- Electromagnetic interference occurring as a result of these partial currents should be taken into account when planning the structure installations and designing the lightning protection electromagnetic zones inside the structure according to IEC 62305-4.
However, the interference will be significantly lower than that caused by an electrical spark at this point.
In the case of roofs, the distance between the LPS and the electrical installations is often found to be shorter than the separation distance, s, given in 6.3. If this is the case, an attempt should be made to install the LPS or the electrical conductor at a different location.
An agreement should be reached with the person responsible for the electrical installation to perform a re-routing of electrical circuits which do not conform to the separation distance to the air-termination conductors on structures.
When the electrical installation cannot be re-routed, bonding to the external LPS should be carried out in accordance with 6.3.
In some buildings it is not possible to maintain the separation distances as required. Internal constructions can prevent the designer or installer from assessing situations and making connections to certain metal parts and electrical conductors. This should be communicated to the owner of the building.
E.6.3.2 Simplified approach
The simplified approach according to 6.3.2 is possible, if the widest horizontal elongation of the structure (length or width) does not exceed four times the height.
E.6.4 Protection against effects of induced currents in internal systems
Currents in the conductors of the external LPS may induce excessive over-voltages in the conductor loops of the internal installations by the effect of magnetic coupling. Overvoltages may cause failures of internal systems.Since practically all buildings contain electronic equipment, the effect of the electromagnetic field of the external and internal down-conductors should be taken into account in the planning of the lightning protection system.
Protection measures against overvoltages are given in IEC 62305-4.
E.7 Maintenance and inspection of the LPS
E.7.1 Scope of inspections
Inspection of the LPS should be conducted by a lightning protection specialist in accordance with the recommendations of Clause E.7.
The inspector should be provided with the LPS design report containing the necessary documentation of the LPS such as design criteria, design description and technical drawings. The LPS inspector should also be provided with previous LPS maintenance and inspection reports.
All LPS should be inspected on the following occasions:
during installation of the LPS, especially during installation of components which are concealed in the structure and will become inaccessible;
after the completion of the LPS installation;
on a regular basis according to Table E.2.
Table E.2 - Maximum period between inspections of an LPS
|
Protection level |
Visual inspection year |
Complete inspection year |
Critical situations a bcomplete inspection year |
|
I and II |
1 |
2 |
1 |
|
III and IV |
2 |
4 |
1 |
|
a Lightning protection systems utilized in applications involving structures with a risk caused by explosive materials should be visually inspected every 6 months. Electrical testing of the installation should be performed once a year. An acceptable exception to the yearly test schedule would be to perform the tests on a 14 to 15 month cycle where it is considered beneficial to conduct earth resistance testing over different times of the year to get an indication of seasonal variations. b Critical situations could include structures containing sensitive internal systems, office blocks, commercial buildings or places where a high number of people may be present. |
|||
The inspection frequencies given in Table E.2 should apply where no specific requirements are identified by the authority having jurisdiction.
NOTE If national authorities or institutions require regular tests of the electrical system of a structure, it is recommended to test the lightning protection system with regard to the functioning of the Internal lightning protection measures including the lightning protection equipotential bonding with electric systems at the same time. Older installations analogously should be related to a lightning protection class or the test intervals should be taken from the local or any other test specifications such as construction guide lines, technical regulations, instructions, industrial safety and protection of labour laws.
The LPS should be visually inspected at least annually. In some areas where severe weather changes and extreme weather conditions occur, it is advisable to visually inspect the system more often than indicated in Table E.2. Where the LPS forms part of the client’s planned maintenance programme, or is a requirement of the building insurers, the LPS may be required to be fully tested annually.
The interval between the LPS inspections should be determined by the following factors:
classification of structure protected, especially with regard to the consequential effects of damage;
class of LPS;
local environment, for example a corrosive atmosphere environment should have short intervals between inspections;
the materials of the individual LPS components;
the type of surface to which the LPS components are attached;
the soil condition and associated corrosion rates.
