INTERNATIONAL TELECOMMUNICATION UNION
STUDY GROUP 5
TELECOMMUNICATION
STANDARDIZATION SECTOR
TD 137 (GEN/5)
English only
STUDY PERIOD 2009-2012
Original: English
Question(s):
4, 8/5
Geneva, 25-29 May 2009
TEMPORARY DOCUMENT
Source:
Rapporteur for Question 13/5
Title:
Testing Ethernet Ports including Power Over Ethernet (802.3at and the 802.3at +
variant)
Summary
This document analyses Ethernet and Power over Ethernet LAN ports to update the
recommendations K.20/21/44/45.There are two types of Ethernet port: one type uses insulation
coordination and the other uses internal or external overvoltage protection.
Contact:
Mick Maytum
IEEE PES SPDC
UK
Tel: 01234838589
Fax:
Email: m.j.maytum@ieee.org
Contact:
Gerhard Ackermann
Deutsche Telekom
Germany
Tel: +49 6151 628 3931
Fax: +49 521 9210 6506
Email: gerhard.ackermann@telekom.de
Attention: This is not a publication made available to the public, but an internal ITU-T Document intended only for use by the
Member States of ITU, by ITU-T Sector Members and Associates, and their respective staff and collaborators in their ITU related
work. It shall not be made available to, and used by, any other persons or entities without the prior written consent of ITU-T.
-2TD 137 (GEN/5)
Applicable tests for Ethernet ports connected to internal unshielded cabling
Ethernet port compliant to UTP isolation requirements of IEEE Std 802.3-2005/COR 1-2006
Table: Lightning test conditions for IEEE Std 802.3 Ethernet ports connected to internal
cables
Test
No.
Test
description
Test circuit
and
waveshape
Basic test
level
see Note 2
Enhanced
test
level
see Note 3
No. of
tests
Primary
protection
Acceptance
criteria
Unshielded
cable
Figure 2
Uc(max) =
2.4 kV
Uc(max) =
6 kV
5 of each
polarity
None
A with
Note 1
10/700
Comments
Note 1. There shall be no insulation breakdown during the test. The insulation resistance after the test shall be at least 2
MΩ when measured at 500 V DC.
Note 2. Applies to K.20, K.21 and K.45. Peak voltage complies with UTP isolation requirements of IEEE Std 802.32005/COR 1-2006.
Note 3. Applies to K.21 only
Current sharing array
V
Suitable return connection may be:
protective earthing terminal/conductor,
touchable conductive surface(s)
or powering conductor
RJ 45
1
VR1 to VR8
MOV
100 V @ 1 mA
5 m A @ 50 V
250 pF
V
V
V
VR1
VR2
VR3
R3
R4
R5
1 kW
1 kW
1 kW
V
V
V
V
VR4
VR5
VR6
VR7
R6
R7
R8
R9
R10
1 kW
1 kW
1 kW
1 kW
1 kW
VR8
RJ 45
1
Pair 3
2
2
4
4
R3 to R10 = 1 k W
Pair 1
Ethernet
Port
Equipment 1
5
5
7
7
Ethernet
Port
Equipment 2
Pair 4
8
8
10/700 Generator
S1
R2 = 15 W
Feed
3
3
Pair 2
Suitable
return
connection
Uc
C1 = 20 m F
R1 = 50 W
C2 = 200 nF
Return
6
6
Cable
Suitable
return
connection
-3TD 137 (GEN/5)
Ethernet ports with overvoltage protection to earth
Table: Lightning test conditions for Ethernet ports with internal or external overvoltage
protection to earth connected to internal cables
Test
No.
Test
description
Test circuit
and
waveshape
Basic
test
levels
Note 2
Enhanced
test
levels
Note 3
No. of
tests
Primary
protection
Acceptance
criteria
Comments
Unshielded
cable
Figure 3
Uc(max) =
2.4 kV
Uc(max) =
6 kV
5 of each
polarity
None
A
Port has internal
overvoltage
protection
Unshielded
cable
Figure 3
—
Uc(max) =
6 kV
5 of each
polarity
Special
A
External
protection
applied to IEEE
Std 802.3 port
Note 1
10/700
10/700
test
protector
Note 1. An Ethernet port meeting IEEE Std 802.3 isolation requirements can be upgraded to an enhanced protected port
by using an agreed external primary protector
Note 2. Applies to K.20, K.21 and K.45.
