Remember to unplug your machine

[yaksplat]

...anytime that you're working on it 

Last night I was wiring in a relay to disable my audio on the machine (for when it's used as an htpc). I'm just finishing the connections on the 12V side and I had the machine powered off, but not unplugged. I let go of a wire after crimping a terminal on to it and the wire springs across the inside of my cab, landing on a hot 120V connection on the relay. 

A nice blue arc pops. 

I unplug the machine,  finish up, hoping that nothing was damaged.  Plug it back in, turn it on, and nothing....

Fuse blew on the switch on the back of the cabinet and of course I have no spare fuse of that size.  So I bypass the switch and just use an external power strip for the connections and I try again.  Still nothing.

Power supply is dead.

Fortunately I have all new computer parts coming today for the machine as I had planned on replacing them.  But now I'm hoping that nothing else was damaged.


So after I get the new computer in, I'll be adding some non-conductive shields over those exposed terminals, or at least some blobs of hot glue.



Hopefully someone learns from my stupidity. 

[spoot]

Ouch.   But I'm guessing alot of us here has done the same thing.   

[lilshawn]

we all learn one way or another.

glad you are still alive though!

[drventure]

Ouch.

But I'm guessing alot of us here has done the same thing.

What? Well I've never!   

Here's hoping it's nothing more than a PS.

[yaksplat]

Here's hoping it's nothing more than a PS.

Well, I'll find out later, as all of those parts were going to become a computer for the kids.  I've had a PS go, that took out the MOBO that took out the memory and CPU.  Not fun damage to chase.  But a new PS, still doesn't work.  Buy a new MOBO, still nothing.  Buy new CPU, memory error.  Replace the memory and everything works.  Then the result is building an old computer out of new parts. 

glad you are still alive though!

120V won't really kill you unless you seriously arc across your heart. So that's the reason that you should never work with both hands on 120V.

From electricians that I've worked with:
120V hurts
220V grabs and kills you
480V throws you and leaves you sore

So from that point of view, 220vac is the most dangerous.

[DaOld Man]

120 volts can kill you. Ive been an electrician most of my long life, and I have been shocked by a door bell circuit (around 16-20 VAC). But I was in the attic and covered in sweat.
I have also been shocked by a telephone wire (10 VDC to 90 VAC), while laying on the moist ground under the house.
Thankfully, none of my shocks have been serious enough to hurt or burn me. (Although I did get the end of my thumb blistered once by pulling a 200 VDC motor field wire off a terminal. I didnt know the field was still on, and DC will arc like crazy.)
I have heard numerous tales of people working in the hot attic and getting into an open 120 volt circuit and not living.
It all has to do with the current flowing through your body, and if you are sweating, your resistance to the current goes very low.
Also, you can get shocked using only one hand, if another part of your body is touching ground.
Please dont assume that any voltage will not seriously burn you or kill you. (Many people have lost fingers  working on 12 VDC car circuits while wearing their gold rings.)
Im sorry to hear about your short circuit, that really sucks.
But a good rule of thumb is "when in doubt, lock it out". (Or in our case, pull the plug).

[paigeoliver]

I have taken 277 volt before and was no fun. I also got shocked really bad adjusting a Vectorbeam monitor (it was quite a bit worse than the 277 volt was, pain wise).

[lilshawn]

This is a case where being right handed is an asset. If you are left handed and get shocked, the voltage phases right past your heart causing cardiac arrest. You have a better chance being right handed because the volts pass on the other side.


Unless You happen to be bracing yourself with your left hand, in which case it goes right across you (and your heart.)


Pro tip for the day: you you are doing something electrical and have to potential to get shocked, put your left hand in your pocket.

[yaksplat]

The damage found so far:

1 power supply
1 motherboard
(cpu and memory status are unknown)
2 led-wiz boards.  Neither are recognized by the system.  One has bleed between ports if terminals are shorted to ground.  At least all of the leds on the system survived though.

doh...
 

[lilshawn]

120 volts into the 12 volt. yeah thats bad.

i imagine anything on the 12 volt rail is toast.

harddrive (if not a laptop drive)
cd rom

you might luck out with the ram and CPU since they have to run through a few regulators before it reaches them.

well, now's a better time than any to upgrade.

[TopJimmyCooks]

As Da Old Man said, 120V can easily kill depending on the current in the circuit.  So if it drives an appliance motor or other decent load be extra careful. 

Same idea goes for working on pinball games.  If you're under the playfield with tools it's easy to short coil voltage to lamp voltage or switches and mess something up.  turn it off before working then back on to test.

[yaksplat]

Oh yeah, the secondary drive failed as well.  However, the main SSD did not.  It's up and running in the new uber-fast setup.

So, lesson learned.  All exposed 120VAC terminals have been covered by hot glue, just to be safe.

[kahlid74]

Isn't it Amperage that kills though?  Something like .6amps to stop the heart?  Apologies for my noob electrical knowledge.

Glad you're safe though.  Anytime I work with anything like that I always unplug it.  Winds up taking me so much longer on stuff but I'd rather be safe than sorry.

[TopJimmyCooks]

Amps are the unit current is measured in.  I could have used more precise language. 

[BobA]

It only takes 100 ma to stop a heart but for it to be deadly depends on how it is applied to the body.  The more conductivity the less the voltage required.  Sweat, contact area, contact location etc all are factors.

[DaOld Man]

A GFCI (Ground Fault Circuit Interrupter, [your bathroom and outside receptacles]) is set to trip at 4-10 MA, if this tells you anything.

A personal note from Prof. Benny B. Expert:
"A GFCI works by measuring the current on both the hot and neutral wires.
 If the current is different by 4 to 10 MA, it means that some current is going elsewhere, so the GFCI trips, opening the circuit and turning off the power to the circuit. You can test a GFCI by pushing the test button on the receptacle (or breaker), or by putting a jumper wire between the neutral and the ground of the outlet."
So, according to the Prof, if you have some GFCI breakers or outlets tripping intermittently, you may have the neutral and the ground circuits downstream getting together (moisture can do this too.)

[DaOld Man]

The damage found so far:

1 power supply
1 motherboard
(cpu and memory status are unknown)
2 led-wiz boards.  Neither are recognized by the system.  One has bleed between ports if terminals are shorted to ground.  At least all of the leds on the system survived though.

doh...
 

That really sucks man, sorry about your loss.