Electric wiring basics

This is may turn into something beyond my original intent, but I will share what I know. I am currently employed as a journeyman level electrician. I troubleshoot and repair industrial electrical systems, including everything from computer controls to 15,000 volt power distribution systems. I've been doing this for 25 years, so I hope I can speak intelligently on enough on this subject to help everyone with any issues that may arise.

Safety first.

Electricity can kill you, it only takes 5 miliamps to stop your heart. (that is any voltage delivering 0.005 amps across your chest)
So do not touch the pretty brass or copper inside the panel, that is the part that carries the electricity.

Seriously, turn off the power before doing anything! Sometimes this means simply making sure a switch is off, sometimes it means pulling the main breaker or fuse in the panel. Take that extra few seconds to be safe it is not time wasted.

So the basics...
well it usually starts with a math class, but we will post pone that for a bit. Electricity is a natural force that has both pressure, and flow, just like water. The pressure is expressed as Voltage or Volts for short. This is the potential for work to be done, much like water has a pressure expressed as pounds per square inch. The flow of electricity is the movement of electrons through a conductive material, like copper, or aluminum. That flow is expressed in amperes or amps for short. Similarly water moving through a pipe or hose has a flow rating expressed as gallons per minute, or per hour. You will often see the term Watt applied to various electrical devices. What this is is a measure of the heat the device can dissipate or generate. 1 Watt is 1 volt at 1 amp. A 100 Watt light bulb (lamp in my world) plugged into a wall socket (120 volts) will draw 0.83 amps while it is operating. If left on for 1 hour, that will equal 0.83 ampere hours for that 100 watt light bulb to be in operation for 1 hour. Multiply that by your electric rate and you will know what it costs you to have that light on for 1 hour.

So time for a little math. OHM's Law as it's called. This is the standard chart used to find what you need to know about how a circuit should work.


I'll let you study this for a bit, and continue later.

This ought to interesting. It reminds me of the time I studied and got my Amateur Radio License. We had to learn all about OHM's law. I think I have forgotten most of it now though.

To be perfectly honest if it weren't for our apprentices I would not remember much of this. (If you want to really learn something, teach it to someone.)

So OHM's law...it is a series of formula's used to analyze electrical circuits. If you've looked at the pie chart you have seen that it uses four letters over and over. Each letter represents something dealing with electricity. W is for Watts or Wattage, E is for Voltage, Resistance is represented by an R, I is for current or amps. If you know any two values you can find the other two by using one or more of the formula's above.

For instance if you know the voltage and wattage of a circuit, you can find the current draw. A 60 watt light bulb (incandescent, not the mislabeled energy efficient bulbs) is in a circuit that is supplied 120 volts. What is the current draw, and what is the resistance of the circuit?
So we take E x E then divide that result by W. This gives us 120 x 120 which is 14,400. Divide that by 60 and we have 240 OHMs of resistance to the flow of electricity. Take the voltage 120, and divide by the resistance 240, and we have 120 divided by 240 equals 1/2 or 0.5 amps.

So that's how we analyze what's going on in an electrical circuit (simplified)

Important to know, especially when you want to put in a new circuit or add to your homesteads electrical system. It does not matter if it's solar or grid connected, AC or DC OHM's law applies.

A few quick tips before I sign off for the night (we will pick up with some more basics later)

1) Remember a circuit breaker or fuse is sized to protect the wiring from over heating and causing a fire hazard. The wire is sized to safely supply the current that is needed to power the load of the circuit.

2) The National Electrical Code (NEC) is a set of guidelines, not laws. Your local Electrical Inspector is the final authority when determining if an electrical circuit is safe.

3) Never plan to load an electrical circuit beyond 80% of the fuse or breaker trip rating. (a 15 amp circuit can be loaded to 12 amps, a 20 to 16 amps, a 30 to 24, a 40 to 32, etc.)

4) an over sized circuit is safer than an undersized one. Our home is wired with a 200 amp panel, however even with all circuits on and drawing full capacity (80%) we still only draw 136 amps from the grid (measured)