1755.397—RUS performance specification for line concentrators.

(a) General. (1) This section covers general requirements for a line concentrator (LC) system. This system shall operate in accordance with the manufacturer's specifications. Reliability shall be of prime importance in the design, manufacture and installation of the equipment. The equipment shall automatically provide for:

(i) Terminating subscriber lines at a location remote from the serving central office;

(ii) Concentrating the subscriber lines over a few transmission and supervisory paths to the serving central office; and

(iii) Terminating the lines at the central office without loss of individual identity. A subscriber connected to a line concentrator shall be capable of having essentially the same services as a subscriber connected directly to the central office equipment (COE). Intra-unit calling among subscribers connected to the concentrator may be provided, but is not required.

(2) Industry standards, or portions thereof, referred to in this paragraph (a) are incorporated by reference by RUS. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552 (a) and 1 CFR part 51. Copies of these standards are available for inspection during normal business hours at RUS, room 2838, U.S. Department of Agriculture, Washington, DC 20250, or at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, call 202-741-6030, or go to: http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.

(3) American National Standards Institute (ANSI) standards are available from ANSI Inc., 11 West 42nd Street, 13th floor, New York, NY 10036, telephone 212-642-4900.

(i) ANSI Standard S1.4-1983, Specification for Sound Level Meters, including Amendment S1.4A-1985.

(ii) [Reserved]

(4) American Society for Testing Materials (ASTM) are available from 1916 Race Street, Philadelphia, PA 19103, telephone 215-299-5400.

(i) ASTM Specification B33-91, Standard Specifications for Tinned Soft or Annealed Copper Wire for Electrical Purposes.

(ii) [Reserved]

(5) Bell Communications Research (Bellcore) standards are available from Bellcore Customer Service, 8 Corporate Place, Piscataway, NJ 08854, telephone 1-800-521-2673.

(i) TR-TSY-000008, Issue 2, August 1987, Digital Interface between the SLC 96 Digital Loop Carrier System and a Local Digital Switch.

(ii) Bell Communications Research (Bellcore) document TR-TSY-000057, Issue 1, April 1987, including Revision 1, November 1988, Functional Criteria for Digital Loop Carrier Systems.

(iii) Bell Communications Research (Bellcore) Document TR-NWT-000303, Issue 2, December 1992, including Revision 1, December 1993, Integrated Digital Loop Carrier System Generic Requirements, Objectives, and Interface.

(6) Federal Standard H28, Screw-Thread Standards for Federal Services, March 31, 1978, including Change Notice 1, May 28, 1986; Change Notice 2, January 20, 1989; and Change Notice 3, March 12, 1990. Copies may be obtained from the General Services Administration, Specification Section, 490 East L'Enfant Plaza SW, Washington, DC 20407, telephone 202-755-0325.

(7) IEEE standards are available from IEEE Service Center, 445 Hoes Lane, P.O. Box 1331, Piscataway, NJ 08854, telephone 1-800-521-2673.

(i) IEEE Standard 455-1985, Standard Test Procedure for Measuring Longitudinal Balance of Telephone Equipment Operating in the Voice Band.

(ii) [Reserved]

(8) RUS standards are available from Publications and Directives Management Branch, Administrative Services Division, Rural Utilities Service, room 0180, South Building, U.S. Department of Agriculture, Washington, DC 20250-1500.

(i) RUS Bulletin 345-50, PE-60 (Sept 1979), RUS Specification for Trunk Carrier Systems.

(ii) [Reserved]

(b) Types of requirements. (1) Unless otherwise indicated, the requirements listed in this section are considered to be fixed requirements.

(2) The concentrator system shall communicate with standard T1 digital transmission format at a minimum between the concentrator and central office terminals. Analog conversion functions at remote and central office terminals shall be capable of being eliminated to accommodate end-to-end digital transmission.

(3) The LC shall operate properly as an integral part of the telephone network when connected to physical or carrier derived circuits and central offices meeting RUS specifications and other generally accepted telecommunications practices, such as Bellcore documents TR-NWT-000303, Integrated Digital Loop Carrier System Generic Requirements, Objectives and Interface; TR-TSY-000008, Digital Interface between the SLC 96 Digital Loop Carrier System and a Local Digital Switch; and TR-TSY-000057, Functional Criteria for Digital Loop Carrier Systems.

