1. Service Connections: in Case of Overhead Line, Check and Ensure That

Unit – 4

List out the points to be checked while carrying out inspection of wiring install(Jan-2016)

Solution: -Internal wiring should be inspected once a year and the following points should be checkedwhile carrying out inspection of the wiring installation.

1. Service Connections: In case of overhead line, check and ensure that:

(i) The lines are terminated at a sufficient distance from the building.

(ii) The danger notice exists to warn the staff.

(iii) The fuse wire of correct rating is provided on the phase line.

(iv) The lead-in wires are of size sufficient to carry the full- load current.

(v) The lead-in pipe is properly earthed and bonded and pipe ends are provided with insulatingbushes to protect the wires from mechanical damage. In case of underground cable check up and ensure that (i) the cables are properly sealed andthere is no leakage of cable oil (ii) there are earth connections to the cable armouring.

2. Main Switchboard: In case of main switchboard check and ensure that

(i) The voltage available is correct. (i.e. within permissible limits of declared voltage.)

(ii) The main switch is provided close to the point of commencement of supply.

(iii) The fuse of correct size is provided on the live pole.

(iv) The main switch is easily identified and is easily accessible so that in case of emergency theentire supply to the building can be switched off at once.

(v) There is a clear working space all round the board (as mentioned in IE rule 51 i.e. 0.914 m).

(vi) The phase and neutral wires are clearly marked for identification.

(vii) Caution notice in Hindi or other local language is placed.

3. Miscellaneous: The points to be checked are :

(i) No branch circuit feeds more than 10 points or 800 watt load.

(ix) The leakage current is not more than 1/5,000 of maximum supply current.

(iii) The insulation resistance between conductor and earth and between conductors is more thanpermissible value as per IE rule.

(iv) The single pole switches are provided on the live conductor.

(v) The electrical resistance from the point of connection with the earth electrode to any point onECC in the complete installation is not more than one ohm.

(vi) The metallic frames of all power equipment are earthed by two independent earthconductors.

(vii) The metallic covering of iron clad switch, distribution board. Sub main distribution boards.GI pipe, conduit pipes enclosing VIR or PVC cables are properly earthed.

2. Mention the different types of tests conducted on wiring installations. Explain in detailtesting of polarity. (Jan-2016)

Solution: -Testing of Polarity of Single Pole Switches. It is necessary that single pole switches are placedin + ve side or live side so that by making switch off the lamp can be made quite dead. Thereason of it is that if the switch in provided on neutral wire, then lamp holder or the fan as well aspart of wiring will remain alive, even when the single pole switch is in open position which mayeasily lead to accidents.

For example, a person who is replacing lamp even after opening thesingle pole switch is liable to get shock if he comes in contact with the line terminal of the lampholder. As regard the function of a single pole switch, it is equally effective whether it isconnected in live or neutral wire but from the safety point of view it is necessary that all singlepole switches are provided on phase or outer wire, never on neutral wire.To ensure that all the switches are placed in phase or live conductors and not in neutralconductor, this test is performed.A convenient and quicker method of performing this test is by means of a small neon tube tester.

While performing polarity test by means of a small neon tube tester, its one terminal is held inthe hand and the other against the feed terminal of the switch; if the switch is correctlyconnected the neon lamp will glow. Pocket neon testing tubes for the purpose are available. An alternative method is by means of a test lamp. In this method all the lamps are removed, mainswitch is put in ‘on’ position, main fuse is inserted, one end of test lamp is connected to earthand the other end is tapped by lead to each contact of each switch in turn. If the test lamp lightson one of the two contacts, it indicates that switch is on the live wire as shown in Fig. 5.2 (a) andIf test lamp, does not give light on either contact of the switch, it indicates that the switch is onneutral wire, so must be connected correctly.

Testing of Earth Continuity Path.For safety all the metal pieces or coverings such as conduits,metal covers of switches etc. must be solidly connected to earth otherwise on the damage ofinsulation, the leakage current will start giving severe shock to the person touching it.In case of conduit wiring there is a possibility of the conduit joints to become loose or to beseparated resulting in high resistance in the earth path.

For earth continuity test, main switchshould be opened, main fuse withdrawn, all other switches in on position and lamps in theirrespective holders. One end of the earth continuity tester is connected to an independent earthand the other end is connected to the wiring say to a switch or conduit. The pointer will indicatethe earth resistance, which should not exceed the value of one ohm. Higher than this value showsthat conduit or switch has not been properly earthed.

3. Write short note on service lines. (Jun -2015)

Solution: -This describes various types of utility electrical services and supply voltages. The nominalsystem supply voltages listed below can vary by ±10% or more. Watt Node meter models areavailable in seven different versions that cover the full range of electrical services types andvoltages. Meters and current transformers are designed for use on either 50 or 60 Hz systems.

