EARTH TESTER

INSTRUCTION FOR USE OF EARTH TESTER:

  1. Zero Adjustment:

Before each measurement, check whether the pointer coincide with blank Zero (0) mark on the scale, when no current is flowing in the instrument. If necessary, set the pointer to zero by using Zero Adjuster screw.

2. Three Terminal Earth Tester for Earth Resistance Measurement:

Connect all the three terminals as shown in fig. 1 Rotate the handle of generator with increasing speed until he pointer of the meter comes to rest to get the direct reading of Earth Resistance in ohms.

Note: In case of multi range instrument, put the range selector switch at an appropriate position. Whenever in doubt connect from the higher range of the selector switch and work downward.

3. Four Terminal Earth Tester for measurement Of Earth Resistivity & Earth Resistance:

The Earth Tester is four Terminal Type. Terminal Marked viz.C1.P1.P2, C2. The instrument is suitable for Earth Resistance as well as EARTH RESISTIVITY (specific Soil Resistance).

4. Measurement of Earth Resistance:

BY means Four Terminal type Earth Tester ( use as Three Terminal Type) In Four Terminals type, short the terminals C1 & P1 and connect as per Fig.NO.2. Rotate the handle of generator until the pointer comes to rest. Read the earth resistance directly in ohms.

5. Measurement of Earth Resistivity:

This is made usually by using Four Terminal EARTH TESTER. Connect the instrument terminals as per Fig.No.3, see that all Four Spikes are one straight line and the distance between all the spikes are kept same. The value of ‘L’ as in Fig.3, may be kept between 50 to 70 feet.

Rotate the generator handle speedily until the pointer comes to rest. Observer the reading of the instrument in ohms (taking care of the range factor). The value of Earth Resistivity o = 2πRL where,

  • R = Value of Earth Resistance measured in ohms.
  • L = Distance between spikes in Cm.
  • π = 3.14
  • p = Earth’s Resistivity in ohms Cms,.

Measurement of Resistance:

Non-Inductive or Non-capacitive:

  • Connected the unknown resistance ‘X’ as per Fig. NO.4,
  • And follow the instruction as mentioned for measurement of Earth Resistivity.

 

Accessories Required

Items

For 4 T type

For 3 T type

Spikes

4 Nos.

2 Nos.

Hammer

1 No.

1 No.

Length of Cable(Leads)

4 Nos.

3 Nos.

Wrench

1 No.

1 No.

Screwdriver

1 No.

1 No.

Safety

NEED FOR PROVIDING EFFECTIVE LIGHTNING

PROTECTION FOR SAFETY OF BUILDING STRUCTURE

 

INTRODUCTION:

Everyone is aware of common news item of loss of lives and damages during monsoon Season due to a bolt of lightning thus it is the need of the hour to provide adequate safety to various installations (factories, offices, residential and public buildings etc.) from the strike of lighting. In this article a brief regarding the lightning protection is highlighted.

LIGHTNING:

A transient, high-current electric discharge whose path is generally measured on kilometer. Lightning occurs when some region of the atmosphere attains an electric charge sufficiently larger than the electric field associated with the charge cause the electrical breakdown of the air.

Lightning strikes can be a major risk to live stock and human lives. Persons and equipment. within a building thus needs to be protected from a direct lightning strike; circumstances may arise where the effects of lighting are transmitted into or within the building structure by various means, placing equipment and possibly persons at risk. communications and electronic equipment are practically susceptible to building/structure damage from lighting and such structure damage may occur at energy levels well below those needed to cause injury to persons.

 

EFFECTS OF LIGHTNING:

There are three principal modes of entry of lightning into building structure or associated buildings, which may occur separately or in combination.

  • DIRECTLY: by the interception of lightning on exterior metal work or other exposed conductors. This is characterized by the full impulse energy being transmitted by the conductor. This can associate extremely high voltages.
  • INDIRECTLY: by the interception of lightning on other structures or services connected to the structure, for example the electricity distribution system or telephone lines to the site. Such an impulse is at a substantially lower energy level than for a direct strike.
  • INDUCTIVELY: by a lightning strike to the ground inducing a transient in conductors in the ground or the building structure or again in the electricity or telephone services to the site. This impulse involves relatively low energy and is thought to occur less frequently than above.

