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Lockout-Tagout

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Re: Lockout-Tagout

#71

Post by ttsda »

jjeaff wrote: post #50
lb1lf wrote: post #43

Earlier quoted context omitted.

-During the annual EE safety refresher course I take at work, the instructor makes a point of the fact that during domestic work, the electric shock is often merely the trigger for the real injury; you get zapped, then fall from the ladder you were on or whatever. (We have 240VAC mains, but I guess an unexpected jolt of 110VAC would be sufficient to make me jump...)

110v or 240v will kill you dead where you stand. But it's not really about the voltage. The higher the voltage, the easier it is for the electricity to ground out through you. But it only takes a few milli-amps across the heart to kill you. A household line can deliver 10-20 amps. Luckily, human skin is not highly conductive and neither are rubber soled shoes. So if you are taking proper precautions and not kneeling…

It's impossible for a 240V outlet to deliver 10A through your body. Unless you're made of metal or something.

Re: Lockout-Tagout

#72

Post by Qwertystop »

taneq wrote: post #46
unlinked_dll wrote: post #41

Earlier quoted context omitted.

I've gotten burned by changing light bulbs without turning off the switch; garnering me the nickname "Uncle Fester" by my family (in my defense - the light bulb was out and I wasn't thinking) and that shit definitely hurts. I've also been burned debugging a power supply for a GSM amplifier used in the test harnesses for a semiconductor fab (this time was carelessness, the power supply rails weren't taped off since I…

Burned or zapped? Light bulbs get thermally hot but glass is non-conductive. I haven't personally been bitten by 240V but from people I've talked to who have, I don't intend to chance it happening.

I'd guess you could get zapped if you accidentally touch the metal part of the bulb (or the socket) while unscrewing the old one or screwing in the new one.

Re: Lockout-Tagout

#73

Post by dsfyu404ed »

michaelt wrote: post #54
jjeaff wrote: post #50

Earlier quoted context omitted.

110v or 240v will kill you dead where you stand. But it's not really about the voltage. The higher the voltage, the easier it is for the electricity to ground out through you. But it only takes a few milli-amps across the heart to kill you. A household line can deliver 10-20 amps. Luckily, human skin is not highly conductive and neither are rubber soled shoes. So if you are taking proper precautions and not kneeling…

> 110v or 240v will kill you dead where you stand. In my experience, when encouraging people to follow safety rules you get better results with true examples that justify the rules than with exaggeration like this. If you tell a person one thing they know isn't true, they're liable to start thinking the other things you tell them aren't true. 240v might kill you if you're up a ladder, elderly, have an undiagnosed hea…

>In my experience, when encouraging people to follow safety rules you get better results with true examples that justify the rules than with exaggeration like this. If you tell a person one thing they know isn't true, they're liable to start thinking the other things you tell them aren't true.

As someone who comes from a compliance/human factors background I absolutely hate internet discussions of safety. They are chock full of people exaggerating everything for up-votes/likes/virtue points and while within a given community that may increase compliance it is the exact wrong way to increase compliance from people who are working under a different set of incentives.

Re: Lockout-Tagout

#74

Post by TheCapn »

RandomBacon wrote: post #12

Always verify the equipment you are working on is still physically LO-TO. I heard a story about one person who LO-TO a breaker on Friday, and Monday it had power when he went to work on it. The guy went to check the breaker, and the breaker was sitting on the ground with the lock still attached, and a new breaker in its place.

Always verify the motor/equipment you're locking out is prevented from running! Coworkers and I were just dishing commissioning job horror stories where folks get too antsy to run their facility and start bumping motors while people are still working elsewhere.

Just because that breaker is labelled to run a specific motor, unless its been verified, it might be wired to the wrong motor, or the labelling is wrong or any other host of oversights.

Had a manager come in, and run his motor. The electrician who was elsewhere in the facility straddling a auger watched it suddenly spin beneath his feet because the lock he put on a breaker was not physically wired to that motor (had not yet been tested).

Lots of horror stories from that particular site. Always verify YOURSELF. Don't trust other people's word

Re: Lockout-Tagout

#75

Post by dreamcompiler »

roenxi wrote: post #37
taneq wrote: post #28

Earlier quoted context omitted.

Honestly if our mains was 110V rather than "240V" (read 250-260V thanks to all of the rooftop solar in our area) I'd probably be a bit more casual about it. I've been nipped by ~100V from poor earthing and it's not that bad. 240V hurts.

I've no particular experience working with electricity so maybe you just know what you are doing - but at risk of being a know-it-all on the internet that is not a very safe approach. In an industrial setting any electricity related accident is cause for a trip to the hospital no matter how minor. For starters you don't want to be casual about 110 volts [0] and for seconds the systems that control heart rhythm use el…

You're right. When I was young and stupid I did wiring repairs on 110v circuits without bothering to switch them off. I got shocked a lot, but now that I'm older and smarter I know I just got lucky.

