Table 310-16 of the National Electrical Code is used to calculate ampacity. For equivalence, a popular rule of thumb for converting the two conductor metals is to have aluminum two AWG sizes bigger than copper. When operating inside the American Wire Gage system, this works in the majority of circumstances. If you run into problems because of specific wiring methods, you will need to refer to your local code book to be sure.
Aluminum conductors are usually thinner than copper conductors and therefore less massive. For equivalent circuits, then, aluminum would be smaller than copper conductors.
The reason that aluminum conductors are considered "less" than copper conductors for ampacity calculations is because aluminum conductors can only carry so much current before they get too hot to touch. The safe working limit for human beings is 40 degrees Celsius (104 degrees Fahrenheit). Aluminum conductors can get much hotter than this during normal operation. The current through them also causes them to heat up, so more current means more heat. If a circuit requires more current than what aluminum wires can safely carry, a special type of wire called "hot backup power supply conductors" must be used instead.
In conclusion, an AWG size larger than the conductor being used would be larger than copper for electrical equivalence purposes.
If you run into problems because your wiring system uses smaller wires, then you should use the table below to make sure you're not missing out on any important information.
Aluminum is more resistant to corrosion and oxidation than copper is, which is why it's used more often as cable armor. Aluminum also has a higher melting point than copper, so it can be used at lower temperatures without being damaged. However, when aluminum and copper are placed in direct contact with each other, such as with cable armor, the metal with the higher temperature rating (aluminum in this case) will cause the joint to fail prematurely. This is because the higher temperature rating is only valid when both metals are heated together.
Because aluminum is heavier than copper, more aluminum in a cable means it'll be stronger yet still very flexible. Aluminium also conducts electricity better than copper does, which is why it's usually used instead as wire inside equipment bodies. But because aluminum oxidizes more easily than copper does, the two are never placed in direct contact with each other unless they're wrapped in plastic or some other material that prevents them from coming in contact.
The National Electrical Code (NEC) specifies the ampacity of copper wire at 30 degrees Celsius as follows: 14 AWG-maximum of 20 Amps in free air, 15 Amps as part of a 3-conductor cable; 12 AWG-maximum of 25 Amps in free air, 20 Amps as part of a 3-conductor cable; 10 AWG-maximum of 40 Amps in free air, 30 Amps as part of a 3-conductor cable. These limits include tolerance levels for size, shape, and material defects.
At room temperature, the ampacity of copper wire is significantly less than at 30 degrees Celsius because its resistance increases with increasing temperature. At 100 degrees Celsius, the resistance of 14 AWG copper rises to about one-seventh of its value at 30 degrees Celsius; that of 12 AWG copper rises to about one-third of its value at 30 degrees Celsius. Both sizes lose more than half their capacity to carry current before they reach 120 degrees Celsius. At this point, they become dangerously hot to handle and should not be used further.
The ampacity of copper wire is also dependent on its cross-section. The smaller the wire, the higher the current it can carry without overheating. For example, 7/16 inch diameter copper has twice the current carrying capacity of 1/2 inch copper of equal length. However, the smaller wire is also more difficult to work with and may not be available in all sizes required by a project.
Finally, the ampacity of copper wire is affected by its use as a conductor in cables.
Insulated Copper Conductor Allowable Ampacities
|Conductor Size (AWG/KCMIL)||60°C/140°F TW, UF||90°C/194°F TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, XHH, XHHW, XHHW-2, USE-2, ZW|
Smaller numbers are used in the AWG system to signify bigger diameters. A cross-section of the copper component of the wire is used to determine the diameter. In terms of general use, 6 AWG wire is on the bigger end of the range, suitable for around 55 amps and an absolute maximum of 60 amps. It's commonly used for computer network connections, light switches, and other low-current applications.
6 AWG has two main uses: power wiring and telephone wiring. It can be used for small appliances such as heaters, air conditioners, and electric blankets as well as for less powerful electrical devices such as security lights and smoke detectors. The smaller size allows more of it to be used when building a project like this. For example, instead of using 12 AWG for all the wires in the house, only 6 AWG will do. 6 AWG is also common for telephone lines because it requires fewer total wires to connect one house to another. Each phone call or text message that is made or received on a 6 AWG line can be carried by a single strand of wire instead of two or three as is the case with larger sizes of wire.
As you may have guessed from its name, 6 AWG is the size of wire used for heavy-duty work with large machines and structures. It's commonly found in industrial settings where power tools require a lot of current to run them properly.
The National Electrical Code (NEC) specifies the following ampacity for copper wire at 30 degrees Celsius: 14 AWG-maximum current of 20 amps in open air, maximum current of 15 amps as part of a three-conductor cable; 12 AWG-maximum current of 15 amps in open air, maximum current of 10 amps as part of a three-conductor cable.
Wire with a diameter less than 26 awg cannot be used as mains power conductors. It may be used for lower voltage circuits such as lighting and small appliances.
As you can see, the ability of a single conductor to carry load depends on its size. The larger the cross section, the more current it can carry. But the larger the cross section, the higher the resistance due to the I squared R formula. So for a given load, the smaller the conductor, the more current it will carry. However, small conductors are difficult to work with and take up much space on a circuit board.
In practice, 22-24 awg is the largest size that can be used for mains power transmission without special permission from national regulatory bodies such as the NEC. Loads up to 15 amps can be carried by wires this size if they're not restricted to a single location or conduit.
For loads greater than 15 amps, two conductors are needed instead of one.
100A The highest permitted ampacity of the same 3 AWG copper conductor at 75°C is 100A. The permissible ampacity is 115A if the temperature rating of the 3 AWG copper conductor is 90 degrees Celsius (see Figure 2). Table 310.104 (A) gives information about 600V conductors. The table shows that a 6AWG copper conductor can carry 100A at 75 degrees Celsius.
The current in an electrical conductor creates heat. If the temperature of the conductor rises to the point where it begins to fail, then it has been exceeded its safe operating temperature. When this happens, the conductor becomes hot and any material attached to it may begin to burn. If enough time passes or if the conductor continues to carry current after it has become hot, then it will eventually cause damage itself. For example, if a hot 6AWG copper conductor touches another object, it could start a fire. Also, if it keeps heating up due to more current being drawn from it, then it might melt, which would also be dangerous.
The safe operating temperature of copper is 38 degrees Celsius. At this temperature, its resistance increases by only 3%. Above this temperature, resistance increases faster than this. For example, at 70 degrees Celsius, its resistance increases by 20%. If a copper conductor is carrying a large load and gets hot, you should avoid touching it until it has cooled down.