Experimental. The NEC Table 310.17 ampacity data and 690.8 logic are cross-checked but not yet human-verified. Do not use for final design without independent verification.

Solar PV Wire Size Calculator

Size PV source/output conductors per NEC 690.8 from module short-circuit current (Isc), using free-air Table 310.17 ampacity. Sizes the OCPD (690.9) and reports voltage drop as advisory.

Building or premises wiring instead? Use the NEC Wire Size & Ampacity Calculator.

Input Parameters

Module/array Isc from the datasheet

One-way distance (calculator uses round-trip)

Advisory target; ~2% typical for PV

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Results

Enter parameters and click Calculate

PV Conductor Sizing (NEC 690.8)

Maximum circuit current

PV source/output circuit current is 125% of the module or array short-circuit current (NEC 690.8(A)(1)), accounting for irradiance and temperature enhancement.

I_max = 1.25 × I_sc

Conductor ampacity (690.8(B))

The conductor must satisfy both rules: its free-air (Table 310.17) ampacity, before adjustment, must be at least 156.25% of Isc; and after temperature/bundling derating it must still carry the maximum circuit current.

A_table ≥ 1.25 × I_max = 1.5625 × I_sc A_table × f_temp × f_bundle ≥ I_max

Overcurrent device (690.9)

Where required, the OCPD is rated at 156.25% of Isc, rounded up to a standard rating (NEC 240.6).

Voltage drop (advisory)

Voltage drop is a design consideration for PV (to minimize losses), not an NEC requirement. A ~2% target is typical.

V_drop = I × R × L_roundtrip V_drop% = (V_drop / V_circuit) × 100

Data & status

Free-air ampacities are from NEC Table 310.17, cross-checked across three references. This tool is Experimental and unverified; verify independently before final design.

References

  • NFPA 70: National Electrical Code (NEC)
  • NEC 690.8: Circuit sizing and current
  • NEC 690.9: Overcurrent protection
  • NEC Table 310.17: Free-air conductor ampacities