(4) For RUS acceptance consideration of a LC, the manufacturer must certify and demonstrate that all requirements specified in this section are available and in compliance with this section.

(5) Certain requirements are included in this section for features which may not be needed for every application. Such features are identifiable by the inclusion in the requirements of some such phrase as “when specified by the owner” or “as specified by the owner.” In some cases where an optional feature will not be required by an owner, either now or in the future, a system which does not provide this feature shall be considered to be in compliance with the specification for the specific installation under consideration, but not in compliance with the entire specification.

(6) The owner may properly request bids from any supplier of an RUS accepted LC whose system provides all the features which will be required for a specific installation.

(7) When required by the owner, the supplier shall state compliance to the Carrier Serving Area (CSA) requirements, as stated in Bell Communications Research (Bellcore) Standard TR-TSY-000057, Functional Criteria for Digital Loop Carrier Systems.

(c) Reliability. (1) The failure rate of printed circuit boards shall not exceed an average of 2.0 percent per month of all equipped cards in all system terminals during the first 3 months after cutover, and shall not exceed an average of 1.0 percent per month of all equipped cards in all system terminals during the second 3-month period. The failure rate for the equipment shall be less than 0.5 percent per month of all equipped cards in all system terminals after 6 months. A failure is considered to be the failure of a component on the PC board which requires it to be repaired or replaced.

(2) The line concentrator terminal units shall be designed such that there will be no more than 4 hours of total outages in 20 years.

(d) System type acceptance tests. General test results will be required on each system type. Any system provided in accordance with this section shall be capable of meeting any requirement in this section on a spot-check basis.

(e) Features required. The network control equipment and peripheral equipment shall be comprised of solid-state and integrated circuitry components as far as practical and in keeping with the state-of-the-art and economics of the subject system.

(f) Subscriber lines— (1) General. The remote LC units shall operate satisfactorily with subscriber lines which meet all of the conditions under the bidder's specifications and all the requirements of this section. This section recognizes that the loop limit of the line concentrator is dependent upon the transmission facility between the LC central office termination and the LC remote unit. When voice frequency (physical) circuits are used, the loop limit from the COE to the subscriber shall be 1900 ohms (including the telephone set). When electronically derived circuits (carrier, lightwave, etc.) are used, the loop limits of the electronic system will control. The bidder shall identify the loop limits of the equipment to be supplied.

(ii) There should be provisions for such types of lines as ground start, loop start, regular subscriber, pay stations, etc.

(2) Dialing. (i) General. The line concentrator remote and central office terminal equipment shall satisfactorily transmit dialing information when used with subscriber dials having a speed of operation between 8 and 12 dial pulses per second and a break period of 55 to 65% of the total signaling period.

(ii) Subscriber dial interdigital time. The remote and central office LC equipment shall permit satisfactory telecommunications operation when used with subscriber rotary dial interdigital times of 200 milliseconds minimum, and pushbutton dialing with 50 milliseconds minimum.

(iii) Subscriber line pushbutton dialing frequencies. The frequency pairs assigned for pushbutton dialing when provided by the central office shall be as listed in this paragraph (f)(2)(iii), with an allowable variation of ±1.5 percent:

Low group frequencies (Hz)	High group frequencies (Hz)
Low group frequencies (Hz)	1209	1336	1477	1633
697	1	2	3	Spare.
770	4	5	6	Spare.
852	7	8	9	Spare.
941	*	0	#	Spare.

(3) Ringing. (i) When LC ringing is generated at the remote end, it shall be automatic and intermittent and shall be cut off from the called line upon removal of the handset at the called station during either the ringing or silent period.

(ii) When ringing generators are provided in the LC on an ancillary basis, they shall be accepted or technically accepted by RUS.

(iii) Where ringing is generated at the remote end, the ringing system shall provide sufficient ringing on a bridged basis over the voltage and temperature limits of this specification and over subscriber loops within the limits stated by the manufacturer. The manufacturer shall state the minimum number (not less than two) of main station ringers that can be used for each ringing option available.

(g) Traffic. (1) The minimum grade of service for traffic in the line concentrator shall be B=.005 using the Traffic Table, based on the Erlang Lost-Calls-Cleared Formula. Required grade of service, traffic assumptions and calculations for the particular application being implemented shall be supplied by the bidder.

