EoW November 2011

technical article

acc. to UL 1581, Section 1080. Based on RHW-2 the flame test FT-2 acc. to UL 1581, Section 1100 is also required. Table 2 compares some important para- meters and tests of both standards against each other. Therefore, another cable construction will be necessary to meet the UL-requirements. 6 Product Properties The newly developed solar cable is a single core cable built with a tinned stranded conductor. All materials are halogen free, flame resistant and fire retardant. No corrosive gases will be released in case of fire and the smoke density is low. The insulation and jacket materials are extremely resistant to weathering, UV-radiation and abrasion. The wide temperature range from -50°C to +150°C (fixed installation) enables the use of this cable in extreme weather conditions. Additionally, it is salt water resistant and resistant to acids and alkaline solutions. The cable is flexible and designed for high mechanical loads. So it is suitable for fixed installation as well as for moving applications without tensile load.

1 Shoulder with sufficient depth for testing the insulation 2 Needle of spring steel 3 Sample

▲ ▲ Figure 3 : Arrangement for penetration test on completed cable

according to European standard EN 50267-2-2. The content of chlorine and bromine is determined according to EN 50267-2-1 and a special test is developed for the content of fluorine in Annex C of the discussed specification [2] . 5 UL 4703 Standard In 2005 the American Underwriters Laboratories (UL) published the UL subject 4703 “Photovoltaic Wire” [3] . It covers single-conductor, insulated and integrally or non-integrally jacketed, sun- light resistant, photovoltaic wire in several temperature and voltage ratings for interconnection wiring of grounded and ungrounded photovoltaic power systems. The standard UL 4703 is based on the service entry cords USE-2 and specifies some additional requirements for photovoltaic cables. It applies for solar cables in North America. These UL-requirements are quite different from the German specification. The UL standard leaves more freedom for the manufacturer as far as the cable construction and the selection of materials is concerned. One or two insulation layers can be chosen optionally as well as a “skinned” single layer construction. For two-layer construction, as specified in the DKE-document [2] , several combinations of wall thicknesses are allowed in UL 4703. But in each case the total sum of wall thickness will be higher than specified in the German specification (see Table 1 ).

Thus the diameter for the same conductor cross section will be higher which reduces the suitability for several connectors. And the increased need of insulation compound will add to the production cost. The main focus of UL 4703 is the fire performance. Tests to be performed are the Vertical Flame Test acc. to UL 1581, Section 1060 or optional flame test VW-1

▼ ▼ Table 1 : Wall thicknesses acc. To UL 4703

Dimension

AWG 10 – AWG 18

AWG 2 – AWG 9

Single layer

1.52mm/60mils

1.91mm/75mils

1.91mm/75mils (1.14mm + 0.76mm)

2.28mm/90mils (1.52mm + 0.76mm) (1.14mm + 1.14mm) (1.52mm + 1.14mm)

Skinned

2.28mm/90 mils 2.66mm/105mils

Double layer

▼ ▼ Table 2 : German specification versus UL 4703

Parameter Cable Type

DKE [2]

UL 4703 [3]

Solar Cable

Based on RHHW/USE-2

Cold Bend/Cold Impact

-40°C

-40°C

Hot Pressure Test

+140°C +150°C

+121°C +121°C

Ageing Test Humidity Test

1000h/90°C/85% rel.

Not required Not required

Dynamic Penetration Ambient temp, 150N * √_

UL 1581 sec. 1060 UL 1581 sec. 1080 UL 1581 sec. 1061 UL 1581 sec. 1100

Fire Performance

IEC 60332.1.2

EN 50267-2 EN 60684-2

Not required

Halogen Free

Weathering/UV-Test

HD 605 S1/A1

UL 1581 sec. 1200

58

EuroWire – November 2011