PV Panel Grounding

NEC 690 - Covers PV Systems

• 690.41 - Equipment Grounding Conductor requirements [1]
  • 690.41(B) also requires ground fault protection except if there are no more than 2 strings (PV source circuits [2])
    • Since NEC 2020, ground fault indicator must be readily visible (but not necessarily readily accessible?) [3]
  • 690.45 - size of PV equipment grounding conductors - Table 250.122 + no less than 14 ga.
• 690.9(A) says that we don't need overcurrent device for PV if the wires can handle short current capacity of PV. But good luck trying to convince a code official.
• PV Grounding PDF [4]. Although the NEC does not specifically require all equipment to be certified/listed, many local jurisdictions and many AHJs establish requirements that all equipment be certified/listed because they feel unqualified to examine uncertified/unlisted equipment for safety as the NEC requires.
  • Good overview doc. Read it from p. 6 on to understand equipment ground, system ground.
  • Additional issue for PV is that in cloudy conditions or when there is little sun (evening), if you get a fault, a breaker may not trip because current is too low. For this reason, specific ground fault protection is required. But, if it's a fuse to solid ground from - of PF to ground rod - why not just use a lower value fuse? I don't get it.
• Is earth ground of a PV system connected to DC negative, or to AC neutral?

PV Fuses

• Special characteristics: high V (larger strings), more cycling (clouds), high temp, [5]
• Expensive
• Fast acting as long as there are no major inductive loads on the system, otherwise these should be slow-acting because PV panels are voltage and current limited.
• Low fault current acting, high voltage fuses - 0.5 - 1A is fine.

• KLKD $12 - [6]
• DMM 1/2A fuse - [7]
• Fuse rating should bd 1.56*Isc and 1.2x for the voltage [8]
• Standards, p6 - BS alert. PV rating means that a fuse is tested to run at 1.45x the nominal current. Ok, but there is already a 1.56 requirement for these fuse sizes - why another 1.45? [9]
• BS alert: there is 'low leakage current functionality' for pv fuses - but why not just use a smaller fuse rating for lower current?

Ground Faults - System Grounding Howto

• Article says that a common ground fault protection device (GFPD) is a fuse to ground - [10]
• NEC Article 690.41 states that grounding for photovoltaic systems includes 2 grounds [11]:
  • The first one is system grounding: the PV system with system voltage over 50 volts should be solidly system-grounded.
  • The other one is the equipment grounding: the exposed non-currentcarrying metal parts of PV module frames, electrical equipment, and conductor enclosures should be grounded .
• System Ground Howto: To achieve that, the negative conductor usually is grounded via the GFPD in the PV inverter at point G [12]:

Source: [13]

More

• Solar PV standards and certifications - [14]. Class II means frames grounded, no system ground.

• Paper on PV grounding, 1984. Fire safety and personnel safety are typically tradeoffs? [15]
  • Solidly grounded means neutral is connected to earth electrode. [16]
  • Class II system had double insulation and equipment ground, but no earth connection.
  • Class I has equipment ground and earth connection.
  • Insulation failures between current-carrying conductors and the ground are known as ground faults.
• Classic video by Mike Holt. Equipment Grounding + system grounding - Ground and grounding electrode conductor basic with Mike Holt - [17]
  • Do not earth ground frames with a ground rod like this - [18]

Equipment Grounding

• PV panels should follow electrical grounding conductor sizes - [19]
• Ie, for 30A DC, we need 10 ga ground.
• PV frames must be connected to PV system equipment grounding conductor [20]
• After leaving the PV array, the equipment ground must run together with the power wires. [21]

What Size Grounding Conductor on PV Panels?

• Australia rules - appear to say 6 ga for lightning protection, and 12 ga for frame grounding [22]
• 6 ga USA if 'subject to damage'?