Earthing and Lightning Protection Systems

MaintenanceIt has been shown that in cases where damage has occurred to a protected structure, the damage was due to additions or repairs to the building or to deterioration or mechanical damage that was allowed to go undetected and unrepaired, or both. Therefore, it is recommended that an annual visual inspection be made and that the system be thoroughly inspected every five years.

INSPECTION CRITERIA

1. The minimum inspection requirements shall be as outlined in Annex D of NFPA 780. Visual inspections should be performed to verify the following:

a) The system is in good repair.b) There are no loose connections that might result in high-resistance connections.c) No part of the system has been weakened by corrosions, vibration, or an obvious

lightning strike.d) All down conductors and grounding electrodes are intact (non-severed).e) All conductors and system components are fastened securely to their mounting surfaces

and are protected against accidental mechanical displacement.f) There have been no additions or alterations to the protected structure that would require

additional protection against lightning strikes or surges.g) There is no indication of damage to surge protection devices.

2. Recommended Testing, Maintenance & Inspection Frequencies

a) An annual visual inspection should be performed on all visible Lightning Protection System (LPS) components per the requirements of NFPA 780 Annex D. In some areas where severe climatic changes occur, it might be advisable to visually inspect systems semiannually or following extreme changes in ambient temperatures.

b) A visual inspection should be performed whenever any alterations or repairs are made to a protected structure, as well as after a known or suspected lightning strike or other natural phenomena that could have damaged the LPS.

c) The annual visual inspection should be scheduled to proceed the normal lightning high frequency period for the site, if practical.

d) All components, conductors, clamps and splicers must be refastened and tightened annually.

e) A complete inspection of the LPS should be performed on 36 to 60 month frequency as practical for the site. It is recommended that critical systems be inspected every 1 to 3

years depending on occupancy or the environment where the protected structure is located. In most geographical areas, and especially in areas that experience extreme seasonal changes in temperature and rainfall, it is advisable to stagger inspections so that earth resistance measurements, for example, are made in the hot, dry months as well as the cool, wet months. Such staggering of inspections and testing is important in assessing the effectiveness of the lightning protection system during the various seasons throughout the year.i) This inspection shall include the visual inspection as well as a ground resistance test

performed on all, or a specified number, of the ground electrode connections.ii) This inspection shall include continuity testing of any components and conductors

that are not located so that they can be visually inspected.iii) Some facilities may have frequency requirement contained in their Safety Basis

Documents (TSR/DSA). These requirements shall take precedence over the frequencies contained in this and all other governing documents.

3. Records and Test Data

The inspector or inspection authority should compile and maintain records pertaining to the following:

(1) General condition of air terminals, conductors, and other components(2) General condition of corrosion-protection measures(3) Security of attachment of conductors and components(4) Resistance measurements of various parts of the ground terminal system(5) Any variations from the requirements contained in this standard

Complete records should be kept of all maintenance procedures and routines and should include corrective actions that have been or will be taken. Such records provide a means of evaluating system components and their installation. They also serve as a basis for reviewing maintenance procedures as well as updating preventive maintenance programs.

RECOMMENDED WORK STEPS FOR INSPECTION OF FACILITY LIGHTNING PROTECTION SYSTEM

1.0 Prerequisites

Obtain the appropriate drawings showing the lightning protection components and installation for use during inspection. (Engineering installation drawings, facility prepared sketches, and/or engineering analyses indicting the components found on an existing facility that does not have engineering drawings indicating the installed components).Obtain safety equipment and tools required to complete the inspection. This should include small wrenches to tighten loose connections, fall protection equipment as required for roof top work, lifts and etc.Obtain reference materials as necessary.

Review previous inspection records and any findings and corrective actions as necessary to ensure that deficiencies have been corrected.Calibrated test instruments as required for ground resistance and/or continuity testing.Individual inspections steps may be performed concurrently.

