Electrical Wire 101


November 04, 2020

Not to play into stereotypes but I’m a woman that knows nothing about home repairs or cars or really anything that requires manual labor. I know, it’s 2020 and I should at least know how to change the oil in my car. In my defense, it’s not that I lack the desire to learn, but the opportunity never arose. I grew up in a family of all girls and my dad would hire professionals to fix any issues around the house. 

Now that I’m living on my own and can’t call someone every time my house makes a weird noise or I need to change a flat tire, I’ve endeavored to teach myself basic information and repair solutions.  I want the ability to 1) locate the source of the problem, 2) know what type of professional to call, and 3) protect my wallet from unscrupulous contractors. 

One of the trades I aimed to learn more about was basic electrical. I began my research with something I thought would be simple, wire.  Let’s just say there are more wire types than in the days of Edison or Tesla (whichever side you’re on).  So, I’m sharing what I’ve learned with you so any clueless woman (or man) can educate themselves and understand what’s going on in their homes. 

Wiring Types

The main factor that determines what type of wire to use is if it is a residential or commercial project. Building codes dictate what type of wire must be used for either application.

Romex is the trade name for a type of electrical conductor with non-metallic sheathing commonly used in residential construction. Different sizes of romex are available and are indicated by the casing color.  12/2 for example, represents the wire gauge(12) and the number of conductors(2) and uses yellow casing.  In addition to the two conductor wires, there will also be a third grounding wire. See table below for wire use reference.  You’ll find them in the walls, attic or basement, anywhere hidden in your home to keep them safe.

Commercial applications, on the other hand require the use of thermoplastic, high-heat resistant nylon coated (THHN) wire contained in conduit. Conduit is used to protect the wires from liquids, corrosive gases, etc. Metal encased or MC cable can also be used in certain commercial applications. Most commercial locations will have the wires in the ceiling rafter so it can be easily accessible for service. 

What I’ve Learned

So if I ever want to add a receptacle in my condo bathroom, now I know that the electrician needs to use a 12 gauge wire encased in conduit and that’s a step in the right direction.

Wire Gauge Reference Guide

Wire UseRated AmpacityWire Gauge
Low-voltage lighting and lamp cords10 amps18-gauge
Extension cords (light-duty)13 amps16-gauge
Light fixtures, lamps, lighting circuits15 amps14-gauge
Kitchen, bathroom, and outdoor receptacles (outlets); 120-volt air conditioners20 amps12-gauge
Electric clothes dryers, 240-volt window air conditioners, electric water heaters30 amps10-gauge
Cooktops and ranges40-50 amps6-gauge
Electric furnaces, large electric heaters60 amps4-gauge



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