Specifications

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APPLYING SURGE PROTECTORS
Surge protectors are relatively simple devices, yet they must
be carefully selected and applied to function properly. When
selecting and applying surge protectors, there are a few
essentials to keep in mind.
First, the operating voltage of the system is important. Surge
protectors are voltage sensitive switches and must not clamp
the normal system voltage. The surge protector clamp voltage
must be higher than the system voltage. For example, a 24
VDC system voltage generally uses a 30 volt surge protector.
Second, some surge protectors have an input side and an
output side. If installed backwards, they will fail prematurely.
Lastly, grounding is often misunderstood when it comes to
proper installation of surge suppressors. This can seriously
affect the performance of protection systems and lead to
electronics damage. Use the Protection Zone Concept to
effectively apply surge protectors to EMS and BAS
installations.
The Protection Zone
The protection zone is an imaginary circle drawn around and
encompassing electronic equipment items that are located
in close proximity to each other (see Figure 1). Everything
passing through the imaginary circle should be commonly
grounded and should have surge protection.
Figure 1. The Protection Zone, Window, and Single Point Ground
S P G
SP
To Approved
Ground
Data Line
PC642C
Surge Protector
AC Service
Power Strip
Data Line
Single Point Ground
AC Service
Surge Protector
HSP-121BT1RU
*Ground wires between
single point ground and
surge protectors must
be very short.
The Protection Zone
Window
*
The Protection Zone
*
The single point ground is a common ground point or node
used in the protection zone to bond together all ground
references inside the zone. Surge currents passing through
a ground conductor generate a voltage across the conductor.
This is primarily due to inductance of the wire. Inductance
is highly dependent on conductor length; therefore, it is very
important to keep suppressor ground wires to the single point
ground very short.
The protection zone window is a hypothetical small opening
in the zone through which all electrical conductors enter or
leave. The single point ground is located at the protection zone
window. Figure 2 illustrates a typical installation of equipment
within a small area; however, there are three problems
associated with the installation depicted.
Problem #1
There are four ground references in Figure 2. AC outlet #1, AC
outlet #2, AC outlet #3, and the data line all present separate
ground references. The three AC outlet grounds are connected
together at the power panel many feet away. The ground wire
lengths offer enough inductance to effectively create separate
grounds. In addition, the data line may run hundreds of feet to
yet another ground reference in remote circuitry.
Problem #2
Notice in Figure 2 there is substantial distance between
various conductors leaving the imaginary circle of the
protection zone. Even if ground conductors were bonded
together, destructive voltages would exist during a surge due
to wire inductance.
Problem #3
While the data line shows a surge suppressor, the lack of
suppressors in the power receptacles leaves an opening in
the protection zone. Even the best data line suppressor cannot
prevent damage under these conditions.
Solving the Problems
The problems listed for the installation in Figure 2 are solved
using the Protection Zone Concept. Figure 1 illustrates the
proper installation:
• All devices are powered from the same AC outlet.
• The AC service incorporates a Model HSP-121BT1RU surge
suppressor.
• The single point ground is established in the protection zone
window.
• Data line suppressor(s), Model PC642C, are added at the
single point ground.
• A ground bus bar is located at the ground area to facilitate
multiple ground connections
March 2014