Download TR41.7-10-05-008-L-SmartGridSurges

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Resistibility to Surges of Smart Grid Equipment
Connected to either DC or 120/240 V Single Phase
AC, and Metallic Communication Line(s)
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1. Overview
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1.1 Scope
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This Standard applies equipment which is connected to one or more metallic conductive communication
line(s) and either a DC power source, or a 120/240 V single phase AC power service with the neutral
grounded at the service entrance. It specifies the test procedures and resistibility requirements under which
the communications ports of the equipment shall continue to demonstrate basic functionality, when
subjected to overvoltages and overcurrents on either the power lines or the communications line(s).
Overvoltages or overcurrents covered by this Standard include surges due to lightning on or near the power
lines or telecommunications line(s). This standard covers the case where two or more services connected to
the equipment have ground connections which may be separated by a significant impedance.
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1.2 Purpose
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Most standards for the resistibility of equipment to electrical surges assume that a zero [or very low]
impedance exists among all the grounds in the equipment, or among the connections to separate earth
grounds. For equipment installed in the Smart Grid (or indeed, anywhere), the impedance of the ground
connections may be significant. The purpose of this standard is to provide tests and performance criteria
for the resistibility to lightning strikes of equipment connected to two or more services having at least one
ground connection separated from the others by a significant impedance.
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1.3 Contents and context
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This standard is divided into 6 clauses. Clause 1 provides the scope and purpose of this standard. Clause 2
lists references to other standards that are needed or useful in applying this standard. Clause 3 provides
definitions that are either not found in other standards, or have been modified for use with this standard.
Clause 4 provides a description of the surge environment for equipment with multiple services, at least two
of which have grounds separated by a significant impedance, and the rationale for the tests for survivability
in this environment. Clause 5 provides test procedures for testing resistibility of equipment to lightning
surges when the equipment has separate grounds in the same local area. Clause 6 provides test procedures
for testing resistibility of equipment to lightning surges when the equipment has a local and a remote
ground.
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2. References
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[note: The clause numbers for the references will be removed in the final draft. They are
here to help the editing process]
Note: Examples of equipment with services having separate grounds include a Smart Grid power meter
which is connected to the AC power at one side of a building and a communications service at the opposite
side; and a roof-mounted photovoltaic system with a communications link to the Smart Grid.
2.1 IEEE Std C62.41.2™, IEEE Recommended Practice on Characterization of Surges in Low-Voltage
(1000 V and Less) AC Power Circuits
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2.2 K. Phipps and F. Martzloff, Application Guidelines: Electromagnetic compatibility of Computer
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2.3 Telcordia GR-1089-CORE, Issue 5, Electromagnetic Compatibility and Electrical Safety - Generic
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2.4 UL1449, 3rd Edition, Surge Protective Devices
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3. Definitions
Networks, Internet Equipment, Medical Equipment, and Home Entertainment systems, EPRI Palo Alto,
CA: 2001, Report No.1005934
Criteria for Network Telecommunications Equipment.
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3.1 Local ground potential difference (LGPD)
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3.2 Port
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3.3 Service
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3.4 Significant impedance
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4. Surge environment and rationale for tests
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For information technology equipment surges at either the power port alone, or the communications port
alone, have been the subject of many EMC standards (e.g. IEEE C62.41.2™ [2.1] and UL 1449 [2.4] for
AC power; Telcordia GR-1089-CORE [2.3], ITU-T K.44 [B5] and UL 60950 [B7] for telecommunications
lines). This standard takes note that Smart Grid equipment needs to be tested to one or more of these EMC
standards. This standard is meant to supplement this EMC testing, and will address the case where a
lightning surge current flowing through the impedance of an earth ground or ground connection can
develop enough voltage to result in damage to the associated equipment. No present standards address this
issue.
The difference in potential between two separate ground points located in the same area, due to a lightning
strike.
The place where a service enters an equipment
A connection to either a power or a communications source
Note: Examples of a service are AC power, telephone, CATV, and surveillance systems
An impedance which is large enough that lightning current flowing through it can develop a voltage
sufficient to cause damage to an associated equipment, or shock hazard
Note: Due to the variability of lightning strikes, a numerical value can’t be assigned to this impedance.
