Sec. 68.312 On-hook impedance limitations.
(a) General. The limitations in this section that involve 2-wire
network ports apply to tip and ring of the public switched network. For
4-wire network ports (tip, ring, tip 1, and ring 1) with loop-start or
ground-start signaling, the limitations apply when tip and ring
conductors are connected together and treated as one of the conductors
of a tip and ring pair and the tip 1 and ring 1 conductors are connected
together and treated as the other conductor of a tip and ring pair.
(b) Limitations on individual equipment intended for operation on
loop-start telephone facilities, including PSDS Type II in the analog
mode:
(1) Registered terminal equipment and registered protective
circuitry shall conform to the following limitations, for each Ringing
Type which is listed as part of its Ringer Equivalence:
(i) The dc resistance between tip and ring conductors, and between
each of the tip and ring conductors and earth ground, shall be greater
than 5 megohms for all dc voltages up to and including 100 volts.
(ii) The dc resistance between tip and ring conductors, and between
each of the tip and ring conductors and earth ground shall be greater
than 30 kilohms for all dc voltages between 100 and 200 volts.
(iii) During the application of simulated ringing, as listed in
table I below, the total dc current, shall not exceed 3.0 milliamperes.
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(iv) During the application of simulated ringing, as listed in table
I below, the impedance between the tip and ring conductors (defined as
the quotient of applied ac voltage divided by resulting true rms
current) shall be greater than the value specified in table I. Except as
provided in paragraph (b)(2) of this section, such impedance shall be
less than 40 kilohms.
(v) During the application of simulated ringing, as listed in table
I below, the impedance between each of the tip and ring conductors and
ground shall be greater than 100 kilohms.
(2) Registered terminal equipment and registered protective
circuitry intended for use on facilities which will always have ringing
detection circuitry in use at the same time such registered terminal
equipment and registered protective circuitry is connected need not
comply with the 40 kilohms maximum impedance specification of paragraph
(b)(1)(v) of this section.
(c) Limitations on individual equipment intended for operation on
ground-start telephone facilities. Registered terminal equipment and
registered protective circuitry shall conform to the following
limitations for each Ringing Type which is listed as part of its Ringer
Equivalence Number:
(1) During the application of simulated ringing, as listed in table
I below, the total dc current flowing between tip and ring conductors
shall not exceed 3.0 milliamperes.
(2) During the application of simulated ringing, as listed in table
I below, the total impedance of the parallel combination of the ac
impedance across tip and ring conductors and the ac impedance from the
ring conductor to ground (with ground on the tip conductor) shall be
greater than the value specified in table I. Except as provided in
paragraph (b)(2) of this section, such impedance shall be less the 40
kilohms.
(d) Ringer equivalence definition. The values of each of the
parameters for which a limitation is imposed in paragraph (b) or (c) of
this section, as appropriate, shall be determined for a representative
unit under test. Quotients of each such value shall be formed according
to the following:
(1) For individual equipment intended for operation on loop-start
telephone facilities:
(i) 25 megohms divided by the minimum measured on-hook dc resistance
for all dc voltages up to and including 100 volts.
(ii) 150 kilohms divided by the minimum measured on-hook dc
resistance for all dc voltages between 100 and 200 volts.
(iii) The maximum total dc current flowing between tip and ring
during the application of simulated ringing as listed in table I below,
in milliamperes, divided by 0.6 milliamperes.
(iv) Five times the impedance limitation listed in table I, below,
divided by the minimum measured ac impedance, defined as in paragraph
(b)(1)(iv) of this section, during the application of simulated ringing
as listed in table I.
(2) For individual equipment intended for operation on ground-start
telephone facilities:
(i) The maximum total dc current flowing between tip and ring
conductors during the application of simulated ringing as listed in
table I below, in milliamperes, divided by 0.6 milliamperes.
(ii) Five times the impedance limitation listed in table I below
divided by the minimum measured ac impedance, defined in paragraph
(b)(2) of this section, during the application of simulated ringing as
listed in table I.
The largest of the unitless quotients so formed, followed by the Ringing
Type letter indicator representing the frequency range for which that
number is valid, is the Ringer Equivalence. If Ringer Equivalence is to
be stated for more than one Ringing Type, testing shall be performed at
each frequency range to which Ringer Equivalence is to be determined in
accordance with the above, and the largest resulting Ringer Equivalence
number so determined will be associated with each Ringing Type letter
designation for which it is valid.
(e) Registered terminal equipment and registered protective
circuitry shall have at least one ringer equivalence number shown on the
registration label. Where options that will vary
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the ringer equivalence are involved, either each option that results in
a ringer equivalence number greater than 0.1 and its corresponding
Ringer Equivalence shall be listed on the registration label, or the
largest ringer equivalence number that can result from such options
shall be stated on the label. A trained, authorized agent of the Grantee
may disconnect ringers, bridge ringers to another line, or execute
options affecting ringer equivalence after the telephone company has
been notified in accordance with Sec. 68.106.
(f) All registered terminal equipment and registered protective
circuitry which can affect on-hook impedance shall be assigned a Ringer
Equivalence. The sum of all such ringer equivalences on a given
telephone line or loop shall not exceed 5; in some cases, a system which
has a total ringer equivalence of 5 or less may not be usable on a given
telephone line or loop.
