IEEE Emerald Book Series --Integrating SPDs into Power Distribution Equipment
White Paper --- May 9, 2007
IEEE Standard 1100-2006 (Emerald Book),
Section 8.4.2.5 (p. 269), “…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…Locating the SPD external to the switchboard or
panelboard allows the 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.”
INTEGRATED SURGE PROTECTION DEVICES
After discussing SPD attributes, the consulting
engineer often asks “Can SPDs be integrated into
service or distribution equipment?” Unfortunately,
there are no simple answers to this question. First, one
needs to identify the probabilities and risks associated
with integrating SPDs into power distribution
equipment. Once the risks have been analyzed, then
the question can be answered in terms of probabilities.
Ultimately, the consulting engineer will need to
determine if the risks are worth the perceived benefits
of integrating the SPD into service or distribution
equipment.
There are two scenarios that represent risk when
integrating SPDs into power distribution equipment.
These are:
1. An end-of-life condition (catastrophic failure)
of the SPD within the equipment
2. A reduced protection condition (repairable) of
the SPD within the equipment
END OF LIFE CONDITION
A majority of SPDs use metal-oxide varistors
(MOVs) as the surge component that diverts
overvoltage transients away from electronic circuits or
systems. MOVs are used because they are readily
available, and are competitively priced.
When MOVs reach an end-of-life condition, they
create a significant power that is dissipated in the form
of heat. The heat from the MOVs is so intense that it
can cause flame retardant plastics to burn; e.g.
enclosures, printed wiring boards.
The intensity of the heat can also melt buss bars,
or copper traces on printed wiring boards. The burning
or melting materials emit conductive smoke or ionized
gases into the local atmosphere (within the distribution
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equipment) . In addition to smoke, the end-of-life
condition also contributes to probability of conductive
material fragments being expelled by the SPD into the
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distribution equipment .
When SPDs fail in this condition, collateral
damage of the distribution equipment is likely.
Collateral damage can take the form of:
•
•
Creation of line-to-line or line-to-ground faults
from the reduction of spacings as a result of
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conductive gases or material fragments
Damage to insulation systems or over-current
protective devices within the distribution
2
equipment
Each of these options has consequences that need to
be examined in the design, or re-design stage of the facility.
Once the facility is designed, it can be expensive to retrofit
because the long term capabilities of the system were not
accounted for.
Removing power from the distribution equipment
requires that the connected loads be de-energized. In
many applications, e.g., data centers, telecommunication
shelters, and industrial plants, the criticality of the process
is so important that connected loads cannot be deenergized without significant loss of revenue to the
organization.
While SPDs are evaluated by UL for safety, two
problems exist with integrated SPDs. First, integrated
SPDs are only required to be UL Recognized
components. The test protocol for UL Recognized
SPDs is less stringent than the test protocol for UL
Listed products.
Second, even the testing
methodology for UL Listed products does not use any
statistical sampling methods for ensuring the safety
of the SPD design. Because statistical sampling
techniques are not used in product safety testing,
samples of SPDs can pass UL testing, but still be
inherently unsafe. The probability of an end-of-life
condition resulting in damage to the distribution
equipment is moderate to low, but still exists. To
minimize the risk and provide the best solution to the
customer, SPDs, or any other devices, should not be
allowed inside the distribution equipment.
REPAIRABLE CONDITION
The second scenario, repair of SPDs integrated
into distribution equipment, has a high to moderate
probability of occurring as most devices, including
SPDs, require repair/maintenance during their lifecycle. Integrated SPDs have unique concerns when it
comes to maintenance. When integrated SPDs
require repair, the maintenance technician has two
options:
1. Remove all power from the distribution
equipment, and then service the SPD
2. Leave power applied to the distribution
equipment, disconnect power to the SPD,
service the SPD
If power cannot be removed because of the criticality
of the process, this leaves the organization to make the
choice of not repairing the SPD or repairing the integrated
SPD while power is applied to the distribution equipment. If
the SPD is not repaired, then the system is not protected
from transient conditions.
The only alternative is to leave power applied to the
distribution panel, but disconnect the power to the SPD.
This decision requires that the protective panels of the
distribution equipment be removed while power is still
available to the distribution panel and the remaining loads.
Removing the panels designed to protect personnel from
faults and arc-flash events has many dangers. To attempt
this type of repair, the proper personal protection
equipment (PPE) is required. The type of PPE required is
based on the amount of specific energy available at the
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distribution equipment . In addition, all personnel are
required to maintain a safe distance from the open
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distribution equipment .
CONCLUSION
The IEEE Emerald Book provides guidance
against integrating SPDs internal to switchboards or
panelboards. Integrating SPDs into switchboards or
panelboards can cause line-to-line or line-to-ground
faults when an SPD fails.
Whenever an SPD needs to be serviced, an
integrated SPD requires the maintenance technician
to access the interior of the switchboard or
panelboard. Integrated SPDs needing repair also
require that power be completely removed from the
distribution equipment, or that repair must be
undertaken by a maintenance technician using the
proper personal protection equipment (PPE).
To increase safety in the workplace, increase
process capability, and reduce the overall
costsforrepair or replacement of the SPD, the
following SPD design considerations should be
applied:
•
•
•
•
SPDs perform an important function by reducing transient conditions so that processes can operate as designed.
Using scientific processes, best engineering practices, and
various codes and standards will create safer, more
efficient, and more profitable processes and installations.
References
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100 Emerson Parkway
Binghamton, NY 13905
P (607) 721 8840
P (800) 288 6169
F (607) 722 8713
E contactsurge@emerson.com
WP-30010 Rev. 2 - 1/13
Use a quality, appropriately rated SPD
Use a dedicated circuit breaker to the power the
SPD
Ensure that the SPD is rated for the point of
application
Connect the SPD externally to the distribution
equipment
Institute of Electrical and Electronic Engineers (2006). Draft Guide
for the Application of Surge Protective Devices for Low-Voltage
(1000 Volts or Less) AC Power Circuits. PC62.72 Draft 4, 2006
July. IEEE: NY, NY USA.
Institute of Electrical and Electronic Engineers (2005). IEEE
Recommended Practice for Powering and Grounding Electronic
Equipment. IEEE Standard 1100TM. IEEE: NY, NY USA.
National Fire Protection Association (2004). Standard for Electrical
Safety in the Workplace.
NFPA 70E.
NFPA: Quincy, M