Generally an impedance of one ohm or greater can be significant
As an illustration of this situation, consider a possible home network as shown in Figure 1. The important
thing to notice is that much of the equipment connected to the home network is connected more than one
service, e.g. AC power, wired communications lines, roof-top antennas. All ports of the equipment may be
grounded at the same point, but frequently this is not the case. If the ground points are different, a
significant impedance can exist between them. The high current from a lightning surge flowing through
this impedance can develop enough voltage to damage the equipment
Two cases need to be considered (and they may occur simultaneously):
Case 1: Equipment with two or more ports having a metallic interface, and whose grounding points are
connected together with a wire that may be 10 meters long
Case 2: The signal lines that terminate at an equipment in a remote site.
Photovoltaic system
Antenna
Surveillance
CATV
Set-top box
NIU
Telecom
Existing wires [TWP, CAT5, Coax]
Power line
Smart power
meter
Appliance
Appliance
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Figure 1. A possible home network
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4.1 Case 1: Same local area but separate grounds
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Appliance
Typically the two ports with separate grounds are the AC power and a communications line. This case has
been discussed by Martzloff and Samotyj [B2], and by Cohen et al [B1], and is illustrated in Figure 2
(where the communications line is shown as a CATV connection). The equipment is referenced on the AC
side to point B (via the branch circuit neutral and ground), but on the signal side, to point A (via the coax
sheath). A lightning strike can develop a large potential difference between point A and point B, either by
the resulting current flowing through a bond wire [as illustrated in Fig. 2]; or if the bond wire is not present,
by a current flowing through resistive earth. For example, with a 3000 A surge (10% of a moderately
strong lightning pulse) having a 3 μs rise time, and a 30 foot (~9 meter) long ground connection between A
and B, the voltage developed in wire A–B is ~10,000 V. This is enough voltage difference to flash over
most ordinary insulating barriers in the equipment, with equipment damage likely to result. If this potential
is developed by a current flowing through resistive earth, the voltage difference is called ground potential
rise, abbreviated as GPR.
Service
Entrance
TV
Set-top
Box
AC Power
A
CATV
High potential
difference
Ground
Block
AC Branch Circuit
COAX Sheath Ground Bond
B
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Figure 2. Equipment [a TV set-top box, in this example] with two ground reference points
connected with a relatively long wire, shown here as the COAX Sheath Ground Bond.
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4.2 Case 2: The signal lines terminate at a remote site.
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This case has been discussed by Melton [B3], and is illustrated in Figure 3. Here the issue is that a
lightning strike at site A will drive a large current IL toward a remote ground. This current flowing through
the ground impedance Zg creates a GPR, which will raise site A to a high potential with respect to the
remote ground at site B. If installations at site A and site B are connected by a conductor [e.g. a telephone
line or coax] a high-energy surge can be propagated down the line from A to B. This surge may cause
damage to equipment connected to either end of the line.
Conductor
Site A
Site B
IL
Zg
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GPR
Figure 3. Lightning striking site A drives a current IL through the impedance of the ground, Zg,
creating a ground potential rise GPR.
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4.3 General considerations
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The tests described in this standard are meant to be applied in addition to tests that should be done for
compliance to standards such as Telcordia GR-1089-CORE [2.3], ITU-T K.44 [B5], and UL 60950 [B7],
UL 1449 [2.4] , and IEC 62368 [B4].
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5. Tests for ports with separate local grounds
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5.1 Rationale
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The wire connecting the two grounds, as shown in figure 2, can have significant inductance. For fast-rising
lightning pulses, the inductance of the wire produces large voltage drops [the inductance of the wire is the
determining factor rather than the resistance of the wire]. The inductance is a property mainly of the length
of the wire, and to a lesser extent, to the diameter of the wire. The inductance of a typical ground wire is
approximately 1 µHy/m. The inductive voltage drop is L × di/dt, so it is proportional to the current rate of
rise (A/μs). Since lightning currents rise very fast (typically less than 3 μs), the current rate of rise is very
large, resulting in a high voltage.
