# Voltage, Wattage

Discussion in 'The Projects Forum' started by Lightfire, Mar 27, 2011.

1. ### Lightfire Thread Starter Well-Known Member

Oct 5, 2010
690
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OK, here we go. Let's start first with voltage.

Which is more lethal, 240 volts AC or 240 volts DC? Some of my friend tells that 240 volts DC is more dangerous. So, which is more lethal and why?

What does it mean if the wattage of my bulb is high? Is it means it's bright if the wattage is high? I have read somewhere, the more wattage the more heat it will produce? Is it true? Why?

Thanks!!!

Mar 6, 2009
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Mar 6, 2009
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4. ### wayneh Expert

Sep 9, 2010
12,390
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My guess is AC. Both have the same force driving current through a given resistance. But with DC, anything that can be polarized sets up a voltage drop. AC would undo that and potentially wreak more havoc. Back in the history of electricity, Edison argued for DC as safer than AC backed by Tesla. He (Edison) backed an execution using AC, to further his argument. It worked, but had the perverse impact; everyone saw that AC was a good way to deliver high power.
For a given technology and thus efficiency level, yes, wattage and brightness are proportional. Such comparisons fail when comparing technology, LED versus fluorescent vs incandescent.
Always true that some power will be lost to heat production instead of light energy. Some techs are better than others, but none can avoid that truth.

Dec 26, 2010
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It is hard to explain Wattage without first talking about energy. In simple terms, energy is a measure of the difficulty of accomplishing some change, like raising a weight up a certain distance. Energy could be said to be like the currency (money) of physics.

Wattage is a measurement of power, which is the rate at which energy is used up. That is pretty much a measure of how much it will cost to use an appliance for a given time. A higher wattage bulb will run your battery down more quickly than a lower wattage one.

Wattage also tells us something about how much an appliance can be expected to do (for instance, how much light your bulb might give). Any light bulb also generates heat, because only a little of the energy it uses is converted into light. A large part of the energy turns up as heat, and we would expect a high wattage bulb to make more heat than a small one.

When we say that some types of lamp are more efficient than others, we mean that more of the energy turns up as light (measured in lumens). This is very important to you if you are trying to economise on power. For instance, a good modern white LED may give more light output than an ordinary filament lamp.

6. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
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Your comment reminds me of this story:

John

7. ### Wendy Moderator

Mar 24, 2008
20,772
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In the beginning, there is Ohm's Law. It is the first thing anyone wanting to learn electricity needs to learn. Because how science evolved, the letters used in the variable don't really make sense in a modern context.

V = I / R

V = Volts, also known as Electromotive force, E is often used in Ohm's Law instead of V
I = Current, in amps
R = Resistance, in ohms

Simple algebra will allow you to figure out an unknown value if you have two.

Have you had algebra yet? If you haven't, do you understand some of it?

V = I R
R = V / I
I = V / R

The power equation is very based on Ohm's Law. You can use Ohm's Law to fill in details of this equation. The base power equation is

P = V * I

P = Power in watts
V = Voltage
I = Current in amps

Using Ohm's Law and algebra these equations are also true.

P = V² / I
P = I² * R

If you can understand and use these equations, you will find many concepts in electronics much easier.

Resistors all have wattage ratings. They are designed to get so hot, and can fail if pushed beyond their limits. This is one major application of the power equation and Ohm's Law.

8. ### ifixit Distinguished Member

Nov 20, 2008
639
110
Hi Lightfire,

With a 240VAC source you could potentially (pun) be exposed to 340 V peak. The higher voltage could breakdown insulation protecting the human exposed where as 240 VDC may not.

On the other hand, a DC shock, received through the muscles, is much more difficult to let go of because the current is continuous rather then AC in which the current is interrupted every few milliseconds providing an opportunity to let go.

Keep one hand in your pocket at all times
Ifixit

9. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
909
Please review the thread linked to by t_n_k (#2) above before launching on a bunch of untested and most likely wrong theories regarding relative safety of AC and DC.

