International Telecommunication Union
ITU-T Study Group 5
Damage to Equipment in
the US
Mick Maytum
UK
Technical Session on
Home Networks
Geneva, 29/04/2011
US Fibre Fed Home Network Configuration
Home
Network
ITU-T
ONT
Optical Network
Termination
Study Group 5
Ethernet
Router
4/8
4/8
4/8
Video
Fibre
Feed
AC
Power
L2
POTS
L1
N
PE
+
Battery
Alternative configuration: (O)NT feeds a Home/Residential
Gate-Way outputting Ethernet, POTS and Video
2
29.04.2011
Technical Session - Home Networks - Geneva
Home Network Port Failures
Home
Network
ITU-T
ONT
Optical Network
Termination
Study Group 5
Ethernet
Router
4/8
4/8
4/8
Fibre
Feed
AC
Power
L2
POTS
L1
N
PE
+
Battery
 Connected ONT POTS and Ethernet ports fail.
 Other connected Ethernet equipment fails
3
29.04.2011
Technical Session - Home Networks - Geneva
ONT Connection to Ground - 1
Home
Network
ITU-T
ONT
Optical Network
Termination
Study Group 5
Ethernet
Router
4/8
4/8
4/8
Fibre
Feed
AC
Power
L2
POTS
L1
N
PE
+
Battery
 Disconnecting ONT grounding lead greatly reduces
failures, but may cause EMC problems
4
29.04.2011
Technical Session - Home Networks - Geneva
ONT Ground Connection - 2
 Shows ONT ground lead completes the destructive current
loop and carries most of that current
ITU-T
Study Group 5
 2008 News Report: Verizon is revisiting NY ONT installs for
grounding issues as a 15 % sample showed 59 % had not
been grounded and/or bonded
 NEC 800.100 Cable and Primary Protector Grounding.
Exception: In one- and two-family dwellings where it is not practicable
to achieve an overall maximum primary protector grounding conductor
length of 6.0 m (20 ft), a separate communications ground rod
meeting the minimum dimensional criteria of 800.100(B )(2)(2) shall
be driven, the primary protector shall be connected to the
communications ground rod in accordance with 800.100(C), and the
communications ground rod shall be connected to the power grounding
electrode system in accordance with 800.100(D).
5
29.04.2011
Technical Session - Home Networks - Geneva
ONT POTS Port Failures
ONT
Component failure levels
Fuse 14 A 2s
SPC bonds 10 A 2s
SPC chip 0.8 A 2s
ITU-T
Study Group 5
Longitudinal
1.5 kV, 5 A 2s
POTS
+
Battery




Connected POTS equipment does not fail
Sometimes only the ONT port RING or TIP components fail
Sometimes the fuse may not be damaged
Most logical explanation is that either one or both POTS wires
are breaking down to a local ground.
Equivalent single wire 10/700 generator withstand setting of
10 A2s is 8 kV, 200 A, 5/320
6
29.04.2011
Technical Session - Home Networks - Geneva
Ethernet Port Failures
Insulation barriers
ITU-T
Study Group 5
AC
Power
Router
ONT
L2
Ethernet
L1
N
PE
+
Battery
4/8
4/8
Power
Power
 For failure to occur two or more insulation barriers must
breakdown
 For Ethernet ports without voltage limiters the total voltage
impulse withstand for 2x1.5 kV rms transformers is likely to
be above 5 kV.
 For severe environments 5 kV isn’t enough
One solution being pursued is to use a 5 kV rms withstand
transformer to give a 7 kV impulse withstand barrier.
7
29.04.2011
Technical Session - Home Networks - Geneva
Miss-Guided use of Ethernet SPDs - 1
Insulation barriers
ITU-T
One twisted pair
Study Group 5
Ethernet
case 1
no SPD
4 kV induced voltage
equally shared
-2 kV
Router
+2 kV
4/8
cable mid-point
voltage = 0
Power
ONT
Ethernet
case 2
one SPD
Ethernet
case 3
two SPDs
4 kV induced voltage
grounded by SPD at one end
-4 kV
4/8
cable mid-point
voltage = -2 kV
0
SPD
Power
GPR Differential
coupled by SPDs at each end
Router
4/8
SPD
SPD
Power
+
Battery
GPR3
Router
GPR2
GPR1
8
29.04.2011
Technical Session - Home Networks - Geneva
Miss-Guided use of Ethernet SPDs - 2
Transverse Surge Generation
400
ITU-T
Wire 1 of pair
Wire 2 of pair
Transverse
surge
300
Voltage — V
Study Group 5
350
250
200
150
100
50
0
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Time — µs
Existing SPD voltage measurements don’t cover the generation of
transverse voltage surges by the asynchronous SPD operation. Ethernet
ports typically have a transverse surge capability below 10 volts and it is
important to characterise any SPD intended for Ethernet protection for the
level of transverse surge generated.
The longitudinal surge on the twisted pair wires (red trace and blue trace) is
converted to an inter-wire transverse surge (green trace) by asynchronous
SPD operation.
9
29.04.2011
Technical Session - Home Networks - Geneva
Calculated Surge Levels (based on 10/700
generator)
For low failure rates in the environment described, the ONT
ports require the following capabilities:
ITU-T
Study Group 5
POTS
 Being low-voltage this port has a current surge
 Withstand at least 10 A2s of surge
 Single wire surged with 10/700 generator setting of
8 kV, 200 A
Ethernet
 To stop current flow this port needs a high value of
insulation voltage
 Insulation to withstand at least 7 kV of surge
 All port conductors connected and surged with a 7 kV
impulse
Further Study Areas
ONT coaxial video port (no failures), Wire fed home
network NTs, Ethernet port with SPCs connected to ground,
External SPDs connected to ground – transverse surge
generation and surge capability, Surge ingress mechanism–
GPR or induced or AC transients or combinations thereof
10
29.04.2011
Technical Session - Home Networks - Geneva