Classification of Different Services:

Alternating current electric power distribution systems can be classified by the followingproperties:

 Frequency: 50 Hz or 60 Hz

 Number of phases: single or three phase

 Number of wires: 2, 3, or 4 (not counting the safety ground)

 Neutral present:

 Wye connected systems have a neutral

 Delta connected systems typically do not have a neutral

 Voltage levels:

 Low Voltage: 600 volts or less

 Medium Voltage: 601 volts to about 34,500 volts

 High Voltage: 46,000 volts and up

 Line-to-line voltages are typically 1.732 times the phase-to-neutral voltages

 In symmetrical three-phase electrical system, the phase-to-neutral voltages should be equal if the load is balanced.

4. Write the reason for excess recording of energy consumption by energy meter (Jan -2015)

When tampering is detected, the normal tactic, legal in most areas of the USA, is to switch thesubscriber to a "tampering" tariff charged at the meter's maximum designed current. AtUS$0.095/kWh, a standard residential 50 A meter causes a legally collectible charge of aboutUS$5,000.00 per month. Meter readers are trained to spot signs of tampering, and with crudemechanical meters, the maximum rate may be charged each billing period until the tamper isremoved, or the service is disconnected.

A common method of tampering on mechanical disk meters is to attach magnets to the outside ofthe meter. Strong magnets saturate the magnetic fields in the meter so that the motor portion of amechanical meter does not operate. Lower power magnets can add to the drag resistance of theinternal disk resistance magnets. Magnets can also saturate current transformers or power-supplytransformers in electronic meters, though countermeasures are common.Rectified DC loads cause mechanical (but not electronic) meters to under-register. DC currentdoes not cause the coils to make eddy currents in the disk, so this causes reduced rotation and alower bill.

Some combinations of capacitive and inductive load can interact with the coils and mass of arotor and cause reduced or reverse motion.All of these effects can be detected by the electric company, and many modern meters can detector compensate for them.The owner of the meter normally secures the meter against tampering. Revenue meters'mechanisms and connections are sealed. Meters may also measure VAR-hours (the reflected load), neutral and DC currents (elevated by most electrical tampering), ambient magnetic fields,etc.

Even simple mechanical meters can have mechanical flags that are dropped by magnetictampering or large DC currents.Newer computerised meters usually have counter-measures against tampering. AMR (AutomatedMeter Reading) meters often have sensors that can report opening of the meter cover, magneticanomalies, extra clock setting, glued buttons, inverted installation, reversed or switched phasesetc.

Some tampers bypass the meter, wholly or in part. Safe tampers of this type normally increasethe neutral current at the meter. Most split-phase residential meters in the United States areunable to detect neutral currents. However, modern tamper-resistant meters can detect and bill it at standard rates.

Disconnecting a meter's neutral connector is unsafe because shorts can then pass through peopleor equipment rather than a metallic ground to the generator or earth.A phantom loop connection via an earth ground is often much higher resistance than the metallicneutral connector. Even if an earth ground is safe, metering at the substation can alert theoperator to tampering. Substations, inter-ties, and transformers normally have a high-accuracymeter for the area served.

Power companies normally investigate discrepancies between the totalbilled and the total generated, in order to find and fix power distribution problems. Theseinvestigations are an effective method to discover tampering.Power thefts in the U.S. are often connected with indoor marijuana grow operations. Narcoticsdetectives’ associate abnormally high power usage with the lighting such operationsrequire. Indoor marijuana growers aware of this are particularly motivated to steal electricitysimply to conceal their usage of it.

5. Find the materials required for 1- overhead service lines of a house located 10 metersaway from pole, with following loads :Lightning =300 watts, Heating= 2500 watts.Assumesafety factor=2 (Jan -2015)

Solution: -power supply and another for domestic supply.Assuming efficiency of motor 85% and power factor 0.8, we have full- load currents of motors as

1 2 34 0.75 1, 000 0.75 , 415 , 3 1.54 3 415 0.85 0.8 3.7 1, 000 3.7 , 415 , 3 7.57 3 415

0.85 0.8 5.5 1, 000 5.5 , 415 , 3 11.25 3 415 0.85 0.8 I I For kW V phase motor A I For kW

V phase motor A I For kW V phase motor A× =

Total full- load current for these motors = 1.54 + 1.54 + 7.57 + 11.25 = 21.9 A

Hence cable from meter board to main board shall have a current carrying capacity 1.6 times offull- load current of the motHence 3-core, 1100 V grade PVC insulated, 16 mm2 aluminium conductor having currentcarrying capacity of 38 A shall be used from meter board to main board.The current rating of main switch in the starting current of one motor of highest rating plus full

1. Length of 31 mm exible conduit from meter board to main switch board and from main switchboard to distribution board, including wastage = 1.0 m

