Surge Protection Excerpts from IEEE Standard 1100-2005.
The Emerald Book: IEEE Recommended Practice for
Powering and Grounding Electronic Equipment
3.2.6 Expectation of surge disturbance: “…Load switching is a common cause of surges in power
wiring.”
3.2.6.1 Nature of lightning strike damage: “…many types of electronic circuits can be damaged or
destroyed when exposed to an excess current or an excess voltage produced by that current.
If lightning strikes on or near overhead electric power or telephone line, a large current will be
injected into or induced in the wires, and the current can do considerable damage both to the power
and telecommunications equipment and to anything else that is connected to the system.”
3.2.6.2 Nature of surge effects in power and communication systems: “Power line surges, whether
caused by lightning, circuit switching, or other events, typically represent the biggest threat because
of larger exposure areas than, for example, a lightning strike.”
3.4.3 Surge protection: “Surges can have many effects on equipment, ranging from no detectable
effect to complete destruction…electronic devices can have their operation upset before hard
failure occurs. The semiconductor junctions of electronic devices are particularly susceptible to
progressive deterioration…few solid state devices can tolerate much more than twice their normal
rating. Furthermore, data processing equipment can be affected by fast changes in voltage with
relatively small amplitude compared to the hardware-damaging overvoltages…For large surge
currents, this diversion is best accomplished in several stages. The first diversion should be
performed at the entrance to the building…a second protective device at the power panel…”
4.4.1 Sources/characteristics: “There exists a large number of potential sources of electrical surges
that can cause harm to electronic equipment and systems. The majority of these sources can be
divided into two major categories—electrical power circuit switching and environmental
causations.”
4.4.1.2.2 Nonarcing and remote-arcing atmospheric charge redistribution: “…effects ranging from
simple data upset and corruption to actual equipment damage. And there maybe no first-hand
report of any nearby lightning strikes to associate the event with.”
4.4.5 Potential impact of EMI: “Depending on the severity of the surge and the susceptibility of the
equipment, three types of occurrences are possible… : data disruption, hardware stress, and
hardware destruction.”
4.4.5.1 Type I, signal-data disruption: “Signal-carrying circuits are susceptible to surge interference
via conduction, inductive and capacitive coupling, and electromagnetic radiation.”
4.4.5.2 Type II, gradual hardware stress and latent failures: “A single lightning or switching surge
often causes immediate, but not readily apparent physical damage to semiconductor devices. This
damage then finally appears at some later time…”
4.4.5.3 Type III, immediate hardware destruction: “The third possible impact of surges is the
immediate obvious and total destruction of hardware components in a single incident”
7.2.4 Surge suppressors: “…Effective surge protection for an entire building power distribution
system requires the coordinated use of large-capacity current-diverting devices at the service
entrance followed by lower capacity voltage-clamping devices applied strategically throughout the
power system.”
8.1 Recommended design/installation practices: “Desired performance of electronic load
equipment typically depends on various items, such as the proper selection and arrangement of the
electrical distribution system, the proper selection and installation of electrical distribution
equipment, the proper selection and installation of a grounding system for both the electrical power
system and the electronic load equipment, and the proper selection and application of surge
protective devices (SPDs).”
8.4.2.5 Surge protective device considerations: “Recommended practice is that SPDs be applied to
service entrance electrical switchboards and panelboards, and panelboards located on the
secondary of separately derived systems that support ITE, telephone, telecommunications,
signaling, television, or or other form of electronic load equipment (refer to 8.6 for further details).
These devices may be installed externally or internally to the switchboard or panelboard.
Panelboards are available that contain integrally mounted SPDs that minimize the length of the
SPD conductors, thus optimizing the effectiveness of the device. However, as pointed out in IEEE
PC62.72TM (Draft 1, 1 November 2005) [B2}, when an SPD is located inside switchboards
or panelboards, there is a concern that failure of the SPD can cause collateral damage to the
switchboard or panelboard, including compromising the insulation system with subsequent L-L
and L-G faults.”
8.4.2.5 Surge protective device considerations: “…It is recommended practice that all SPDs have a
means to disconnect them for service. Locating the SPD external to the switchboard or panelboard
allows a disconnecting means to be located inside the switchboard or panelboard and does not
require access to the switchboard or panelboard interior when servicing the SPD.”
8.6 Lightning/surge protection considerations: “…a listed and properly rated SPD should be
applied to each individual or set of electrical conductors (e.g., power, voice, and data) penetrating
any of the six sides forming a structure.”
8.6.1 Selection: “…SPDs for three-phase, 4-wire circuits are generally recommended to be
connected in all combinations of line-to-line, line-to-neutral, line-to-ground, and neutral-toground.”
8.6.2 Installation: “…Recommended SPD installation practice is for all lead lengths to be short and
shaped to minimize open-loop geometry between the various conductors…by twisting all the phase,
neutral, and equipment grounding conductors together; and by avoiding any sharp bends and coils
in the conductors.”
8.6.3 Service entrance surge protection: “Facilities housing electronic load equipment of any type
should have service entrances equipped with …Category “C” SPDs, as specified in IEEE Std
C62.41.”
8.6.4 Premise electrical system surge protection: “…it is recommended that additional surge
protective devices of listed Category “B” or Category “A,” as specified in IEEE Std C62.41, be
applied to downstream electrical switchboards and panelboards, and panelboards on the secondary
side of separately derived systems if they support communications, ITE, signaling, television, or
other form of electronic load equipment”
8.6.5 UPS system surge protection: “…It is recommended practice that both the input circuit to the
UPS and the associated bypass circuits (including the manual bypass circuit) be equipped with
effective Category “B” SPD”
8.6.6 Data/communication/telecommunication systems surge protection: “Electronic equipment
containing both ac power and metallic data cabling should also be properly protected via SPDs on
both the ac power and data cables.”
8.6.8 Exterior building systems and piping lightning/surge protection: “All exterior mechanical
systems items (e.g., cooling towers, fans, blowers, compressors, pumps, and motors) that are in an
area not effectively protected by a lightning protection system per NFPA 780 should be considered
as targets for a lightning strike. Therefore, it is recommended practice to individually provide SPD
protection on both the power input and data circuits connected to all such equipment.”
9L.1.3.1 Damage caused by SPDs: “…SPD overcurrent protection is the most important (and often
overlooked) aspect of reliability and safety. Any SPD component can fail, open or shorted, due to
surge voltage stress or temporary overvoltage (TOV) stress (such as a lost neutral). This TOV
stress causes many more SPD failures than actual transient surges. The result may be smoke, fire,
or explosion for some of the metal-oxide varistor (MOV) based SPDs. This occurs regularly in real
world SPD installations, but can be controlled with component level fusing or thermal fusing. Done
properly, this fusing will interrupt excessive continuous current through the component, interrupt
available utility fault current, and yet pass transient current. Component level fusing in a SPD can
provide a fail-safe system preventing catastrophic failure or complete loss of protection.”
9L.1.6.3 SPD topology and mounting considerations: “At some point in the process of acquiring
surge protection the decision must be made on whether a series or parallel device is the better
choice for the application. For example, if surge protection is required for a building or factory,
parallel-connected devices may be sufficient to proactively stop high-energy transients from
mitigating downstream. On the contrary, if a susceptible or critical piece of equipment needs to be
protected from transients or isolated from induced high frequency, than a series connected filter
may be the better choice.”