Traffic Systems
design guide
S
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Contactors
Control Relays
Today’s electronic world is becoming more intolerant to surges. The most effective way
to prevent the damaging effects of surges is to install hardwired surge protective devices
(SPDs) throughout the electrical distribution system. By addressing the following two
questions you can design a SPD protection scheme that will maximize your electrical
systems’ surge immunity.
1- Where should hardwired SPDs be
installed in the electrical system?
2- What size and type of SPD is
appropriate for my application?
Ideally, every electrical panel should be surge
protected. In reality this is typically not practical or
feasible. The IEEE C62.41 series promotes a
cascaded design whereby SPDs of appropriate size
are installed in each of the IEEE electrical system
location categories A, B, and C. One also has to
take into account surges that can back feed into a
system bypassing the electrical service entrance
as well as protecting against internally generated
surges that account for 70% of all surges
experienced by a facility.
There are a number of SPD characteristics
that one should look for when deciding what
type of SPD is appropriate for their
application:
The acronym, SOLID, can be used to easily
remember where to install SPDs:
Service Entrance
Outside loads powered from distribution panels
Lower voltage distribution panels
Individual critical equipment
Data, telephone, and coaxial cables
UL Listed SPD having the ‘UL Mark’
• Ensures UL 96A and NEC 285.5 Compliance
20 kA I-nominal Rating
• Ensures UL 96A and NFPA 780 4.18.3.1.2
100 kA – 200 kA Short Circuit Current Rating
• Ensures compliance with NEC 285.6
Low Voltage Protection Ratings:
• 120V Systems – 700V (L-N, L-G)
• 480V Wye Systems – 1200V (L-N, L-G)
• 480V Delta Systems – 1800V (L-G)
Type 1 SPD Designation
• Avoids addition of supplemental breakers or
fuses that can add cost and liability
Surge Protecting a TRAFFIC SYSTEM
APT SOLID Solutions
APT design guide
GENERAL TRAFFIC SYSTEM DESIGN CONSIDERATION:
It is considered ‘good’ engineering practice to require all modes of protection (L-N, L-G, N-G) in traffic systems. Consider a
lightning strike that hits ground. The ground potential rises, creating surge problems from G-N and G-L. Surges are unlikely to
propagate to the power system ground due to inductive effects. Because the surge is partially trapped at the load end,
additional modes of protection make sense in traffic system applications.
Contactors
Control Relays
Service Entrance/Traffic
Cabinet Power Entry
ITS/Traffic electrical systems typically do
not have a traditional service entrance
panel. Rather, they have power entry in the
ITS/Traffic roadside cabinet. Installing a
SPD at the power entry will stop surges
coming from the utility before they get in.
Due to cabinet space constraints, a smaller
footprint SPD is required. In lightning prone
areas, 100kA per phase (L-N + L-G) surge
capacity is appropriate. In less lightning
prone areas 40kA per phase (L-N + L-G) is
appropriate.
RECOMMENDATIONS:
TEXCS: 100kA per phase
SPDEE: 50kA per phase
Outside Loads
ITS/Traffic cabinets feed a number of
outside loads. Including traffic signals and
cameras that are all susceptible to surges.
To prevent surges from back feeding into
the cabinet and damaging cabinet
components, surge protection should be
installed in the cabinet prior to the power or
data signal exiting the cabinet and going to
the outside load.
RECOMMENDATIONS:
SPDEE: 50kA per phase (for power)
DxxxVxP: 50kA per phase (for power)
D60401: Low Voltage Data Signals
BNC SPD: Cable Protection
Lower Voltage Panels
(likely not to apply)
If the ITS/Traffic system has a higher voltage at
power entry and is stepped down to a lower
system voltage surges can be back feed through
the windings of the transformer to upstream
equipment. A SPD should be applied on the
secondary side of the step down transformer
because it is a separately derived system. If the
X0 connection is tied directly to the upstream
ground surge problems can be minimized.
RECOMMENDATIONS:
SPDEE: 50kA per phase
APT has guide specifications written
specifically for ITS/Traffic System
applications. Please contact APT
Engineering Sales at info@apttvss.com.
Individual Loads
Data Lines
ITS/Traffic individual loads are typically a
large distance away from the traffic cabinet
so localized redundant protection for
sensitive expensive equipment such as
Dynamic Message Signs (DMS) should be
included.
ITS/Traffic uses data lines for cameras,
automation, sensors, etc. Not only do those
data lines need to be protected at the
cabinet, but they also need localized
protection at the equipment.
RECOMMENDATIONS:
SPDEE: 50kA per phase (for power)
DxxxVxP: 50kA per phase (for power)
RECOMMENDATIONS:
D60401: Low Voltage Data Signals
BNC SPD: Cable Protection
Advanced Protection
Technologies
14550 58th Street North
Clearwater, Florida 33760
727.535.6339
fax: 727.539.8995
800.237.4567
wwww.aptsurge.com
info@aptsurge.com
RevC 10.11.10