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Guide to BS EN/IEC 62305 BS EN/IEC 62305-4
Electronic systems now pervade almost every aspect of
our lives, from the work environment, through filling
the car with petrol and even shopping at the local
supermarket. As a society, we are now heavily reliant
on the continuous and efficient running of such
systems. The use of computers, electronic process
controls and telecommunications has exploded during
the last two decades. Not only are there more systems
in existence, the physical size of the electronics
involved has reduced considerably (smaller size means
less energy required to damage circuits).
BS EN/IEC 62305 accepts that we now live in the
electronic age, making LEMP (Lightning
Electromagnetic Impulse) protection for electronic and
electrical systems integral to the standard through
part 4. LEMP is the term given to the overall
electromagnetic effects of lightning, including
conducted surges (transient overvoltages and currents)
and radiated electromagnetic field effects.
LEMP damage is so prevalent such that it is identified
as one of the specific types (D3) to be protected
against and that LEMP damage can occur from ALL
strike points to the structure or connected services -
direct or indirect - for further reference to the types of
damage caused by lightning see Table 5 on
page 270. This extended approach also takes into
account the danger of fire or explosion associated with
services connected to the structure, e.g. power,
telecoms and other metallic lines.
Lightning is not the only threat…
Transient overvoltages caused by electrical switching
events are very common and can be a source of
considerable interference. Current flowing through a
conductor creates a magnetic field in which energy is
stored. When the current is interrupted or switched
off, the energy in the magnetic field is suddenly
released. In an attempt to dissipate itself it becomes a
high voltage transient.
The more stored energy, the larger the resulting
transient. Higher currents and longer lengths of
conductor both contribute to more energy stored
and also released!
This is why inductive loads such as motors,
transformers and electrical drives are all common
causes of switching transients.
Significance of BS EN/IEC 62305-4
Previously transient overvoltage or surge protection
was included as an advisory annex in the BS 6651
standard, with a separate risk assessment. As a result
protection was often fitted after equipment damage
was suffered, often through obligation to insurance
companies. However, the single risk assessment in
BS EN/IEC 62305 dictates whether structural and/or
LEMP protection is required hence structural lightning
protection cannot now be considered in isolation from
transient overvoltage protection - known as Surge
Protective Devices (SPDs) within this new standard. This
in itself is a significant deviation from that of BS 6651.
Motors create switching events
BS EN/IEC 62305-4 Electrical and
electronic systems within structures