice

[Sheograth]

I gave myself a nice 230V when I was in india last summer. The electrical systems in houses there aren't as well made or protected as the better ones in 1st world countries, and old wireing with over-rated fuses is the norm. I blew a fuse when plugging a mobile A/C into my bedroom wall outlet, and proceeded to replace it. In the process, I somehow made the connection in the fuse box with my finger :(. Thankfully, I used one hand and one finger, but it was still unpleasant. I have since convinced my family there to replace the damn fuse box with a breaker box, much easier and safer.

[Stewie007]

I've been zapped by 120V. Went to unplug an extension cord at a friends house and the wire was exposed and all frayed at the plug. Man, I could feel it shoot through my nerves.

[Thrilla]

How much amps does lighter ignitors produce? Once I was so bored I was zapping myself on my left arm, found some nerves that triggers my figer movement, quite fun, lol.

Well, once I was fixing a friend's computer at his house, I went to toilet break, came back with damp hands, and started unplugging power plugs. I had my left hand on the carpet, right hand on the switch, trying to pull those big transformers out. Those transformers are hard to get off, so I inserted my fingers under it..... the index finger on my right hand felt some strong currents, so I pulled it out, and it was numb for minutes.

Anyways, does wearing anti static glove help when working with electricity? What's the safest way to discharge a capacitor and does not damage the capacitor? (Direct lead-to-lead will damage the capacitor I think)

[tennvols_69]

battery is DC which is half as dangerous as AC.

this is not entirely true. the killer for electricity is not voltage its the Amperage. as chilly said it only takes 3 milliamps to kill you.it does this mainly by causing your heart beat to become irregular. however with the correct amperage it can stop your heart also. dc is more dangerous to an extent as it is a constant source which is harder to get loose from then AC as AC functions by the alternating peaks on the sine wave, and the change in the wave will make it easier to get loose from then DC. with that being said AC usually has the capacity to carry more amperage which is worse. it really all depends on the circuit. the main thing like chilly said is to try not to work on live circuits, always remove any jewlery watches ect before working on any electronics. i was once shocked by a CRT that had a 41KV charge on it because i had a watch on and i was a foot and a half away from it when it hit me. another thing to remember is not only can caps provide a deadly discharge but also inductors. ALWAYS use the one hand method. and as another precaution never work on electronics alone, never know when you might be needing someone to trip a breaker or pull you from a circuit. when i was in the navy i seen a guy get shocked my a 1amp circuit he seemed fine but due to the rule of if you get shocked you got and get hooked up to a EKG for 24hours hes is still alove today. cause his heart had a fluter which they were able to correct.

What's the safest way to discharge a capacitor and does not damage the capacitor? (Direct lead-to-lead will damage the capacitor I think)
direct lead to lead can damage a cap but not usually. the correct way is to have a probe with a 1MEG OHM resistors in line with it this will discharge the cap properly.

[Unknown_road]

How much amps does lighter ignitors produce? Once I was so bored I was zapping myself on my left arm, found some nerves that triggers my figer movement, quite fun, lol.

Well, once I was fixing a friend's computer at his house, I went to toilet break, came back with damp hands, and started unplugging power plugs. I had my left hand on the carpet, right hand on the switch, trying to pull those big transformers out. Those transformers are hard to get off, so I inserted my fingers under it..... the index finger on my right hand felt some strong currents, so I pulled it out, and it was numb for minutes.

Anyways, does wearing anti static glove help when working with electricity? What's the safest way to discharge a capacitor and does not damage the capacitor? (Direct lead-to-lead will damage the capacitor I think)

lighter ignitors are like a few nanoamp I think.

anti static glove? you mean those things you should use when working with hardware? Don't exactly know witch kind you mean but I no the ones I've seen won't help.
discharging a capacitor can be done with a resistor (make sure you got one with a high enough resistance so you don't burn it). Don't touch the leads offcourse.

@tennvols: I know all that but the current through your body depends on 2 things. 1 your body's electrical resistance and 2 the current a power supply can deliver. Ohm's law states that when resistance stay's the same, higher voltage means higher current. A rule of thumb is (for normal conditions) AC becomes dangerous above 30 volt and DC becomes dangerous above 60 volt.

probably because the 30 volt is rms voltage and not amplitude. and maybe because a sine might disrupt your body's electrical signals more?

[yngndrw]

What's the safest way to discharge a capacitor and does not damage the capacitor? (Direct lead-to-lead will damage the capacitor I think)
For small capacitors, I just short it with a screwdriver. I am yet to damage a capacitor this way. However for larger capacitors, it is advisable to use a resistor.

The formula T = 1.1 * R * C, where T is the total charge / discharge time in Seconds, R is the resistance of the resistor in Ohms, and C is the capacitance in Farads, can be useful to calculate the correct resistor to use. I try to aim for a 2 second discharge time. After the resistor has been used, I then always short with a screwdriver just to be sure.

Hope that helps. :)

[aussie_guy00000]

And moreover the most of the current will choose the fastest way across your body which is along the skin. and a battery is DC which is half as dangerous as AC.