Note 3. Applies to K.21 only
Current sharing array
Th1
Th2
Th3
Th4
Suitable return connection may be:
protective earthing terminal/conductor,
touchable conductive surface(s)
or powering conductor
R3
RJ 45
R5
R6
Th8
R7
R8
R9
R10
100 W 100 W 100 W 100 W
1
2
R12
4
R11 to R18 = 10 W ( 6.8 W for PoE+ )
4
R13
Ethernet
Port
Equipment 1
Pair 1
5
5
R14
7
7
R15
R2 = 15 W
Ethernet
Port
Equipment 2
Pair 4
8
10/700 Generator
8
R16
Feed
3
3
R17
Suitable
return
connection
Uc
R1 = 50 W
Th7
Pair 3
2
R3 to R10 = 100 W
C1 = 20 m F
Th6
RJ 45
R11
Th = Bidirectional thyristor
V(BO) < 115 V, 50 pF @ -2 V
R4
100 W 100 W 100 W 100 W
1
S1
Th5
R19
R11
C2 = 200 nF
Pair 2
6
6
R18
Cable
Suitable
return
connection
Return
Introduction
This document summarises the situation on Power Over Ethernet, PoE, regarding power levels,
voltage withstands and surge testing. Ethernet port tests are given for ports without overvoltage
protection (insulation voltage level) and for ports with overvoltage protection (resistability) at basic
and enhanced levels.
IEEE Std 802.3af ™-2003 (PoE) defined methods of delivering powers up to 13 W over
conventional Ethernet cabling for powering equipment. The coming IEEE Std 802.3at ™ (PoE+)
doubles the delivered power to 25.5 W - subject to certain restrictions.
An overview of Ethernet signal connections is given in Annex A, powering connections in Annex B
and port insulation voltage levels in Annex C.
Powering Voltages and Currents
The original IEEE 802.3af (Power Over Ethernet, PoE) is now called a Type 1 system and delivers
up to 13 W to the PD (Powered Device). Draft 4 of IEEE 802.3at (Power Over Ethernet +, PoE+) is
now called a Type 2 system and delivers up to 26 W to the PD. Type 2 systems are backwards
-4TD 137 (GEN/5)
compatible with Type 1 systems. The power can be delivered either in mode A or B as described in
Annex B and shown in Figure 1.
PSE
RJ 45 Cable RJ 45
1
PD
RJ 45 Cable RJ 45
4
Rx
2
4
Pair 1
2
5
Factors
Loop:
Resistance
Current
Power loss
Factors
Voltage range
Power sourced
Factors
Voltage range
Power delivered
5
Factors
Loop:
Resistance
Current
Power loss
Factors
Voltage range
Power sourced
7
3
6
Factors
Voltage range
Power delivered
7
Pair 4
3
Pair 2
Rx
PD
1
Pair 3
Tx
PSE
Tx
8
8
6
Mode A
Mode B
Figure 1. Powering: Mode A, pairs 2 &3, and B, pairs 1 and 4
Tables 1 and 2 list the powering characteristics of the Type 1 and Type 2 systems.
