The aim of this method statement is to describe electrical works associated with installation of earthing / grounding system, lightning surge protection systems.
The grounding & lightning protection system are designed to ensure the complete safety of both persons and equipment throughout the project buildings and facilities.
Storage of exothermic welding materials should be in a clean, dry, “NO SMOKING” area and should be restricted to access by authorized personnel only.
Storage condition shall be such that exothermic welding materials are not subject to rough handling or physical damage. Storage shall be in cool place and in condition no humidity and moisture.
All boxes or container of material should be stored in accordance with container (carton) or label marking “This Side Up”
These materials must be stored under shelter to protect the boxes from the elements and raised to protect them from dampness or wet surface.
Safety control method
The safety procedure generally has to be applied for all Engineers, Supervisors, Workers as following bellow:
Make sure that all personal protection equipment (PPE) be provided on site before starting work such as helmet, safety boot, safety glasses, glove, mask etc.
Make sure that PPE must be wear in the correctly way when working.
Tools and equipment shall be inspected by authorized person before carried out the work.
Barricades and sign posts for warning shall be provided on site.
Fire extinguishers shall be provided on site wherever exothermic welding works and always ready to use.
Working with welding machine and exothermic welding
Ensure worker wear safety glasses, gloves, helmet etc.
Fire extinguisher shall be always ready at work place
Welding machine must be checked carefully before using.
Welder must be qualified and skill.
Working at height
Ensure every worker wear safety harness when working at more than 2 m height.
Safety protected handrail on top layer of scaffolding shall be provided.
Ensure A ladders are in good condition/quality.
List of necessary equipment & tools:
- Copper earth rods
- Bare copper cable
- Cable clamp for earth rod and copper cable
- Copper tape and clips
- PVC pipe
- Concrete grounding pit
- Cable lugs
- Air terminal
- Earth bar with disconnecting link
- Furse
- Earth Tester/.
- Welding Machine/
- Welding rod
- Field Tester
Type of Connections
- Connect earth rod to bare copper wire
- Connect rebar to bare copper wire
- Connect copper bar to bar copper wire
- Connect cable trays/ladders and pipes to grounding system (Detail of electric continuity for cable tray shall be provided in method statement for trays/ladders installation.)
Installation of Exothermic Welding System
The mould crucible with suitable size shall be used for exothermic welding. The following procedures shall be followed before conduct the exothermic welding.
Ensure that the mould is always clean and free of moisture.
Ensure that the tap hole is always in well-defined condition.
Ensure that the correctness of connection selector.
Ensure that the correctness of welding powder
Procedure to conduct the exothermic connections.
Fix the connection selector to the handle clamp as per the require sizes of conductor to be welded.
Place the conductor in the mould, ensure that connection selector is used in accordance to the conductor to be welded.
Close the handle clamp and lock in the lock position, drop the metal retaining disc into the bottom of the mould crucible. Ensure that the metal retaining disc is correctly, completely seated and cover up the tap hole.
Deposit the welding power into the crucible and spread a little amount on top of the mould edge as a role of starting power.
Close the mould lips, and ignite with the flint gun.
Open the mould after a few seconds where the reaction is completed or the metal has been solidified.
Do not touch the welding surface after the reaction.
Clean up the mould for the next joint.
Earthing Cable Installation
The earthing conductor, bare copper cable shall be installed as per approved shop drawing.
Ensure that the copper cable is straight (not wavy) so that it fits nicely into the exothermic mould prior to the exothermic welding.
Ensure that the copper cable is free of dirt / oil and dry keeping.
Earth Rod Installation
The copper rod is to be driven into the ground by means hammer drill / sledge hammer.
Make sure the rods are coupled with coupling and driving studs before hammering as it will protect the thread or the head of the rods from damaged.
After the desired depth has achieved, the earthing conductor will be joint to the earth bar / rod clamp of the earth pit and fastened it securely.
Resistivity check should be taken and if the resistivity is not achieved to required value then it is advisable to drive it deeper.
The rod shall be driven at least 40 cm under ground level possible and do not force to drive it as it may break the coupler and loose the rod.
The number of rods driven into the ground will be dependable to the soil resistivity on that particular area and as per approved shop drawing.
Earth Pit
Install the inspection pit and ensure that it is flush with the external ground / road level.
Ensure that the earth pit is free from dirt and rubbish.
Ensure that the rod is appear and we can make test
Grounding connection
Detail-1: Connect earth rod to bare copper wire
Detail-2: Connect rebar to bare copper wire
Execution work for Earthing of Lightning Protection
Drive the earth rods into the earth by hammer.
Excavate a trench (D x W: 800:500) to link earth rods together by soft drawn bare copper wire.
Link earth rods to Grounding network.
Backfilling the trench.
Testing and record earthing resistant value.