(ii) Service to customers served by a traffic sensitive LC should not be noticeably different than the service to customers served by the dedicated physical pairs from the central office so that uniform grade of service will be provided to all customers in any class of service. Reference § 1755.522(p)(1)(i), RUS General Specification for Digital, Stored Program Controlled Central Office Equipment.

(2) Traffic and Plant Registers. Traffic measurements consist of three types—peg count, usage, and congestion. A peg count register scores one count per call attempt per circuit group such as trunks, digit receivers, senders, etc. Usage counters measure the traffic density in networks, trunks and other circuit groups. Congestion registers score the number of calls which fail to find an idle circuit in a trunk group or to find an idle path through the switching network when attempting to connect two given end points. These conditions constitute “network blocking.”

(3) When required, traffic data will be stored in electronic storage registers or a block of memory consisting of one or more traffic counters for each item to be measured. The bidder shall indicate what registers are to be supplied, their purpose and the means for displaying the information locally (or at a remote location when available).

(h) Transmission requirements— (1) General. Unless otherwise stated, the requirements in paragraphs (h) (2) through (20) of this section are specified in terms of analog measurements made from Main Distributing Frame (MDF) terminals to MDF terminals excluding cabling loss.

(2) Telephone transmitter battery supply. A minimum of 20 milliamperes, dc, shall be provided for the transmitter of the telephone set at the subscriber station under all loop conditions specified by the bidder. The telephone set is assumed to have a resistance of 200 ohms.

(3) Impedance—subscriber loops. For the purpose of this section, the input impedance of all subscriber loops served by the equipment is arbitrarily considered to be 900 ohms in series with 2.16 microfarad capacitor at voice frequencies.

(4) Battery noise. Noise across the remote terminal battery at power panel distribution bus terminals shall not exceed 35 dBrnC during the specified busy hour.

(5) Stability. The long-term allowable variation in loss through the line concentrator system shall be ±0.5 dB from the loss specified by the bidder.

(6) Return loss. The specified return loss values are determined by the service and type of port at the measuring end. Two-wire ports are measured at 900 ohms in series with 2.16 microfarads, and 4-wire ports are measured at 600 ohms resistive. When other balance networks are supplied, test equipment arranged for operation with the supplied network(s) may be used. The requirement given shall meet the following cited values on each balance network available in the system:

Line-to-Line or Line-to-Trunk (2-Wire)

Echo Return Loss (ERL)—18 dB, Minimum

Singing Return Loss (SRL)—Low—15 dB, Minimum

Singing Return Loss (SRL)—High—18 dB, Minimum

(7) Longitudinal balance. The minimum longitudinal balance, with dc loop currents between 20 to 70 mA, shall be 60 dB at all frequencies between 60 and 2000 Hz, 55 dB at 2700 Hz and 50 dB at 3400 Hz. The method of measurement shall be as specified in the IEEE standard 455, “Standard Testing Procedure for Measuring Longitudinal Balance of Telephone Equipment Operating in the Voice Band.” Source voltage level shall be 10 volts root mean square (rms) where conversation battery feed originates at the remote end.

(8) 60 hz longitudinal current immunity. The LC 60 Hz longitudinal current immunity shall be measured in accordance with Figure 1 of this section. Under test conditions cited on Figure 1 of this section, the system noise shall be 23 dBrnC or less as follows:

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(9) Steady noise (idle channel at 900 ohm impedance). Steady noise: Measure on terminated call. Noise measurements shall comply with the following:

Maximum—23 dBrnC0

Average—18 dBrnC0 or Less

3KHz Flat—Less than 35 dBrnO as an Objective

(10) Impulse noise. LC central office terminal equipment shall have an impulse noise limit of not more than five counts exceeding 54 dBrnC0 voice band weighted in a 5-minute period on six such measurements made during the busy hour. A WILCOM T-194C Transmission Test Set, or equivalent, should be used for the measurements. The measurement shall be made by establishing a normal connection from the noise counter through the switching equipment in its off-hook condition to a quiet termination of 900 ohms impedance. Office battery and signaling circuit wiring shall be suitably segregated from voice and carrier circuit wiring, and frame talking battery filters provided, if and as required, in order to meet these impulse noise limits.