Table 1. Type 1 (IEEE Std 802.3af) PSE, Cable and PD powering values
Item
PSE
Cable
PD
Parameter
Output voltage
Power
DC per pair
DC pair loop resistance
Power loss
Input voltage
Class 0 and Class 3 PD
Class 1 PD
Class 2 PD
Unit
V
W
A
Ω
Min
44
V
W
W
W
37
Max
57
15.5
0.35
20
2.5
57
13
3.84
6.49
Table 2. Type 2 (IEEE Std 802.3at) PSE, Cable and PD powering values
Item
PSE
Cable
PD
Parameter
Output voltage
Power
DC per pair
DC pair loop resistance
Power loss
Input voltage (Class 4)
Class 0 and Class 3 PD
Class 1 PD
Class 2 PD
Class 4 PD
Unit
V
W
A
Ω
W
V
W
W
W
W
Min
50
42.5
The Type 2 power increase results from:
• Higher minimum voltage (44 V to 50 V at PSE)
• Higher pair current (0.35 A to 0.6 A)
• lower cable loop resistance (20  to 12.5  maximum)
Max
57
30
0.6
12.5
4.5
57
13
3.84
6.49
25.5
-5TD 137 (GEN/5)
Wire Connections
Table 3 lists the wire and pair connections together with the data amplitudes.
Table 3. Ethernet wire connections
RJ-45
Wire
Pin #
Colour
1
white/green
Ethernet pair data voltage levels
Pair # 10BASE-T 100BASE-TX 1000BASE-T
3
2
green
4
blue
1
5
white/blue
7
white/brown
brown
3
white/orange
—
B
Power feed
—
Power feed
—
±1 V
±1 V
—
Power feed
—
—
±1 V
—
Power return
Power return
2
6
—
±1 V
A
Power feed
4
8
±2.5 V
PoE mode
±2.5 V
±1 V
orange
Power return
—
Power return
—
±1 V
Ethernet ports without overvoltage protection
Ethernet port basic insulation level
Ethernet ports designed to be compliant to criteria “a” (1500 Vrms) will withstand a longitudinal
impulse of 2.1 kV. Criteria “c” (2.4 kV) ports will withstand a longitudinal impulse of 2.4 kV,
Annex C. Current multi-pair standards testing use a 1.5 kV impulse and hence fail to verify
competent port design. There are cases where cheap transformer manufacturers don’t do a
1500 Vrms “hipot” insulation test. These transformers often fail a 1500 Vrms “hipot” insulation test
and have caused field failures in office installations. The invalid argument some transformer
manufacturers use is that the 1500 V rms test is for the port; it is up the designer to make the port
meet this and not the component manufacturer.
Competently designed ports will withstand 2.4 kV. If the voltage differential between the ends of a
balanced system line does not exceed 4.8 kV, there will not be any insulation breakdown.
Problems occur when the end-to-end voltage exceeds 4.8 kV or internal or external surge protection
is used on only one port.
Applying 2.4 kV to the cable charges the two 1 nF port decoupling capacitors to that voltage. The
average rate of impulse voltage rise will be 2400/10 = 240 V/s. For an exponential wavefront rise,
the initial rate of rise is about three times the average rate, making the initial capacitor charging
current 3 x 240 x 2 mA = 1440 mA or 180 mA per wire. The 10/700 generator 10 s rise time is set
by the generator values of R2, C2 see Figure 2. These components have a time constant of 15 x
200 n = 3000 ns. To preserve the 10 s rise time, the effective charging time constant of the 2 nF
capacitance should be less 300 ns — a maximum charging resistance of 150 . The port parallel
75  termination resistors represent 75/8 = 9.4  of charging resistance, leaving a maximum wire
to generator resistance of 8 x (150 – 9.4) = 1125 . Using a high value of feed resistance means that
the signal attenuation caused by the extra shunt resistance is low and the system operate normally.
This level of DC loading can interfere with the operation PoE systems where there is a DC bias of
up to 57 V.
The feed resistor DC loading can be minimised by standing off the feed resistance loading with a
series voltage limiter of >57 V. A clamping voltage limiter rather than a switching voltage limiter is
used to avoid the possibility of switching oscillation caused by the low currents and high resistances
-6TD 137 (GEN/5)
of the test circuit. PoE supply loading is avoided loading by selecting a clamping voltage limiter
that does not conduct more than 10 A at 50 V (>5 M). Typically the >5 M value can be met by
components that have a nominal conduction voltage of 100 V at 1 mA. Figure 2 could use a 100 V,
5 mm MOV for the voltage limiter. For the predicted charging current of 180 mA, this MOV
develops about 150 V.
