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Tuesday, July 1, 2014

Nothings Shocking Now: An Electrical Primer (Part 1)

Electricity seems to many people some great mystery who go through life  happily flipping switches and expecting the lights to come on, and feeling helpless when they do not, feeling betrayed by every ideal of technological persistence and reliability.  I promise it is neither mystery nor given right.  It is science, tried, tested, and true.  Electricity powers our lives- its good to have some basic knowledge about it. These basics, what electricity is, how to determine the type of fault, and what can be done about it, are all basic skills that I can pass in fairly directly over the course of a few articles.  

 Since I was a young child, I have been fascinated by nature and physics, in particular, anything that flows.  Water flows through a hose in much the same way that electricity flows through a wire.  In fact, the analogy works so well it has helped numerous people over the years grasp the concept of how electricity works when they ask me about it.  I will take the water analogy as far as I can to help convey the ideas, but in the more complex ways, the analogy breaks down and we must proceed with electricity by itself.

Electricity is a very cool form of energy that flows like water can, but only through metal conductors instead of hoses, tubes or plumbing.  Electricity is part of everything, it is fundamental to the nature of matter.  Every atom of every bit of matter in the universe has an electron cloud surrounding it.  In most materials, it is not hard to make those electrons move from one cloud to another next to it and continue on to create a 'flow' of electrons through a metal object.  In metals, that electron cloud is loose enough to move easily, to shift electrons down the line by bumping them out of one cloud into another.  

At its most basic, electricity can be thought of as a liquid under pressure in the wire and when a switch is flipped, like a valve being opened, the electricity can flow to provide energy for loads like motors, computers, and coffee makers.  The pressure behind the water determines the flow- the higher the pressure, the greater the flow.  By increasing the pressure, the flow increases correspondingly.  Pressure is to water what voltage is to electricity.  The higher the voltage the higher the flow (current) moving in the wire. 

Conductors for electrical flow have similar mathematical properties to hoses or plumbing for water flow.  Both water in a hose and electrons flowing in a wire are prevented from flowing freely by resistance to that flow.  Friction losses are a normal part of plumbing flow calculations.   Imagine a rough surface inside a hose and how the water would flow through it compared to a smooth internal liner that allows water to slide easily through it.  Anytime anything resists flow, energy is wasted.  In water systems, the power is wasted in the pump having to push water through a rough hose and being made very turbulent instead of flowing smoothly.  The same concept can be applied to wires and electrical conductors.  

When a power source is pushing electrons through a wire, the resistance of that wire creates wasted heat in the wire.  The higher that resistance, the lower the flow and the higher the amount of wasted heat.  If the heat builds up in that wire too much, the insulation around the wire can smoke or catch fire.  Wire can only flow so much electricity based on its physical size and composition.  Wire is rated with an 'ampacity' or wire gauge size  to be able to properly utilize the necessary amount of wire to carry the amount of electrical flow planned for that wire.  A tiny signal can flow through a tiny wire, a large amount of power needs a large wire to carry it.  If too small a wire is used for a given amount of current flow, the apparent resistance rises quickly and results in tremendous heat buildup, power loss and wasted energy.

 Loads that we power with electrical energy have resistance too, in using that energy to do work, we remove power from that flow of electrons.  Too low a value for resistance in a circuit means that current flow can go too high and burn up wires or ruin other electrical equipment.  A certain amount of resistance must be present in electric circuits- in the loads we are powering though, not in the wires.  

Proper circuit design utilizes wire size of the minimum size needed for the anticipated current flow and will protect that wire from over-loading with a fuse or circuit-breaker that will stop current flow if the expected current flow is exceeded.  The minimum amount of conductor is a monetary choice, while the minimum size of wire is a safety issue.  Using more wire than a circuit needs is a waste of metal and money, while using too small a wire risks fire or overheating.  

Hoses are rated for water flow based on pressure and is rated by the strength of the jacket that contains that water pressure.  The same is true of wires- the insulator around a conductor will break down at high voltage, just as a the hose will burst under high pressure.   By raising the pressure or voltage, you will increase the flow or current, but only up to a certain level based on safety standards for each situation.  Special hoses can handle high pressure, special wires are designed to deal with high voltages.  

So, for now, know that electricity flow in a wire is corollary to water flow in a hose.  The pressure causes water to flow through a hose.  To flow more water through that hose, you need to raise the pressure or increase the size of the hose.  The same is true for electrical flow.  In a given wire, the flow is controlled by the voltage that pushed it down the line and the size and type of wire being used.  By increasing the voltage, the current increases proportionally.   Next article, I will go into short circuits, open circuits, diagnosing and analyzing systems for accurate description to repair personnel.  Til next time...   MW out

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