(11) Crosstalk coupling. Worst case equal level crosstalk shall be 65 dB minimum in the range 200 to 3400 Hz. This shall be measured between any two paths through the system by connecting a 0 dBm0 level tone to the disturbing pair.

(12) Digital error rate. The digital line concentrator shall not introduce more than one error in 10 8 bits averaged over a 5-minute period, excluding the least significant bit.

(13) Quantizing distortion. (i) The system shall meet the following requirements:

Input level (dBm0) 1004 or 1020 Hz	Minimum signal to distortion with C-message weighting
0 to −30	33 dB
−30 to −40	27 dB
−40 to −45	22 dB

(ii) Due to possible loss of the least significant bit on direct digital connections, a signal to distortion degradation of up to 2 dB may be allowed where adequately justified by the bidder.

(14) Overload level. The overload level shall be 3 dBm0.

(15) Gain tracking (linearity) shall meet the following requirements:

Input signal level 1	Maximum gain deviation
3 to −37 dBm0	±0.5 dB
−37 to −50 dBm0	±1 dB
1 1004 Hz reference at 0 dBm0.

(16) Frequency response (loss relative to 1004 Hz) for line-to-line (via trunk group or intra-link) connections shall meet the following requirements:

Frequency (Hz)	Loss at 0 dBm0 input 1
60	20 dB Min. 2
300	−1 to 3 dB
600 to 2400	1 dB
3400	−1 to 3 dB
1 (−) means less loss and ( ) means more loss.
2 Transmit End.

(17) Envelope delay distortion. On any properly established connection, the envelope delay distortion shall not exceed the following limits:

Frequency (Hz)	Microseconds
1000 to 2600	190
800 to 2800	350
600 to 3000	500
400 to 3200	700

(18) Absolute delay. The absolute one-way delay through the line concentrator, excluding delays associated with the central office switching equipment, shall not exceed 1000 microseconds analog-to-analog measured at 1800 Hz.

(19) Insertion loss. The insertion loss in both directions of transmission at 1004 Hz shall be included in the insertion loss requirements for the connected COE switch and shall not increase the overall losses through the combined equipment beyond the values for the COE alone, when operated through a direct digital interface. Systems operated with a (VF) line circuit interface may introduce up to 3 dB insertion loss. Reference § 1755.522(q)(3).

(20) Detailed requirements for direct digital connections. (i) This paragraph (h)(20) covers the detailed requirements for the provision of interface units which will permit direct digital connection between the host central office and line concentrator subscriber terminals over digital facilities. The digital transmission system shall be compatible with T1 type span lines using a DS1 interface and other digital interfaces that may be specified by the owner. The RUS specification for the T1 span line equipment is PE-60. Other span line techniques may also be used. Diverse span line routing may be used when specified by the owner.

(ii) The output of a digital-to-digital port shall be Pulse Code Modulation (PCM), encoded in eight-bit words using the mu-255 encoding law and D3 encoding format, and arranged to interface with a T1 span line.

(iii) Signaling shall be by means of Multifrequency (MF) or Dual Pulsing (DP) and the system which is inherent in the A and B bits of the D3 format. In the case where A and B bits are not used for signaling or system control, these bits shall only be used for normal voice and data transmission.

(iv) When a direct digital interface between the span line and the host central office equipment is to be implemented, the following requirements shall be met:

(A) The span line shall be terminated in a central office as a minimum a DS1 (1.544Mb/s) shall be provided;

(B) The digital central office equipment shall be programmed to support the operation of the digital port with the line concentrator subscriber terminal;

(C) The line concentrator subscriber terminal used with a direct digital interface shall be interchangeable with the subscriber terminal used with a central office terminal.

(i) Alarms. The system shall send alarms for such conditions as blown fuses, blocked controls, power failure in the remote terminal, etc., along with its own status indication and status of dry relay contact closures or solid-state equivalent to the associated central office alarm circuits. Sufficient system alarm points shall be provided from the remote terminal to report conditions to the central office alarm system. The alarms shall be transmitted from the remote terminal to the central office terminal as long as any part of the connecting link is available for this transmission. Fuses shall be of the alarm and indicator type, and their rating designated by numerals or color code on fuse positions.