That thread resulted from a question regarding electric shock in the ebook. A lot of effort was put into researching the answer by several of us. Simply put, there is very little comparative data. Simple comparison of number of deaths from AC vs. DC shock does not account for exposure differences and non-reported shocks.

As for all of this business about which type causes the subject to freeze vs. retain ability to let go, there are some data on non-lethal shocks:

That result, while interesting, does not show relative risk of death or serious injury.

John

10. ### bribri Member

Feb 20, 2011
133
5
getting a jolt can cause injury because of involuntary muscle contractions...
a hand which recoils and hits something sharp for example.
or even having tools in hand can do damage in the event of a shock.

oh wow, there's some freaky stories there.
...
i actually worked on 180KV transmission-lines for a while.
well just on the actual poles thank you very much. but that didn't stop our boss from going through the whole list of scary mishap stories 0.0
he also mentioned that in the unlikely case of a wire coming down, we were advised to 'hop' away on one leg.

11. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
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Which one? Why?

John

12. ### bribri Member

Feb 20, 2011
133
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you mean "which wire?", "or which leg?"
i never bothered to ask. i really don't think that it matters.

and why?
well the reasons had to do with trying to not get killed ; )

...but it was something about the power going up one leg and down the other.
perhaps resulting in the projection of different parts of your body in different directions to one another..
but i don't know what would happen, didn't ask... in light of some of the freaky stories i chose to assume that: it would be bad to touch the wire.

we were also not allow to work if there were lightening storms around. not a rule in the mountains apparently, but on the prairies, not allowed.

13. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
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Frankly, it sounds to me like made up advice. As to "which one," I meant which leg.

Now, why would hopping on one leg be better than hopping/running/skipping on both or alternate legs to get away?

Your comment just doesn't make sense, even though you attribute it to someone else..

John

14. ### bribri Member

Feb 20, 2011
133
5
so you think that electricity-co contractors just make-up advice?
you've made a truly bizarre statement here. i can't tell whether you're just trying to pick on me, provoke a verbally strong reaction or what.

well if you think it through, a downed wire can energize the ground. a difference in voltage on two different parts of the ground, contacted between two different parts of your body could be bad news. maybe running would be fine, i don't don't know, it might get you away from the source... but your feet would tend not to lift particularly high off the ground in a normal run. i've been lead to believe that higher-voltages tend to jump gaps.

look it up and let me know what you find out.

15. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
909
Advice from a nameless supervisor with an unknown company at a indefinite time just doesn't create an air of credibility for someone who admits to arguing for the sake of arguing.

If you have facts to present, please do. Otherwise, your advice is silly and potentially deadly to someone who needs to escape such an accident site quickly.

John

16. ### beenthere Retired Moderator

Apr 20, 2004
15,815
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Let me save you both the trouble - http://electricsubstationsafety.com/photo3.html

I might suggest some less edgy encounters in the future.

17. ### bribri Member

Feb 20, 2011
133
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i admit to standing my ground when challenged. call it what you want.

i'm just relating some common wisdom. 'facts' if you will. the burden of proof lies upon you my friend.

but since i've been called out...

18. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
909
Thank you beenthere for the reference. A shuffle sounds reasonable or even a two-legged hop. Many people find it difficult to hop on one leg controllably. It is a common test in physical diagnosis. Falling on one's hands while trying to hop on one foot sounds like one of the worse positions to be in.

John

Feb 20, 2011
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20. ### Lightfire Thread Starter Well-Known Member

Oct 5, 2010
690
21
OK OK.

AT Bill_Marsden, I knew already about Ohm's Law. I have read it somewhere... No, I don't know algebra yet.

OK, guys, for example, my two fingers got touched the two terminals of a 240 volts line. :O: 000____0000... What would happen? Is it possible for me to die quickly because my body will short-circuit? DDDDDDDDDD