2. Length of 25 mm exible conduit from HG conduit to motor terminals fan machine no. 4,including wastage = 1.0 m

3. Length of 19 mm exible conduit required for connecting motor switches to motor starters forall the four machines and HG conduit to motor terminals for machines no. 1,

7. Explain points to be checked while carrying out inspection of wiring installed(Jan-2015)

Solution: -Conductors configuration spacing and clearances, Span lengths

1) No conductor of an overhead line, including service lines, erected across a street shall at anypart thereof be at a height less than-

(a) For low and medium voltage lines 5.8 metres

(b) For high voltage lines 6.1 metres

(2) No conductor of an overhead line, including service, lines, erected along any street shall atany part thereof be at a height less than-

(a) For low and medium voltage lines 5.5 metres

(b) For high voltage lines 5.8 metres

(3) No conductor of an overhead line including service lines, erected else- where than along oracross any street shall be at a height less than-

(a) for low, medium and high voltage lines up to and including 11,000 volts, if bare ;4.6 metres

(b) for low, medium and high voltage lines up to and including 11,000 volts, if insulated 4.0

(4) For extra-high voltage lines the clearance above ground shall not be less than 5.2 metresplus 0.3 metre for every 33,000 volts or part thereof by which the voltage of the line exceeds33,000 volts: PROVIDED that the minimum clearance along or across any street shall not beless than 6.1 metres.

8. Write the reason for excess recording of energy consumption by energy metre (June-2014)

Solution: -Meters can be manipulated to make them under-register, effectively allowing power use withoutpaying for it. This theft or fraud can be dangerous as well as dishonest.Power companies often install remote-reporting meters specifically to enable remote detection oftampering, and specifically to discover energy theft. The change to smart power meters is usefulto stop energy theft.When tampering is detected, the normal tactic, legal in most areas of the USA, is to switch thesubscriber to a "tampering" tariff charged at the meter's maximum designed current.

AtUS$0.095/kWh, a standard residential 50 A meter causes a legally collectible charge of aboutUS$5,000.00 per month. Meter readers are trained to spot signs of tampering, and with crudemechanical meters, the maximum rate may be charged each billing period until the tamper isremoved, or the service is disconnected.

Rectified DC loads cause mechanical (but not electronic) meters to under-register. DC currentdoes not cause the coils to make eddy currents in the disk, so this causes reduced rotation and alower bill.Some combinations of capacitive and inductive load can interact with the coils and mass of arotor and cause reduced or reverse motion.

All of these effects can be detected by the electric company, and many modern meters can detector compensate for them.The owner of the meter normally secures the meter against tampering. Revenue meters'mechanisms and connections are sealed. Meters may also measure VAR-hours (the reflectedload), neutral and DC currents (elevated by most electrical tampering), ambient magnetic fields,etc.

Substations, inter-ties, and transformers normally have a high-accuracymeter for the area served. Power companies normally investigate discrepancies between the totalbilled and the total generated, in order to find and fix power distribution problems. Theseinvestigations are an effective method to discover tampering.Power thefts in the U.S. are often connected with indoor marijuana grow operations. Narcoticsdetectives’ associate abnormally high power usage with the lighting such operationsrequire. Indoor marijuana growers aware of this are particularly motivated to steal electricitysimply to conceal their usage of it.

9. Find the material required for 1pase overhead service line of a house located 10 meters away from pole, with full loads : Lighting = 300 Watts; Heating= 2500 Watts Assume safetyfactor=2. (June-2014)

Solution: -power supply and another for domestic supply.Assuming efficiency of motor 85% and power factor 0.8, we have full- load currents of motors as

1, 000 0.75, 415, 3 1.54 3 415 0.85 0.8 3.7 1, 000 3.7, 415, 3 7.57 3 415 0.85 0.8 5.5 1, 000 5.5, 415 , 3 11.25 3 415 0.85 0.8 I I For kW V phase motor A I For kW V phase motor A I For

kW V phase motor A=Total full-load current for these motors = 1.54 + 1.54 +7.57 + 11.25 = 21.9 A

Hence cable from meter board to main board shall have a current carrying capacity 1.6 times offull- load current Hence 3-core, 1100 V grade PVC insulated, 16 mm2 aluminium conductor having currentcarrying capacity of 38 A shall be used from meter board to main board.The current rating of main switch in the starting current of one motor of highest rating plus fullload current

1. Length of 31 mm exible conduit from meter board to main switch board and from main switchboard to distribution board, including wastage = 1.0 m

2. Length of 25 mm exible conduit from HG conduit to motor terminals fan machine no. 4,including wastage = 1.0 m

3. Length of 19 mm exible conduit required for connecting motor switches to motor starters forall the four machines and HG conduit to motor terminals for machines.