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Lightning & Surge Protection &
Earthing/Grounding
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Data from space-based optical sensors reveal the uneven distribution of worldwide lightning strikes. Units: flashes/km2/yr.
Image credit: NSSTC Lightning Team.
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COMPARATIVE PROBABILITY OF DEATH FOR AN INDIVIDUAL PER YEAR OF EXPOSURE (ORDER OF MAGNITUDE)
����� � ��� � ������ � ��� � ������ � ��� � ������ � ��� � � � ��������� � ������� � � �������� ��������� � ������� � � �������� ��������� � ������� � � �������� ��������� � ������� � � ���������������� "!$# % &(')� !+*�, -). . -)/10"-�,�2+*)3"4 %5� 76�&+&8:9 9 *+'�')� 2+-� �. / %5� �;�< &+&+&= , *)> > � '�*+'�')� 2+-� �. / %5� �?�< &+&+&@ ��, �7� 1A "2�B�/�. , 3 %5� (C+&�< &+&+&D , �)E5 +� "! %5� (C+&�< &+&+&F ��� /"�� +� "! %5� G% &+&�< &+&+&H *). B+, * 9+D � /"*)/�. -�, / %5� (I+&+&�< &+&+&D , � J+� "!K?L&L� �NM�3(, �+*+2 %5� G%"< &+&+&�< &+&+&1# 0"-�,��+'�')B+, , -� "'�-+4O -�� "!(/�. , B"')�7M�3 9 � !�P�. +� "! %5� �;�< &+&+&�< &+&+&
Source: BS 6651:1992
In Australia: Between 6 and 10 people are killed each year by lightning. Most common causes: - Playing golf- Swimming, sailing, fishing, being in large open areas
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Myths about lightningLIGHTNING NEVER STRIKES TWICE (Truth: it hits the Empire State Building about 25 times a year.)
RUBBER (TYRES) WILL INSULATE ME FROM LIGHTNING (Truth: it has travelled miles through space…a few inches of rubber mean nothing at all.)
YOU SHOULD NEVER TOUCH SOMEONE AFTER HE/SHE HAS BEEN HIT BY LIGHTNING (Truth: It is perfectly safe.)
LIGHTNING CAN BE PREVENTED (unconfirmed/sheer advertising.)
FIRST STRIKES FROM LIGHTNING CAN BE PREDICTED (unconfirmed/sheer advertising.)
NEW HIGH-TECH TYPES OF LIGHTNING RODS CAN CONTROL LIGHTNING (unconfirmed/sheer advertising.)
BOLT FROM THE BLUE (Misconception)
Source: National Lightning Safety Institute (USA)
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The localized nature of lightning
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“Bolt from the blue” phenomenon
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“Bolt from the blue” phenomenon
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The unpredictability of lightning
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Fairly accurate average distance
Ignore
Boltek StormTracker Lightning Detector- RF type detector
- Direction accurate if antenna installed correctly
- Distance only approximate indication: Strong strikes appear closer than what they really are, weak strikes appear further away.
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When is lightning an immediate threat?- AS1768 suggests 5 km
- New research in USA found distance between subsequent strikes greater than previously thought: frequently up to 8km and sometimes more
- NLSI recommends 30/30 rule: Employ safety measures / seek shelter when Flash-to-Bang time is 30 seconds or less (10 km); wait 30 minutes after last local lightning
- Sound of thunder travels approx. 1 km every 3 seconds
- Audible range of thunder approx. 8 – 13 km
- Safe shelters: Substantial buildings, fully metal enclosed vehicles, large metal sheds
- Unsafe shelters: TREES, vehicles with open sides or non-metal roofs / canopies, tents, fibre-glass cubicles, close to isolated towers / masts
- Surface arc: May be lethal up to 40m from object struck (step potential) –mitigated by good earthing
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Effects of lightning discharge currents in the ground
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� � � � � � � � � � � � � � � � � � � � � �� � � � � � � � � � � �� � � ! � � � � � � � � � �� � � � " � � � � � � � # � � � � � � $ � � � � � � � � � � � � � �� $ � � � � � � � � � � � � � � � �
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Incorrect / Unnecessary: Air terminal on top of metal structure
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Incorrect / Unnecessary: Air terminal on top of metal structures
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Incorrect / Unnecessary: Air terminal on top of metal structures
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Incorrect earthing practice: Earth conductor coiled – high impedance
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Incorrect practice: Surge arrester not earthed adequately
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Incorrect practice: Surge arrester not earthed adequately
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Incorrect practice: Surge arrester earthing introduces surges again into wiring
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Incorrect practice: Surge arrester earthing introduces surges again into wiring
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Incorrect practice: Surge arrester earthing introduces surges again into wiring
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Interest: Plane hit by lightning
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