Overvoltage protection
(surge arrester)
Agenda
●Choose the best surge protection.
●Install overvoltage protection.
●Choose the best upstream protection for a surge arrester.
●Installation rules.
Electrical overvoltage,
unique characteristics
Sources Characteristics
Lightning
● Lightning ● Ultra-rapid transient
phenomenon. Unit Voltage
of measurement =
kV/ µs Operations
● Highly destructive
energy.
● Overvoltage ● Repetitive
generated by phenomenon
operations or leading to
Irms
incidents on the premature aging.
network.
● Malfunction which
may even result in
permanent damage.
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Lightning and its consequences
●The main effect of lightning is electrical overvoltage which
exposes the electrical installations to a serious risk of:
● malfunction,
● destruction of equipment,
● unavailability of production tools,
● etc.
The overvoltages come either from the electricity
network from the earth.
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The damage caused by lightning
● 90% of sockets power sensitive equipment and an overvoltage
can damage them (Total values estimated amount = €3,650).
Living-room: TV, home
Bedroom: computer, hi-fi, cinema, rolling shutters,
telephone (€650) air-conditioning, ADSL
modem (€1,000)
Kitchen: microwave oven,
oven, fridge, dishwasher
Laundry: freezer, washing (€500)
machine, dryer, boiler, alarm
(€1,500)
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Choose the best
surge protection
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A means of protection for every situation
No LPS* With LPS* Type of
Type 2 surge arrester Types 1 and 2 surge arrester surge
arrester
T1: only used
Distance of the when LPS is
loads < 30m present
T2: used
systematically.
T3: only used in
addition to a
T2 (as lower
Distance of the discharge
loads T3 capacity), if the
> 30m** T3 loads are more
T3 than 30m from the
T2 T1 + T3
T3 T2 incoming T2 surge
arrester
Types 2 and 3 surge arrester Types 2, 1 and 3 surge arrester
* LPS (Lightning Protection System) = lightning rod, meshed cage on buildings)
** After 30m (between the surge arrester and the loads) lightning wave reflection phenomena appear
in the cables.
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In practice: distance of equipments >30
metres
Case No.1 T2
(the most Distance under than 30 metres
common)
Mainboard
T2 = type 2 surge arrester
T2
Case No.2 Distance of more than 30
metres
Mainboard
T2 = type 2 surge arrester
T3
T2 Floor
switchboard
Install the surge arrester
Mainboard as close as possible to the
sensitive equipment
* T2 = type 2 surge arrester, T3 = type 3 surge arrester.
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To summarise
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Install surge arrester
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Location in the switchboard: in parallel
Incoming
circuit-
circuit-breaker
Lightning *
current
Sensitive equipments
* SPD = Surge Protection Device.
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Lifetime of the surge arrester
●The surge arrester has the same lifetime as the switchboard.
●At the end of its life, a thermal protector integrated into the surge
arrester:
●isolate the surge arrester from the rest of the installation.
●activates the red end-of-life warning light, indicating that the surge
arrester needs to be changed.
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The upstream protection of the surge
arrester
●The role of the surge arrester is to drive the lightning current to the
earth in a very short time (< 350 microseconds).
●However, the surge arrester is not intended
to be
exposed to a permanent overvoltage
(phase/neutral inversion, or neutral rupture). In this case, it would be
short-circuited and may damage the switchboard.
●A device protecting the surge arrester against short circuits is
therefore required to ensure the safety of the electrical installation.
The surge arrester must be protected
upstream by a disconnection SPD
circuit breaker.
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Choose the best upstream
protection for a surge arrester
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2 aspects must be taken into account
● When making your choice, take into account:
● lightning current withstand capacity (to avoid nuisance trpping),
● short-circuit withstand capacity of the installation (Isc).
Isc
25kA C60L C60L NG125N NG125N
15kA C60H C60H C60H C60H
6kA C60N C60N C60N C60N
8kA 20kA 40kA 65kA Lightning current
● E.g. the best disconnection circuit breaker for a breaking capacity of 15kA
and Imax of 40kA is a C60H.
The surge arrester/protection device coordination table is
supplied by Schneider Electric.
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Example of Schneider Electric coordination table
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Schneider Electric innovates for safe
coordination and easy installation
●Quick PF and Quick PRD include both an upstream circuit breaker
and a surge arrester, thus ensuring:
●no risk of coordination error,
●continuity of service.
Safe
Efficient
Easy selection
Quick PF and Quick PRD
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Installation rules
The surge arrester is effective
only if it is properly installed!
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Installing a surge arrester
● Lightning is a phenomenon that generates a high frequency voltage:
● The length of the cables must be taken into account in cases of high
frequency
● 1 metre of cable crossed by a lightning current generates an overvoltage of 1,000V.
1000V
500V
U spd Load U spd Load
1000V Uload = Uload =
USPD + 2000V USPD + 500kV
For an effective surge protection, shorten the length of cables.
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In practice: consider the intermediate earth
terminal to shorten cables length
L1 L1
L ≤ 50cm
L2 L2
L3
L3 Intermediate
Main earth earth terminal
bar Main earth
L > 50cm bar
Mandatory in Standard IEC 60364-5-534: L = L1 + L2 + L3
● L (length of cables) < 50cm,
● cable cross-section S < 4mm²(Type 2) and S< 16mm² (Type 1).
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Installation in a plastic enclosure
(e.g. Pragma)
L1 ~ 12cm
L1+L2+L3 < 50 cm
L2 ~ 0cm
L3 ~ 5cm
Main incoming earth via the bottom
(main earth bar and intermediate earth terminal).
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Installation in a plastic enclosure
(e.g. Pragma)
L1 ~ 12cm
L2 ~ 0cm L1+L2+L3 < 50 cm
L3 ~ 15cm
Incoming earth cable via the top
(main earth bar and intermediate earth terminal).
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Installation in a metal enclosure
(e.g. Prisma Plus)
●Directly on "metal chassis".
●Use a lock washer to connect the
cable to the chassis to give a good
electrical contact.
The installation is possible
only if the enclosure complies
with standard
IEC 60439-1.
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ELECTRICAL DISTRIBUTION PROTECTION
Protection of people Circuit Protection of sensitive
protection equipment
Against permanent failure (due to Against temporary
overcurrent, overload, earth fault) failure (overvoltage, lightning)
In the low-voltage system, the surge arrester is essential to
ensure complete protection.
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