Design Requirements for Protective Devices

Protective Devices

• A protective device should not decrease the efficiency of speech or signaling circuits.
• The device should promptly operate in cases of specified voltages or currents being reached.
• The voltage rating of the protective device should be only slightly above the exchange fed voltage levels in the subscriber circuits.
• The device should promptly isolate the equipment and prevent further damage in cases of overload due to artificial or natural causes.
• The current/voltage rating of the device should not produce noticeable heat in the components of the main equipment.
• The device should be self-restoring type.
• The prospective devices should consist of a normal fuse or self-restoring type fuse and lightning discharger.
• The fuse should be connected in series with each external line.
• The Integrated Protection Modules should be provided in case of Krone type connectors.
• The rating of the fuse should be as per the requirement of exchange equipment.
• The Protection arrangement should be installed on IDF or MDF if there is no IDF.
• The subscriber's protective device assembly should consist of a single compact dust-proof unit containing a fuse and lightning arrester.

Maintenance

• Preventive maintenance is required to ensure the system's reliability.
• Measurements are to be taken manually in case of non-availability of continuous automatic logging features.
• Daily measurements include:
  • Battery set voltage and UPS/charger output/input voltage.
  • Failure list of the subscribers.
• Fortnightly measurements include:
  • Individual cell voltage and load test of the batteries.
  • Testing of all the trunk circuits.
• Monthly measurements include:
  • Specific gravity in case of non-VRLA batteries.
  • The different modes of operation of FCBC.
  • Earthing connections of all equipment with earth electrodes.
  • All cabinets of equipment, man-machine interaction, terminal printer, and attendant consoles to be cleaned.
  • Cable termination MDF and IDF to be cleaned and checked.
  • Cable runs-inter rack, rack to IDF, MDF, and attendant consoles to be checked.
  • BER test of all trunk circuits.
  • Checking of lightning and surge protection devices.
  • Functional testing of attendant console if available.
  • Wiring and connecting terminals of power supply arrangement to be checked.
  • Data backup to be updated.
• Quarterly measurements include:
  • Testing of all service features from the test telephones.
  • Cleaning of terminations in CT boxes, location boxes.
  • Complete testing of power supply system.
• Six monthly measurements include:
  • Earth resistance value measurement.
  • Line loop resistance and insulation testing.
• Yearly measurements include:
  • Checking of wiring of subscribers' premises, CT boxes, and location boxes.
  • Testing of spare cards.

Inspection

• Subscriber's office:
  • CT boxes to be checked.
  • Wiring to be checked.
  • Lightning/surge arrester to be checked.
  • Batteries/power supply arrangement to be checked.
• Cables:
  • Type of cable and length to be checked.
  • Cable route conditions to be checked.
  • All registers pertaining to cable laying and testing to be checked.
• Exchange:
  • MDF/IDF wiring, connectors, terminals, fuses, and protection devices to be checked.
  • Earth connections and earth readings to be checked.
  • Power supply arrangement, battery registers, battery terminals, wiring, charger, and power panel to be checked.
  • Internal cabling, cabinets, and visual inspection of wiring to be checked.
  • Fault register (Electronic/Paper) to be checked.
• Periodical inspection:
  • All exchanges and related installations should be inspected by ADSTE/DSTE/Sr.DSTE at least once in a year.
  • Maintenance records and fault registers should be checked for their proper upkeep.

Testing and Commissioning

• Cable testing shall be conducted for each subscriber.
• Insulation, loop resistance for cable is to be tested and recorded.
• Provision of fuses, IPMs are to be checked for all lines.
• The earth resistance for each earth electrode is to be measured.
• The connectivity of earth wires to each equipment is to be checked.
• Hardware testing shall be conducted as per the manufacturer's instructions.

Civil Infrastructure

• The exchange room should be dustproof, with a false ceiling, mosaic/tile flooring, and windows with double doors.
• Underground duct or overhead trough for running of indoor cables should be provided.
• Separate Operator Console room, Power supply room, Battery room, DG set room, and MDF room should be provided.
• Floor should be strictly level and high enough to avoid flooding.

Electrical Supply

• Standard 230V AC single phase supply with voltage level display continuously should be available.
• Alternate supply should be provided - either traction supply or DG supply.
• The power supply should enter the room through MCB and changeover switch (preferably auto change-over) with proper earthing arrangement.

Environmental Conditions

• The exchange equipment room should be air-conditioned.
• 22-25 degree C should be maintained inside the room.
• 50% standby air conditioners should be provided.
• Lighting should be adequate for maintenance.

