NEC 690.7 – Maximum Voltage

NEC 690.7 – Maximum Voltage

This article governs how to determine maximum system voltage — a crucial design parameter for ensuring code compliance and equipment safety.

Key Rules:

1. 690.7(A) – Maximum System Voltage Calculation
   • Required calculation:
     Module Voc at lowest expected temperature × number of modules in series.
   • Must use manufacturer-specified Voc and the lowest expected ambient temperature (often based on ASHRAE data).
2. 690.7(B) – Cold-Weather Voltage Correction
   • Use the temperature correction factor provided in Table 690.7(B)(2) or use module-specific voltage-temperature coefficients.
3. 690.7(D) – 1000V / 1500V Limits
   • Maximum PV system voltage:
     • 1000 Vdc for most residential/commercial applications.
     • 1500 Vdc allowed for utility-scale and commercial systems if components are listed for it.
4. 690.7(E) – Interactive Systems
   • Voltage limits apply to interactive (grid-tied) systems as well.
   • Care must be taken with rapid shutdown and listed equipment ratings.

NEC Table 690.7(B)(2): Voltage Correction Factors for PV Modules at Low Ambient Temperatures

Ambient Temperature (°C)	Correction Factor
+25	1.00
+20	1.02
+15	1.04
+10	1.06
+5	1.08
0	1.10
–5	1.12
–10	1.14
–15	1.16
–20	1.18
–25	1.20
–30	1.21
–35	1.23
–40	1.25