White Paper • CT1003
Integrated vs
Non-Integrated
By: Chris Martin
SPD Product Manager
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current technology ® Integrated vs Non-Integrated
Hard wired surge protection is typically installed two ways, internally or externally to the switch gear. The benefits of internally
mounted units have been touted by the panel board manufacturers. This benefits are overstated, as these manufactures sell their
own SPD devices. This paper will dispel key benefits of internally installed units and demonstrate the advantages of externally
mounted Surge Protection Devices (SPD) units.
Shortest Lead Length
All SPD manufacturers suggest in their installation instructions to keep the lead length as short as possible, realizing the
impact lead length has on the installed performance of surge devices. Per UL 1449 and IEEE C62.45, all surge manufacturers
evaluate their products with six inches of lead length. The six inch lead length is chosen so that all SPD products can be
evaluated based on the same test setup and criteria. The diagram below illustrates how the test is performed.
The surge is
injected here
Figure 1
Clamping characteristics
are recorded by an Oscilloscope
The test is performed by providing 6 inches of lead length outside of the enclosure of the unit under test. A surge is applied across
a mode, such as line to neutral. The surge current will flow through the phase conductor and travel a path inside the surge device,
with any remaining current flowing back through the neutral conductor. An oscilloscope will also be attached across the leads of
the mode being tested to capture how the surge unit effectively mitigated the effects of the surge. The lead length of the phase
conductor and the lead length of the neutral conductor will both have an impact on the overall performance of the surge device.
The key point is that the surge has to travel not only through the line conductor, but also through the neutral conductor. In this
example, the surge current travels a minimum of
twelve inches; the length of the neutral conductor
plus the length of the phase conductor and distances
internal to the SPD.
Tests have shown that every foot of standard cabling
added to the installation length of an SPD increases
the clamping levels (or let-through voltage) by as
much as 100–150 volts per foot, severely impacting
the installed performance of the surge device. This
exposure to higher let-through voltages can put the
downstream loads at serious risk.
Figure 2
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current technology ® Integrated vs Non-Integrated
The overall installed system lead length required to install
the surge device dictates the let-through voltage capability
(or performance) of the installed SPD. An integrated SPD
tapped directly to the bus may have very short connections
to the phases but the installed clamping levels must also
take into account the lead length of the Neutral and Ground
conductors that are part of the installation. Most integrated
SPDs are installed at the top or bottom of an extended panel
board where the Neutral and Ground buses are typically at the
opposite end. If you follow the path the surge would have to
take, the overall length for this type of installation can be up
to six feet or longer, which is a significantly longer lead length
than most integrated surge manufacturers mention in their
marketing material. The overall lead length for this internally
mounted surge protective device will have a negative impact
on the installed performance of the surge device.
With proper installation, it is possible for an externally mounted
SPD to be tapped to the bus or occupy a breaker position close
to the Neutral and Ground bus. This provides a shorter overall
system lead length, allowing for better clamping performance
and a better performing unit than an integrated SPD.
Surge Handling Capability
Some internally mounted surge protection devices are being
listed as Type 2 SPDs to the UL 1449 3rd Edition standard.
Type 2 SPDs must be installed behind an upstream, overcurrent protection device because the SPD cannot pass the
UL 1449 tests without having the upstream OCPD to remove
it safely from the circuit. These devices are relying on the
upstream device to trip or open, removing the SPD from the
circuit before it fails destructively. If an SPD that is rated at
200kA per mode is installed behind a 30A breaker, the single
surge rating of that system will be reduced to the lowest single
surge rated component of that installed system. Breaker
manufacturers publish an SCCR (short circuit current rating)
or kAIC value which is based on how much 60Hz current the
device can handle before tripping or opening. Surges are subcycle events and typically last as long as 20 microseconds, so
the breakers SCCR rating has no bearing on how it will respond
to a surge event. Figure 3 depicts a circuit breaker’s trip and
fail kA levels when subjected to an 8 x 20 microsecond wave
shape. A 200kA SPD installed behind a 30A breaker would
only be able to handle a 62kA surge before the breaker trips
and removes it from the circuit.
Figure 3
SPD Failures
SPD devices have a finite life. In UL 1449 (February, 2007),
changes to the safety regulations that pertain to SPDs
addressed real world concerns regarding catastrophic failures
of SPDs. Prior to the introduction of intermediate fault currents
that were included to expose the metal oxide varistor’s
weakness to temporary over voltage events, SPDs subjected
to a temporary over voltage event would continually conduct
and go into thermal runaway, potentially catching fire and
causing damage. SPDs internal to the gear that failed in this
manner ended up, in most cases, taking out the entire panel.
Fortunately UL 1449 was changed to include testing that would
ensure this kind of failure does not happen. However even a
benignly failed SPD must be repaired or replaced. Replacing
any part of an internally mounted SPD device leaves the end
user with the following options:
Option 1: An internally mounted surge device is typically
mounted behind the dead front to the panel. The safest method
for repairing or replacing the defective SPD requires shutting
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current technology ® Integrated vs Non-Integrated
down the main breaker to the panel, terminating power to all
down stream equipment, so that all power is off during the
repair or replacement of the internally mounted SPD.
Summary
Option 2: Leave the failed SPD installed and do nothing. It is
common for failed integral SPDs to be left un-repaired because
they are attached to a panel feeding a critical load that cannot
be shut down, or they are located in common public areas
where it would be unsafe to repair or replace them.
Option 3: The operator must work on the panel live because
critical equipment connected to the panel cannot be shut
down. The operator must wear the appropriate personal
protective equipment based on equipment ratings and
available fault current, which may require the operator to
wear tinted glasses, gloves, protective clothing, or a hood.
Working on live gear is never a safe option. Statistics based
on hospitalization records suggest that every day in the United
States, five to ten arc flash events occur that involve a fatality
or serious injury to an employee.
Internally mounted SPDs do not necessarily offer a better
performing system. When taking into consideration the total
surge path of the integral SPD, a long neutral or ground
connection may have an adverse affect on the installed
performance. Internally mounted SPDs may fail in a safe,
benign manner, but may require unnecessary exposure to the
worker who must repair or replace the unit. Type 2 SPDs must
be mounted behind an over current protection device, limiting
the overall surge current rating of the installation.
Externally mounted SPDs can have lead lengths just as short,
if not shorter, than internally mounted SPDs. The repair or
replacement of an externally mounted SPD does not require
the shut down of the entire panel or unnecessary exposure
to live voltage. An externally mounted Type 1 SPD is a more
robust offering that does not limit the surge rating of the device
by requiring an upstream over current protection device.
OSHA and the NFPA are taking arc flash issues very seriously
and suggest to all building owners that personnel working
on live gear must wear the appropriate protective personal
equipment.
Externally Mounted SPD Replacement
An externally mounted surge unit eliminates the concern for
the safety of the operator who must perform the service or
repair. If the unit is connected to the panel through a breaker,
then the breaker can be turned off that feeds the surge device
without disrupting power to the rest of the load. If the unit is
equipped with an option integral disconnect, ensure that the
line side of the disconnect is covered by a barrier. In each of
these scenarios the surge unit can be repaired or replaced
without exposing the operator to live voltage and without
disrupting power to down stream equipment.
Thomas & Betts Power Solutions
5900 Eastport Blvd. • Richmond, VA U.S.A. 23231-4453 USA
Tel: (804) 236-3300 • Toll free: (800) 238-5000 • Fax: (804) 236-4841
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