A few elementary topics

- S
- Scale
  
  Contact options for registered users
posted
17 years ago

Wed, Sep 13, 2006 3:05 PM

Hello everyone, I don't know if this is the best place to ask, but I just had a few questions about elementary wiring / circuits topics

Firstly, when looking at a circuit diagram with a voltage sourse in it, which terminal of the voltage source / battery is the flow of electricity coming from? I was told that the positive terminal is the terminal with a higher potential and is thus the origin of the electricity, but I was also told that electrons flow from the negative terminal. Which is correct? The flow of electricity is essentially the flow of electrons, right? I've heard of "conventional current" which is the flow of the holes left by the electrons as they move in the opposite direction (er, I think.). Does this somehow factor into this topic?

Secondly, What purpose does a ground/earth connection serve in an electrical circuit? I've heard its a safety device. If so, how does it function as a safety device, and if not, what is the significance of it?

Thanks a lot everyone!!

- S
- Salmon Egg
  
  Contact options for registered users
Vote on answer
posted
17 years ago

Wed, Sep 13, 2006 9:41 PM

You seem to be at the beginning of your electrical study. I will pontificate a bit of good advice that you will find useful in the years to come. FORGET ABOUT ELECTRONS for most of your time. Electrons were not invented until the

20th century. Holes weren't invented until decades later The concept of electrons becomes useful only when trying to understand electronic devices! Nevertheless flow of current was understood BE (before electrons)

Current flowed from the positive electrode of a voltaic pile through an external circuit to its negative electrode. Credit or blame Benjamin Franklin who arbitrarily defined the direction of current flow during the

18th century. Edison, who truly understood Ohm's law when many academics did not, was able to calculate the flow of current BE.

Bill

-- Fermez le Bush

- B
- Bud--
  
  Contact options for registered users
Vote on answer
posted
17 years ago

Thu, Sep 14, 2006 3:29 PM

Earthing an electrical system limits the voltage with respect to earth. For instance, if a 2400 volt primary distribution wire touched a 120/240 volt secondary wire you don't want the power wires in your house floating 2400 volts above earth potential.

Earthing is likely to blow the fuse on the 2400 volt distribution wire and provides a place to dump surge currents.

Bonding exposed metal of the wiring system and devices connected to it, and connecting to earth, keeps those objects at the same potential so you don't get a shock touching 2 pieces of exposed metal or touching exposed metal and earth.

If a hot wire of the electrical system touches exposed metal (a fault) you want to rapidly blow a fuse/trip a circuit breaker. Earting is NOT used to do that because the resistance is to high. The fault current is carried through the common bonding back to the neutral through a neutral-bond connection at the service panel.

The description is specific to the US but similar in function elsewhere. Bonding and earthing are both called "grounding" in the US. Rumor is that the terminology is changing slightly in the next NEC.

bud--