<s>
An	O
optical	B-Device
ground	I-Device
wire	I-Device
(	O
also	O
known	O
as	O
an	O
OPGW	B-Device
or	O
,	O
in	O
the	O
IEEE	O
standard	O
,	O
an	O
optical	B-Device
fiber	I-Device
composite	I-Device
overhead	I-Device
ground	I-Device
wire	I-Device
)	O
is	O
a	O
type	O
of	O
cable	O
that	O
is	O
used	O
in	O
overhead	O
power	O
lines	O
.	O
</s>
<s>
An	O
OPGW	B-Device
cable	O
contains	O
a	O
tubular	O
structure	O
with	O
one	O
or	O
more	O
optical	B-Architecture
fibers	I-Architecture
in	O
it	O
,	O
surrounded	O
by	O
layers	O
of	O
steel	O
and	O
aluminum	O
wire	O
.	O
</s>
<s>
The	O
OPGW	B-Device
cable	O
is	O
run	O
between	O
the	O
tops	O
of	O
high-voltage	O
electricity	O
pylons	O
.	O
</s>
<s>
The	O
conductive	O
part	O
of	O
the	O
cable	O
serves	O
to	O
bond	O
adjacent	O
towers	O
to	O
earth	O
ground	O
,	O
and	O
shields	O
the	O
high-voltage	O
conductors	O
from	O
lightning	B-Architecture
strikes	O
.	O
</s>
<s>
The	O
optical	B-Architecture
fibers	I-Architecture
within	O
the	O
cable	O
can	O
be	O
used	O
for	O
high-speed	O
transmission	O
of	O
data	O
,	O
either	O
for	O
the	O
electrical	O
utility	O
's	O
own	O
purposes	O
of	O
protection	O
and	O
control	O
of	O
the	O
transmission	O
line	O
,	O
for	O
the	O
utility	O
's	O
own	O
voice	O
and	O
data	O
communication	O
,	O
or	O
may	O
be	O
leased	O
or	O
sold	O
to	O
third	O
parties	O
to	O
serve	O
as	O
a	O
high-speed	O
fiber	O
interconnection	O
between	O
cities	O
.	O
</s>
<s>
The	O
optical	B-Architecture
fiber	I-Architecture
itself	O
is	O
an	O
insulator	O
and	O
is	O
immune	O
to	O
power	O
transmission	O
line	O
and	O
lightning	B-Architecture
induction	O
,	O
external	O
electrical	O
noise	O
and	O
crosstalk	O
.	O
</s>
<s>
Typically	O
OPGW	B-Device
cables	O
contain	O
single-mode	B-Device
optical	I-Device
fibers	I-Device
with	O
low	O
transmission	O
loss	O
,	O
allowing	O
long	O
distance	O
transmission	O
at	O
high	O
speeds	O
.	O
</s>
<s>
The	O
outer	O
appearance	O
of	O
OPGW	B-Device
is	O
similar	O
to	O
aluminium-conductor	O
steel-reinforced	O
cable	O
(	O
ACSR	O
)	O
usually	O
used	O
for	O
shield	O
wires	O
.	O
</s>
<s>
An	O
OPGW	B-Device
cable	O
was	O
patented	O
by	O
BICC	O
in	O
1977	O
and	O
installation	O
of	O
optical	B-Device
ground	I-Device
wires	I-Device
became	O
widespread	O
starting	O
in	O
the	O
1980s	O
.	O
</s>
<s>
In	O
the	O
peak	O
year	O
of	O
2000	O
,	O
around	O
60,000	O
km	O
of	O
OPGW	B-Device
was	O
installed	O
worldwide	O
.	O
</s>
<s>
Asia	O
,	O
especially	O
China	O
,	O
has	O
become	O
the	O
largest	O
regional	O
market	O
for	O
OPGW	B-Device
used	O
in	O
transmission-line	O
construction	O
.	O
</s>
<s>
Several	O
different	O
styles	O
of	O
OPGW	B-Device
are	O
made	O
.	O
</s>
<s>
In	O
one	O
type	O
,	O
between	O
8	O
and	O
48	O
glass	O
optical	B-Architecture
fibers	I-Architecture
are	O
placed	O
in	O
a	O
plastic	O
tube	O
.	O
</s>
<s>
Fibers	O
for	O
OPGW	B-Device
are	O
single-mode	B-Device
type	O
.	O
</s>
<s>
Optical	B-Architecture
fibers	I-Architecture
are	O
used	O
by	O
utilities	O
as	O
an	O
alternative	O
to	O
private	O
point	O
to	O
point	O
microwave	O
systems	O
,	O
power	B-Device
line	I-Device
carrier	I-Device
or	O
communication	O
circuits	O
on	O
metallic	O
