Furse Total Solution to Earthing & Lightning Protection

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Furse, Wilford Road, Nottingham, NG2 1EB • Tel: +44 (0)115 964 3700 • Email: • Web:
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Installation
The performance of SPDs is heavily dependent upon
their correct installation. Thus, it is vital that SPDs are
supplied with clear installation instructions.
The following is intended to supplement the detailed
guidance given with each product in order to give a
general overview of installation.
This should not be viewed as a substitute for the
Installation Instructions supplied with the SPD. Copies
of these are available separately on request.
Installing parallel connected SPDs for mains
power supplies:
SPDs should be installed very close to the power
supply to be protected, either within the
distribution panel or directly alongside of it (in
an enclosure to the required IP rating)
Connections between the SPD and phase(s), neutral
and earth of the supply should be kept very short
(ideally 25 cm or less, but no more than 50 cm)
SPD performance is further enhanced by tightly
binding connecting leads together (simply using
cable ties or similar), over their entire length
For safety and convenient means of isolation, the
phase/live connecting leads should be suitably
fused using HRC fuses or switchfuse, MCB or MCCB
Installing in-line SPDs for data, signal, telephone
or power:
SPDs are usually installed between where cabling
enters or leaves buildings and the equipment being
protected (or actually within its control panel)
The installation position should be close to the
system’s earth star point (usually the mains power
earth) to enable a short and direct connection
to earth
In-line, or series, connected SPDs generally have
connections marked line and clean.
The line end of the SPD should be connected to the
incoming or “dirty” line (from where the transient
is expected).
The clean end of the SPD should be connected to
the line or cable feeding the equipment
Cables connected to the SPD’s clean end should
never be routed next to dirty line cables or the
SPD’s earth bond
Unless ready-boxed, SPDs should be installed
within an existing cabinet/cubicle or in an
enclosure to the required IP rating
Note: further information on the satisfactory
installation of SPDs on mains power supplies, to
meet the requirements of IET Wiring Regulations
17th Edition, BS 7671:2008(+A1:2011), can be found
on page 288.
How to apply protection
Transient overvoltages are conducted into the sensitive
circuitry of electronic equipment on power and data
communication, signal and telephone lines. Protection
is recommended for:
all cables which enter or leave the building (except
fibre optic)
the power supply local to important equipment
electronic equipment outside the main building(s)
Protect incoming and outgoing
electrical services
Lightning strikes between clouds or to ground (and
objects upon it) can cause transient overvoltages to be
coupled on to electrical cables, and hence into the
sensitive electronic equipment connected to them.
To protect the electronic equipment inside a building,
all cables that enter or leave the building must be
protected. Cables leaving the building can also provide
a route back into the building for transients.
For each building protect incoming/outgoing:
mains power supplies (including UPS supplies)
data communication and local area network cables
signal, control, instrumentation and alarm lines
CCTV, satellite, TV and antenna cables
telephone and telemetry lines
Protect the power supply locally to
important equipment
In addition to installing protection on the mains power
supply as it enters/leaves the building, protection
should also be installed locally to important
equipment. Protection at the main LV (low voltage)
incomer(s) is necessary to prevent large transients from
entering the building’s power distribution system,
where they could have farreaching effects.
However, where the cable run to equipment exceeds
10 metres (to BS 7671 Clause 534.2.3.1.1), transient
overvoltages may appear on the mains after the
protector at the main LV incomer. These transients can
result from:
the electrical switching of large inductive loads
within the building
a lightning strike to the building - as lightning
currents flow through down conductors transient
overvoltages can be induced on to nearby power
cables
the natural inductance and capacitance of long
cable runs, `amplifying’ the voltage `let-through’
the protector at the main LV incomer
Additionally, local protection guards against the
possibility of a supply which enters/leaves the building
being overlooked and left unprotected.