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NEC 690.7 Maximum System Voltage

NEC 690.7 · Temperature-Corrected String Voltage

When to use: Determining the maximum PV system voltage to size conductors, disconnects, inverters and overcurrent devices. Per NEC 690.7(A), the maximum voltage of a PV source/output circuit equals the sum of module Voc corrected to the lowest expected ambient temperature. Because Voc rises as temperature falls, the cold-weather voltage governs equipment ratings and must stay at or below the system voltage limit (600 / 1000 / 1500 V).

String Parameters
per module
V
#
negative
%/°C
°C
Calculation Steps
String Voc (STC) = 40 × 12 = 480.0 V
Factor = 1 + (-0.29/100) × (-10 − 25) = 1.1015
Voltage rise = +10.15% (cold weather)
Corrected Voc = 480.0 × 1.1015 = 528.7 V
✓ PASS — Within 1000 V Limit
528.7V
Max System Voltage (cold)
Results
String Voc (STC)480.0 V
Correction Factor1.1015 (+10.15%)
Corrected Voc528.7 V
Voltage Limit1000 V
Margin471.3 V
NEC References
NEC 690.7(A) — Max voltage at lowest temp
NEC Table 690.7(A) — Crystalline correction
IEC 61730 / UL 1741 limits
Common limits: 600 / 1000 / 1500 V