cables	O
.	O
</s>
<s>
OPGW	B-Device
as	O
a	O
communication	O
medium	O
has	O
some	O
advantages	O
over	O
buried	O
optical	B-Architecture
fiber	I-Architecture
cable	O
.	O
</s>
<s>
Effectively	O
,	O
the	O
optical	O
circuits	O
are	O
protected	O
from	O
accidental	O
contact	O
by	O
the	O
high	O
voltage	O
cables	O
below	O
(	O
and	O
by	O
the	O
elevation	O
of	O
the	O
OPGW	B-Device
from	O
ground	O
)	O
.	O
</s>
<s>
A	O
communications	O
circuit	O
carried	O
by	O
an	O
overhead	O
OPGW	B-Device
cable	O
is	O
unlikely	O
to	O
be	O
damaged	O
by	O
excavation	O
work	O
,	O
road	O
repairs	O
or	O
installation	O
of	O
buried	O
pipelines	O
.	O
</s>
<s>
Since	O
the	O
overall	O
dimensions	O
and	O
weight	O
of	O
an	O
OPGW	B-Device
is	O
similar	O
to	O
the	O
regular	O
grounding	O
wire	O
,	O
the	O
towers	O
supporting	O
the	O
line	O
do	O
not	O
experience	O
extra	O
loading	O
due	O
to	O
cable	O
weight	O
,	O
wind	O
and	O
ice	O
loads	O
.	O
</s>
<s>
An	O
alternative	O
to	O
OPGW	B-Device
is	O
use	O
of	O
the	O
power	O
cables	O
to	O
support	O
a	O
separately-installed	O
fiber	O
bundle	O
.	O
</s>
<s>
Other	O
alternatives	O
include	O
fiber-bearing	O
composite	O
power	O
conductors	O
(	O
OPCC	O
)	O
,	O
wrapped	O
fibre	B-Architecture
optic	I-Architecture
cable	O
(	O
SkyWrap	B-Device
or	I-Device
OPAC	I-Device
)	O
,	O
or	O
using	O
transmission	O
towers	O
to	O
support	O
a	O
separate	O
All-Dielectric	B-Device
Self-Supporting	I-Device
fiber	O
cable	O
with	O
no	O
conductive	O
elements	O
.	O
</s>
<s>
Rental	O
fees	O
for	O
these	O
"	O
dark	B-Protocol
fibers	I-Protocol
"	O
(	O
spares	O
)	O
can	O
provide	O
a	O
valuable	O
source	O
of	O
revenue	O
for	O
the	O
electrical	O
utility	O
.	O
</s>
<s>
Lower-voltage	O
distribution	O
lines	O
may	O
also	O
carry	O
OPGW	B-Device
wires	O
for	O
bonding	O
and	O
communications	O
;	O
however	O
,	O
utilities	O
may	O
also	O
install	O
all-dielectric	B-Device
self-supporting	I-Device
(	O
ADSS	O
)	O
cables	O
on	O
distribution	O
pole	O
lines	O
.	O
</s>
<s>
While	O
OPGW	B-Device
is	O
easily	O
installed	O
in	O
new	O
construction	O
,	O
electrical	O
utilities	O
find	O
the	O
increased	O
capacity	O
of	O
fiber	O
to	O
be	O
so	O
useful	O
that	O
techniques	O
have	O
been	O
worked	O
out	O
for	O
replacement	O
of	O
ground	O
wires	O
with	O
OPGW	B-Device
on	O
energized	O
lines	O
.	O
</s>
<s>
Live-line	O
working	O
techniques	O
are	O
used	O
to	O
re-strand	O
the	O
towers	O
with	O
OPGW	B-Device
replacing	O
the	O
all-metal	O
type	O
of	O
overhead	O
shield	O
wires	O
.	O
</s>
<s>
Installation	O
of	O
OPGW	B-Device
requires	O
some	O
additional	O
planning	O
because	O
it	O
is	O
impractical	O
to	O
splice	O
an	O
OPGW	B-Device
cable	O
in	O
mid-span	O
;	O
the	O
lengths	O
of	O
cable	O
purchased	O
must	O
be	O
coordinated	O
with	O
the	O
spans	O
between	O
towers	O
to	O
prevent	O
waste	O
.	O
</s>
<s>
Where	O
fibers	O
must	O
be	O
joined	O
between	O
lengths	O
,	O
a	O
weatherproof	O
splice	O
box	O
is	O
installed	O
on	O
a	O
tower	O
;	O
a	O
similar	O
box	O
is	O
used	O
to	O
transition	O
from	O
the	O
OPGW	B-Device
to	O
an	O
outside	O
plant	O
fiber-only	O
cable	O
to	O
connect	O
the	O
fibers	O
to	O
terminal	O
equipment	O
.	O
</s>