Current sharing array
V
Suitable return connection may be:
protective earthing terminal/conductor,
touchable conductive surface(s)
or powering conductor
RJ 45
1
VR1 to VR8
MOV
100 V @ 1 mA
5 m A @ 50 V
250 pF
V
V
V
VR1
VR2
VR3
V
VR4
V
V
V
VR5
VR6
VR7
VR8
R3
R4
R5
R6
R7
R8
R9
R10
1 kW
1 kW
1 kW
1 kW
1 kW
1 kW
1 kW
1 kW
RJ 45
1
Pair 3
2
2
4
R3 to R10 = 1 k W
4
Pair 1
Ethernet
Port
Equipment 1
5
5
7
7
Ethernet
Port
Equipment 2
Pair 4
8
8
10/700 Generator
R2 = 15 W
S1
Feed
3
3
Pair 2
Suitable
return
connection
Uc
C1 = 20 m F
R1 = 50 W
C2 = 200 nF
6
6
Cable
Suitable
return
connection
Return
Figure 2. Test circuit for basic insulation level
The impulse is applied in alternating polarity ten times. The maximum application rate is two
impulses each minute. After the test, the insulation resistance of each loop pair of the tested port
shall be measured at 500 V DC.
There shall be no insulation breakdown during the test. The insulation resistance after the test shall
be at least 2 MΩ.
A Midspan box is series Ethernet equipment that converts standard Ethernet systems into PoE
systems by introducing power feeding to the downstream equipment see Figure 3. Midspan boxes
need to be tested at corresponding unpowered and powered Ethernet ports.
Ethernet
Ethernet and Power
(PoE)
Ethernet
PD
Equipment 1
Ethernet
PD
Equipment 2
Standard
Ethernet
Equipment
Ethernet
Midspan
Equipment
Ethernet
PD
Equipment 3
Ethernet
PD
Equipment 4
Ethernet
PD
Equipment 5
Figure 3 Conversion of standard Ethernet system into a PoE system using a Midspan box
-7TD 137 (GEN/5)
This Ethernet port basic insulation level test may be used on Recommendation K.20, K21 and K.45
equipment for ports that do not have internal voltage limiting.
Ethernet port enhanced insulation level
In this test the insulation level of the Ethernet port is tested using the basic insulation test procedure
but with a higher 6 kV impulse test level. This Ethernet port enhanced insulation level test may be
used on Recommendation K21 equipment for ports that do not have internal voltage limiting.
Ethernet ports with overvoltage protection
Longitudinal surge protection will attempt to limit the voltage below the port insulation voltage. In
operation, the surge protection is likely to divert the surge current and apply the surge voltage to the
port at the other end of the line. Unless the port at the other end of the line has surge protection, it
may suffer insulation breakdown.
The test circuits for ports with overvoltage protection must allow substantial currents to flow. As
the currents are higher than the insulation level tests a low-capacitance switching overvoltage
protector can be used to standoff the feed resistor from the wire see Figure 4. To maintain the same
short-circuit total current and current decay time as a single twisted pair, the individual wire feed
resistance should be 25 x 8/2 = 100 . The individual peak wire current is 27 A at a 6 kV generator
voltage.
Current sharing array
Th1
Th2
Th3
Th4
Th5
R3
RJ 45
R5
R6
R7
R8
R9
R10
100 W 100 W 100 W 100 W
1
Pair 3
2
2
R12
R3 to R10 = 100 W
4
R11 to R18 = 10 W ( 6.8 W for PoE+ )
4
R13
Ethernet
Port
Equipment 1
Pair 1
5
5
R14
7
7
R15
Ethernet
Port
Equipment 2
Pair 4
8
10/700 Generator
8
R16
R2 = 15 W
Feed
3
3
R17
Suitable
return
connection
Uc
R1 = 50 W
Th8
RJ 45
R11
Th = Bidirectional thyristor
V(BO) < 115 V, 50 pF @ -2 V
R4
100 W 100 W 100 W 100 W
1
C1 = 20 m F
Th7
R19
R11
Suitable return connection may be:
protective earthing terminal/conductor,
touchable conductive surface(s)
or powering conductor
S1
Th6
C2 = 200 nF
Pair 2
6
6
R18
Cable
Suitable
return
connection
Return
Figure 4. Test circuit for enhanced resistibility
A 6 kV impulse is applied in alternating polarity ten times. The maximum application rate is two
impulses each minute. Resistors R11 through R18 simulate the wire resistance and help to channel
most the surge into equipment 2. During setup the currents flowing into equipment 1 and equipment
2 ports are measured. Most of the current, >80 %, should flow into equipment 2. Equipment 1
should be selected, modified or common-mode wire-pair chokes be added to maximise the current
into equipment 2.
