Electrical Systems 102

Earlier this week, I wrote about the basics of electricity in the hopes that I could fill in some homeowner blanks!  I specifically wrote about amperage and voltage: that voltage is the constant pressure of electricity, and amperage is the volume.  I'm still not an electrician.  But I do believe everyone should know the basics, so I'm sharing them here.

This week, I'm jumping off right where I left off to demystify why wiring size matters, and how watts fit into the electrical equation.  

Wiring Gauges

​What is wire gauge?  Wire gauge is the first big thing to affect amperage:  it's the difference between a garden hose and straw.  The confusing part, is that as the amperage of a circuit goes up, the gauge goes down.  

The gauge (g) is the inverse of the diameter in inches.
So, 14g wire is 1/14 of an inch in diameter. 
12g wire is 1/12" wide.
8g wire is 1/8" wide... and so on. 

Wire gauge needs and calculations are typically handled by electricians, so I'm not going to dive too much deeper into that.  But it is the first thing that affects wattage after a circuit breaker (if you're still on fuses, future-planning should include upgrades!).  12g wire is used in 20 amp circuits, and 14g wire is used in 15 amp circuits.  Since 14g wire is smaller than 12g, it has a lower safe capacity.  In modern wiring the outer sheathing is color-coded: 12g wire is yellow and 14g wire is white.  It should always be labelled with the gauge and number of wires inside, excluding the ground. So, a simple two-wire circuit run of 12g wire with a ground ("Non-metallic sheathed cable" is the technical term, the major brand is Romex.) would be labelled "12/2."

​Wattage is Volts x Amps

​The wattage of a device determines the demand, or the amperage, on a circuit.  Since the voltage is always the same, and the wattage is the demand, the amperage is what shifts to provide power to a device.

Wattage = Voltage x Amperage.  
Amperage = Wattage / Voltage.

If an incandescent light bulb uses 60 watts, and it is on a 120V circuit, the amperage is .5 amps.  
60 watts/120V = 1/2 amp. 
If a stove burner on a 220V circuit uses 3360 watts, the burner is using around 15 amps.  
3360/220V = ~15 amps. 

Think about an incandescent bulb: the filament that creates light does so by only allowing a small amount of electrons to pass through it at a given time.  That bottleneck forces the energy in the electrons to go from moving through wire to creating light and heat.  (Thanks, Magic School Bus!)

Which Wire is Which?

In standard circuits, there are three wires: a hot, a neutral, and a ground.  When wiring is labelled, it includes the gauge and number of wires inside the outer jacket, excluding the ground wire.  So, 14/2 will be 14g wire with 1 hot, 1 neutral, and a ground wire.  14/3 will be 14g wiring and will have two hot wires, a neutral, and a ground wire.  The second hot wire makes a three-pole switch (lights with more than one switch) and a lot of smart switches possible.

The hot wire is the wire that brings electrical current to a device.  In new wiring, it's black or red (in oldish wiring, it might be blue).  The neutral brings return current back to the panel; it's typically white.  In some older wiring or in switch loops, it can be hard to tell which wire is the hot and which is the neutral.  A device like a voltage tester can test them to see which is which.  The ground is a safety device that returns excess current or any escaped electrons back to the ground where they can be absorbed easily.  It is either bare copper or coated in green (in extremely rare circumstances, it is aluminum.  If you ever run into aluminum wiring in your walls, consult an electrician).  All three are needed for a safe, and complete circuit. 

Safety with electrical wiring is one of the most important things to know!  By keeping an eye on how many amps -or how much wattage- are being used in a circuit, making sure to have a little extra, it's easier to keep electrical systems safe. I hope this helped to demystify home electrical!  Drop any questions in the comments, and I may double back to this topic later or do a Q and A with a licensed electrician.