I'm not electrician, but I was under the impression that DC is a lot more dangerous because in the even of an electrical shock, your muscles contract, With AC because the currents alternating (i.e - to +) it's easier to overcome the contraction and let go of what ever you're holding (i.e live terminal). But with DC, it's just straight current and your muscles just contract and stay that way till the circuit breaks. I was also told that with large DC currents (not really experienced in what we're doing) it can be extremely difficult/impossible to turn off the main power switch due to the huge currents passing through it when a short occurs. These are just a few things that my old man told me when I was an inquisative kid (he's an electrician). I might not have remember it exactly, but I believe it's something like that.

[yngndrw]

Yea that was the impression that I always had also, that DC is more dangerous than AC for them reasons.

Was told that by my dad too, who is also an electrician. (For industrial control systems.)

[MeltedDuron]

I was working on an amp a few weeks ago, and somehow touched the live terminal while my hand was resting on the chassis.... I'm glad we have a breaker!

[IYP]

i should be dead, so many times now

the 120v shock last week
that time i touched the lamp post and got the doo doo shocked outa me
the car battery
the cap inside cameras
i used to lick electrical plugs / wires when i was little

god no wonder im so messed up

the disposable camera one is actualy pretty funny....the damned thing jammed up on me...i proceded to crush it with my hand and i got a shock like something out of this world...turns out the flash runs off a 300v cap...dont no the amperage. i ended up marketing those at my school, was great fun...

that 120v shock last week was hell....i couldent feel my own pulse...not sure if it was due to a numb hand or a weak pulse...im fine now tho

heh, gotta be safer bout this stuff

[star882]

the car battery
How did you get shocked from just 12v? Even a 48v phone line can not be easily felt (unless it happens to be ringing), let alone a 12v battery. Unless you cut yourself on the wiring or were soaked in sea water, I can't imagine how it happened.

[MeltedDuron]

I stripped a LIVE phone wire with my teeth a while back... that hurt :(

[IYP]

How did you get shocked from just 12v? Even a 48v phone line can not be easily felt (unless it happens to be ringing), let alone a 12v battery. Unless you cut yourself on the wiring or were soaked in sea water, I can't imagine how it happened.

pool...trust me its a long story

[Thrilla]

I thought phones are like 3v?

[Celeron Gamer]

How did you get shocked from just 12v? Even a 48v phone line can not be easily felt (unless it happens to be ringing), let alone a 12v battery. Unless you cut yourself on the wiring or were soaked in sea water, I can't imagine how it happened.


Sorry to necro, but AFAIK isn't those amps on car batteries friggin' huge? It could be possible to be electrocuted by car bat right?

[Carlz0r]

Sorry to necro, but AFAIK isn't those amps on car batteries friggin' huge? It could be possible to be electrocuted by car bat right?
Battery im getting for my car is 3600 amps peak. So far, I've been shocked by mains wiring three times, shocked by two power supply capacitors (one from my computer, one from my home theatre amp), and once by a phone line.

[star882]

Sorry to necro, but AFAIK isn't those amps on car batteries friggin' huge? It could be possible to be electrocuted by car bat right?
By itself, not through intact skin. It certainly can cause burns, of course, and it can deliver a shock if you cut yourself on powered wiring, but the voltage is too low to put much current through skin.
With the help of an external circuit, it's possible to generate millions of volts from a 12v battery.

On a side note, I remember a time many years ago when I helped my friend Caitlin Williams install a 48v battery for a server room. She said that the "nipples" are covered by plastic caps because it could vaporise(!) a wrench if it shorted the battery. It's gigantic, though (it was about as big as a file cabinet and weighed about 500 pounds). Thankfully, it was on sliders so we just had to push it.

[jinu117]

Well forgot to ground the case and well... electricuted myself again yesterday. Thankfully it was from fingertip to armpit so nothing dangerous really. Can't believe I was playing with live circuit again -_-;

[Celeron Gamer]

heh. I created a small explosion not long ago from accidentally shorting 120V AC

[Xeon th MG Pony]

Well this is old but non the less deadly serious, ALL WAYS USE SOME SORT OF BREAKER OR FUSE on the system its self. I personally use a combo of fuses and breakers.

All ways ensure ground lines with an impediance no larger then 2 Ohms.

[Stabbin]

heh. I created a small explosion not long ago from accidentally shorting 120V AC

Hehe.. Plasma balls are neat looking.:D

On a more serious note, great topic and nice to see it brought back to the top. Safety first. Always.:)



~S~

[SexyMF]

It is the MEN (multiple earthed neutral) electrical system which gets people killed. I don't like it. It means that eveybody has one foot in the grave. The earth is one half of the power system, so it only takes contact with the hot wire to get a zap. For instance if you use a isolation transformer there is no ground - you are still producing an AC voltage waveform but you can safely touch either secondary terminal because there is no potential (voltage) to ground.

If the neutral wire wasn't joined to earth then a shock can only occur is you complete a path between phase (hot) and neutral. If a live wire shorted to case, the case itself would not exhibit a potential to earth, and hence not be a shock hazard if touched. There are odd failure scenarios within a non MEN system.

There are merits to the MEN system but I see it being more dangerous than helpful.

Also, inductors don't hold charge. An inductor will create a voltage spike in the opposite polarity when the voltage is disconnected (back EMF). Car batteries can delivery lots of amperage but lack the voltage to push any significant current through you.

PS// NZ electrical specs call for not more than 1ohm for the ground line and insulation resistance of at least 1 Megaohm