(j) Electrical protection— (1) Surge protection. Adequate electrical protection of line concentrator equipment shall be included in the design of the system. The characteristics and application of protection devices must be such that they enable the line concentrator equipment to withstand, without damage or excessive protector maintenance, the dielectric stresses and currents that are produced in line-to-ground and tip-to-ring circuits through the equipment as a result of induced or conducted lightning or power system fault-related surges. All wire terminals connected to outside plant wire or cable pairs shall be protected from voltage and current surges.

(ii) Equipment must pass laboratory tests, simulating a hostile electrical environment, before being placed in the field for the purpose of obtaining field experience. For acceptance consideration RUS requires manufacturers to submit recently completed results (within 90 days of submittal) of data obtained from the prescribed testing. Manufacturers are expected to detail how data and tests were conducted. There are five basic types of laboratory tests which must be applied to exposed terminals in an effort to determine if the equipment will survive. Figure 2 of this section, Summary of Electrical Requirements and Tests, identifies the tests and their application as follows:

Figure 2—Summary of Electrical Requirements and Tests

Test	Application criteria	Peak voltage or current	Surge waveshape	Number of applications and maximum time between	Comments
Current surge	Low impedance paths exposed to surges	500A or lesser current (see fig. 4)	10×1000 µs	5 each polarity at 1 minute intervals	None.
60 Hz current carrying	High or low impedance paths exposed to surges	10A rms or lesser current (see fig. 6)	11 Cycles of 60 Hz (0.183 Sec.)	3 each at 1 minute intervals	None.
AC Power service surge voltage	AC power service connection	2500V or 3 σ clamping V of arrester employed at 10kV/µs	1.2×50 µs	5 each polarity at 1 minute intervals	AC arrester, if used, must be removed. Communications line arresters, if used, remain in place.
Voltage surge	High impedance paths exposed to surges	1000V or 3 σ dc breakdown of arrester employed	10×1000 µs	5 each polarity at 1 minute intervals	All primary arresters, if used, must be removed.
Arrester response delay	Paths protected by arresters, such as gas tubes, with breakdown dependent on V. rate of rise	3 σ breakdown of arrester employed at 100V/µs of rise	100V/µs rise decay to 1/2 V. in tube's delay time	5 each polarity at 1 minute intervals	All primary arrestors, if used, must be removed.

(iii) Electrical protection requirements for line concentrator equipment can be summarized briefly as follows:

(A) Current surge tests simulate the stress to which a relatively low impedance path may be subjected before main frame protectors break down. Paths with a 100 Hz impedance of 50 ohms or less shall be subjected to current surges, employing a 10×1000 microsecond waveshape as defined in Figure 3 of this section, Surge Waveshape. For the purpose of determining this impedance, arresters which are mounted within the equipment are to be considered zero impedance. The crest current shall not exceed 500A; however, depending on the impedance of the test specimen this value of current may be lower. The crest current through the sample, multiplied by the sample's 100 Hz impedance, shall not exceed 1000 V. Where sample impedance is less than 2 ohms, peak current shall be limited to 500A as shown in Figure 4 of this section, Current Surge Tests. Figures 3 and 4 follow:

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Code of Federal Regulations

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(B) Sixty Hertz (60 Hz) current carrying tests shall be applied to simulate an ac power fault which is conducted to the unit over the cable pairs. The test shall be limited to 10 amperes Root Mean Square (rms) of 60 Hz ac for a period of 11 cycles (0.1835 seconds) and shall be applied longitudinally from line to ground.

(C) AC power service surge voltage tests shall be applied to the power input terminals of ac powered devices to simulate switching surges or lightning-induced transients on the ac power system. The test shall employ a 1.2×50 microsecond waveshape with a crest voltage of 2500 V. Communications line protectors may be left in place for these tests.

(D) Voltage surge tests which simulate the voltage stress to which a relatively high impedance path may be subjected before primary protectors break down and protect the circuit. To ensure coordination with the primary protection while reducing testing to the minimum, voltage surge tests shall be conducted at a 1000 volts with primary arresters removed for devices protected by carbon blocks, or the 3 sigma dc breakdown voltage of other primary arresters. Surge waveshape should be 10×1000 microseconds.