Ethernet ports using an external SPD for overvoltage protection
When an Ethernet port has an agreed SPD specified, the above tests can be performed on the
equipment with the SPD connected. The SPD earth terminal is connected to the generator ground.
-8TD 137 (GEN/5)
Equipment Ethernet ports verified to a 2.4 kV basic insulation voltage level can be uprated to the
6 kV enhanced level by the use of an external agreed protector.
Cable
RJ 45
RJ 45
1
1
Pair 3
2
2
4
4
Pair 1
Ethernet
Port
Equipment 1
5
5
7
7
Ethernet
Port
Equipment 2
Pair 4
8
8
3
3
Pair 2
6
6
Longitudinal voltage
Pair
transverse
voltage
Inter-powering
pair transverse
voltage
Figure 5 - Longitudinal overvoltage protection generating transverse surges
The operation of longitudinal overvoltage protection may not be simultaneous on all wires and that
will create transverse pair and transverse inter-pair surges Figure 5. On the signal pair the maximum
signal level is normally less than ±5 V and a 20 V protection limit might be a design target.
Between powering pairs the DC is less than 57 V and a 100 V protection limit might be a design
target for powering pairs. To coordinate, any external SPD should be treated as an agreed protector
as in ITU-T recommendation K.44, so that longitudinal surge testing automatically creates the
transverse surges from the agreed protector. Ethernet SPDs should be characterised for their
longitudinal to transverse surge conversion (NOTE: standalone SPD testing is not covered by
Recommendation K.20, K.21 or K.45).
Surges – magnetic or differential earth potential rise.
Most standards assume that the surge is the result of magnetic coupling and use short waveshapes
like 1.2/50. This is wrong for the current waveshape. The induced current waveshape will be a long
duration as it follows the magnetic field waveshape. The induced voltage waveshape is short
duration as it is a differential of the magnetic field waveshape.
The typical resistive current sharing test technique used isn’t reality as the magnetic field tries to
create an AT balance and it doesn’t matter if all the current flows in one wire or a lesser current in
many wires provided the AT balance is achieved. A test method is needed, such as transformer
coupling that creates a given total current flow in the cable.
Differential earth potential rise results from the lightning dispersion current flowing in the earth. If
SPDs at both ends of the line operate the line is a parallel bridge path for the lightning current. In
this case there isn’t an AT balance, more a resistive sharing between the line wires and the earth
impedance.
People have reported Ethernet failures when using shielded cables. Shielded cables should reduce
magnetic surges, but increase the differential earth potential rise current through the line shield. It
maybe that differential earth potential rise surges and equipment failures are much more of a
problem than people appreciate.
Test techniques should be developed to verify the Ethernet port performance both for magnetic and
differential earth potential rise surges.
-9TD 137 (GEN/5)
Annex A
(Normative)
Ethernet wiring — signal connections
Ethernet cable and RJ45 connections
Ethernet cable normally consists of 8 wires arranged as four twisted pairs. The cable connection to
equipment RJ45 port pins is shown in Figure A1.
Ethernet 8-wire,
4 twisted-pair (4P) cable
RJ 45
1
RJ 45
1
Pair 3
2
2
4
4
Pair 1
5
5
7
7
Pair 4
8
8
3
3
Pair 2
6
6
Figure A1. Ethernet cable port wiring
10BASE-T and 100BASE-TX connections
10 Mbps and 100 Mbps Ethernet systems use pairs 3 and 2 for signal and don’t use pairs 1 and 4. A
simplified equipment port circuit is shown in Figure A2.