In addition to the above, an LPS should be inspected whenever any significant alteration or repairs are made to a protected structure and also following any known lightning discharge to the LPS.
A total inspection and test should be completed every two to four years. Systems in critical environmental conditions, for example parts of the LPS exposed to severe mechanical stresses such as flexible bonding straps in high wind areas, SPDs on pipelines, outdoor bonding of cables etc., should have a complete inspection every year.
In most geographical areas, and especially in areas which experience extreme seasonal changes in temperature and rainfall, the variation of the earthing resistance should be taken into account by measuring the resistivity depth profile in different weather periods.
An improvement of the earthing system should be considered when the measured resistance values show larger changes in the resistance than anticipated in the design; especially when the resistance increases steadily between inspections.
E.7.2 Order of inspections
E.7.2.1 Inspection procedure
The purpose of this inspection is to ensure that the LPS conforms to this standard in all respects.
The inspection includes checking technical documentation, visual inspections, testing and logging in an inspection report.
E.7.2.2 Checking of technical documentation
Technical documentation should be checked for completeness, conformity to this standard and agreement with the plant as executed.
E.7.2.3 Visual inspections
Visual inspections should be made to ascertain that
the design conforms to this standard,
the LPS is in good condition,
there are no loose connections and no accidental breaks in the LPS conductors and joints,
no part of the system has been weakened by corrosion, especially at ground level,
all visible earth connections are intact (functionally operational),
all visible conductors and system components are fastened to the mounting surfaces and components which provide mechanical protection are intact (functionally operational) and in the right place,
there have not been any additions or alterations to the protected structure which would require additional protection,
there has been no indication of damage to the LPS, to SPDs or any failures of fuses which protect SPDs,
correct equipotential bonding has been established for any new services or additions which have been made to the interior of the structure since the last inspection, and that continuity tests have been performed for these new additions,
bonding conductors and connections inside the structure are present and intact (functionally operational),
separation distances are maintained,
bonding conductors, joints, shielding devices, cable routing and SPDs have been checked and tested.
E.7.2.4 Testing
Inspection and testing of the LPS includes visual inspections and should be completed by the following actions:
performing continuity tests, especially continuity of those parts of the LPS which were not visible for inspection during the initial installation and are not subsequently available for visual inspection;
conducting earth resistance tests of the earth-termination system. The following isolated and combined earth measurements and checks should be made and the results recorded in an LPS inspection report.
NOTE 1 High-frequency or impulse measurements are possible and useful to determine the high frequency or impulse behaviour of the earth-termination system. These measurements may be performed at the installation stage as well as periodically for the maintenance of the earthing system to check adequacy between the designed earthing system and the need.
The resistance to earth of each local earth electrode and where reasonably practical the resistance to earth of the complete earth-termination system.
Each local earth electrode should be measured in isolation with the test joint between the down-conductor and earth electrode in the disconnected position (isolated measurement).
NOTE 2 For earth networks incorporating both vertical earth rods and a partial or full ring earth electrode, disconnection and testing should be performed at the earth inspection pit. If such inspection is difficult to perform, routine test should be completed by high frequency or impulse tests.
If the resistance to earth of the earth-termination system as a whole exceeds 10 Q, a check should be made to ascertain that the electrode conforms to Figure 3.
If there is a significant increase or decrease in the value of the earth resistance, additional investigations should be made to determine the reason for the change.
For earth electrodes in rocky soil, the requirements of E.5.4.3.5 should be followed. The 10 Ci. requirement is not applicable in this case.
The results of a visual check of all conductors, bonds and joints or their measured electrical continuity.
If the earth-termination system does not conform to these requirements, or checking the requirements is not possible because of a lack of information, the earth-termination system should be improved by installing extra earth electrodes or installing a new earth-termination system.
SPDs without a visual indicator need to be tested, preferably using the guidelines or equipment provided by the manufacturer.
E.7.2.5 Documentation of inspection
LPS inspection guides should be prepared to facilitate LPS inspections. They should contain sufficient information to guide the inspector through the inspection process so that all areas of importance are documented such as the method of LPS installation, the type and condition of the LPS components, test methods and the proper recording of the test data obtained.
