Larger cables may be necessary if the distance from the inverter to the battery is greater than 10 feet (not recommended). Formula 1 Dn (D0) r( (N (d + n) ) ÷ N) Where, Dn Diameter of ‘n’ gauge wire r Ratio between the largest and the smallest wire N Number of draws needed to obtain the smallest wire from the I d Offset of the largest gauge from 0. The table below will help you choose your cable size and fuse or breaker size for a common inverter. Recommended Inverter Cable and Overcurrent Protection * The overcurrent protection device may not exceed 30A for 10 AWG wire, 20A for 12 AWG wire and 15A for 14 AWG wire.įor ambient temperatures above 86☏ (30☌), multiply the approved ampacities from the table above by the correction factor listed under the insulation temperature below. The NEC code allows rounding up cable ampacity to the next standard fuse or breaker size. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).The table below displays approved ampacities of wires in conduit, raceway, cable or directly buried, based on an ambient temperature of 86☏ (30☌). See the actual NEC ® text at NFPA.ORG for the complete code section. Step 3, compare results from the first two steps and pick the larger wire which is 3 AWG copper.īelow is a preview of the NEC. Select a THW copper conductor from Table 310.15(B)(16) that can carry 90 amps from the 75° column (#3 AWG). Various tables and charts indicate conductor ampacity, temperature correction factors, and adjustment factors in NFPA 70, National Electrical Code (NEC). Select a THW copper conductor from Table 310.15(B)(16) that can carry 75 amps from the 75° column (#4 AWG). The table below shows allowable ampacities of conductors (wires) in conduit, raceway, cable or directly buried, in an ambient temperature of 30☌ (86☏). Step 1, take 60 amps X 125% which = 75 amps. See the example below for the 3-step method to properly size a feeder:Įxample: What minimum size copper type THW feeder conductors are required to supply a 60-amp continuous load where the feeders are installed in an area where the ambient temperature is 125☏? (Assume all terminations are rated 75☌ for simplicity) 100% of the load (not 125% of it) after applying adjustment and correction factors.īefore this code change, some electrician were taking 125% of the continuous load and then applying additional adjustment or correction factors which results in an oversized feeder conductor.Full-Load Current and Circuit Protection Data for Three-Phase AC Motors Note: The wire size in this table is based on 75☌ terminations and insulation. Either 125% of the continuous load without any additional adjustment or correction factors, The chart below displays information for motor wire size, breaker size, thermal overload ratings, and other data for three-phase AC motor circuit protection. Now, it is clear than when sizing a feeder, the larger of two values is used for the final selection of the conductor: Feeder conductors are still calculated the same way as before but the revised code language is a bit more user friendly. For other conditions, refer to National Electric Code or an engineering. The code language added to this section in the 2014 NEC ® is not a new concept. Information on wire sizing and a universal AWG/mm2 wire sizing chart to help in. Code Change Summary: New code language was added to clarify how a feeder is sized.
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