Re: Lockout-Tagout

#76

Post by dreamcompiler »

JoeAltmaier wrote: post #56
kozak wrote: post #55

Earlier quoted context omitted.

Can someone please point me to details of a biological mechanism that can cause someone to die hours after having seemingly survived an electric zap just fine? I never thought such things are possible.

There's a term ambulance drivers use, "Walk, talk and die". For victims of car crashes that got a hard knock to the head. A brain bleed in the brain stem (if I'm remembering it right) will build up pressure until the stem suddenly disconnects. Not electrical, but such syndromes seem to be real.

It's quite real. This is why we try very hard (everything short of kidnapping) to take people to the hospital after a bad car wreck ("high energy mechanism of injury" is the term we use) even if they're walking around saying they're fine.

Re: Lockout-Tagout

#77

Post by vorpalhex »

fargle wrote: post #40
ebiester wrote: post #13

Earlier quoted context omitted.

How would you recommend people working on their own house implement anything more than turning off the circuit breaker? (I'm not doing anything electrical in general, but sometimes small fixes are necessary for home owners.)

Simple answer: close the breaker box lid and put a cheap padlock on it. You don't need a tag or special clip. That ensures that your wife or roommate doesn't try to flip the breaker back on while your arm is in the garbage disposal or you are holding the hot wire with your teeth. You can and should use a test light or DVOM to verify the power is out. You can and should treat the wires as if they were "hot" anyhow. Yo…

I uh, have been guilty of similar lack of safety protocols in the distant past. I fortunately learned my lesson by shorting a $900 AC control board and not shocking myself, but needless to say it really is worth taking the time to do it right.

Re: Lockout-Tagout

#78

Post by kube-system »

dreamcompiler wrote: post #76
JoeAltmaier wrote: post #56

Earlier quoted context omitted.

There's a term ambulance drivers use, "Walk, talk and die". For victims of car crashes that got a hard knock to the head. A brain bleed in the brain stem (if I'm remembering it right) will build up pressure until the stem suddenly disconnects. Not electrical, but such syndromes seem to be real.

It's quite real. This is why we try very hard (everything short of kidnapping) to take people to the hospital after a bad car wreck ("high energy mechanism of injury" is the term we use) even if they're walking around saying they're fine.

Adrenaline is a heck of a thing. I know someone who similarly said they were fine and wanted to go home after being hit by a car. They had fractured vertebrae and their spinal cord would have likely suffered permanent damage if it wasn’t immobilized as soon as it was.

Re: Lockout-Tagout

#79

Post by habnds »

dgemm wrote: post #39
taneq wrote: post #9

After working in mining for a long while, where this kind of isolation procedure is standard and is taken very seriously (pretty much any breach of procedure is an instantly firable offense) it's terrifying coming back home and seeing people working on house wiring etc. with nothing more than a turned-off circuit breaker protecting them from electrocution or other injury. I've seen some trades start to pick up isolat…

I worked in mining as well and it's often terrifying watching the stuff that goes on all day at every urban construction site, even the things you can see from street level. Construction workers that stand directly below suspended crane loads in order to guide them down to the ground is something I see constantly and makes me nervous just to watch. If you tried anything like that at any of the mines I worked at you w…

My experience has been that the divide in culture tends to coincide with union/non-union workplaces.

Re: Lockout-Tagout

#80

Post by wlesieutre »

6nf wrote: post #53
jjeaff wrote: post #50

Earlier quoted context omitted.

110v or 240v will kill you dead where you stand. But it's not really about the voltage. The higher the voltage, the easier it is for the electricity to ground out through you. But it only takes a few milli-amps across the heart to kill you. A household line can deliver 10-20 amps. Luckily, human skin is not highly conductive and neither are rubber soled shoes. So if you are taking proper precautions and not kneeling…

> But it only takes a few milli-amps across the heart to kill you. A household line can deliver 10-20 amps. 10-20 amps? Not across your skin! Usually a 220V zap at home won't cause instant death.

That's the point made in the line after your quote

> Luckily, human skin is not highly conductive and neither are rubber soled shoes.

Could also note that depending on your circuit breakers, a short circuit will continue delivering higher than its 20A rated capacity for some time until the overcurrent protection goes off.

Thermal breakers won't react as quickly to overcurrent as thermal magnetic breakers, so it depends on what kind of protective equipment is installed.

EDIT: some reference on circuit breakers https://www.se.com/ww/resources/sites/SCHNEIDER_ELECTRIC/con...

> For example: based on the curve on page 3, an iC60 circuit breaker of curve C, 20 A rating, will interrupt a current of 100 A (5 times the rated current In) in: 0.45 seconds at least, 6 seconds at most.

6 seconds is a pretty good chunk of time for a 20A circuit to happily be delivering 100A of current.

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