Electrical Safety

Hello again from the dungeon...

As I start to get into building line-driven power supplies and such, where should I start REALLY being careful? 40V? 60V? 110V? I realize that current is what does the damage, but you don't have it without voltage. (I also realize that other factors will factor).

What is the realistic neighborhood of where I shouldn't be grabbing wires and/or switching out caps or resistors in a live circuit?

The physics and shop teacher in HS talked about 110 AC Line current like it would knock you dead instantly. An electrician that was installing a 208v-->480v step up transformer said "110 won't hurt you at all. It's just enough to scare you a little bit".

I'm not about to strip a power cord and bite down on it, obviously, but he's not the first to say 'I've been bit by 110 a bunch of times. It's no big deal'..

Thoughts?

Reply to
phaeton
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There should be no need to be doing that at all. But if you want a ballpark - anything mains powered (except plugpacks which are ok).

If you don't know the answers to these questions then you shouldn't be playing with mains powered stuff at all. The mains can kill you.

Generally speaking, anything over 50V or so is potentially dangerous and should be treated as such.

Dave.

Reply to
David L. Jones

IIRC, the cutoff for "safe" is somewhere around 60v, which determined the rail voltage for telephone switches or something.

I've gotten bitten by 120v before. It hurt, but caused no permanent damage, not that I'd want to do it again. "Safe" is different than "I got away with it" too - a little current in the wrong place is fatal, especially if it has to cross your chest to get to ground.

As for lower voltages, I've destroyed ICs by inserting bypass caps without discharging them first. Safe for me, not safe for the chips.

Reply to
DJ Delorie

48 volts.

John

Reply to
John Larkin

In , phaeton said

I think do some bit of research into body count or annual body count as a function of voltage.

110-120 volts AC is "up-there", maybe 2nd place to industrial 460-480 volts AC or so. Body count of 110-120 volts AC exceeds that from 440-480 volt AC range on US Navy ships among those where both of these voltage ranges are present.

I suspect that 110-120 volts AC at 50-60 Hz has a high body count due to high carelessness due to survival rate of shocks from 110-120 volts AC

50-60 Hz being high, though short of 100%.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

Sorta like the drunk: "I've driven home from the bar while totally sloshed a bunch of times. It's no big deal."

Or the guy who never wears his seat belt.

Or the cyclist or biker who never wears a helmet.

It only has to be a "big deal" one time.

But even at low voltages, there is a good reason to switch things off: If you work on live equipment, sooner or later you will slip and short something and let the magic smoke out. (Ask me how I know this!)

Best regards,

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

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Reply to
Bob Masta

I was surprised by some of the answers given.

First off, disregard the notion that 120 volts can't kill you. The effect it has on you depends on many factors, such as whether the current passes through your chest (i.e., heart), and how much current passes through your body. The latter depends, for example, on whether you are an older tradesperson with calloused, dry fingers.

But if you have soft, moist fingers and contact high enough voltages (definitely less than 120 volts), you may easily pass enough current to kill. The point here is not that you need to measure your skin moisture, but rather that you need to have a good understanding of Ohm's law and why someone might escape direct "contact" with lethal voltages.

Statistics show that even among experienced industrial electricians, the greater cause of injury and death is the consequence of massive muscle contraction causing falls from ladders, or being thown violently into some deadly object.

I would try to learn a great deal more about the dangers of working with high voltages before attempting to do so. Do a Google search on some of these issues and consider soliciting opinions from the deceased to balance those available from the fortunate! ;-)

Chuck

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Reply to
Chuck

Bear in mind that it isn't just a case of being directly harmed by the electricity itself. Even 50V can give you enough of a "surprise" that you reflexively pull your arm away and ram a soldering iron into your face or send a tank of FeCl3/NaOH/etc flying.

I've been bit by 240 a bunch of times (in the UK, where 240V is 240V above ground, not +/-120V). At least one of those was the "bad" case: right hand on the live, left hand resting on the grounded chassis. Mind you, that was when I was 16-17, young and healthy; the consequences might be a bit more serious these days.

Reply to
Nobody

Here in Britland we have an old saying,

"It's volts that jolts But mills that kills"

Reply to
Anonymous.

Ah, we do tend to forget that fact (it's not 240 a.g. here in the USA). But touching 480 3-phase (what's that a.g.?) "got my attention".

--
Dr. Leonard. H. McCoy
"I\'m a *doctor*, Jim, not a *magician*!"
Reply to
Dr. Leonard H. McCoy

And if it has high current capability it can have nasty interactions with jewelry. By brother bears a scar on his wrist from a metal watch band that got shorted (thanks to a wrench) between a truck battery and ground. That was just 12 volts, but it stripped the skin off his wrist underneath the segmented metal watch band.

--
Tim Wescott
Wescott Design Services
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Reply to
Tim Wescott

Ours are still 240V line-to-line, though -- grabbing one hot lead of a US 240V circuit in each hand is every bit as dangerous as grabbing the hot lead of a UK 240V circuit in one hand and the neutral in the other.

--
Regards,
        Doug Miller (alphageek at milmac dot com)
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Reply to
Doug Miller

In the US, it is:

There are some old electricians, There are some bold electricians, But there are no old, bold electricians.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
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Reply to
Michael A. Terrell

Just today i was bitten by 240v twice. As long as you dont actually grab hold of a wire, its fells and acts like a warning to to stay away from the hot wires. Any time I have to work on a hot circuit, I have learned not to grab things, and use proper insulated tools. And any time you let your attention slip a little bit, you get a stinging lesson to re-train your reflexes. :) It also sometimes causes nice sparks. Oh, and make sure your footware is isolating you from ground.

Reply to
Sjouke Burry

Here in the states, 50 Volts or more, you're in a whole new world.

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
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Reply to
Jamie

Now.

Good Luck! Rich

Reply to
Rich Grise

Well, if he can drive safely, it's not.

That's trivial: Look in front of the car. If there's something there, don't go there.

Oh, feh. This is just too much. A helmet on a freaking BICYCLE?

You're supposed to learn how to ride the bike so that you don't fall on your head.

Cheers! Rich

Reply to
Rich Grise

Since I do a lot of bike riding for delivering delivered restaurant food, I have to ride bikes while being a restaurant worker. That is my "day job" and I am an engineer as my side job since I have some need to make my living from my brain only about 15 hours per week, so I have to make my living from my feet quite a bit. Restaurant workers and those juggling 2 lines of work due to brain load issues should be expected to have "senior moments" at any age.

I expect that most who do major work or major commuting with a bicycle are only a step or 2 better off - as in still having *some* vulnerability to a crash where a helmet makes a difference in brain injury outcome.

For this matter, about a year and a half ago I did suffer a crash that had me landing on my head. First time after maybe 1/4 million miles of cycling. Prior to that I had a crash resulting from a minor brief brain lapse where I failed to avoid a smallish known obstacle and went flying and my head missed a tree trunk by only about 10 inches (about 30 cm).

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

Then again, I guess there's no sense protecting anything that isn't getting used anyway...

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

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Reply to
Bob Masta

I work around 480V, but I've heard 12V can kill if there's enough current available. I had to spend a whole day watching videos of arc-flash accidents.

When I was a kid, I got my pinkie stuck on 120V. Since it was just a trickle along one finger, it didn't hurt me, but DJ's advice is important: "Safe" is different than "I got away with it" too - a little current in the wrong place is fatal, especially if it has to cross your chest to get to ground.

--
Al in St. Lou
Reply to
Al in Dallas

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