2.0 Annual Inspection Criteria

2.1 Visually inspect that the System is in Good Repair: Air terminals are in the vertical position Verify no broken conductors Ensure all LPS components are present Inspection of surge suppression devices on communication and power lines

entering the building Visually inspect bonding jumpers to sanitary water lines, fire protection

risers, and ground electrode system Verify components on roof stacks and other components

2.2 Visually inspect for loose connection or high resistance joints: Air terminal bases Bonding jumpers & connections Cross connected cables connectors Tighten loose connection, splices, and bolts as necessary

2.3 Visually inspect for components and joints weakened by lightning discharge, corrosion or vibration:

Air terminal bases Any bi-metallic connections Cable connections and cables Verify firm attachment to roof and other surfaces – 36-in maximum spacing

on fasteners Verify attachment to roof stacks and components – 36-in maximum spacing

on fasteners Tighten loose connection, splices, and bolts as necessary

2.4 Visually inspect to ensure that all down conductors and grounding electrodes are intact:

Verify down conductors are firmly attached to building walls or steel – 36-in maximum spacing on fasteners

Verify no broken or frayed conductors Inspect guards on down conductors to ensure integrity – 6-ft minimum above

ground surface If visible inspect ground electrode connections Tighten loose connection, splices, and bolts as necessary

2.5 Visually inspect all conductors and components to ensure that they are securely fastened to their mounting surface:

Verify Air terminals are firmly connected their bases Verify roof and structure attachments are adequate – 36-in maximum spacing

on fasteners Tighten loose connection, splices, and bolts

2.6 Visually inspect that there are no additions or alterations to the structure that would require additional protection:

Compare to system drawings and/or component listing2.7 Visually inspect surge protection devices for indication of damage or overvoltage to

devices: Inspect for damage to the devices Verify indicator lights are on and in correct sequence

2.8 Visually inspect and compare to referenced drawings to ensure that the system complies with NFPA 780 requirements

3.0 Testing Criteria

3.1 Test to verify continuity of those components of the system that were concealed (built in) during the initial installation and are not now available for visual inspection

Perform continuity testing on a representative sample of concealed building LPS components

3.2 Perform ground resistance tests of the ground termination system and its individual electrodes that are accessible or visible to test, if adequate disconnecting means have been provided. These test results should be compared with previous or original results or current accepted values, or both, for the soil conditions involved. If it is found that the test values differ substantially from previous values obtained under the same test procedures, additional investigations should be made to determine the reason for the difference.

Perform fall of potential ground (three point) test at each test point Use visible down conductors at building exterior as necessary Use of a clamp on resistance meter shall be approved prior to use.

3.3 Perform continuity testing to determine that suitable equipotential bonding has been established for any new services (utility, communication, fire protection, power, CCTV, etc.) or construction that has been added to the structure since the last inspection.

3.4 Testing of surge suppression devices to determine effectiveness compared with similar new devices

ACCEPTANCE CRITERIA

1. General Criteria – The LPS shall be maintained equal to its original installed condition. Deficient conditions identified by the Testing, Maintenance & Inspections shall be corrected so that the system will function as intended to protect the structure, installed equipment and processes, and personnel.

2. When conducting required follow up inspections on building LPS, maintenance inspectors shall utilize the following categories/ classifications for reporting any identified LPS deficiencies.

a) Level 1 (Non-Functional): Personnel and Sensitive Operations protection:

Deficiencies that significantly compromise the ability of the LPS to effectively protect facility occupants, special nuclear material or hazardous contents from a lightning related event. Examples may include but are not limited to:

1. Missing, improperly spaced, or fallen air terminals (usually two or more adjacent air terminals).

2. Disconnected, broken, or damaged conductors or down leads.3. Disconnected, broken, or damaged connections between the LPS and the

associated ground electrode system.4. Broken or missing bonding connections (25% or greater).5. Damage to or failure of surge protection devices (2 or more for the facility).