The inspector should compile an LPS inspection report, which should be kept together with the LPS design report and the previously compiled LPS maintenance and inspection reports.
The LPS inspection report should contain the following information:
general conditions of air-termination conductors, and other air-termination components;
general level of corrosion and the condition of the corrosion protection;
security of attachment of the LPS conductors and components;
earth resistance measurements of the earth-termination system;
any deviation from the requirements of this standard;
documentation of all changes and extension of the LPS and any changes to the structure. In addition, the LPS construction drawings and the LPS design description should be reviewed;
the results of the tests performed.
E.7.3 Maintenance
The LPS should be maintained regularly to ensure that it does not deteriorate but continues to fulfil the requirements to which it was originally designed. The design of an LPS should determine the necessary maintenance and inspection cycle according to Table E.2.
The LPS maintenance programme should ensure a continuous updating of the LPS to the current issue of this standard.
E.7.3.1 General remarks
LPS components tend to lose their effectiveness over the years because of corrosion, weather-related damage, mechanical damage and damage from lightning strokes.
The inspection and maintenance programmes should be specified by an authority, the LPS designer or the LPS installer, in conjunction with the owner of the structure or an appointed representative.
To carry out maintenance work and to perform inspections of an LPS the two programmes, inspection and maintenance, should be coordinated.
Maintenance of an LPS is important even though the LPS designer has taken special precautions to provide corrosion protection and has dimensioned the LPS components according to their particular exposure to lightning damage and weather elements in addition to the requirements of this standard.
The mechanical and electrical characteristics of the LPS should be fully maintained throughout the entire lifetime of the LPS in order to conform to the design requirements of this standard.
It may be necessary to modify the LPS if modifications are carried out on the building or its equipment or if the purpose for which the building is utilized is altered.
If an inspection shows that repairs are necessary, those repairs should be executed without delay and not be postponed until the next maintenance cycle.
Е.7.3.2 Maintenance procedure
Periodic maintenance programmes should be established for all LPS.
The frequency of maintenance procedures is dependent on the following:
weather- and environment-related degradation;
exposure to actual lightning damage;
protection level assigned to the structure.
LPS maintenance procedures should be established for each particular LPS and should become a part of the overall maintenance programme for the structure.
A maintenance programme should contain a list of routine items to serve as a checklist so that definite maintenance procedures are followed regularly in order to make it possible to compare recent results with previous ones.
A maintenance programme should contain provisions for the following:
verification of all LPS conductors and system components;
verification of the electrical continuity of the LPS installation;
measurement of the resistance to earth of the earth-termination system;
verification of SPDs;
re-fastening of components and conductors;
verification to ensure the effectiveness of the LPS has not been reduced after additions to, or changes in, the structure and its installations.
E.7.3.3 Maintenance documentation
Complete records should be kept of all maintenance procedures and should include corrective actions taken or required.
Maintenance procedure records should provide a means of evaluating LPS components and the LPS installation.
The LPS maintenance record should serve as a basis for reviewing maintenance procedures as well as for updating maintenance programmes. The LPS maintenance records should be kept together with the LPS design and the LPS inspection reports.Bibliography
NFPA(National Fire Protection Standards), 780:2008, Standard for the Installation of Lightning Protection Systems
IEC 61400-24, Wind turbines - Part 24: Lightning protection
IEC 60050-826:2004, International Electrotechnical Vocabulary - Part 826: Electrical installations
IEC 60050-426:2008, International Electrotechnical Vocabulary - Part 426: Equipment for explosive atmospheres
IEC/TR 61000-5-2, Electromagnetic compatibility (EMC) - Part 5: Installation and mitigation guidelines - Section 2: Earthing and cabling
IEC 60728-11, Cable networks for television signals, sound signals and interactive services - Part 11: Safety
1In preparation.
2
At draft stage.
3References in square brackets refer to the bibliography.
4In preparation.
