Residential PV Systems: Common Code Violations: Page 4 of 6

Intermediate

Inside this Article

Bad wire and wiring photo.
Not only are these conductors not rated for the environment in which they are installed, but they are also exposed to potential physical damage from the hardware edges.
Conductor routing code violation photo
Conductors need to be properly supported and protected from damage to ensure system longevity, performance and safety. This photo shows a myriad code violations.
NEMA box install photo
NEMA 3R-rated boxes should not be installed at angles less than 14 degrees.
Homemade mount photo
This homemade mounting system appears to put dissimilar metals in direct contact with one another. Sloppy mechanical work is often an invitation to inspectors to look even harder for other Code violations.
Disconnect Labeled per NEC photo
To comply with the NEC, a system’s electrical parameters need to be clearly labeled, as shown here.
Bad module ground method photo
This is a violation because equipment-grounding conductors must be installed such that removal of any one module will not disrupt the array’s reference to ground. Properly rated lugs and wire also need to be employed in a Code-compliant manner.
Inappropriate module grounding lug photo
Aluminum lugs are not rated for outdoor use and also do not include stainless-steel set screws.
Bad flashing photo
Unlike this example shown, roof penetrations need to be properly flashed. Always follow the equipment manufacturer’s instructions during installation.
Corrosion from dissimilar metals photo
When dissimilar metals are installed in direct contact with one another, the result is galvanic corrosion. Over time, this causes a loss of the bond to ground.
Bad wire and wiring photo.
Conductor routing code violation photo
NEMA box install photo
Homemade mount photo
Disconnect Labeled per NEC photo
Bad module ground method photo
Inappropriate module grounding lug photo
Bad flashing photo
Corrosion from dissimilar metals photo

Labeling

Required labels. Article 690 lists numerous requirements for labeling equipment, with more requirements added each Code cycle. For proper signage, installers must refer specifically to Sections 690.17, 690.31(E)—see 2011 NEC Section 690.31(E) sidebar—690.35, 690.53, 690.54 and 690.64 (705.12 in the 2011 NEC). Labeling the equipment is an extremely important, yet commonly overlooked, requirement in PV installations. It is one of the final steps in an installation, but the labeling requirements should be identified before the first module is placed.

“Direct-Current Photovoltaic Power Source,” one of the labels required in NEC 690.53, calls for a permanent label for the DC disconnecting means that specifies the PV maximum system voltage, short-circuit current, and the rated maximum power point voltage and current.

The following example calculations for a typical residential system illustrate how to obtain the values for labels:

  • PV array capacity: 5,390 W STC; 22 SolarWorld 245 W modules
  • Module specifications: SolarWorld Sunmodule SW245; 37.7 Voc, 30.8 Vmp, 8.25 Isc, 7.96 Imp, -0.124 V/°C Voc temperature coefficient
  • Array configuration: 11 modules per series string with two strings paralleled in a roof-mounted combiner
  • Record-low site temperature: -10°C
  • Inverter: PV Powered PVP4800, 4.8 kW, 500 VDC maximum input, 200–450 VDC MPPT range

The rated maximum power point voltage and current values are rather straightforward—they are determined by the module manufacturer’s specifications at STC. The 2005 Code requires listing the operating current and voltage, and the 2008 Code helps clarify that language.

Imp = Module Imp × strings in parallel

7.96 A × 2 = 15.92 A

Vmp = Module Vmp × number of modules per string
30.8 V × 11 = 338.8 V

Section 690.53(3) in the 2008 Code contains a fine-print note (FPN) that instructs listing the maximum voltage as calculated in Section 690.7. Depending on the Code version you are working with, this value may be the array’s open circuit voltage at STC multiplied by the correction factor listed in 690.7, or it may be calculated from module manufacturer data.

Max Voc = {37.7 V + [(T_min - T_STC) x coeff]} x 11 

{37.7 V + [(-10°C- 25°C) x -0.124 V/°C)]} x 11 = 462.4 V

The fourth piece of information required is the array’s short-circuit current. Again, the 2008 NEC  has added an FPN to clarify this calculation that references Article 690.8(A), which requires multiplying the array’s short-circuit current by 1.25 to determine the value to list on the label.

Isc = Module Isc rating x strings in parallel x 1.25

8.25 A x 2 x 1.25 = 20.63 A

Rounding to the nearest whole numbers, the label applied at this site should read:

DC PV POWER SOURCE

Imp: 16 A

Vmp: 339 V

Max Voc: 462 V

Isc: 21 A

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