A Level 1 deficiency shall be repaired within one week.

b) Level 2 (Impaired but Functional): Equipment Protection:Deficiencies that leave rooftop mounted equipment and high value asset equipment within the building subject to damage from a lightning related event. Examples may include but are not limited to:

1. Existing rooftop mounted equipment that is not bonded.2. SPDs not installed (electrical, communications data, etc.).3. Building components subject to sideflash that are not properly bonded (door &

window frames, roof flashings, structural supports, bollards, ladders etc.).4. New rooftop equipment not bonded to LPS.

A Level 2 deficiency shall be repaired within 30 days.

c) Level 3: Component Protection and Testing:Existing equipment and metal structures that are constructed of materials that are less than 3/16" in thickness and are not properly bonded with required conductors and/or terminals. Ground resistance testing that is not completed due to the inability to isolate the system or inability to meet the distance requirements of NFPA-780 Annex-E. Examples may include but are not limited to:

1. Exhaust fan housings, ventilation stacks, other metal components less than 3/16" thick which require separate bonding and air terminals.

2. Improper height or support of air terminals.3. Equipment with less than two paths to ground.4. Conductor bend radius less than 8".5. Conductors supported at lengths greater than 3ft.

A Level 3 deficiency shall be repaired as soon as practical.

3. Consult with the LPS Subject Matter Experts to ensure these priority classifications are acceptable for individual sites.

NFPA_780 ANNEX E

E.1 General.

E.1.1 In order to determine the ground resistance of a lightning protection system, it is necessary to remove it from any other ground connection. This can prove a virtually impossible task, necessitating certain assumptions. In reality, ground resistance–measuring equipment works at low frequencies relative to the lightning discharge. The resistance it computes is therefore often affected by the resistance of power-system ground electrodes or a similar ground medium that can be several thousand feet from the structure being protected. The ground resistance to be used to calculate lightning conductor potentials when a high-frequency lightning discharge strikes a building must be the grounds in the immediate area of the building, not the remote ones that ground-measuring equipment probably monitor.

E.1.2 If the building is small, and the lightning protection system can be disconnected totally from any other grounding network, its resistance can be measured by the three-point technique described in E.1.3. If the building is large or cannot be disconnected totally from any other grounding network, then the ground resistance of individual isolated lightning protection ground rods should be measured by the three-point technique described in E.1.3 and this resistance multiplied by a factor depending on the number of ground rods.

E.1.3 The principle of ground resistance measurement is shown in Figure E.1.3. L is the lightning ground rod or ground rod system, P is a test probe, and A is an auxiliary current probe. M is the standard ac measuring equipment for three-point technique ground resistance measurements.Convenient distances for LP and LA are 23 m (75 ft) and 36 m (120 ft), respectively. In general, P should be at 62 percent of the distance from L to A. If 36 m (120 ft) is not convenient, it could be increased significantly [or reduced to no less than 15 m (50 ft)], provided LP is increased proportionately.

FIGURE E.1.3 Measurement of Ground Resistance.

A current, I, is passed through the electrode or electrodes to be tested, L, and through an auxiliary probe, A. The distance, LA, is long compared to the electrode length. The voltage, V, between L and P is measured by the test equipment, which also monitors I and calculates the ground resistance, R, as V/I. Alternating current is used to avoid errors due to electrolytic factors in the soil and to remove effects due to stray currents.Three-point ground resistance–measuring equipment using these principles is relatively inexpensive and allows direct reading of R.

E.1.4 Variations in soil resistivity due to temperature and moisture fluctuations can affect the measured ground resistance. A good designer will measure ground resistance under average or high resistivity conditions in order to design a lightning protection system to function adequately. If the building ground is complex in nature, the resistance of single ground rods can be measured and certain assumptions made. The average single ground rod resistance, Rm, must be multiplied by a factor depending on the number of lightning protection ground rods, n, spaced at least 10.7 m (35 ft) apart. The total system ground resistance, R, can be calculated from the formula:

Where:R = total system ground resistanceRm = average single ground rod resistancen = number of lightning protection ground rods