New Telecom TIA-968-B Surge Testing Compliance Now Required
TIA-968-B, Telecommunications Telephone Terminal Equipment Technical Requirements for
Connection of Terminal Equipment to the Telephone Network, specifies a series of tests for
terminal equipment directly connected to the public switched telephone network (PSTN). These
tests are designed to protect the telephone network from damage or interference caused by the
connection of terminal equipment.
Although TIA-968-B was originally published August 2009, the telecommunications industry was
given time to adapt these new procedures. The “MUST COMPLY WITH” date was March 22,
2011. Any new equipment, or significantly modified equipment, that is connected to the PSTN
must now comply with TIA-968-B, including:
T1(DS1)
ADSL/ADSL2/VDSL2
MDC modem
CPE POTS
FAX interface
FXO interface
DAA interface
Power strip protectors (with RJ11 interface)
DSL splitters/filters
IAD (Integrated Access Devices)
Among the many changes made in going from revision A to revision B are changes to the
waveforms used for voltage and current surge testing. The reason these changes were made was
to make the surge tests more realistic. That is to say these waveforms more closely simulate the
voltage and current surges that equipment will experience in the field.
Figure 1.
An example of how the surge waveforms have changed is shown in Figure 1. The TIA-968-A Type
A common mode, or longitudinal, voltage surge waveform is shown in black, while the new TIA 968-B waveform is shown in red. As you can see, the TIA-968-B has a higher peak value, a
slightly faster rise time, and a significantly longer decay. This results in a higher energy content
under the curve for TIA-968-B compared to TIA-968-A for worse case conditions.
Figure 2.
The common mode current surge waveform has been modified in much the same way as the
common mode voltage surge waveform. As shown in Figure 2, the TIA-968-B common mode, or
longitudinal, surge waveform has a higher peak value, a slightly higher slope for the leading edge
of the surge and then a significantly longer decay shape.
Some waveforms have stayed the same. The Type B waveforms, for example, are identical in both
TIA-968-A and TIA-968-B.
To pass the surge tests, equipment MUST continue to operate after a Type B surge, while for Type
A surge, the equipment may stop working, but cannot cause “harm to the PSTN (Public Switched
Telephone Network).” For example, the equipment cannot be in a permanent off-hook condition
after the test.
Of course, it is preferable that the EUT (Equipment Under Test) continue to operate after both
Type A and Type B surges. Littelfuse SIDACtor devices in
combination with the TeleLink fuses (0461 1.25) will ensure
that the EUT survives both Type A and Type B surges. For
TIA-968-B compliance, your equipment will need a “C” rated
SIDACtor device for either “metallic only” solutions OR for
“metallic and longitudinal” solutions.
Finally, there is the question of the surge repetition rate.
Although the repetition rate for TIA-968-B tests is the same as
the repetition rate specified in TIA-968-A, TIA-571B,Telecommunications - Telephone Terminal Equipment Electrical, Thermal, Mechanical Environmental Performance Requirements, requires ±8 surges for
Type A and Type B events. You should, therefore, consider a higher surge repetition rate, even
though it is not specifically required by TIA-968-B.
Learn more at http://www.littelfuse.com/searchresults.html?NttP=TIA-968-B&Ntt=TIA-968-B or by
contacting Phillip Havens, phavens@littelfuse.com.
Phillip Havens is the technical marketing and applications manager at Littelfuse and brings a wide
range of electronics engineering expertise. Phillip possesses a BSEE and MSEE from Louisiana
Tech University, is a licensed Professional Engineer, and interfaces extensively with technical
teams of many leading electronics manufacturers to develop circuit protection solutions for their
specialized applications. He represents Littelfuse at electronics safety, circuit protection and
telecom-related industry associations and helps define, direct and support the company’s siliconbased protection products lines. He can be reached at phavens@littelfuse.com.
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