RJ 45
1
Signal Pair 3
2
75 W
4
Unused Pair 1
1 nF
2 kV
75 W
5
75 W
7
Unused Pair 4
75 W
8
3
Signal Pair 2
6
Figure A2. 10BASE-T and 100BASE-TX signal pairs
- 10 TD 137 (GEN/5)
1000BASE-T (Gigabit) connections
A 1000 Mbps Ethernet system is four parallel 250 Mbps connections using pairs 1, 2, 3 and 4 for
signal. A simplified equipment port circuit is shown in Figure A3.
RJ 45
1
Signal Pair 3
2
75 W
4
Signal Pair 1
5
75 W
1 nF
2 kV
75 W
7
Signal Pair 4
75 W
8
3
Signal Pair 2
6
Figure A3. 1000BASE-T signal pairs
- 11 TD 137 (GEN/5)
Annex B
(Normative)
Ethernet wiring — powering connections
Powering pairs
POE and PoE+ powering can be in one of two modes. Mode A powering uses signal pairs 2 and 3
for power feed and return. Mode B powering uses the unused pairs 1 and 4 in 10BASE-T and
100BASE-T for power feed and return. The Power Sourcing Equipment, PSE, provides a voltage
Vport to the Powered Device, PD. Circuits for modes A and B powering in a 1000BASE-T system
are shown in Figure B1. In the 1000BASE-T case, pairs 1 and 4 also carry signal.
PSE
RJ 45 Cable RJ 45
1
PD
PSE
RJ 45 Cable RJ 45
1
1
2
2
4
4
Signal Pair 3
2
4
Signal Pair 3
Pair 1
5
PD
Load
PD
Load
7
7
7
Pair 4
8
8
3
3
Signal Pair 2
6
5
VPort
Pair 4
3
4
5
VPort
8
2
Pair 1
5
7
PD
1
8
3
Signal Pair 2
6
6
Mode A - Pairs 2 and 3
6
Mode B - Pairs 1 and 4
Figure B1. 1000BASE-T mode A and mode B powering
Port configurations for PoE
The normal Ethernet port circuit (Figures A2 and A3) would DC load the PSE with the 75 
termination resistors. To avoid DC loading, each termination resistor is AC coupled with a 22 nF,
250 V capacitor to the signal transformer centre tap. Figure B2 shows how the four termination
resistors are AC coupled for a 1000BASE-T interface.
RJ 45
1
Signal Pair 3
2
22 nF
250 V
75 W
4
Signal Pair 1
5
75 W
22 nF
250 V
1 nF
2 kV
75 W
7
75 W
22 nF
250 V
Signal Pair 4
8
3
Signal Pair 2
6
Figure B2. Removal of termination resistor DC loading on PSE
- 12 TD 137 (GEN/5)
Power connections
The power source and sink connections are the line-side centre taps of the signal transformers. To
allow for mode A or B powering the PD uses a four-phase diode bridge normally protected by an
avalanche diode, Figure B3
RJ 45
PD
1
Signal Pair 3
2
4
VPORTP
Signal Pair 1
5
100 nF
100 V
Cable
To DC/DC
Convertor
SMAJ58A
VPORTN
7
Signal Pair 4
8
3
Signal Pair 2
6
Figure B3. Power extraction at PD
The PSE design will set the powering mode. Figure B4 shows the two modes. For decoupling,
common mode chokes are often used to make the connections to the centre taps.
