Now, we have to check the required AWG value for given wire lengths, depending on the wire surface temperature - values are given in the following chart: Wire Length / Surface feet (125 Amps) There are several rules and standards that may be used when calculating the required wire thickness, but the general rule of thumb is to increase the required Ampacity by 10% for every 50 feet (~15 m) of the wire length - some standards increase Ampacity by 20% for every 100 feet (~30 m) which provides the same or very similar results.įor example, when calculating the required Ampacity for the 50 feet, 100 feet, 150 feet, and 200 feet wires, we can use (default value is 125 Amp, after applying the '80% Rule'):ĥ0 feet wire: Ampacity = 125 Amps * 1.1 = 137.5 Ampsġ00 feet wire: Ampacity = 125 Amps * 1.2 = 150 Ampsġ50 feet wire: Ampacity = 125 Amps * 1.3 = 162.5 AmpsĢ00 feet wire: Ampacity = 125 Amps * 1.4 = 175 Amps 90☌/194☏: 2 gauge wire (AWG 2) features an Ampacity of 130A.Īnd these values are for relatively short wires, usually less than 50 feet (less than ~15 meters), which raises the question about the wire thickness of longer wires. 75☌/167☏: 1 gauge wire (AWG 1) features an Ampacity of 130A, 60☌/140☏: 0 gauge wire (AWG 0) features an Ampacity of 125A, Thus, for 100 Amp service, the required wire thickness is: Hence, we should not look for wires being able to carry 100 Amps, but 125 Amps: The 80% Safety RuleĨ0% Rule states that actual wire current should be at most 80% of its default Ampacity. 90☌/194☏: 3 gauge wire (AWG 3) features an Ampacity of 115A.īut, these wire thicknesses are not recommended for actual use since wires should never carry current that equals their default values for safety reasons - hence the 80% Rule. 75☌/167☏: 3 gauge wire (AWG 3) features an Ampacity of 100A,

60☌/140☏: 1 gauge wire (AWG 1) features an Ampacity of 115A, Shall be permitted to be smaller than the ungroundedĬonductors, provided the requirements of 215.2, 220.Note: Ampacities are given for enclosed wires ambient temperatures.Īs one can see, the Ampacity of wires is given at three different temperatures (60☌/140☏, 75☌/167☏, and 90☌/194☏), but for most residential installations, 60☌/140☏ is the maximum allowed wire surface temperature.Īlso, if the value is not given for a required current, one has to look for a wire with a larger Ampacity.įor example, if we are going to look for 100 Amp wire size using default Ampacities for solid copper wire, then:

Not be required to have an allowable ampacity rating greater The feeder conductors to a dwelling unit shall The panelboard that supplies, either by branch circuits or byįeeders, or both, all loads that are part or associated with the dwelling unit. For application of this section, the main powerįeeder shall be the feeder between the main disconnect and Raceway or cable with or without an equipment groundingĬonductor. Main power feeder to each dwelling unit and are installed in In Table 310.15(B)(7), shall be permitted as 120/240-volt,3-wire, single-phase service-entrance conductors, service lateralĬonductors, and feeder conductors that serve as the Two-family, and multifamily dwellings, conductors, as listed For individual dwelling units of one-family, In order for the “other” table to be used those conductors would need to be the main power feeder and they are not.ģ10.15(B)(7) 120/240-Volt, 3-Wire, Single-Phase Dwelling ServicesĪnd Feeders.

Since 85 amps is not a standard size in 240.6 then you can go up to the next standard size which is 90 amps. OK since the conductors are in conduit then it’s likely that they can be used at the 75° C ampacity in Table 310.15(B)(16). I am trying to up load a picture but nothing happens Sub panel is right beside main wire is run through conduit

Sub panel wire size 100 amp