Touching low voltage cables

[eonibm]

Why is it that you can touch a 12V low voltage cable and not get a big shock but you'll really notice touching a 120V with cable with 6-9ma running through it? Does that mean it's not the number of amps running through as system but the voltage of the system? I read something about the human body being a conductor in the 12V range so that's why we can touch 12V cables without being harmed. Does that mean a 12V cable with 30 amps running through it would not harm us if we touched it? Or is there a maximum amp limit too?

Can anyone shed some light on this?

[clighting]

You have to think of the voltage as the electrical pressure as in a hose. With a 12 volt system there is not enough "pressure" and we are not a good enough conductor to let the voltage pass through us in a noticable way. As the voltage increases so does its ability to pass through things of verying resistances. Amperage on the other hand is different. It does not come into play by simply touching a wire. You need to be in line with a given load. Like for instance if you had one side of your circut tied in at your transformer and you were connecting your common to its terminal with the transformer on. Now you have to be touching the wire with one hand and the terminal with the other. If you made a good connection in both instances you would then be carrying the load of that circut through your body. The neutral or common in any circut is forever seeking ground and if you happen to be the path of least resistance, it will use you. Trust me it's no fun.

[SteveP]

In defense of the safety of low voltage lighting I did extensive research reviewing the past 20 years of OSHA, medical and engineering records on the subject. Here's a quick summary of the findings:

1. In the past 20 years there are no records of any serious injury or death resulting from contact with conductors carrying less than 30V.

2. A widely respected organization, the International Electrotechnical Commision (IEC), has recently concluded studies on the effects of low voltage shock on humans. They concluded that there is no risk of death with any current under 30 mA.

3. To calculate the mA exposure of low voltage lighting, you need to consider two things – voltage and resistance. The highest voltage we encounter in landscape lighting is 22 volts. The applicable resistance is the path from the conductor to the hand through the body to either another conductor or through ground. The lower the resistance the higher the amperage going through the body. A reasonable (but unlikely) worst case scenario would be grasping a terminal block (say, a common) in one wet hand and the 22 volt terminal in the other wet hand. The resistance going from hand to hand would be approximately 1000 ohms. Since Current=Voltage/Resistance, this worst case scenario would result in a current of 22 mA (well below the danger threshold of 30 mA).

4. A more likely scenario would be touching bare wires (at 22 volts) with wet bare fingers - this would result in in a current of around 2 mA (just above the 1 mA threshold of a tingling sensation.)

5. Touching two wires with dry hands (at 22 volts) results in a current of 0.02 mA.

6. Lastly, to address the question of the effect of wattage load on the system in terms of shock extent. System load should have a negligable effect on the current that passes through the body.