PSE
RJ 45
RJ 45
PSE
1
1
Signal Pair 3
Signal Pair 3
2
2
4
4
Signal Pair 1
0V
Isolated
5
Signal Pair 1
0V
Isolated
100 nF
100 V
5
100 nF
100 V
Cable
Cable
SMAJ58A
SMAJ58A
-48 V
Isolated,
switched &
current limited
7
Vport
Signal Pair 4
-48 V
Isolated,
switched &
current limited
Vport
8
7
Signal Pair 4
8
3
3
Signal Pair 2
Signal Pair 2
6
Mode A, pairs 3 and 2
6
Mode B, pairs 1 and 4
Figure B4. Power feed at PSE
- 13 TD 137 (GEN/5)
Connection Summary
Ethernet wire connections
RJ-45
Wire
Pin #
Colour
1
white/green
Ethernet pair data voltage levels
Pair # 10BASE-T 100BASE-TX 1000BASE-T
3
2
green
4
blue
1
5
white/blue
7
white/brown
brown
3
white/orange
orange
—
B
Power feed
—
Power feed
—
±1 V
±1 V
—
Power feed
—
—
±1 V
—
Power return
Power return
2
6
—
±1 V
A
Power feed
4
8
±2.5 V
PoE mode
±2.5 V
±1 V
Power return
—
Power return
—
±1 V
- 14 TD 137 (GEN/5)
Annex C
(Normative)
Ethernet port — electrical separation
UTP isolation requirements
The IEEE Std 802.3-2005/COR 1-2006 in clause 25.4.5 (Replacement of 8.4.1), “UTP isolation
requirements” specified a port withstand at least one of the following three longitudinal voltage
requirements:
a) 1500 V rms at 50 Hz to 60 Hz for 60 s, applied as specified in subclause 5.2.2 of IEC
60950-1:2001.
b) 2250 V dc for 60 s, applied as specified in subclause 5.2.2 of IEC 60950-1:2001.
c) A sequence of ten 2400 V impulses of alternating polarity, applied at intervals of not less
than 1 s. The shape of the impulses shall be 1.2/50 μs (1.2 μs virtual front time, 50 μs virtual
time of half value), as defined in IEC 60950-1:2001 Annex N.
There shall be no insulation breakdown, as defined in subclause 5.2.2 of IEC 60950-1:2001, during
the test. The resistance after the test shall be at least 2 MΩ, measured at 500 V dc.
Typically Ethernet interface transformers have an insulation withstand voltage test (Hipot) of
1.5 kV rms and the port termination capacitor has a 2 kV rating.
DTE Power via MDI Insulation voltage level
The IEEE Std 802.3-2005/COR 1-2006 in clause 33.4.1 “Isolation” specified a port withstand at
least one of the following three longitudinal voltage requirements: This electrical separation shall
withstand at least one of the following electrical strength tests.
This electrical isolation shall withstand at least one of the following electrical strength tests:.
a) 1500 V rms at 50 Hz to 60 Hz for 60 s, applied as specified in subclause 5.2.2 of IEC
60950-1:2001.
b) 2250 V dc for 60 s, applied as specified in subclause 5.2.2 of IEC 60950-1:2001.
c) An impulse test consisting of a 1500 V, 10/700 μs waveform, applied 10 times, with a 60 s
interval between pulses. The shape of the impulses shall be 10/700 μs (10 μs virtual front
time, 700 μs virtual time of half value), as defined in IEC 60950-1:2001 Annex N.
There shall be no insulation breakdown, as defined in subclause 5.2.2 of IEC 60950-1:2001, during
the test. The resistance after the test shall be at least 2 MΩ, measured at 500 V dc.
Comment
The 2006 DTE Power via MDI doesn’t make sense – the 1500 V impulse voltage of “c” is far too
low when compared with the “a” (2121 V peak) and “b”(2250 V peak) test options. A
recommendation has been made to the 802 group to use a 2500 V impulse voltage, which
corresponds to the preferred voltage values of IEC 60644-1.
- 15 TD 137 (GEN/5)
Bibliography
Power Over Ethernet (PoE) What is it? How to Protect it?, Michael J Maytum, ATIS PEG 2007
Annual Meeting (PoE)
Standards — Under attack from reality, Michael J Maytum, ATIS PEG 2009 Annual Meeting
(PoE+)
Testing Equipment Internal Line Ports, Michael J Maytum, ATIS PEG 2005 Annual Meeting
(Lightning coupling and waveshapes)
________________