(E) Arrester response delay tests are designed to stress the equipment in a manner similar to that caused by the delayed breakdown of gap type arresters when subjected to rapidly rising voltages. Arresters shall be removed for these tests, the peak surge voltage shall be the 3 sigma breakdown voltage of the arrester in question on a voltage rising at 100 V per microsecond, and the time for the surge to decay to half voltage shall equal at least the delay time of the tube as explained in Figure 5 of this section, Arrester Response Delay Time as follows:

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(iv) Tests shall be conducted in the following sequence. As not all tests are required in every application, non-applicable tests should be omitted:

(A) Current Impulse Test;

(B) Sixty Hertz (60 Hz) Current Carrying Tests;

(D) Voltage Impulse Test; and

(E) Arrester Response Delay Time Test.

(v) A minimum of five applications of each polarity for the surge tests and three for the 60 Hz Current Carrying Tests are the minimum required. All tests shall be conducted with not more than 1 minute between consecutive applications in each series of three or five applications to a specific configuration so that heating effects will be cumulative. See Figure 6 of this section, 60 Hz Current Surge Tests as follows:

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[Please see PDF for image: ER29AU95.006 ]

(vi) Tests shall be applied between each of the following terminal combinations for all line operating conditions:

(A) Line tip to ring;

(B) Line ring to ground;

(D) Line tip and ring tied together to ground.

(2) Dielectric strength. (i) Arresters shall be removed for all dielectric strength tests.

(ii) Direct current potentials shall be applied between all line terminals and the equipment chassis and between these terminals and grounded equipment housings in all instances where the circuitry is dc open circuit from the chassis, or connected to the chassis through a capacitor. The duration of all dielectric strength tests shall be at least 1 second. The applied potential shall be at a minimum equal to the plus 3 sigma dc breakdown voltage of the arrester, provided by the line concentrator manufacturer.

(3) Insulation resistance. Following the dielectric tests, the insulation resistance of the installed electrical circuits between wires and ground, with the normal equipment grounds removed, shall not be less than 10 megohms at 500 volts dc at a temperature of 68 °F (20 °C) and at a relative humidity of approximately 50 percent. The measurement shall be made after the meter stabilizes, unless the requirement is met sooner. Arresters shall be removed for these tests.

(4) Self-protection. (i) All components shall be capable of being continuously energized at rated voltage without injury. Design precautions must be taken to prevent damage to other equipment components when a particular component fails.

(ii) Printed circuit boards or similar equipment employing electronic components should be self-protecting against external grounds applied to the connector terminals. Board components and coatings applied to finished products shall be of such material or so treated that they will not support combustion.

(iii) Every precaution shall be taken to protect electrostatically sensitive components from damage during handling. This shall include written instructions and recommendations.

(k) Miscellaneous— (1) Interconnect wire. All interconnect wire shall be of soft annealed tinned copper wire meeting the requirements of ASTM Specification B33-91 and of suitable cross-section to provide safe current carrying capacity and mechanical strength. The insulation of installed wire, connected to its equipment and frames, shall be capable of withstanding the same insulation resistance and dielectric strength requirements as given in paragraphs (j)(2) and (j)(3) of this section at a temperature of 120 °F (49 °C), and a relative humidity of 90 percent.

(2) Wire wrapped terminals. These terminals are preferred and where used shall be of a material suitable for wire wrapping. The connections to them shall be made with a wire wrapping tool with the following minimum number of successive non-overlapping turns of bare tinned copper wire in contact with each terminal:

(i) 6 turns of 30 gauge;

(ii) 6 turns of 26 gauge;

(iii) 6 turns of 24 gauge; or

(iv) 5 turns of 22 gauge.

(3) Protection against corrosion. All metal parts of equipment frames, distributing frames, cable supporting framework and other exposed metal parts shall be constructed of corrosion resistant materials or materials plated or painted to render them adequately corrosion resistant.

(4) Screws and bolts. Screw threads for all threaded securing devices shall be of American National Standard form in accordance with Federal Standard H28, unless exceptions are granted to the manufacturer of the switching equipment. All bolts, nuts, screws, and washers shall be of nickel-copper alloy, steel, brass or bronze.

(5) Environmental requirements. (i) The bidder shall specify the environmental conditions necessary for safe storage and satisfactory operation of the equipment being bid. If requested, the bidder shall assist the owner in planning how to provide the necessary environment for the equipment.

