Telephone companies and exchange carriers have long
recognized the disruption and equipment damage that lightning
induced transients can cause to equipment connected to their
networks. To insure safe and continued network operation,
telecommunications carriers have required the equipment that
they purchase to undergo surge immunity testing designed to
emulate the worst case conditions that can be expected in the
field. Telcordia GR-1089 is the immunity standard which applies
to telecommunications equipment in North America. Telcordia
GR-1089 represents the most stringent of lightning immunity
standards used for equipment compliance. The GR-1089 standard
contains immunity requirements for both inside and outside plant
network equipment and customer premises equipment which will
be used in carriers networks.

Lightning Immunity

Lightning immunity tests are performed for equipment which is
installed either on inside lines only or outside lines. These tests
are the result of more than 30 years of field studies measuring
actual lightning events in the United States. The studies found that
lightning strikes in close proximity produced the fastest rise times,
while distant strikes produced slower, longer lasting strikes. The
actual shape of the waveforms also varied but Telcordia settled on
a double exponential waveform as being representative of lightning
surges. The double exponential surge waveform is shown in Figure
1. The double exponential waveform is defined as having an
exponential rate of rise to the peak and an exponential decay from
that peak.

First Level & Second Level Criteria

GR-1089 specifies two levels of surge immunity. First level tests call
for metallic (line-to-line) and longitudinal (line-to-ground) surges.
After the first level test, the equipment must function correctly and
should not have any degraded performance.

Depending upon the equipment port type, second level surge
testing may also be applied. Compliance to the second level criteria
requires that the EUT may be damaged but must not become a fire,
fragmentation, or safety hazard.

GR-1089 Port Types

GR-1089 categorizes telecommunications ports into various port
types based upon the equipment location electrically within the
network. As the surge threat is a function of the port location within
the network, different levels of immunity testing may be required
depending upon the port type. The latest revision of the GR-1089
standard (Issue 4) calls for 8 different port types as shown in Table 1:

Type

Number

Definitinon

Example

Type 1

Directly connected to metallic

outside plant (OSP)

Broadband coax

Type 2

Not directly connected to metallic

outside plane (OSP)

Ethernet