Sec. 68.306  Hazardous voltage limitations.

    (a) General. Under no condition of failure of registered terminal 
equipment or registered protective circuitry, or of equipment connected 
thereto, which can be conceived to occur in the handling, operation or 
repair of such equipment or circuitry, shall the open circuit voltage on 
telephone connections exceed 70 volts peak for more than one second, 
except for voltages for network control signaling and supervision, 
which, in any case, should be consistent with standards employed by the 
telephone companies.
    (1) Registered terminal equipment shall assure that at the MR 
channel interface, no continuous ac or dc voltages appear across the tip 
(MR) and ring (MR) leads, from the tip (MR) lead to PBX ground, or from 
the ring (MR) lead to PBX ground.
    (2) Registered terminal equipment shall assure that during normal 
operation, at an AIOD data channel interface, (i) no significant ac 
voltage to ground other than for data transmission appears on the tip 
(AI) and ring (AI) leads; (ii) no open circuit dc voltage to ground 
appears on the tip (AI) and ring (AI) leads other than in the range from 
0 to -56.5 volts.
    (3) Registered terminal equipment shall also assure that at either 
the MR channel interface or an AIOD data channel interface, voltage 
transients appearing on either the tip (AI or MR) or ring (AI or MR) to 
ground as a result of inductive components in the registered terminal 
equipment shall not be capable of delivering more than 2 joules to a 500 
ohm resistive termination.
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    * The ac component should not exceed 5 volts peak or the 
dc component 5 volts, where not otherwise controlled by Sec. 68.308.
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    (4) Type I E&M leads. Conditions for ``A'' side of interface with 
conditions for ``B'' side in parentheses. Registered terminal equipment 
shall assure that the dc current in the E lead does not

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exceed 100 milliamperes, no significant ac voltage to ground appears on 
the E&M leads,* no significant ac or dc voltage to ground appear on the 
(E) & (M) leads,* and the open circuit dc voltage to ground on the E&M 
leads does not exceed 56.5 volts and is not positive. M lead protection 
shall be provided to assure that voltages to ground do not exceed 80 
volts. For relay contact implementation a power dissipation capability 
of 0.5 watt shall be provided in the shunt path. If the registered 
terminal equipment contains an inductive component in the E lead, it 
must assure that the transient voltage across the contact as a result of 
a relay contact opening, does not exceed the following voltage and 
duration limitations:
    (i) 300 volts peak,
    (ii) A rate of change of one volt per microsecond, and
    (iii) An 80 volt level for more than 10 milliseconds.
    (5) Type II E&M leads. Conditions for ``A'' side of interface with 
conditions for ``B'' side in parentheses. Registered terminal equipment 
shall assure that the dc current in the E and (SB) leads does not exceed 
100 milliamperes and no significant ac voltage to ground appears on the 
E and (SB) leads,* no significant ac or dc voltages to ground appear on 
the M, SG, SB (E), (SG), and (M) leads from sources in the registered 
terminal equipment,* and the open circuit dc voltage to ground on the E 
and (SB) leads does not exceed 56.5 volts and is not positive. If the 
registered terminal equipment contains an inductive component in the E 
or (M) lead, it must assure that the transient voltage across the 
contact, as a result of a relay contact opening, does not exceed the 
following voltage and duration limitations;
    (i) 300 volts peak,
    (ii) A rate of change of one volt per microsecond, and
    (iii) An 80 volt level for more than 10 milliseconds.
    (6) Off-premises station voltages. (i) Talking battery or voltages 
applied by the PBX (or similar systems) to OPS interface leads for 
supervisory purposes must be negative with respect to ground, shall not 
exceed 56.5V dc for Classes A, B, and C, and shall not have a 
significant ac component.*
    (ii) Ringing signals applied by the PBX (or similar systems) 
to OPS interface leads shall be applied for the purpose of station 
alerting only, and shall comply with requirements in paragraph (d) of 
this section. Ringing voltages shall be applied between the ring 
conductor and ground.
    (7) For Local Area Data Channel interfaces, during normal operating 
modes including terminal equipment initiated maintenance signals, 
registered terminal equipment shall assure, except during the 
application of ringing (limitations specified in paragraph (d) of this 
section), with respect to telephone connections (tip, ring, tip 1, ring 
1) that:
    (i) Under normal operating conditions, the rms current per conductor 
between short-circuited conductors, including dc and ac components, does 
not exceed 350 milliamperes. For other than normal operating conditions, 
the rms current between any conductor and ground or between short-
circuited conductors, including dc and ac components, may exceed 350 
milliamperes for no more than 1.5 minutes.
    (ii) The dc voltage between any conductor and ground does not exceed 
80 volts. Under normal operating conditions it shall not be positive 
with respect to ground (though positive voltages up to 80 volts may be 
allowed during brief maintenance states);
    (iii) Ac voltages are less than 42.4 volts peak between any 
conductor and ground, (Terminal equipment shall comply while other 
interface leads are both (A) unterminated and (B) individually 
terminated to ground); and,
    (iv) Combined ac and dc voltages between any conductor and ground 
are less than 42.4 volts peak when the absolute value of the dc 
component is less than 21.2 volts, and less than (28.8 + 64  x  Vdc) 
when the absolute value of the dc component is between 21.2 and 80 
volts.
    (8) During normal operation, registered terminal equipment for 
connection to ringdown voiceband private line interfaces or voiceband 
metallic channel interfaces shall assure that:
    (i) Ringing voltage is used for alerting only, does not exceed the 
voltage