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5.2 Purpose
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The high voltage that a lightning surge can apply to an equipment with multiple local ground connections
can cause flashover and resulting equipment damage. The purpose of these tests is to verify that after
applying a lightning surge as described in clause 5.3 and its subclauses, the equipment operates normally
after the test.
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5.3 Test Setup and Procedure
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There are 2 general cases to test: One for the existence of the bond [if any] between the various ports with
metallic interfaces; and one for the robustness of a selected port to surges on the other ports. The test for
the former is a modification of the test illustrated in Figure 3-3 of the EPRI report [2.2].
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Bond impedance
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5.3.1.1 Introduction
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Bonding of the grounds within an equipment to establish a common ground will eliminate the possibility of
damage due to GPR or LGPD. This test verifies that the individual services of the equipment have a
robust common ground connection by applying the surge generator (Hi) output to the power line ground or
The separation of two or more grounds by a significant impedance raises two issues. If the grounds of all
the services entering the equipment do not have a common low impedance bond in the equipment, then a
high voltage due to LGPD can occur in the equipment, with likely damage resulting. If the grounds of all
the services entering the equipment have a common low impedance bond in the equipment, then no voltage
due to LGPD will occur in the equipment [although the equipment itself may be at a high potential relative
to a nearby ground]. Clause 5.3.1 addresses this issue.
The second issue is that if two or more ports of the equipment do not have common low impedance
grounds, then a potential at one port, whether due to an LGPD or to a GPR, can cause insulation flashover
and resulting equipment damage. Even if all ports have a common low-impedance bond, there is a
possibility that a surge on one port can couple enough voltage or current into another port to damage the
equipment. Clause 5.3.2 and 5.3.3 test for these cases.
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neutral and connecting the generator return (Lo) to a selected service port ground. A 10 µH air-core
inductance having a 6 kV insulation withstand rating is connected across the terminals of the surge
generator, to simulate the inductance of an assumed worst-case of a 10 meter length of wire connecting the
ground of the power service to the ground of the selected service port. If the equipment has a common
ground between the power port and the selected service port, very little voltage will be developed across
the inductor, and no damage to the equipment is expected. If the equipment does not have a common
ground between the power port and the selected service port, a high voltage will be developed across the
inductor, potentially damaging the equipment. If the common ground is not robust, circuit board traces
may be damaged.
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5.3.1.2 Test procedure
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Refer to Figure 4. For this test the 6 kV combination wave generator specified in UL 1449 [2.4] is used.
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5.3.1.3 Verification values
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After the test sequence in clause 5.3.1.2 has been completed, verify that the EUT operates normally, and
that all bonds between the grounds are intact.
1)
Connect a 10 µH air-core inductance having a 6 kV insulation withstand rating
across the terminals of the surge generator [see Figure 4].
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Select a service port
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Connect the (Hi) output terminal of the surge-generator-plus-inductor [see step 1] to
the neutral terminal of the power feed.
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Connect the surge-generator-plus-inductor return (Lo) to the selected service port B,
C, or S terminal [see figure 4]
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Power the generator and set the voltage to 6 kV
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Surge the circuit as connected in both positive and negative polarities.
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Power down the generator
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Connect the surge-generator-plus-inductor return (Lo) to another untested service
port B, C, or S terminal.
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Power the generator and set the voltage to 6 kV
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Surge the circuit as connected in both positive and negative polarities.
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Power down the generator
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Repeat tasks 8, 9, 10 and 11 until all available B, C, or S connections have been
tested.
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If the power feed has a ground terminal, move the (Hi) output terminal of the surgegenerator-plus-inductor to the ground terminal of the power feed.
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Repeat tasks 2 through 12.
Generic Equipment
Communications terminals
A = Signal
B = Ground (if present)
C = Common
S = Screen or shield
L,N,G Power in
Power terminals
L = Line
N = Neutral
G = Ground
Combination
Wave
Generator
S
A
C
Assymetrical
Cable
input
A1
Symmetrical
Cable Pair
input
10 μH
Lo
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Coaxial
Cable
input
A
Hi
Power
Circuits
B
A2
Figure 4. Generic equipment with AC power and various communications inputs. Test set-up to
verify a common service ground connection
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Robustness of communications ports to power line surges
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5.3.1.4 Introduction
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This test checks for two things: The presence of a protector on the AC or DC power service; and for
collateral damage that a surge on the power service can cause to communications ports in the equipment.
