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NABCEP PVDS study materials
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NABCEP PVDS: PV System Electrical Design

NABCEP PVDS · Work through your exam, one topic at a time.

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PV System Electrical Design

What the exam tests

Electrical design questions ask you to size and protect PV source/output circuits, calculate cold-temperature voltage, apply the 125% continuous-current factors in NEC 690.8, select overcurrent devices under 690.9, and document grounding, rapid shutdown, and interconnection. Know which code edition the AHJ enforces, because 690.12 thresholds changed between editions.

Core rules

  • Maximum PV system voltage: correct module Voc to the lowest expected ambient using the manufacturer's temperature coefficient or Table 690.7(A); do not use STC Voc for conductor or equipment voltage ratings.
  • Maximum current: Isc × 1.25 for a single string; parallel strings add. Conductor ampacity is generally 125% of that value, then adjusted for temperature, conduit fill, and terminal ratings.
  • OCPD: rated at least 125% of maximum current and not above the adjusted conductor ampacity.
  • Interconnection: load-side breakers commonly use the 120% busbar rule in 705.12; supply-side connections avoid the busbar limit but need service-rated equipment and utility approval.
  • Rapid shutdown 690.12: controlled conductors outside the array boundary must be reduced to the edition's voltage/time limit; label the disconnect.
  • Grounding and bonding: follow 690.41–690.47 and 250; array frames, racking, and equipment grounding conductors must be bonded.

Worked example

A string of 10 modules has Voc = 41.2 V, Isc = 9.8 A, and a Voc temperature coefficient of −0.30%/°C. Lowest ambient is −10°C. Correction = 1 + (−0.0030 × (−10 − 25)) = 1.105. Cold Voc = 41.2 × 1.105 = 45.5 V; string Voc = 455 V. Maximum current = 9.8 × 1.25 = 12.25 A. Conductor ampacity must be at least 12.25 × 1.25 = 15.3 A before derating. A 15 A OCPD is too small for 15.3 A; increase conductor/OCPD or use the next standard size only where 690.9 permits.

Traps

Using STC Voc; applying 1.25 once instead of twice; sizing OCPD above conductor ampacity after derating; forgetting 690.12 labels; assuming the 120% rule applies to supply-side taps.