Depending on the kind of wire used, an 8 AWG wire may carry 40 to 55 amps of electrical current. Nonmetallic cables can transport 40 amps, copper wire 50 to 55 amps, and aluminum wire 40 to 45 amps. Knowing the ampacity of a wire allows you to identify which electrical devices can be connected to it. For example, an appliance such as a hair dryer or vacuum cleaner cannot be plugged into an outlet that is not large enough to handle its load.
The actual current carrying capacity of any given cable is defined by several factors, including the size of the conductors, the distance between them, and the type of insulation surrounding them. The current carrying capacity of a wire is measured in amperes (amps). Because amperes are calculated with units of voltage over length, the amount of current that can be carried by an electric conductor is determined by the size of the conductor used and the maximum voltage expected to be applied to it.
For example, if you need to connect a lamp to a circuit breaker panel, the circuit breakers there must be able to handle the load of the lamp. If the circuit breakers can't handle at least half of the load, then you will need larger breakers. Larger breakers can handle a load of up to 100 amps instead of 20 amps for smaller breakers. The wiring diagram will tell you what size wires go where and how far they are separated from each other.
Amperage and wire size ratings
| Wire Size | 75°C (167°F) | |
|---|---|---|
| AWG | (mm²) | Copper |
| 8 | (8.4) | 50 |
| 6 | (13.3) | 65 |
| 4 | (21.2) | 85 |
At 120 or 240 volts, a 12 gauge wire (AWG, American wire gauge, copper wire) has a constant load rating of 16 amps. At any other voltage it will overheat and break.
The amp rating of wire determines how many amperes it can safely carry while maintaining its integrity. The actual current that a conductor of AWG wire will carry depends on its size as well as its distance from the source of current. For example, two 14 AWG wires connected in parallel can safely carry 28 amps if they are not closer than 24 inches to each other.
12-gauge wire is used in most residential wiring systems because it is easy to work with and its resistance does not change much within its length. The only time you need to be concerned about ampacity is if you are trying to determine what type of circuit breaker to use for a specific application. For example, if you want to install a dedicated lamp circuit but do not want to pay for a 20-amp service, then you should use a 10-amp breaker. Or if you plan to use more than one lamp in a room then you should use a 15-amp breaker instead of a 20-amp breaker so that each lamp does not overload the others' circuits.
Size and AMP Ratings
| NM, TW, & UF WIRE (Copper Conductor) | SE CABLE (Copper Conductor) |
|---|---|
| 14 AWG – 15 AMPS | 8 AWG – 50 AMPS |
| 12 AWG – 20 AMPS | 6 AWG – 65 AMPS |
| 10 AWG – 30 AMPS | 4 AWG – 85 AMPS |
| 8 AWG – 40 AMPS | 2 AWG – 115 AMPS |
Amperage and wire size ratings
| Wire Size | 75°C (167°F) | |
|---|---|---|
| AWG | (mm²) | Copper |
| 1 | (42.4) | 130 |
| 1/0 | (53.5) | 150 |
| 2/0 | (67.4) | 175 |
Size and AMP Ratings
| NM, TW, & UF WIRE (Copper Conductor) | SE CABLE (Copper Conductor) |
|---|---|
| 12 AWG – 20 AMPS | 6 AWG – 65 AMPS |
| 10 AWG – 30 AMPS | 4 AWG – 85 AMPS |
| 8 AWG – 40 AMPS | 2 AWG – 115 AMPS |
| 6 AWG – 55 AMPS | 1 AWG – 130 AMPS |
Amperage and wire size ratings
| Wire Size | 75°C (167°F) | |
|---|---|---|
| AWG | (mm²) | Copper |
| 250 kcmil | (127) | 255 |
| 300 | (152) | 285 |
| 350 | (177) | 310 |
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