(g) Ringing type Z equipment. Equipment which has on-hook impedance
characteristics which do not conform to the requirements of this section
may be conditionally registered, notwithstanding the requirements of
this section, provided that it is labelled with a Ringing Type
designation ``Z''. It should be noted that registration of equipment
bearing the designation ``Z'' does not necessarily confer any right of
connection to the telephone network under these rules; any equipment
registered with the type Z designation may only be used with the consent
of the local telephone company, provided that the local telephone
company does not discriminate in its treatment of equipment bearing the
type Z designation.
(h) Limitations on PBX equipment with an off-premises interface and
direct inward dialing (DID). PBX ringing supplies whose output appears
on the off-premises interface leads shall not trip when connected to the
following tip-to-ring impedance which terminates the off-premises
station loop:
------------------------------------------------------------------------
ac impedance ohms
-----------------------
Ringing frequency Hz Class B,
or C Class A
------------------------------------------------------------------------
7000 1400
20 plus-minus 3............................... ----
N
5000 1000
30 plus-minus 3............................... ----
N
------------------------------------------------------------------------
N--Number of ringer equivalences, as specified by the manufacturer,
which can be connected to the off-premises station loop.
(i) Limitations on individual equipment intended for operation with
message register signaling channels:
(1) Registered terminal equipment and registered protective
circuitry shall conform to the following limitations in all operating
states.
(2) The dc resistance between each of the tip (MR) and ring (MR)
conductors and ground shall be greater than 30 kilohms for voltages up
to and including 200 volts.
(j) Limitations on individual equipment ports with ringdown or
inband signaling or voiceband metallic channels for connection to
voiceband private line interfaces.
(1) Registered terminal equipment and registered protective
circuitry with 2-wire ports for ringdown, inband signaling or voiceband
metallic channels shall provide a dc resistance between tip and ring
conductors and between each of the tip and ring conductors and earth
ground greater than 30 kilohms for all dc voltages up to and including
200 volts.
(2) Registered terminal equipment and registered protective
circuitry with 4-wire ports for ringdown, inband signaling or voiceband
metallic channels shall provide a dc resistance between each of the tip,
ring, tip 1 and ring 1 conductors and earth ground greater than 30
kilohms for all dc voltages up to and including 200 volts.
(k) Registered terminal equipment and registered protective
circuitry shall not by design leave the on-hook state by operations
performed on tip and ring leads for any other purpose than to request
service or answer an incoming call, except that terminal equipment which
the user places in the off-hook state for the purpose of manually
placing telephone numbers in internal memory for subsequent automatic or
repertory dialing shall be registrable. Make-busy indications shall be
transmitted by the use of make-
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busy leads only as defined in Secs. 68.3 and 68.200(j).
Table I
------------------------------------------------------------------------
Range of compatible Simulated ringing Impedance
Ringing type ringing frequencies voltage superimposed limitation
Hz 56.5 volts dc (ohms)
------------------------------------------------------------------------
A............. 20 plus-minus 3...... 40 to 130 volts rms.. 1400
30 plus-minus 3...... 40 to 130 volts rms.. 1000
B............. 15.3 to 68.0......... 40 to 150 volts rms.. 1600
C............. 15.3 to 17.4......... 54 to 120 volts rms.. 1600
D............. 19.3 to 20.7 \1\ 54 to 120 volts rms.. 1600
(frequency-
selective).
E............. 24.3 to 25.7......... 54 to 120 volts rms.. 1600
F............. 29.3 to 30.7 \1\ 54 to 120 volts rms.. 1600
(frequency-
selective).
G............. 32.6 to 34.0......... 54 to 130 volts rms.. 1600
H............. 39.2 to 40.9......... 62 to 130 volts rms.. 1600
J............. 41.0 to 43.0......... 62 to 130 volts rms.. 1600
K............. 49.0 to 51.0......... 62 to 140 volts rms.. 1600
L............. 52.9 to 55.1......... 62 to 140 volts rms.. 1600
M............. 58.8 to 61.2......... 68 to 150 volts rms.. 1600
N............. 65.4 to 68.0......... 68 to 150 volts rms.. 1600
P............. 15.3 to 34.0......... 54 to 130 volts rms.. 1600
Q............. 20 plus-minus 3...... 40 to 130 volts rms.. 1400
------------------------------------------------------------------------
\1\ Note: Requirements at these frequencies, which are identical to Type
A frequencies, are not consistent with the Type A requirements;
equipment intended for use both on Type A facilities and facilities
using frequency-selective ringing must comply with the requirements on
Types A, D and F independently.
[ 45 FR 20853 , Mar. 31, 1980, as amended at 45 FR 61632 , Sept. 17, 1980;
45 FR 79486 , Dec. 1, 1980; 46 FR 40192 , Aug. 7, 1981; 48 FR 34044 , July
27, 1983; 51 FR 950 , Jan. 9, 1986; 51 FR 28237 , Aug. 6, 1986; 61 FR 42394 , Aug. 15, 1996; 61 FR 47434 , Sept. 9, 1996]
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