[SOLVED] Conductivity of Marble floor

[DasPreetam]

Okay, when I'm using a Neon Line tester (The screwdriver ones), I need to stand barefooted on my marble floor in order to make the neon bulb glow. Does this imply that the marble floor acts as a conductor between me and the ground/earth ?

Also, will the same line tester work on an isolated power supply ?

 

[betwixt]

Basically yes.

Those neon testers only pass a very tiny current, in fact so small that it isn't considered dangerous. Some current has to flow though before the neon lamp will start to glow. The path current normally flows is from the live (line) voltage, a high value series resistor inside the screwdriver, then one side of the neon lamp. The other side of the neon usually connects to a conductive rivet or a clip at the end of the screwdriver. The current from there has to flow to a lower potential, typically ground, either by body resistance or body capacitance. Marble is a relatively good insulator and so are your shoes, together they are not allowing enough current to flow to make the neon light up.

Brian.

 

[DasPreetam]

But the bulb doesn't glow when my slippers are on ! As per your answer, the bulb should glow even when my slippers are on because my slippers are at zero potential.

 

[chuckey]

Your rubber/plastic based slippers are a good insulator. Marble is normally a good (ish) insulator as it was used in switch boards in the 1920s, but I suspect yours has a layer of moisture/polish/grime on it to make it some sort of conductor. The current for a weak glow would be in the order of 50 micro amps, as the neon needs about 90V across it to make it work , means that (230 -90)/50 meg ohms would be the resistance, say 3 megohms. A brilliant glow would be a current of 1mA, so the neons have an inbuilt resistor of 250K - 2 M.
Frank

 

[betwixt]

...and how do you know your slippers are at zero potential?

If the neon doesn't light up it means there is either no voltage across it or a voltage too low to make it operate. As you are connecting the screwdriver to a high voltage and there is little voltage scross the neon, the conclusion has to be that your feet are 'live' and the slippers/shoes are insulating you from the real low voltage. Although having live feet may sound funny, it really is what is happening. If you don't believe me, connect an AC voltmeter between Earth and your toes, either you will read a fairly high voltage or the neon will light, indicating the meter itself is conducting current away from you.

Brian.

 

[DasPreetam]

Okay I get it... My concept has been cleared. But either it will give a high voltage or the neon will glow... Why it will give high voltage even if the neon doesn't glow ? Wouldn't it mean that the voltage is too low to light the neon ?

 

[chuckey]

" either it will give a high voltage or the neon will glow... " it?, what do you mean by "it".
Frank

 

[Audioguru]

If your slippers are insulating your toes from ground and you measure a fairly high AC voltage from your toes to ground then your body is picking up (capacitive coupling) mains electricity from the high voltage power lines nearby.
Does a fluorescent light tube that is not connected to anything light up when you touch its connector?

 

[DasPreetam]

@Chuckey : It means the voltmeter betwixt mentioned in post #5
@Audioguru :

Does a fluorescent light tube that is not connected to anything light up when you touch its connector?

No, it will not... Why would it light up ?

 

[Audioguru]

@Audioguru : No, it will not... Why would it light up ?

It would light if you are grounded though a resistance that can be fairly high like your bare feet on your marble floor and the other terminal of the fluorescent light tube picks up (capacitive coupling) a high voltage from high voltage power lines nearby.

My multimeter picks up 300mVAC when one terminal is connected to mains earth and the other terminal is up in the air. But a high voltage power line is about 2km away.

 

[DasPreetam]

Wow.. So the flourescent tube should light up if I live close to the high-tension lines, but won't I get an electric shock ? The current will flow through my bod to reach the ground right ?

 

[Audioguru]

The capacitance coupling the 50Hz from the high voltage power lines to the small end of your fluorescent tube light is very small so not much current will flow through the light and through you to ground. You might not feel it and you will not get a shock. the light will not be bright.