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EuroWire – November 2011
58
technical article
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
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
Dimension
AWG 10 – AWG 18
AWG 2 – AWG 9
Single layer
1.52mm/60mils
1.91mm/75mils
Skinned
1.91mm/75mils
(1.14mm + 0.76mm)
2.28mm/90mils
(1.52mm + 0.76mm)
Double layer
2.28mm/90 mils
2.66mm/105mils
(1.14mm + 1.14mm)
(1.52mm + 1.14mm)
Parameter
DKE
[2]
UL 4703
[3]
Cable Type
Solar Cable
Based on RHHW/USE-2
Cold Bend/Cold Impact
-40°C
-40°C
Hot Pressure Test
+140°C
+121°C
Ageing Test
+150°C
+121°C
Humidity Test
1000h/90°C/85% rel.
Not required
Dynamic Penetration Ambient temp, 150N * √_
Not required
Fire Performance
IEC 60332.1.2
UL 1581 sec. 1060
UL 1581 sec. 1080
UL 1581 sec. 1061
UL 1581 sec. 1100
Halogen Free
EN 50267-2
EN 60684-2
Not required
Weathering/UV-Test
HD 605 S1/A1
UL 1581 sec. 1200
▼
▼
Table 1
:
Wall thicknesses acc. To UL 4703
▼
▼
Table 2
:
German specification versus UL 4703