 

THE NEED FOR PROTECTION:

Data collected by the expensive equipment installed at the building structure gather more importance significance around monsoon when heavy rains lash the catchment areas. It is also known that maximum lightning occurs during the same period. The sensitive electronics within building structure can be very easily damaged in the event a direct lighting strikes and as per studies conducted around the world, 99%of the lightning strikes have strength of 3000 amp and above.

The effect of the direct strike described above would be sometimes very obvious, especially when sensors and cable are accessible and can be examined. At other times, lightning damages to building structure has to be deducted from symptoms such as electrical leakage from conductors to ground, excessive electrical noise, and inconsistent readings.

A typical strike that destroys an instrument can also leave pinhole punctures in cable jackets. Even when the sensor is not destroyed, the pinholes in the cable jackets will allow the entry of water, creating numerous other problems including instability through increased electrical noise. commonly routed cables can be building structure damaged due to arcing between adjacent cable such as in trenches or common bore holes.

 

And most importantly we have to ensure that LIFE & LVE STOCKS are adequately protected from lightning strikes.

What Indian standard Says

As per IS 2309 1989 Clause 8.1 shows following point for needs of protection

  • Where Large number of people congregate.
  • Where essential public services are concern.
  • Where area in which lightning, strokes are prevalent.
  • Where they are very tall or isolated structures.
  • Where they are structures of historic or cultural importance.

 

How to PROTECT against DIRECT Lightning Strikes

 

The most effective way to provide protection against direct lightning strike would be to provide the lightning current a predetermined path to the safety of the earthing system.

This can be achieved by providing appropriate type and technology of lightning arrestors (LA). The traditional method is by using lightning rods of 1-3m made of either copper or GI with 3-5 spikes at the top of the structure. The more advanced and currently popular LA is based on the principle of ‘Early Streamer Remission (ESE).

In the ESE type of lightning arrestor, a streamer is sent in to the air to meet, 60m above the tip of the LA, the downward leader of the lightning strike and directing the strike to safety. As compared the conventional type of LA doesn’t meet the downward lightning after a considerable delay and therefore the impact is very much closer to the structure /equipment being protected.

Comparison between conventional ROD and the Advanced ESE LA

 

Description

ESE type LA

Conventional ROD type LA

Working Principal

Active device seeks for the lightning & engages it 25 to 60 meter above the tip of the LA. This ensures the impact is much above the structure and no currents get into the stray infrastructure.

Based on spike or finial, wait for the lightning to strike on its tip. The tip may align with the upward leader around 24 meters above the tip. In this case there could be stray currents getting into the structure.

Probability On strike

Only one device is sufficient to give a zonal protection up to 214 meters

To provide adequate protection several

Spikes are required to be installed.

 

 

Diameter

In general, the spike provides protection in a cone of 45 deg around the LA. These LA needs to be mounted at 20-meter diameter if tip of LA is 10 mtr above the structure being protected.

Level Of protection

Only one system install at a height of 2 meter above the structure gives protection of 98% from lightning less than 10 KA

A grid is required to be formed a top the building to provide the protection and a passive device with the height of 1.2 meter gives a protection of 40% form lightning less than 10 KA., which may be hazardous to electronics components

Installation

Only one down conductor from top to bottom is required for effective drain path.

Several down conductors due to the presence of several LAs.

Effectiveness

Designed to perform effectively with 99% reliability

Non-reliable

 

Conclusion

The importance of the protection of live stock and sensitive high value electronics assets within the building structures is maximum during monsoon, also there is a likelihood of personnel around the building structure in the case of any emergencies which are likely during the time of heavy rains lashing the region which needs to be adequately protected. considering the importance of the assets, life and live stocks in the proximity, protection against lightning is conclusive. Based on the comparison of the available technology and the value of assets to be protected it is strongly recommended to use advanced ESE type Lightning Arrestors.