Equipment Installation

• All equipment should be provided on racks.
• Mounting on the walls should be avoided.
• The equipment rack should be minimum 1 meter away from the wall.
• The racks should be fixed on the floor with proper arrangement.
• Underground ducts should be provided for entry of UG cables.
• Duct/overhead troughs should be provided to run the indoor cables.
• In case of UG cable entry, the duct should be filled with sand and plastered on the top.

IP Phone Requirements

• IP phones in the network must be PoE enabled and draw power from PoE switches with UPS backup.
• IP phones should have two Gigabit Ethernet ports: one for connecting to LAN on PoE and another for connecting PC through IP phone.
• Local adaptors for phones may be avoided.

SIP Trunk/PRI Gateway Requirements

• SIP Trunk/PRI gateway shall be used to connect to NGN or PSTN.
• In cases where PRI from PSTN is a challenge, FXO can be used.

Telephone Requirements

• Telephones used in VoIP exchanges shall be open standard, working with third-party exchanges/SIP servers.
• Third-party SIP clients loaded on mobile phones using Wi-Fi shall also be possible.

Trunk Exchanges

• Separate trunk exchanges are not required as trunk exchange function is handled by NGN network.
• NGN uses MPLS network of RCIL to provide a distributed trunk exchange with which all zonal and divisional exchanges are connected using E1 links.
• A backup for trunk connectivity at Zonal and divisional level may be done using direct E1/SIP/PRI connectivity.

Remote Maintenance

• Provision for remote maintenance of the exchange from a remotely located operation & maintenance center shall be available.
• Remote maintenance devices/interface should be built within the system.
• All access should be through a secure method like SSH, HTTPS, etc.

System Capability

• The system shall be capable of use as a local, tandem, transit exchange or combination of these.
• The system shall also support Video telephony, allowing IP video phones to be used for telephony.

Subscriber Telephone Set

• IDF shall have disconnecting type connectors with facility for isolating exchange indoor and outdoor side.
• Cable terminals shall be installed on a rack, with protection arrangement available on the IDF.

Main Distribution Frame (MDF)

• All outdoor cables shall be terminated on a rack forming the MDF, providing connectivity between outdoor cable and indoor switchboard cable.
• The MDF shall be installed in a separate room, not in the exchange room, with an earth connected across the frame for its entire length.

Cables

• Outdoor cables shall be jelly-filled underground type.
• Indoor cables shall be twisted pair switchboard cables.
• Outdoor cable shall have outdoor termination box/location box with terminals for proper termination of the cable.

Lightning and Surge Protection

• It shall be provided as per chapter on "Protection of Telecom Equipments against Lightning".
• The device shall promptly operate in cases of specified voltages or currents being reached.
• The device shall promptly isolate the equipment and prevent further damage in cases of overload due to artificial or natural causes.

Maintenance Schedules

• Daily: battery set voltage and UPS/charger output/input voltage, failure list of subscribers, working of lights, air conditioners, system status listing, failure history list, alarm checking, room temperature recording.
• Fortnightly: individual cell voltage and load test of batteries, sulphation of terminals, testing of all trunk circuits.
• Monthly: specific gravity in case of non-VRLA batteries, earthing connections of all equipment with earth electrodes, all cabinets of equipment to be cleaned, cable termination MDF and IDF to be cleaned and checked, BER test of all trunk circuits, checking of lightning and surge protection devices, functional testing of attendant console if available, wiring and connecting terminals of power supply arrangement, data backup to be updated.
• Quarterly: testing of all service features from the test telephones, cleaning of terminations in CT boxes, location boxes, complete testing of power supply system.
• Six-monthly: earth resistance value measurement, line loop resistance and insulation testing.
• Yearly: checking of wiring of subscribers' premises, CT boxes and location boxes, testing of spare cards.

Inspection

• Subscriber's office: CT boxes, wiring, lightning/surge arrester, batteries/power supply arrangement.
• Cables: type of cable and length, cable route conditions, all registers pertaining to cable laying and testing.
• Exchange: MDF/IDF wiring, connectors, terminals, fuses, protection devices, earth connections, earth readings, power supply arrangement, battery registers, battery terminals, wiring, charger and power panel.
• Periodical inspection: all exchanges and related installations shall be inspected by ADSTE/DSTE/Sr.DSTE at least once a year, maintenance records and fault registers shall be checked for their proper upkeep.