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and current limits specified in paragraph (d), and is:
    (A) Applied to the ring conductor with the tip conductor grounded 
for 2-wire interfaces, or
    (B) Simplexed on the tip and ring conductors with ground simplexed 
on the tip (1) and ring (1) conductors for 4-wire interfaces.
    (ii) Except during the signaling mode or for monitoring voltage, 
there is no significant positive dc voltage with respect to ground (not 
over +5 volts):
    (A) For 2-wire ports between the tip lead and ground and the ring 
lead and ground, and
    (B) For 4-wire ports between the tip lead and ground, the ring lead 
and ground, the tip 1 lead and ground, and the ring 1 lead and ground.
    (iii) The dc current per lead, under short circuit conditions shall 
not exceed 140 milliamperes.
    (b) Connection of nonregistered equipment to registered terminal 
equipment or registered protective circuitry--(1) General. Leads to, or 
any elements having a conducting path to telephone connections, 
auxiliary leads or E&M leads shall:
    (i) Be reasonably physically separated and restrained from and be 
neither routed in the same cable as nor use the same connector as leads 
or metallic paths connecting power connections;
    (ii) Be reasonably physically separated and restrained from and be 
neither routed in the same cable as nor use adjacent pins on the same 
connector as metallic paths to leads to nonregistered equipment, when 
specification details provided to the Commission pursuant to 
Sec. 68.200(g) do not show that interface voltages are less than non-
hazardous voltage source limits in Sec. 68.306(b)(4).
    (2) Connections to registered terminal equipment. The voltage 
measurable between auxiliary leads, auxiliary leads to ground, E&M leads 
and ground, tip and ring, tip to ground, ring to ground, tip 1 and ring 
1, tip 1 to ground, and ring 1 to ground shall not exceed 70 volts peak 
for more than 1 second, with tip to ring, tip 1 to ring 1, and auxiliary 
lead to auxiliary lead each terminated with 1500 ohms center-tapped 
through 1000 ohms to ground and each E&M lead terminated in 1500 ohms to 
ground, if 120 volts rms 60 Hz, ac is applied between all connections to 
other equipment tied together (except connections to non-hazardous 
voltage sources) and ground. The source shall not be limited to less 
than 20 amperes continuously, not to less than 50 amperes for 1 minute, 
and shall not be interrupted by an overcurrent device permitting less 
total energy flow than a 20 ampere time delay fuse or breaker.
    (3) Connections to registered protective circuitry. The voltage 
measurable between auxiliary leads, auxiliary leads to ground, E&M leads 
and ground, tip and ring, tip to ground, ring to ground, tip 1 and ring 
1, tip 1 to ground, and ring 1 to ground shall not exceed 70 volts peak 
for more than 1 second, with tip to ring, tip 1 to ring 1 and auxiliary 
lead to auxiliary lead each terminated with 1500 ohms, center-tapped 
through 1000 ohms to ground, and each E&M lead terminated in 1500 ohms 
to ground if either 120 or 300 volts rms to 60 Hz. ac is applied:
    (i) Between all protective circuitry connections other than 
telephone connections (and connection to non-hazardous voltage sources), 
tied together and ground; and
    (ii) Across all protective circuitry connections, other than 
telephone connections (and connections to non-hazardous voltage sources) 
which have a transmission path to the telephone connections, with 
alternative leads grounded; under all reasonable applications of earth 
ground to the protective circuitry. The source shall not be limited to 
less than 20 amperes continuously, nor to less than 50 amperes for 1 
minute, and shall not be interrupted by an overcurrent device permitting 
less total energy flow than a 20 ampere time delay fuse or breaker.
    (4) Non-hazardous voltage source. A voltage source is considered a 
non-hazardous voltage source if it conforms with the requirements of 
Secs. 68.302, 68.304, and 68.306(b)(1), with all connections to the 
source other than primary power connections treated as ``telephone 
connections,'' and if such source supplies voltages no greater than the 
following under all modes of operation and of failure:

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    (i) Ac voltages less than 42.4 volts peak;
    (ii) Dc voltages less than 80 volts; and
    (iii) Combined ac and dc voltages less than 42.4 volts peak when the 
absolute value of the dc component is less than 21.2 volts and less than 
(28.8 + 0.64  x  V dc) when the absolute value of the dc component is 
between 21.2 and 80 volts.
    (c) Hazards from exposed surfaces (to be applied for intentional 
conductive paths to ground as required by Sec. 68.304). The voltage 
measurable between auxiliary leads, auxiliary leads to ground, E&M leads 
and ground, tip and ring, tip and ground, ring and ground, tip 1 and 
ring 1, tip 1 and ground, ring 1 and ground, shall not exceed 70 volts 
peak for more than 1 second, with tip to ring, tip 1 and ring 1, and 
auxiliary lead to auxiliary lead each terminated with 1500 ohms, center-
tapped through 1000 ohms to ground, and each E&M lead terminated in 1500 
ohms to ground, if 120 volts rms 60 Hz. ac is applied between conductive 
exposed surfaces and ground. The source shall not be limited to less 
than 20 amperes continuously, nor to less than 50 amperes for 1 minute, 
and shall not be interrupted by an overcurrent device permitting less 
total energy flow than a 20 ampere time delay fuse or breaker.
    (d) Ringing sources. Ringing sources, except for class A OPS 
interfaces, shall meet all of the following restrictions:
    (1) The ringing signal shall use only frequencies whose fundamental 
component is equal to or below 70 Hz.2
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    2 33 Hz may be the highest frequency necessary for OPS 
service.
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    (2) The ringing voltage shall be less than 300 V peak-to-peak and 
less than 200 V peak-to-ground across a resistive termination of at 
least 1 megohm.
    (3) The ringing voltage shall be interrupted to create quiet 
intervals of at least one second (continuous) duration each separated by 
no more than 5 seconds. During the quiet intervals, the voltage to 
ground shall not exceed the voltage limits given in paragraph (a)(6)(i) 
of this section.
    (4) As specified below, ringing sources shall be required to (a) 
include a series current-sensitive tripping device in the ring lead 
which will trip ringing as specified in Figure 68.306(d), and/or (b) 
provide a voltage to ground (monitoring voltage) on the tip or ring 
conductor with a magnitude of at least 19 volts peak (but may not exceed 
the voltage limits given in paragraph (a)(6)(i) of this section) 
whenever the ringing voltage is not present (idle state). Tripping 
devices and/or monitoring voltages are required dependent upon the 
current flow through a specified resistance connected between the 
ringing source (R(OPS)) and ground as follows:
    (i) If the current through a 500 ohms (and greater) resistor does 
not exceed 100 mA peak-to-peak, neither a tripping device nor a 
monitoring voltage are required, or
    (ii) If the current through a 1500 ohms (and greater) resistor 
exceeds 100 mA peak-to-peak, the ringing source shall include a tripping 
device. If the tripping device meets the operating characteristics as 
specified in Figure 68.306(d) with R=500 ohms (and greater), then no 
monitoring voltage is required. If, however, the tripping device only 
meets the given operating characteristics with R=1500 ohms (and 
greater), then the ringing source must also include a monitoring voltage 
as described above, or
    (iii) If the current through a 500 ohms (and greater) resistor 
exceeds 100 mA peak-to-peak but does not exceed this value of current 
with a 1500 ohms (and greater) termination, the ringing source shall 
include either a tripping device which meets the operating 
characteristics as specified in Figure 68.306(d) with R=500 ohms (and 
greater), or a monitoring voltage.

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[GRAPHIC] [TIFF OMITTED] TCJN91.014


[45 02 FR 20854 , Mar. 31, 1980, as amended at  45 FR 54342 , Aug. 15, 1980; 
 45 FR 61632 , Sept. 17, 1980;  47 FR 39686 , Sept. 9, 1982;  51 FR 945 , Jan. 
9, 1986;  51 FR 16689 , May 6, 1986;  60 FR 54814 , 54815, Oct. 26, 1995]

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