Joints shall be protected against rust by cold galvanized paint.
Contact surfaces shall be flush prior to jointing.
Bolt connections of copper wire with hot dip galvanized steel bar and copper wire with copper bar should reach mechanical effect and electrical effect.
During the driving of the rods into the earth, it is better to measure value of the resistance to earth in order to quantity of necessary grounding rod.
Handling of chemicals to reduce soil resistivity:
Prepare wiring trench
Ensure no garbage on the trench
Put the chemicals along the track covers a thick layer of copper 3mm
Backfilling the trench.
Procedure of installation of Lightning Protection system
The Grounding system for Lightning protection system must be established prior to install Lightning protection system (refer to item 4.4 for Grounding installation).
Down conductor shall not be isolated nor enclosed in PVC pipe .
The down conductor should be fixed with a test joint in a position that is convenient for the tests but shall not be reached by irresponsible persons.
Down conductor 95mm2 bare copper wire shall be connected directly to the mounting base of the lightning arrester by terminal lug.
The lightning arrester should be fitted into the mounting base before lifting them .
General Requirements / Procedure
Down conductor for air terminal (ESE type) shall be connected to earthing rods to ensure direct connection to earth of any stroke current before interconnection with the general Grounding System.
All equipment connected to power supply must be grounded.
All metal parts, structural steel, cable trays, piping, reinforced concrete must be grounded.
All joints shall be according to shop drawing.
Safety control
To secure an exit entrance whenever it has contingencies.
Keep water out where is necessary.
To keep workplace and amenities is always clean.
Barricade and sign post are available around the site work.
To pay attention to equipment/ tools as below:
- Welding machine: insulation
- Drill machine: insulation and earthing terminal
- Cylinders: Pressure Gauge Set shall be inspected by authorities
- Cutting machine: insulation and earthing terminal
Inspection & Testing of Earthing and Grounding System
The Grounding and Lightning Protection System shall be given a visual inspection by the electrical engineer during the installation.
The Contractor should not allow any backfilling of trenches or pits where these system are installed before inspection by the consultant engineer and the appropriate documents are signed.
Material delivered shall be inspected under the Engineer’s supervisor about size, quality and quantity.
After performing, works shall be inspected. Inspection of lightning should be included two steps: check underground system and general. For equipment fitted inside structural work or fix underground shall be checked and inspect before backfilling.
Check Grounding and Lightning Protection.
Shop-drawing approved.
Material approved.
Visual Inspection
- Check quality of grounding conductor and grounding electrode delivered on site.
- Installation checking (connection, routing, and quantity) according to approved shop drawings.
- Check dimension, level and finishing of foundation of air terminal.
- Check installation according to approved shop drawings and manufacturer’s recommendation.
- Functional Test: As per design and manufacturer’s recommendation.
- Grounding Resistance Value shall be measured.
Field testing of Lightning System
Grounding rods shall be tested for ground resistance value before any wire is connected. The test shall be perform in normal dry weather, not less than 48 hours after rainfall.
Ground resistance shall also be measured for each piece of equipment to the ground electrode. Testing shall be with a portable ground testing megger for each ground or group of grounds. The instrument shall be equipped with ammeter reading directly in Ohms or fractions thereof to indicate the ground value of the electrode under test.
All test equipment including test meter shall be provided and one copy of the ground megger manufacturer’s directions, including the method shall be provided.
The minimum resistance based on the allowable capacity of the conductor shall be as indicated in the following table:
Earth Resistance tests table
| Amperes | Ohms |
| 25 through 50 | 250000 |
| 51 through 100 | 100000 |
| 101 through 200 | 50000 |
| 201 through 400 | 25000 |
| 401 through 800 | 12000 |
| Over 800 | 5000 |
The earth resistance shall be measured either soil resistivity testing or earth resistance testing method.
Soil Resistivity Testing (based on Wenner method)
The test instrument used is Mega Digital Earth Tester. The instrument is connected to the electrodes as per below detail:
Four electrodes are driven into the ground, in a straight line with equal spacing between them.
Let the spacing be called ‘a’.
The soil resistivity can then be calculated using the equation:
ƒ = 2 x 3.14 x a x R
Where
ƒ = soil resistivity (ohm meters)
a = electrode spacing (meters)
R = measured resistance (ohms)
Soil Earthing Resistivity Test Procedure
Confirm the proposed test locations.
Insert four electrodes into the ground in a straight line a= 2 meters spacing. Connect instrument to the electrodes as shown above.
Perform test and record measured resistance in Soil Resistivity Test Form.
Shift electrodes to next spacing a= 4 meters and repeat test.
Repeat tests at 6 meters, 8 meters and 10 meters electrode spacing.
Recorded measurements will be analyzed and presented in Soil Resistivity Test Report.