I'm working on a VAN DE GRAAFF generator and I need to connect the bottom comb to the earth ground. But in my country we do not have a ground line . Can i use the neutral line instead and connect the bottom comb to the neutral ?
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2\$\begingroup\$ It would probably help to say what country you're in and if you're not in the US or EU what kind of distribution network you have. \$\endgroup\$– The PhotonCommented Mar 28, 2016 at 15:37
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\$\begingroup\$ Run a cable out the window \$\endgroup\$– Voltage Spike ♦Commented Apr 7, 2016 at 3:33
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3 Answers
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The bottom comb is biased against the bottom housing, and for shock safety it is usual to ground the bottom housing (the base) and consider the top (ball) housing to be the 'live' electrode. That's only a convention, however; electrostatics was practiced for years before grounding stakes and house wiring existed. It is not generally safe to connect your neutral wire directly to the comb, nor to the base. This is because wiring of buildings is not immune to confusions (like, misidentified neutral wires).
Connecting the base through a resistor (1 Mohm) to any available ground is good practice; that's how technicians' antistatic workstations are set up.
If the motor in the base works on AC power, maybe an indirect neutral connection is appropriate There are safety-approved components that can connect the base to the neutral wire, which are usually reliable mega-ohm resistors or resistor/capacitor combinations. These were used commonly at the antenna terminals in inexpensive hot-chassis cathode-ray tube televisions.
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Actually you do not need to connect the bottom of the Van De Graaff generator to ground. But you will need to complete the circuit from the top ball to the bottom in order to get fun sparks.
For example if you use a soup ladle to get a nice spark from the top then the handle of the ladle should be connected to the bottom.
A very convenient sort of conductor to use for connecting the bottom to experiments is a ball-chain. You would never use a ball-chain as a wire for low voltage but it works very nicely for high voltages.
Have Fun!
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\$\begingroup\$ I do not need to connect the bottom comb to the ground ? how is that ? I need an electron supply for the belt ! \$\endgroup\$ Commented Mar 28, 2016 at 16:58
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\$\begingroup\$ @jad_obeid You are making a strange assumption about electrons and where they live. Try putting your hand on the base and hold a round object like a spoon with your other hand near the top. You will see it works fine. You just need a circuit from the top to the bottom of the van de graaf generator, that is all. \$\endgroup\$– Craig KCommented Mar 28, 2016 at 20:43
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That would not be a good idea because you would most likely end up with a broken machine. Since outlets are AC, the "negative" terminal will be positive for the amount of time it is negative. This switching depends on your country. In the US, it's 60 times a second, in Europe it's 50. So not only would it not be a good ground source, you could end up breaking the components in the machine /get some (unintended) nasty shocks. It would be better to simply take a metal rod and shove it in the ground and connect the ground line to that.
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2\$\begingroup\$ I'm sorry, but your description isn't correct. Generally an AC system will have "Line" (or "hot") and Neutral. The Neutral serves as the "zero-volt" reference. It is generally connected to an earth ground at the service feed or at the transformer closest to the house. The Line presents the alternating voltage, which will be both higher and lower than the Neutral. Now, if the OP has two Lines (as opposed to a Line and a Neutral), what you say is correct. But this would be an uncommon configuration. \$\endgroup\$– bitsmackCommented Mar 28, 2016 at 16:32
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\$\begingroup\$ Of course, you're still right that an actual rod shoved into the ground would be the best solution! \$\endgroup\$– bitsmackCommented Mar 28, 2016 at 16:32
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\$\begingroup\$ Ah my apologies. I'll edit the post to correct it. Thanks for the correction \$\endgroup\$– bit0funCommented Mar 28, 2016 at 16:37
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\$\begingroup\$ The first part of this answer is not correct. There is no "negative" terminal on AC. A true neutral connection will be at or very close to zero volts continuously - that's why it's called "neutral". \$\endgroup\$ Commented Mar 28, 2016 at 19:28