We thus feel the need of providing effective Lightning Protection to all the building especially where the masses gather like schools, colleges, temples, stadiums, Highrise Buildings and also recommended that this should be made mandatory by law so as to avoid casualty and other damages due to LIGNTNING

TECHNICAL COMPARSION

  • Ensure that pit is not watery.
  • Pack electrode with compound nicely and tightly so that it stands firmly in pit.
  • Pour a few buckets of water in and around pit.
  • Test earth resistivity of electrode. if result is satisfactory, connect it with equipment.
  • If result is not satisfactory, give some for-electrode system to set in soil.
  • Then check ohmic value and connect with equipment.
  • Make chamber with bricks if required.
  • In hard soil conditions, do not mix compound with dug out soil. (Ref: Point C)
  • Incase of difficult in installation contact your nearest dealer if Pour a few buckets of water in and around the pit everyday for 3 days for system to set.

 

TECHNICAL COMPARSION: –

Power Fast Earth Electrode (P.F.E.E.)

Traditional Earthing System

 

Pipe-in-pipe & Copper Best technology. Two B class IS mild steel pipes, one inside the other, hot dip galvanized with 100-micron coating outside and about 300-micron coating inside, filled with high conductive and corrosion resistant crystalline mixture and backfill compound around electrode

Copper plate earthing inclusive of MS pipe, 5mm dia,2.75 meter long, copper plate 450 x 450 x 3 mm with copper strip 25 x 36 nos plus charcoal and salt around electrode. Oxidation takes place. Resistance to dissipation increases when corrosion starts.

Tom models available: Model P.F.E.E. 88mm & 100mm diameter 1.5-meter,2 Meter & 3 Meter used

GI pipe Electrode earthing: 5 to 1 micron galvanization Size: 65NB or 38 mm x 2.75 m Ionc-PLUS charcoal & Salt etc. Pipe corrodes fast over period of 3 years causing high resistance to smooth dissipation of current.

Own: E.F.C. compound is used as in fill material. EFC retains moisture 13 times its dry volume: enhances conduction around electrode.

Charcoal & salt are used in the pit as fill material. Common salt hastens corrosion of GI/CI electrodes and the ohmic value goes high over a period of time.

Watering around the earth pit is required for about 3 days after installation and for a few days in peak summer when water goes down.

Watering of pit required REGULARLY to enhance conductivity around the electrode.

Ohmic value always within safe limits.

Ohmic value fluctuates resulting in frequent maintenance of costly machinery and appliances and danger to human life.

Maintenance of pit is not required in normal soil conditions.

 

Maintenance of earth pit required at regular intervals.

Low enough impedance to activate fault relays to high conductive soil around the electrode, charge dissipation through electrode is very high, current density across electrode is very low, which results in very high fault current enough to trip fault relays.

 

Sometimes fails to activate safety devices. Distribution of short circuit currents is less in terms of charge dissipation and, therefore, generates high potential at the pit resulting in low fault current, insufficient to trip fault protection relays.

Always provides safe discharge path to fault current and lightning current.

 

M some times fails to provide safe discharge path fi fault current.

Requires less space and time for installation.

 

Requires large space and time for installation.

Practically no need to charge, expected life 15 to 20 + years.

GI pipe earthing needs to be hanged every 3 years and copper plate earthing every 12 years due to corrosion attacks.

Our back Fill Compound (E.F.C) is not soluble in water.

Salt as in fill material is washed away during rainy season.

Very safe and stable platform for electronic machinery, equipment and appliances.

 

Not a stable platform for sensitive electronic equipment and appliances

Can easily cope with the earthing demands of the new generation electrical/electronic machine.

 

Can’t cope with the earthing demands f the new generation machine.

Cost Effective

The cost of maintenance over a 15 to 20 plus year period will be about three times more than the one-time cost of Power Fast Earth Electrode (P.F.E.E)