This is a good way to compensate for variables like wire length, expansion, surges, etc. If you draw more power than the circuit or cable was designed for, the circuit breaker is designed to “trip” or shut down power so that you don’t reach the ampacity (melting) point of the wire.Ī rule of thumb is the 20% rule. A standard residential home will have circuits with a breaker that is usually rated to 20 amps (15 for older homes and certain specific uses or 14 gauge wiring). Determining the Right Size for Electrical Circuitsĭetermining the correct gauge of wire for your application involves checking the amount of amps (current) you expect to pull on the wire. The British made wire long before us… but we figured out first how to pass electricity across it on a regular basis and turned it into an industry. As the machine draws the wire through, it gets progressively thinner. Remember how we defined gauge in the beginning? Well, SWG gauge numbers (since they don’t apply to electrical cable) specifically correspond to how many times the metal needs to be drawn through a die plate to reduce it to the desired diameter. SWG is a British-developed system, but before you write it off, realize that it’s also used in America-just for ferrous metals and non-electrical applications. Conversely, thin wire carries fewer electrons, and it has a higher resistance and a larger gauge number. Thicker wire can have more electrons running along it, hence it has lower resistance and a lower gauge number. The number of the gauge corresponds to the electrical resistance of the wire. for the electrical industry and is designed for use with non-ferrous metals (non-magnetic metals with no iron). The wire gauge system we use here is known as American Wire Gauge (AWG) or “Browne & Sharpe”. Here is how the gauge rating reflects cable size and determines the amount of current that can flow through the wire: GaugeĪs you can see, the larger wire (lower gauge number) can support more current, and thus a higher breaker size. OK, back to copper wiring and wire gauge measurements. American Wire Gauge, Current, and Cable Diameter It is always a good idea to have anti-oxidant paste on aluminum wire terminations. Aluminum oxide, which acts as an insulator, can also result in poor connections and cause arcing and overheating. This process is referred to as “cold flow.” It is typically the cause of arcing and overheating.Īluminum wire also oxidizes much more readily than copper wire. When the current stops and the wire cools, it contracts and leaves gaps between the conductor and the terminal. The aluminum wire expands and the dimension changes as the current heats it. Older aluminum wire is soft and has a greater tendency for thermal expansion than copper wire. Experience has proven, however, that solid aluminum wire is not nearly as reliable as copper wiring. The Consumer Products Safety Commission Weighs InĪluminum wire was used for branch circuits starting in the early 1960s and used through the mid-1970s, largely because of the copper shortage during those years. As you can imagine, those who have aluminum wiring in their homes might want to take a look at updating their system or at least having it inspected regularly. It also expands and contracts more, and it corrodes. Aluminum serves as a good conductor but has a lower ampacity (the point at which the current causes the cable to begin to melt down). However, homes built or remodeled during the ’60s and ’70s used it quite a bit as copper prices skyrocketed. This is because all current electrical wire is made primarily of copper.Īluminum wiring almost never rears its head in residential construction except for larger gauge stranded aluminum wire (larger than #8 AWG). Wire gauge can also, as a matter of simple calculation, tell you the weight of the wire per unit of length. Since we’re talking about electrical wire, for all practical purposes wire gauge determines the amount of electric current it can safely carry, as well as its electrical resistance. In our desire to explain wire in terms of electrical use, however, we’ll deal mostly with a wire’s electrical resistance – more on that later. You can figure that a wire doubles in size every 6 steps in gauge. The term “wire gauge” refers both to how wire is made and the electrical resistance of the wire. The sizes (gauges) range from 0000 (“four aught” the largest) to 40 (the smallest). It’s easy to be confused by wire gauge, especially since, as the number gets lower, the size of the actual wire goes up! AWG stands for American Wire Gauge and is a specification of sorts that gives specific wire dimensions for, among other things, electrical wires.
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