12v outdoor vs 110v outdoor vs OUCH!

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Old 05-20-02, 01:37 PM
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BobCrane
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Question 12v outdoor vs 110v outdoor vs OUCH!

Please help my feeble mind.

The 12v systems advertise better safety for people and less power req than a 110v system.

However, if I do the math, won't a 50 watt 12v light require 4 amps of power vs. a 50 watt 110v requiring 500 milliamps? Or am I doing something wrong with the math.

I understand that 12v is not going to get a hold of you like 110, but high current in whatever state is gonna knock your socks off.
 
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Old 05-20-02, 03:47 PM
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The two good parts of 12V lighting vs 120V is the transformer and the transformer.
1st, the transformer significantly reduces current let through to the cirucit during a fault by it's internal impedance.
2nd, the transformer reduces the voltage to the circuit. Current equals voltage divided by resistance. So the lower the voltage, the lower the current. Hense, somewhat safer.
In the right situation, I beileve the 12V lighting could give you a good hurt, anyway.
Keep in mind that you could put you tounge across a 9V battery and survive (not burn your toungue), for similar reasons.
 
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Old 05-20-02, 06:28 PM
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Wgoodrich
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Power and volts are the same thing.

Less amps used whether 110 volt or 12 volts through a transforemer equals less lumen output experienced.

If you are looking for safety from shock install a GFI protective device on your 120 volt lighting.

If you install 12 volt system you are limited to excessive distances and to excessive light output limited by the ability of the transformer to carry much more that 10 watts per light bulb where 120 volts can go longer distances and limited to up to 20 - 100 watt bulbs depending on the watt rating of your light fixture watt rating.

GFI protection should help with your safety concerns.

Good Luck

Wg
 
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Old 05-20-02, 06:41 PM
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First let's clarify your terminology:

50 Watts is power
12 volts or 120 volts is voltage
4 amps or 110 milliamps (mA) is current

You are correct in one sense: 4 amps of current flowing through your body would give you quite a jolt (most likely fatal). However, there is no way 12 volts is going to push that much current through your body.

Why?

Resistance. The 12 volt transformer can push 4 amps through a 50W light because the light has a resistance of 3 ohms. The resistance of an electrical path through your body is dominated by the resistance of your skin. Dry skin has a very high resistance of several hundred kohms (several hundred thousand ohms) so that even 120V causes a shock but far less than fatal current. When wet, your skin resistance falls to about 1000 ohms, so the 120V allows 120 mA (70 mA will interfere with breathing, 100 mA will cause fatal heart fibrillation), but 12V still allows only 12 mA. Shocking, but not dangerous.

Note: your skin is rarely completely dry, so the 100+ kohm number cited above is unusual. 20 kohm is frequently used as an "average" skin resistance.
 
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Old 05-20-02, 06:42 PM
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Power and volts are the same thing
Say what? I realize Wg that we sometimes take license with the truth in order to simplify things, but this goes a bit too far.
 
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Old 05-21-02, 05:39 AM
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BobCrane
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Thank you for all of your replies. Never factored in resistance of body vs bulb for safety.

Thanks also to the person who put some definitions with my terminology. One or two of the answers implied some confusion. :)

Bob
 
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