Objective of the Lesson : The tough inspection will bring out the lacuna in the procedures adopted in various activities of the planning, construction, installation and other maintenance works which has a being on the efficiency of the system and ultimately the customer satisfaction is the barometer for the efficiency. So the importance of inspection in various are discussed here in this chapter.
* * * INTRODUCTION
When there was only electromechanical SXS Auto Exchanges the Acceptance Testing of External Plant was carried out only for the conversion of manual C.B. Exchanges to S&S Auto Exchange. No A/T was done subsequently on expansion of the system unless there was cutover at the same of the system.
With the introduction of Electronic Exchanges fault liabilities in the Switching Equipment have reduced considerably. It is well known that a well maintained External Plants provide an improve service to subscribers. therefore it has been decided to conduct 100%
Acceptance Testing for the external plants before they are put into service. Equipment’s provided in subs premises and its wiring are subjected to Acceptance Testing by choosing 20% of the equipment at random selection ( In MTNL 100% check is conducted. No telephone connection can be opened without Acceptance Testing of the subs equipment &
wiring.
2. Preparation before offering External Plant for A/T Some of the important points which requires attention of all concerned before external Plant is offered for A/T
2.1 CABLESCHEMES SHOULDBEGIVENTOPPRIORITYIFTHEAREAWILLBEEXPANDEDBYELECTRONIC EXCHANGES .
a. Fault Prone cables with low insulation should be replaced.
b. All heavy over head alignment should be replaced by new DPs.
c. Cabinets and pillars should be installed for more than 500 line exchanges.
d. Old DPs should be rehabilitated.
2.2 Subscribers loops of less than 4 spans should be replaced by drop wire. Drop wire should be provided from DP to rosette.
2.3 Pressurization of junction primary and secondary cable may be done and if possible cable should be laid in ducts.
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2.6 All the testing parameter for each subscriber’s line should be measured and recorded in subscriber’s fault cards before commissioning the exchange.
2.7 Electronic dial/loop resistance testers should be procured for a quick testing.
3. Definitions
3.1 Service line:- Service line is the portion of the subscriber line from pole mount DP to the terminal points.
3.2 Subscriber’s Installations:- Subscriber’s installation is the portion of subscriber’s line starting from the distribution points and ending at rosette.
3.3 Subscriber Line:- Subscriber line is the portion of the line starting from the line side of the MDF and ending at rosette
3.4 Subscriber Local System:- Subscriber local system includes telephone set subscriber’s line and exchange feeding bridge.
3.5 Resistance of Subscriber Loop :- Resistance of subscribers line loop is equal to the sum of resistance’s of each limb of subscriber’s line and telephone set.
Internal DP when underground cable is laid directly to the subscriber’s premises the distribution point is know as internal DP
P
ROCEDUREOFA/T
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Details of O/D plant of cabinet, pillar, DP lines, to be connected are to be procured and first of all physical inspections of External Plant is carried out by checking Dps/cabinet Pillars and subscriber lines. After rectification of faults detected in physical inspection, electrical parameters of the lines and dials are tested.
For Acceptance Testing of External plant the following should be physically inspected and tested.
a. Cabinets and pillars.
b. Pole- Mounted DP c. Internal DP
d. Service line.
e. Indoor House Wiring g. Electric Parameters of Line h. Dial of subscriber’s instrument I. Junction cable
4.1 Points should be carried out at cabinets and pillars for the
following:-a) The Cabinets /pillars should be located at obstruction free place on concrete base and height should be above flood level.
b) The cabinet / pillars should be numbered properly
c) General condition of the plant outside and in side should be without any rust.
d) The doors should open and close freely.
e) The cabinet/pillar should be neat & clean from inside.
f) The cabinet/pillar shell should be firmly fixed and bolts should be tight.
g) CT Box should be fixed firmly to the frame and all fixing screws should be tight.
h) The jumper field should be tidy there should not be unnecessary long.
i) The position of spare pairs should be according to the records.
j) all the records should be available in the cabinet /pillar.
k) There should be no dust. cobwebs inside the cabinet/ pillar.
l) Check the locks.
4.2 Points to be checked of pole mounted DP 100% check of DP is necessary.
a) DP should be located at obstruction free place and no way in the vicinity of electric poles etc.
b) The DP should be painted and numbered.
c) Minimum height of DP should be 9’feet (2.75M) from the ground.
d) The DP should be properly fitted to the post by means of standard U back and saddles. The back of the U backs should be flattered for giving good grip on the tubular posts.
e) The cable should be taken to DP base through GI pipe of 50 mm internal diameter.
The GI pipe should be securely fixed to the posts with the usual galvanized iron fixing clamps . The lowest clamp should be 50 to 60 cm from the ground level and the upper most clamp should be 50 to 60 cm below the top end of the pipe. The third clamp should be fixed in midway. Distance between two clamps should not be more than 200 cm.
f) The DP should be properly fitted using washer O/H connections of GI Wires and drop wires ( if provided) should be soldered.
g) Earthing arrangement should be provided.
h) Updated DP cards should be available.
i) The drop wire lead should be properly secured on the wooden batton / board.
j) The DP should have locking facility.
k) A bracket should be provided below the DP to facilitate maintenance.
l) The lowest bracket on DP pole should be fitted at the minimum height 2.75m from the ground.
m) All the brackets should be fitted with ties and struts.
n) DP Post should be fitted with proper stays.
4.3 Points to be checked of internal DP a) 100 % Dps should be checked.
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c) The same should be on the inside wall building and easily accessible for inspection.
d) Location for telephones termination box should be different from that of the power meter. Where it is unavoidable, a minimum distance of 1M between the two should be insured.
4.4(A) Check of service
line:-a) Selected at random minimum 20% service line should be checked.
b) In city/town areas open wire should not be used only drop wire or overhead cable should be used in such areas
c) Drop wire should be erected on standard fittings d) Drop wire should not be loose
e) Jungle should not touch the drop wire/open wire.
f) All the bare wire at the power crossing should be properly guarded.
g) The open/open wire should be properly secured at the two ends.
h) Parallelism for a long distance with power line should be avoided ( In case of long distance telephone connection).
i) If the length of open wire lines exceeds 400 m. protection in the form of GD tubes should be provided at subs premises . The value of earth resistance should be less than 5 ohms.