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CABLES + ACCESSORIES
ELECTRICAL PROTE TION + SAFETY
Rolling sphere method
In accordance with a lightning protection level 1 system a sphere with
a radius of 20 m was used to determine the height and positioning
of the air terminals.
There are two applicable distances between the air terminals; namely
12 m apart and 16 m apart. The sag of the sphere (20 m radius - LPL1)
is calculated using the following formula:
P = r - [r² - (d/2)²]
Where:
P
= Penetration depth (sag)
r
= Radius of sphere (20 m)
d
= Distance between air terminals
The calculated sag between the air terminals is therefore:
- 12 m distance = 0,92 m
- 16 m distance = 1,67 m
The area between the air terminals is therefore covered via the rolling
sphere method of protection.
Isolated air termination system
Air termination masts and brackets
In order to comply with the design requirements, i.e. two 3 m masts
to be installed to the top of the steel LED frames, specialised mast
brackets had to be designed and manufactured to house the 3 m
long HVI power masts.
Down conductor system
Each mast location is equipped with two HVI power down conductors
that run from the mast connection point to the zero potential con-
nection point (concrete steel reinforcing). The HVI down conductors
are fixed to the structural steelwork (I-Beams) by means of stainless
steel clamps and brackets.
Installation of HVI Down conductors.
Earthing and equipotential bonding
The correct earthing and equipotential bonding of the Lumen light-
ning protection system is imperative for the effective protection of
the LED screens. To this end the following measures were employed:
• The HVI conductors were positively bonded to the concrete steel
reinforcing of the structure at a level below the LED frames
• The concrete steel reinforcing was tested in numerous positions
and found to be electrically continuous with various parallel paths
to earth
• The use of the concrete steel reinforcing vastly increases the cur-
rent division capabilities of the entire lightning protection system
Earthing of HVI power conductors.
Equipotential bonding
The semi-conductive sheath of the HVI power conductors were equi-
potentially bonded to the electrical earthing system at a level below
the LED frames. In turn the electrical earthing system was bonded to
the concrete steel reinforcing at ground floor level. The LED screens
and frames are equipotentially bonded to the electrical earthing
system via the electrical reticulation.
In order for the HVI system to work properly it is imperative that
this equipotential bonding be performed.
3m Air
Terminal
Top of Steelwork
S= 1,67m
HVI Power
Conductor
PVC Insulated
Copper Conductor
Mini Earth Bar
Concrete Steel
Reinforcing
Clamped
Connection To
Reinforcing
r = 20m
16m
Electricity+Control
April ‘15
18