(ii) To the extent practicable, the following temperature range objectives shall be met:

(A) For equipment mounted in central office and subscriber buildings, the carrier equipment shall operate satisfactory within an ambient temperature range of 32 °F to 120 °F (0 °C to 49 °C) and at 80 percent relative humidity between 50 °F and 100 °F (10 °C and 38 °C); and

(B) Equipment mounted outdoors in normal operation (with cabinet doors closed) shall operate satisfactorily within an ambient temperature range (external to cabinet) of −40 °F to 140 °F (−40 °C to 60 °C) and at 95 percent relative humidity between 50 °F to 100 °F (10 °C to 38 °C). As an alternative to the (60 °C) requirement, a maximum ambient temperature of 120 °F (49 °C) with equipment (cabinet) exposed to direct sunlight may be substituted.

(6) Stenciling. Equipment units and terminal jacks shall be adequately designated and numbered. They shall be stenciled so that identification of equipment units and leads for testing or traffic analysis can be made without unnecessary reference to prints or descriptive literature.

(7) Quantity of equipment bays. Consistent with system arrangements and ease of maintenance, space shall be provided on the floor plan for an orderly layout of future equipment bays. Readily accessible terminals will be provided for connection to interbay and frame cables to future bays. All cables, interbay and intrabay (excluding power), if technically feasible, shall be terminated at both ends by connectors.

(8) Radio and television interference. Measures shall be employed by the bidders to limit the radiation of radio frequencies generated by the equipment so as not to interfere with radio, television receivers, or other sensitive equipment.

(9) Housing. (i) When housed in a building supplied by the owner, a complete floor plan including ceiling height, floor loading, power outlets, cable entrances, equipment entry and travel, type of construction, and other pertinent information shall be supplied.

(ii) In order to limit corrosion, all metal parts of the housing and mounting frames shall be constructed of suitable corrosion resistant materials or materials protectively coated to render them adequately resistant to corrosion under the climatic and atmospheric conditions existing in the area in which the housing is to be installed.

(10) Distributing frame. (i) The line concentrator terminal equipment located at the central office shall be protected by the central office main distribution frame. The bidder may supply additional protection capability as appropriate. All protection devices (new or existing) shall be arranged to operate in a coordinated manner to protect equipment, limit surge currents, and protect personnel.

(ii) The distributing frame shall provide terminals for terminating all incoming cable pairs. Arresters shall be provided for all incoming cable pairs, or for a smaller number of pairs if specified.

(iii) The current carrying capacity of each arrester and its associated mounting shall coordinate with a #22 gauge copper conductor without causing a self-sustaining fire or permanently damaging other arrester positions. Where all cable pairs entering the housing are #24 gauge or finer, the arresters and mountings need only coordinate with #24 gauge cable conductors.

(iv) Remote terminal protectors may be mounted and arranged so that outside cable pairs may be terminated on the left or bottom side of protectors (when facing the vertical side of the MDF) or on the back surface of the protectors. Means for easy identification of pairs shall be provided.

(v) Protectors shall have a “dead front” (either insulated or grounded) where live metal parts are not readily accessible.

(vi) Protectors shall be provided with an accessible terminal of each incoming conductor which is suitable for the attachment of a temporary test lead. They shall also be constructed so that auxiliary test fixtures may be applied to open and test the subscriber's circuit in either direction. Terminals shall be suitable for wire wrapped connections or connectorized.

(vii) If specified, each protector group shall be furnished with a factory assembled tip cable for splicing to the outside cable; the tip cable shall be 20 feet (6.1 m) in length, unless otherwise specified. Tip cable used shall be RUS accepted.

(viii) Protector makes and types used shall be RUS accepted.

(l) Power equipment— (1) General. When specified, batteries and charging equipment shall be supplied for the remote terminal of the line concentrator.

(2) Operating voltage. (i) The nominal operating voltage of the central office and remote terminal shall be 48 volts dc, provided by a battery with the positive side tied to system ground.

(ii) Where equipment is dc powered, it must operate satisfactorily over a range of 50 volts ±6 volts dc.

(iii) Where equipment is ac powered, it must operate satisfactorily over a range of 120±10 volts or 220±10 volts ac.

(3) Batteries. (i) Unless otherwise specified by the owner, sealed batteries shall be supplied for the remote line concentrator terminal.

(ii) The batteries shall have an ampere hour load capacity of no less than 8 busy hours. When an emergency ac supply source is available, the battery reserve may be reduced to 3 busy hours.

(iii) The batteries shall be sealed when they are

Tips