If a protector is not present, the applied surge can cause significant damage to the equipment. Even if a
protector is present, the applied surge may cause damage to other circuits due to magnetic coupling
between the power circuits and circuit affected. This coupling can be enhanced by the presence of an
impedance (possibly unintended, but a result of the installation) between the neutral or ground of the power
system and the ground of the affected communications port.
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5.3.1.5 Test procedure
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A combination wave generator having a 6 kV open-circuit voltage and a 3 kA short-circuit current is used
for this test
As pointed out in clause 5.3.1.1, a significant impedance may exist between the AC or DC power ground
and one or more communications port grounds. The assumed worst-case is that the grounds between the
power service and the communications service are connected by a 10 meter length of wire, resulting in a 10
µH inductance between the two grounds. This test verifies that a surge on the AC or DC power port of the
equipment does not cause damage to the power circuits, or to any communications port of the equipment,
when the grounds of the AC or DC power port and the communications port are connected by a 10 µH
inductance.
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1) Select a communications port
2) Short the signal line(s) of the port to its ground.
3) Leave all other signal lines open
4) Connect the ground of the selected port to the AC or DC power ground with a 10 µH air-core
inductance having a 6 kV insulation withstand rating.
5) Connect the Hi side of the combination wave generator to the Line terminal.
6) Skip steps 7 – 10, if the power source is DC
7) Connect the generator return (Lo) to the Neutral terminal
8) Power the generator and set the voltage to 6 kV
9) Surge the circuit as connected, in both positive and negative polarities.
10) Power down the generator
11) Move the generator return (Lo) to the AC or DC power Ground terminal
12) Power the generator and set the voltage to 6 kV
13) Surge the circuit as connected, in both positive and negative polarities.
14) Power down the generator
15) Open the connection to ground of the signal line(s) at the selected port.
16) Connect the Hi side of the combination wave generator to the Line terminal.
17) Skip steps 18 – 21, if the power source is DC
18) Connect the generator return (Lo) to the Neutral terminal
19) Power the generator and set the voltage to 6 kV
20) Surge the circuit as connected, in both positive and negative polarities.
21) Power down the generator
22) Move the generator return (Lo) to the AC or DC power Ground terminal
23) Power the generator and set the voltage to 6 kV
24) Surge the circuit as connected, in both positive and negative polarities.
25) Power down the generator
26) Select another port, and repeat steps 2 - 23
27) Continue selecting ports, until all ports have been tested.
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5.3.1.6 Verification values
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After the test sequence in clause 5.3.2.2 has been completed, verify that the EUT operates normally.
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Robustness of one communications port to surges on another communications port
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5.3.1.7 Introduction
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If an equipment has two or more communications ports, a lightning strike on one of the communications
ports could cause damage on another communications port, if a significant impedance exists between their
grounds. The damage could be due to GPR or LGPD, as was discussed in clause 5.3.1.1. The assumed
worst-case is that the grounds between the two communications services are connected by a 10 meter
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length of wire, resulting in a 10 µH inductance between the two grounds. This test verifies that a surge on
one of the equipment communications ports does not cause damage to any other port of the equipment,
when the grounds of the two services are connected by a 10 µH inductance.
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5.3.1.8 Test procedure
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This test applies only to equipment having two or more communications ports. A combination wave
generator having a 6 kV open-circuit voltage and a 3 kA short-circuit current is used for this test
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5.3.1.9 Verification values
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After the test sequence in clause 5.3.3.2 has been completed, verify that the EUT operates normally.
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6. The signal lines that terminate at a remote site
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6.1 Rationale
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Figure 5 shows two separate sites connected together by one or more communications lines. These could
be phone lines, coax lines, or any wired connection. If lightning strikes at site A, it will cause a GPR there.
1) Select a communications port to be surged
2) Short all other ports to their respective grounds.
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Connect the ground of each of the non-surged ports to the ground of the surged port with a
10 µH air-core inductance having a 6 kV insulation withstand rating.
