![]() Use these tables to determine the maximum distance one-way in feet of various gauge two-conductor copper wire from power source to load for 2% voltage drop in 48-volt and 120-volt system wiring. Note that a 24 VDC array can be placed much further from the battery bank than a 12 VDC array of the same size due to the lower current. A 4% to 5% loss is acceptable between batteries and lighting circuits in most cases. Do not exceed 2% drop for wire between PV modules and batteries. If a 4% loss is acceptable then the distance can be doubled. Use this table to determine the maximum distance from power source to load for 2% voltage drop. Wire Loss Tables for 12 VDC and 24 VDC Systems Note that we stock battery-to-inverter cables in #2, 2/0 and 4/0 AWG. Ode below for NEC code requirements when going transformer-less: Please click the Going Transformer-less Electrical Contractor Magazine article by Mark C. Larger cables may be necessary if the distance from the inverter to the battery is greater than 10 feet. Smaller cable sizes can be used if fuse or breaker size is reduced but this can cause problems if the inverter is running near its maximum output wattage. Use this table to decide cable size and fuse or breaker size for common inverter models. ![]() Recommended Inverter Cable and Overcurrent Protection National Electrical Code (NEC) allows rounding up cable ampacity to next size standard fuse or breaker.įor ambient temperatures above 30☌ (86☏), multiply the allowable ampacities shown at right by the correction factor listed under the insulation temperature rating below. The table below shows allowable ampacities of conductors (wires) in conduit, raceway, cable or directly buried, in an ambient temperature of 30☌ (86☏). Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).Establish a Solar Panel Decommissioning Program 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). Select a THW copper conductor from Table 310.15(B)(16) that can carry 75 amps from the 75° column (#4 AWG). 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.Either 125% of the continuous load without any additional adjustment or correction factors,.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. The code language added to this section in the 2014 NEC ® is not a new concept. Code Change Summary: New code language was added to clarify how a feeder is sized.
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