Criteria to Protect Telecommunication
Cabling During a Power Cross Event
Presented by:
Mick Maytum
ICT Surge Protection Consultant
ictsp-essays.info
Rational for this work
• North American standards, UL 60950-1 and GR1089-CORE, test for power fault wiring damage.
• International standards, IEC and ITU-T, don’t test
for power fault wiring damage.
• This work created ITU-T Supplement 3 (2015):
ITU-T K.20, K.21, K.45 and K.82 – Additional
criteria to protect telecommunication cabling
during a power cross event
© M J Maytum 2016
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Just a piece of wire
Area = pD2/4
R = rL/(pD2/4)
n
=
gth
Le
L
Power Loss = P = i2R
Surface Area = SA = pDL
i
Surface power density = P/SA = 4i2r/(p2D3)
© M J Maytum 2016
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Insulation damage sets temperature limit
© M J Maytum 2016
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DC fusing current of wires in free air (Preece)
𝐼 = 𝐴 ∗ 𝑑1.5
Where I is the wire fusing current, d is the wire diameter
and A is a constant, dependent of units system and the
wire material. For a copper wire of diameter of d mm, the
equation becomes:
𝐼 = 80 ∗ 𝑑1.5
For example, 32 AWG has a diameter of 0.2019 mm,
making 𝐼 = 80 ∗ 0.20191.5 = 7.3 A.
Preece W. H., On the Heating Effects of Electric Currents, Proc. Royal Society 36, 464 ‐
471 (1883). No. II, 43, 280 ‐ 295 (1887). No. III, 44, 109 ‐ 111 (1888).
(Retrieved 2015-09 from www.ultracad.com/articles/reprints/preece.zip)
© M J Maytum 2016
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DC Insulation damage current
• MIL-STD-975 section 3.16 Wire and Cable Derating
Criteria gives maximum currents for an ambient of 70
°C and various insulator maximum temperatures
(Teflon at 200 °C down to types of PVC at 105 °C).
• For cable bunches, a derating factor of (28-N)/27
should be applied, where N is the number of
conductors. The derating factor is taken as a constant
value once the bundle exceeds fifteen conductors.
MIL-STD-975M NASA, Standard Electrical, Electronic and Electromechnical (EEE) Parts List, 5 August 1994
© M J Maytum 2016
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DC levels to avoid insulation damage
Single wire with 200 °C insulation
Single wire with 105 °C insulation
Single wire curve set to 1.3 A @ 0.4 mm
20
Derated current - A
15
10
9
8
7
6
5
4
3
2
1.5
1
0.9
0.8
0.7
0.6
0.5
0.4
0.2
0.3
0.4
0.5
0.6 0.7 0.8 0.9 1
1.5
2
Copper wire diameter - mm
MIL-STD-975 derated current versus wire diameter
© M J Maytum 2016
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Adiabatic (thermal capacity) conditions
Onderdonk equation
 T

I 2t  7.28 *104 * d 4 * LOG
 1
 274 
Where
I (A) is the wire current,
d (mm) is the wire diameter,
t (s) is the current flow time, and
T is the temperature difference (°C) between the wire and ambient.
For an ambient of 30 °C and the copper melting temperature of 1083 °C, the
equation becomes:
2
4
4
I t  5 *10 * d
Adam J. & Brooks D., In Search for Preece and Onderdonk, 2015 (retrieved 2015-09
http://www.ultracad.com/articles/preece.pdf)
ANSI/ICEA PUBLICATION P-32-382-2007, Short circuit characteristics of insulated cables
© M J Maytum 2016
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Current
Typical wire current-time curve
UNACCEPTABLE REGION
ACCEPTABLE REGION
Time
© M J Maytum 2016
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Insulation damage limit current-time curve for
0.2 mm and 0.4 mm copper wire
100
Current — A
0.2 mm diameter Cu wire
0.4 mm diameter Cu wire
10
1
0.01
0.1
1
10
100
1000
Time — s
Based on the P-32-382 i2t values and the IEC 60950 equivalent DC values from Table I1 in Appendix I.
