SPD Decision Flow Chart Surge Protection
Non-Dwelling
Devices
Hager Ltd.
Hortonwood 50
Consequences Telford
Shropshire
caused by TF1 7FT
overvoltage leads to; Yes
a) serious injury to or loss Sales Service Centre: 01952 675612
Technical Service Centre: 01952 675689
of human life
b) interruption of public services Hager.co.uk
and/or damage to cultural heritage SPD sales@hager.co.uk
c) interruption of commercial or Required technical@hager.co.uk
industrial activity
d) interruption to an Hager Ltd. - Ireland
Unit M2
installation with a large Furry Park Industrial Estate
number of collocated Swords Road
individuals. Santry
Dublin 9
No D09 NY19
Ireland
Republic of Ireland Tel: 1890 551 502
Perform risk Republic of Ireland Fax: 1890 551 503
Northern Ireland Tel: 00 44 7968 147444
assessment Northern Ireland Fax: 00 353 1 8869520
to determine
Calculated Risk CRL value Hager.ie
customer.service@hager.ie
Level (CRL) value is < 1000
(443.5) or if no risk
assessment is
performed.
CRL value is > No SPD
1000 Required
Dwelling
At a
Glance
SPD
Consequences No Required
caused by
overvoltage for a
single dwelling unit
where an assessment
shows the total value of the
electrical installation and
connected equipment
does not justify
the cost of SPD No SPD
protection. Yes
Required
For the full SPD decision flow chart for installations, please May 2019
see Figure 3.7.2.2 in the 18th Edition On-Site guide. AAGSUR418
Surges & Surge Protection Devices Selection Criteria
The Dangers
SPD’s protect electrical Surge protection devices are classified according to
and electronic equipment their functions:
against transients, originating
from lightning, switching of Type 1
transformers, lighting and SPD which can discharge partial lightning current with
motors. a typical waveform 10/350 μs. Usually employs spark
The whole nature of how electrical gap technology. This, if required, will be installed
equipment is used in homes and These transients can in the primary distribution board at the origin of the
at work has evolved; with everyday cause premature ageing electrical installation. A Type 1 SPD does not in itself
activities relying on electronic of equipment, downtime, offer the required protection level and must be used
equipment. or complete destruction of in conjunction with coordinated type 2 devices. An
electronic components and installation with a lightning protection system will
Products such as computers, printers, TVs, materials. require a Type 1 SPD.
industrial control equipment such as PLC’s,
alarms, microwaves and LED lighting are Type 2
common place. These can all be vulnerable 18th Edition Requirements SPD which can prevent the spread of overvoltages
to transient overvoltages, which can in the electrical installations and protects equipment
significantly reduce the equipment’s lifespan The 18th edition BS 7671 now stipulates: connected to it. It usually employs metal oxide varistor
through degradation and damage. Protection against transient overvoltages shall be (MOV) technology and is characterised by an 8/20
provided where the consequences caused by an μs current wave. This device would normally be in
A transient overvoltage or surge is a short overvoltage could sub-distribution boards and in the primary distribution
duration increase in voltage measured board if there was no requirement for a type 1 device.
between two or more conductors. In short (i) result in serious injury to, or loss of, human life, or
this means anything from microseconds (ii) result in interruption of public services and/or Type 3
(millionths of a second) to a few damage to cultural heritage, or These SPDs have a low discharge capacity. They
milliseconds (thousandths of a second) (iii) result in interruption of commercial or industrial must therefore only be installed as a supplement to
in duration. activity, or Type 2 SPD and in the vicinity of sensitive loads. Type
(iv) affect a large number of co-located individuals. 3 SPD’s are characterised by a combination of voltage
waves (1.2/50 μs) and current waves (8/20 μs).
For all other cases, a risk assessment according to
Regulation 443.5 shall be performed in order to Maintenance
determine if protection against transient
overvoltages is required. If the risk assessment is not Most SPDs have an indication window that they are
performed, the electrical installation shall be operational. If the indicator is green they are providing
provided with protection against transient protection. If they are red then they have reached
overvoltages. ‘end of life’ and will need replacing. Often there is a
replaceable cartridge which can simply be withdrawn
For a single dwelling unit it will be a decision for the and replaced with a new operational device.
house owner to make whether they consider the
small additional cost of the surge protection device
justified to protect their installation and equipment
against these damaging overvoltages.
