Standards for System Installation and Wiring

This overview on standards for system installation and is an extract of the publication: GTZ, Division 44, Environmental Management, Water, Energy, Transport: Quality Standards for Solar Home Systems and Rural Health Power Supply. Photovoltaic Systems in Developing Countries, February 2000.

Comment: The CENELEC committee CLC BTTF 86-2 recently (06/98) drafted a standard-proposal entitled "Photovoltaic Systems–Solar Home Systems, Safety and Performance Test Requirements and Procedures", which was kindly made available by TÜV-Rheinland. This proposal mainly provides recommendations for system installation, wiring, earthing/grounding and system documentation. The technical specifications given in this proposal are not very precise yet; therefore, most of the following text proposals are taken from other sources.

Stranded and flexible insulated copper wires and cables must be used for all outdoor and indoor installations. Indoor installation of the lighting distribution system might be performed with solid wires, if appropriate and common practice.

External cables should be specifically adapted to outdoor exposure (see IEC 60811). Especially the outer insulation must be sunlight (UV)-resistant, weatherproof and designed for underground installation. Preferably rubber-coated and PE-coated cables shall be used. (H07 R-NF, NYCWY, RV 0.6/1kV, DV 0.6/1kV, VV-K 0.6/1kV, RVkO. 6/lkV, according to VDE 0281, 0282 and CENELEC HD-361). US-American standard cable types are USE (Underground Service Entrance), SE (Service Entrance) and UF (Underground Feeder). The following types are recommended in IEEE P 1374 “Draft guide for terrestrial PV power system safety”: USE-2, USE, RHW, RHH, SE, RHW-2, XHHW-2.

The temperature resistance of all interconnecting wires and cables should be > 85° C. The minimum acceptable cross-section of the wire in each of the following sub-circuits is as follows:

• From PV generator to charge regulator: 2.5 mm² (American AWG 13)
• From charge regulator to battery: 4 mm² (American AWG 11)
• From charge regulator to loads: 1.5 mm² (American AWG 15)

Notwithstanding the above minimum wire-size requirements, all wiring must be sized to keep line voltage losses to less than 3% between PV generator and battery, less than 1% between battery and charge regulator, and less than 5% between battery and load, all of them at the maximum current conditions. The minimum cross-section must also allow the circuit to operate within the ampacity rating of the wire.

For copper cables and 12 V of nominal voltage, the following formula can be used:

A[mm² ] = 0.3 * l * I_Max[A] /  DV [%]

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