© M J Maytum 2016
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Parameters for 18 to 32 AWG
Wire
AWG
Dia
(mm)
Preece
DC
Fusing
(A)
Onderdonk
transient
melting
i2t (A2s)
ICEA
standard
P-32-382
i2t (A2s)
IEC 60950-1
DC
Figure I.1
(A)
18
1.0237
82.7
64787
8881
4.99
19
0.9116
69.5
40745
5588
4.19
20
0.8118
58.4
25625
3516
3.53
21
0.7229
49.1
16116
2212
2.98
22
0.6438
41.2
10135
1392
2.51
23
0.5733
34.7
6374
876
2.13
24
0.5106
29.1
4009
551
1.81
25
0.4547
24.5
2521
347
1.54
26
0.4049
20.6
1586
218
1.32
27
0.3606
17.3
997
137
1.14
28
0.3211
14.5
627
86.3
0.98
29
0.2859
12.2
394
54.3
0.85
30
0.2546
10.3
248
34.2
0.73
31
0.2268
8.61
156
21.5
0.63
32
0.2019
7.24
98
13.5
0.53
© M J Maytum 2016
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Evolution of North American wiring
simulators
• ANSI/TIA/EIA-571 and ANSI/TIA/EIA571A
• UL 1459-1998
• UL 60950-1
• GR-1089-CORE, Issue 6
• Stub links and block cable
© M J Maytum 2016
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EIA-571(A), 1992 (1999), Telecommunications User Premises
Equipment Environmental Considerations – current division
i2t = 45 A2s
e.g. 13.3 A for 0.25 s
i2t = 400 A2s
e.g. 40 A for 0.25 s
i2t = 45 A2s
e.g. 13.3 A for 0.25 s
Feed
i2t = 45 A2s
e.g. 13.3 A for 0.25 s
i2t = 100 A2s
e.g. 20 A for 0.25 s
Terminal
Equipment
Terminal
Equipment
Terminal
Equipment
i2t = 400 A2s
e.g. 40 A for 0.25 s
Feed
Terminal
Equipment
571 Branches
i2t = 100 A2s
e.g. 20 A for 0.25 s
Terminal
Equipment
571-A Branches
(a)
(b)
© M J Maytum 2016
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EIA-571(A), 1992 (1999), Telecommunications User Premises
Equipment Environmental Considerations – I-t curves
100
Current – A rms
500-type 'phone
'phone line cord
modular jack
26 AWG riser cable
10
1
0.01
0.1
1
10
Duration – s
100
1000
© M J Maytum 2016
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UL 1459 (1995): UL standard for safety telephone equipment
UL 60950-1: Information Technology Equipment - Safety - Part 1: General Requirements used an MDL-2 fuse
© M J Maytum 2016
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GR-1089-CORE, Issue 6, 2011, Electromagnetic Compatibility and Electrical
Safety - Generic Criteria for Network Telecommunications Equipment
102
100
70
60
50
ACCEPTABLE REGION LIMITS
CURRENT MAXIMUM TIME
(A)
(s)
60
0.013
30
0.065
7
2.5
2.2
900
70
60
50
40
40
30
30
CURRENT (Amperes)
CURRENT (Amperes)
20
UNACCEPTABLE REGION
101
7
6
5
4
ACCEPTABLE REGION
20
UNACCEPTABLE REGION
10
7
6
5
4
3
3
2
2
100
10-2
10-1
100
101
102
103
ACCEPTABLE REGION
1
0.01
0.1
1
10
100
1000
TIME (Seconds)
TIME (Seconds)
© M J Maytum 2016
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Stub links and block cable
© M J Maytum 2016
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Closing Remarks
• All simulations are based on an i2t limitation for adiabatic
times and a fixed current value for thermal equilibrium times.
• The derivation of Norther American simulation curves are
based on testing.
• Simulation curves based on insulation temperature rise are
more conservative. Example, 26 AWG has a North American
fixed current limit of 2.2 A, but in IEC safety standards it is
1.3 A.
© M J Maytum 2016
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