Your wrong there. DC is much more dangerous. I don't mean for the body. I mean for short circuit faults. Have you ever dropped a spanner across a fully charged car battery. No, well I have. It's not pretty. DC shorts can take your arm off. AC will just hurt or if your unlucky kill you at the same currents. That's why DC is used in welding and not AC. Because AC will just go through the metal and not arch like DC.

DC caused too many fires and that's why it's not used in transmission lines.

Larry

 

rezer, I'm sure it will depend on 10 types of takers.
But I'll cast my vote for AC being safer.

But make no mistake, both can kill you easily. Your heart only requires 35mA to make it on or off, depending on its current state.

 

I don't know where you got that titbit. But it only takes 6mA AC across the heart to stop it. I think you mean 35ma between arms maybe.

However my point was DC is much more likely to cause fires and sparking than AC at the same currents.

Larry

 

[quote=Larry4911;339846]I don't know where you got that titbit. But it only takes 6mA AC across the heart to stop it. I think you mean 35ma between arms maybe.

However my point was DC is much more likely to cause fires and sparking than AC at the same currents.

Larry[/QUOT



Ooooooh, I see

Muhammad89

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At the same potential and impedance, the safety concerns for AC or DC should be considered equivalent. Respect both as neither care a bit about your safety

Lefty

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It's also depending on the frequency of the AC voltage

if the frequency is close to man's avarage heart beat rate (60 a 70 Hz) than the chance it will disturb the heart beat is pretty big and more lethal than just a DC voltage with the same values

of course it starts all about 63V or higher (that's what I learned on school )

i normaly say every thing lower than 48 Volt is considered safe (not lethal) you still can burn your self and have a not so good time if you are a conductor for many amps at that voltage

Robert-Jan

 

Yes, I have heard the same thing, that frequency plays a big part. Evidently the lower frequencies are far more dangerous than the higher frequencies for the reason Robert mentioned. As far as AC or DC being more dangerous, I was tought DC is "potentially"more harmful.

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Ssshh! You'll give my AC-only 180A stick welder a complex, dude!

DC is used for various reasons: penetration, choice of positive or negative, easier arc control and a greater selection of rods are some. However, AC is still used and is still available on a lot of stick machines--it's easier to build an AC welder, and you don't have as many problems with arc blow.

AC arcs just fine. Ever seen the sparks in a power outlet when you unplug a fan while it's turned on?


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I don't have the "right" answer, but if the above is true (that lower frequencies tend to be more dangerous) then DC should be inherently more dangerous than AC since its frequency is 0. But I've also read the thing about near-heartbeat frequencies being dangerous because they confuse the heart.

This is interesting reading: http://en.wikipedia.org/wiki/Tesla_c...ctrical_safety

Whether AC or DC is worse, I don't really worry about. I'm with Leftyretro--treat it all with respect. Even if it won't kill directly, you can even start a fire with a 9V battery, or get a slight zap, jerk your hand back, and gash yourself on the sharp metal of the hard drive cage because you didn't turn off the computer before reaching in to plug in a fan (happened to me).


Torben

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I don't know about starting fires. I imagine AC and DC are equally bad. DC only tends to be worse because the usual source is batteries which can provide huge currents. At higher voltages AC is probably worse because the peak voltage is higher than the RMS and dielectric heating also becomes a more significant factor.

As far as electricution is concerned I know for a fact that power line frequency AC is more worse than DC. For a start the peak voltage is 1.414 times higher (this should be pretty obvious) as it interferes with the heart beat more than DC.

http://www.allaboutcircuits.com/vol_1/chpt_3/2.html

The electrical code in the UK allows much higher DC voltages than AC voltages in situations where people might be electricuted e.g.

Any conductors with a greater potential difference (which respect to each other or earth) greater than 60VDC or 25VAC in a dry area or 30VDC or 12VAC in a wet area (damp skin is much more conductive than dry skin) need to be insulated from the user.

Any appliance with a only basic insultion between the user and the live parts does not require an earth conductor if it's operated with a voltage below 120VDC or 50VAC.

These aren't exact quotes, just what I can remember from the 17th edition of the wiring regulations.

I think this is a pretty dangerous myth which needs to be crushed as someone might incorrectly assume that 50VAC is pretty safe because 48VDC is and be electricuted as a result.

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I also have to agree AC is safer, IN A WAY. As alot of people know, say if you grab onto a peice of wire being fed AC, most people know that your muscles will contract, and cause you to grip the wire! With AC, you have a small chance of actually getting your hand off when the voltage is 0. With DC, there is no 0V point, so your hand is pretty much stuck there. AC is also dangerous in its own ways. like the heart fillibration stuff. AC is more likely to fillibrate your heart than DC, since its more like pulses. And also, AC arcs just as good as DC! Maybe the DC causing more fires/arcing was because there was no low point in the voltage, where the arc could possibly exinguish.

Interesting thread!

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Although you have a point this doesn't make as much difference as you might think because the zero crossing time is so short it doesn't give you much chance to let go.

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Transmission losses are much the same for DC and for AC at the same voltage.

AC is usually used because it is so much easier to transform the voltages with AC.

The power grid generators run at 35,000 volts or so, but the voltage is stepped up to 400,000 V or 132,000 volts for transmission on pylons, then down to 33,000 V, 11,000 V, and so on depending on what the final voltage is. All those voltage changes are much easier with AC.

AC motors are also simpler and can be made without brushes or electronics.

For undersea cables, the capacitance of the cable makes AC more lossy so DC is used, but at very high voltage. It also has the advantage that a DC link can join two networks of different frequencies or ones that are not synchronised.

http://en.wikipedia.org/wiki/HVDC_Cross-Channel

 

Sorry guys but that's dog pucky! All things being equal in that we are talking about the same voltages and currents vis-à-vis RMS equivalence, then AC has more transmission losses than DC. Clearly you guys have never heard of AC Effective Resistance.

And in any case it's current not voltage that is often the higher function of specific losses due to I squared Z.

 

Not so! In one major way DC is more difficult to work with.

Given the same heating effect when making the comparison, and given the same volts and amps when making the comparison, the DC arc will be herder to quench than the AC arc. Thus the switch gear and arc suppression must be more robust for the equivalent DC system.

Why you might ask? Because DC is steady state yet AC falls to zero twice per cycle.