WIRE AMPACITY CHART CODE
WIRE AMPACITY CHART FREE

WIRE AMPACITY CHART FREE

Single Conductor in Free Air 30☌ Ambient Temp.

These charts should only be used as a guide when attempting to establish current ratings on conductor and cable.

The fallowing table gives a derating factor to be used when the conductors are bundled. The chart shows the current required to raise the temperatures of single insulated conductor in free air (30☌ ambient) to the limits of various insulation types. Taking into account all the variables involved, no simple chart of current ratings can be developed and used as the final word when designing a system where amperage ratings can become critical. This restriction can also be alleviated somewhat by using proper ventilation methods, forced air cooling, etc. Restricting the heat dissipation by installing the conductors in conduit, duct, trays or raceways lessens the current carrying capacity. Heat dissipation is lessened as the number of individually insulated conductors, bundled together, is increased. The higher the ambient temperature, the less heat required to reach the maximum temperature rating of the insulation. The amount of heat generated should never exceed the maximum temperature rating of the insulation. The larger the circular mil area, the greater the current capacity. These major determining factors are: Conductor Size: There are many factors which will limit the amount of current that can be passed through a wire. Theoretically, the amount of current that can be passed through a single bare copper conductor wire can be increased until the heat generated reaches the melting temperature of copper. Heat, caused by an electrical current flowing through a conductor, will determine the amount of current a wire will handle. Note: Allowable ampacity shown above is per the NFPA79 Electrical Standard for Industrial Machinery 2018 Table 12.5.1 Conductor Ampacity Based on Copper Conductors with 60 ☌ 140 ☏. Once there, click on their link to free access to the 2017 NEC edition of NFPA 70.Current Carrying Capacity of Copper ConductorsĬurrent carrying capacity is defined as the amperage a conductor can carry before melting either the conductor or the insulation. Type MTW Wire Specifications Size (AWG or kcmil) Number of Strands mm2 Equivalent Insulation Thickness Overall Outside Diameter Allowable Ampacities Agency.

WIRE AMPACITY CHART CODE

Many electricians have confused these rules and think a type THWN, 10 AWG copper wire is only rated at 30 amps when in fact it is rated to carry 35 amps according to Table 310.15(B)(16) but in most cases a fuse or circuit breaker installed to protect the wire is not permitted to be larger than 30 amps as stated in 240.4(D).įor complete code sections, refer to the actual NEC text at NFPA.ORG.

Section 240.4(D) has nothing to do with the actual rating of the wire but everything to do with the maximum allowable fuse or circuit breaker used to protect the wire. These values are generally true unless specifically permitted in 240.4(E) or (G). This section is where the all too familiar rules come from that require no larger than a 15 amp overcurrent device to protect a 14 AWG copper conductor, or a 20 amp max overcurrent device to protect a 12 AWG copper conductor, or a 30 amp max overcurrent device to protect a 10 AWG copper conductor. Unless specifically permitted in 240.4(E) or (G), the overcurrent protection shall not exceed that required by (D)(1) through (D)(7) after any correction factors for ambient temperature and number of conductors have been applied. Conductor sizes 18 AWG through 10 AWG are considered “small conductors” and are subject to the rules for small conductors in 240.4(D). When using conductor ampacity Table 310.15(B)(16), it is important to understand why some conductor sizes have a double asterisk (**).

Wire ampacity chart