4) Connect the Hi side of the surge generator to the signal line of the port being surged
5) Connect the generator return (Lo) to the ground of the port being surged
6) Power the generator and set the voltage to 6 kV
7) Surge the circuit as connected, in both positive and negative polarities.
8) Power down the generator
9) Open all ports except one being surged.
10) Surge the circuit as connected, in both positive and negative polarities.
11) Power down the generator
12) Select another port, and repeat steps 1 - 10
13) Continue selecting ports, until all ports have been tested.
Communications line
Equipment
Site B
B
A
Ze
Equipment
Site A
Equipment
ground
GPR
Zg
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Figure 5. Effect of a lightning strike on equipment with a communications line connected to a
remote ground
Because the wires have a low resistance, the high potential at A will appear at B, and fire the protectors
there. As a result, the lightning current will flow through the equipment impedance Ze, through the
protector at B, and will return back through the ground impedance Zg. If Ze is small [e.g. if Ze is the
impedance of a secondary protector, such as a thyristor], then the voltage drop across Z e caused by the flow
of lightning current may not be sufficient to fire the protector at A. In that case the equipment at site A
may not be protected, and the high lightning current can damage or disable the equipment. If Ze is large
enough that the voltage drop across it caused by the flow of lightning current is sufficient to fire the
protector at A (coordinated protection – see T1-338-2004 [B6]), then the lightning current will be diverted
around the equipment at site A, and the equipment at site A will generally not be damaged (although the
equipment at site B could be).
The surge applied should approximate the largest surge that the equipment would experience in service. To
coordinate with GR-1089-CORE 5th Edition, Clause 4.7, a 10/250 surge generator capable of a 4 kV, 500 A
surge is used for this test
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6.2 Purpose
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The high currents that can be driven down a wire by a GPR can disable or cause damage to the equipment
to which the wire is connected. The purpose of this test is to verify that the equipment operates normally
after the test.
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6.3 Test Setup and Procedure
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All signal lines shorted together
Equipment
Under Test
Ground
R=3Ω
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10/250 4 kV, 400 A
Surge Generator
Figure 6. Test setup for testing robustness of equipment with a remote ground reference to a
local GPR
Refer to Figure 6. Use a 10/250 surge generator capable of a 4 kV, 500 A surge
1) Select a communications port to be tested
2) Short all signal lines of the selected port together; leave all other signal lines open.
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3) Connect one side of a 6 kV impulse rated, 3  resistor to the (shorted) communications line(s) of
the selected port
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4) Connect the other side of the 3  resistor to the Lo side of the combination wave generator.
5) Connect the Hi side of the combination wave generator to the ground of the EUT
6) Power the generator and set the voltage to 6 kV
7) Surge the circuit as connected, in both positive and negative polarities.
8) Power down the generator
9) Select another communications port, and repeat steps 1 – 8
10) Continue selecting communications ports, until all ports have been tested.
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6.4 Expected Results and Pass Criteria
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The equipment shall operate normally after the test, and shall not become a fire or fragmentation hazard.
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Annex A
Bibliography
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[B2] F. D. Martzloff and M. Samotyj, “An Important Link in Whole-House Protection: Surge Reference
equalizers”. Proceedings, 1993 EMC Zurich Symposium
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[B3] B. Melton, “Metallic Wire Line Service for Cell Sites”. ATIS PEG General Meeting -2007
[B1] R. L. Cohen, D. Dorr, J. Funke, C. Jensen and S. F. Waterer, How To Protect Your House and Its
Contents From Lightning: IEEE Guide for Surge Protection of Equipment Connected to AC Power and
Communication Circuits. 2005, ISBN: 0-7381-4634-X
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[B4] IEC 62368-1, Audio/video, information and communication technology equipment - Part 1: Safety
requirements
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[B5] ITU-T K.44, Resistibility tests for telecommunication equipment exposed to overvoltages and
overcurrents – Basic Recommendation
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[B6] T1-338-2004, Electrical Coordination of Primary and Secondary Surge Protection for use in
Telecommunications Circuits
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[B7] UL 60950, 3rd Edition, Safety of Information Technology Equipment