#WIRE AMPACITY CHART CODE#
#WIRE AMPACITY CHART FREE#

Letter codes like these are only used for general-purpose wires such as those used in households and businesses. Therefore, a “THWN” conductor has Thermoplastic insulation, is Heat resistant to 75° Celsius, is rated for Wet conditions, and comes with a Nylon outer jacketing. Z = Modified ethylene tetrafluoroethylene.TFE = Polytetrafluoroethylene (“Teflon”).For example, the letter “T” by itself means “thermoplastic” as an insulation material, as in “TW” or “THHN.” However, the three-letter combination “MTW” is an abbreviation for Machine Tool Wire, a type of wire whose insulation is made to be flexible for use in machines experiencing significant motion or vibration. Some of these letters symbolize individual properties of the wire while others are simply abbreviations. There is meaning in the letter sequences used to identify conductor types, and these letters usually refer to properties of the conductor’s insulating layer(s). This is because the NEC concerns itself primarily with power wiring (large currents, big wires) rather than with wires common to low-current electronic work. As you will notice, the table fails to specify ampacities for small wire sizes. These ampacity ratings are given for copper conductors in “free air” (maximum typical air circulation), as opposed to wires placed in conduit or wire trays. This is due, again, to the thermal limits (60°, 75°, 90°) of each type of insulation material. Notice the substantial ampacity differences between same-size wires with different types of insulation. * = estimated values normally, these small wire sizes are not manufactured with these insulation types

#WIRE AMPACITY CHART FREE#

A table derived from an NEC listing is shown for example: Copper Conductor Ampacities, in Free Air at 30 Degrees C Insulation:Ĭurrent 60 degrees 75 degrees 90 degrees C Voltage dropped as a result of excessive wire resistance is also a factor in sizing conductors for their use in circuits, but this consideration is better assessed through more complex means (which we will cover in this chapter). Though the melting point of copper theoretically imposes a limit on wire ampacity, the materials commonly employed for insulating conductors melt at temperatures far below the melting point of copper, and so practical ampacity ratings are based on the thermal limits of the insulation. Typical NEC wire ampacity tables will show allowable maximum currents for different sizes and applications of wire.

#WIRE AMPACITY CHART CODE#

Primarily for reasons of safety, certain standards for electrical wiring have been established within the United States, and are specified in the National Electrical Code (NEC). A conductor’s current-carrying limit is known as its ampacity.

Thin wires will, therefore, tolerate less current than thick wires, all other factors being equal. A wire with greater resistance will dissipate a greater amount of heat energy for any given amount of current, the power being equal to P=I 2R.ĭissipated power due to a conductor’s resistance manifests itself in the form of heat, and excessive heat can be damaging to a wire (not to mention objects near the wire), especially considering the fact that most wires are insulated with a plastic or rubber coating, which can melt and burn. The smaller the cross-sectional area of any given wire, the greater the resistance for any given length, all other factors being equal.

Wire ampacity chart