Voltage stabilizer: UPS or constant voltage transformers for regular bulbs?

[Leigh B]

DC current is less dangerous than 50/60Hz AC current.
(Less dangerous, it does not mean safe... Though 120V DC is still tolerated as touchable by safety regulations!)

Sorry to disagree, but that's simply not true.

AC current goes to zero 100 or 120 times every second, giving opportunity to break the circuit.
DC current never goes to zero.

What safety regulators describe 120volts of any type as being "touchable"?
Here in the US any circuit over 50 volts is considered dangerous, AC or DC doesn't matter.

- Leigh

 

[Leigh B]

The stability of the output from generating plants is far better than it was 50 years ago.

That's certainly true, but ...

It does not address the quality of the power at the user's premises.
AC power in the distribution grid is degraded by all sorts of noise, transients, and high loads.
When analyzed with proper equipment, the AC coming out of your wall socket can look very nasty indeed.

- Leigh

 

[AgX]

Sorry to disagree, but that's simply not true.

AC current goes to zero 100 or 120 times every second, giving opportunity to break the circuit.
DC current never goes to zero.

What safety regulators describe 120volts of any type as being "touchable"?
Here in the US any circuit over 50 volts is considered dangerous, AC or DC doesn't matter.

-) There is a vulnerable frequency for the human heart, making it likely to go into fibrillation. Mains current frequency is located in that range.
(Outside that frequency range AC current can be applied without harm, which is used since decades for electrical coagulation in surgery.)

-) Passing zero voltage is of little interest. Though it happens at the moment of touching.
(You likely thought of cramping of muscle and as result sticking to the electrical conductor.)

-) In Germany and other parts of Europe, touchable voltage of max. 120V DC at maximum is tolerated by certification regulations at appliances of general use. That takes into account the typical high skin resistance. For use in damp surroundings or with children that maxium value is lower (12V DC, resp. 25V DC).

-) For instance arc-welding power supplies deliver by design non-loaded voltages of up to 100V DC.
Again, in the special case of working in confined coductive spaces, that voltage must be lower.

 

[NJH]

AgX you will have to elaborate on the above. I am familiar with the EUs Low Voltage Directive and the harmonised standards EN 60950, EN 62368 through my work. The europe wide regulations much like as Leigh describes treat 50v AC and above, or 75V DC and above as hazardous (hence the low voltage directive). Touch current is then carefully tested to determine if an equipment can be dangerous to the end user as there are well established current levels that can cause fibrillation etc.

 

[NJH]

Should add that the most dangerous piece of electrical equipment I have worked with ran at 6v, it was a whacking big vacuum heater used for scientific research, only 6v but the high current probably enough to incinerate anything physically touching it (think like shorting a car battery).

 

[Leigh B]

Current flowing through the heart is what kills people.
It only takes 50 milliamps.

The current flowing through a load depends on the source voltage and other factors in the load.
There's no way a 6 volt source will hurt anybody, regardless of how much current it can produce.

- Leigh

 

[AgX]

AgX you will have to elaborate on the above. I am familiar with the EUs Low Voltage Directive and the harmonised standards EN 60950, EN 62368 through my work. The europe wide regulations much like as Leigh describes treat 50v AC and above, or 75V DC and above as hazardous (hence the low voltage directive).

Please check with
DIN VDE 0100-410 Chapter 414

This is the reference for tolerating accessible voltage of up to 120V DC.

 

[NJH]

Leigh hold a spanner across your 12v car battery terminals and see what happens, I shorted mine to the body work by accident a few years back and burned a 2mm notch out of one of my most used spanners where it contacted the body work. Luckily I avoided getting burned by letting go straightaway, the smoke and sparks was pretty spectacular.

Stunned by the lack of basic electrical knowledge on this forum to be quite frank, we have one contributor who doesn't understand how much damage high current can cause and another who doesn't understand that reasonable amounts of current at not much over 40 to 50v is enough to cause fibrillation.

 

[AgX]

Burns from high current are something complete different than electrical shock.

You can bridge the contacts of any 12V battery by your body and no burn will happen, actually nothing will happen. The resistance of your body, especially that of your skin are way too high.

If you have a good conductor though and a source that can deliver high curent and the conductor being too small to stand that load thermal damage will happen. And if you are near to that you may get harmed by that.


40-50V DC will by no means cause fibrillation.

40-50 AC may cause fibrillation, if the current is high enough. This will not be the case in common situations.
50V AC is even tolerated by the above DIN regulation as touchable voltage.

 

[Leigh B]

Leigh hold a spanner across your 12v car battery terminals and see what happens, I shorted mine to the body work by accident a few years back and burned a 2mm notch out of one of my most used spanners where it contacted the body work. Luckily I avoided getting burned by letting go straightaway, the smoke and sparks was pretty spectacular.

Stunned by the lack of basic electrical knowledge on this forum to be quite frank, we have one contributor who doesn't understand how much damage high current can cause and another who doesn't understand that reasonable amounts of current at not much over 40 to 50v is enough to cause fibrillation.

I'm not talking about protecting tools from stupid technicians.
If you're dumb enough to short a wrench to a car body you deserve a 2mm notch.

My comments were about the safety of HUMAN operators.

Given that I've designed defibrillators and cardiac monitors (EKGs), I'm reasonably familiar with the operation of the human heart.

- Leigh

 

[Leigh B]

40-50 AC may cause fibrillation, if the current is high enough.

Voltage does not cause any physiological problems.
That's why birds can sit on high-voltage power lines.
And why people can touch million-volt van de Graaff generators and only get fluffy hair.

Current through the heart muscle is what causes problems, often fatal ones.

50V AC is even tolerated by the above DIN regulation as touchable voltage.

50 volts (DC or rms AC, samo samo) is considered safe here in the US.
That's why telephone lines operate at 48 volts (DC).

- Leigh