---

Mechanical and electrical characteristics as well as corrosion resistance properties shall meet the requirements of the future IEC 62561 series.

^b Shall be embedded in concrete for a minimum depth of 50 mm.

° Lattice plate constructed with a minimum total length of the conductor of 4,8 m.

^d Different profiles are permitted with a cross-section of 290 mm² and a minimum thickness of 3 mm, e.g. cross profile.

° In case of a Type В arrangement foundation earthing system, the earth electrode shall be correctly connected at least every 5 m with the reinforcement steel.

’ In some countries the diameter may be reduced to 12,7 mm.

6. Internal lightning protection system

   1. General

The internal LPS shall prevent the occurrence of dangerous sparking within the structure to be protected due to lightning current flowing in the external LPS or in other conductive parts of the structure.

Dangerous sparking may occur between the external LPS and other components such as:

• metal installations;

• internal systems;

external conductive parts and lines connected to the structure.NOTE 1 Sparking occurring within the structure with danger of explosion is always dangerous. In this case additional protective measures are required which are under consideration (see Annex D).

NOTE 2 For protection against overvoltages of internal systems, refer to IEC 62305-4.

Dangerous sparking between different parts can be avoided by means of

• equipotential bonding in accordance with 6.2, or

• electrical insulation between the parts in accordance with 6.3.

Equipotentialization is achieved by interconnecting the LPS with

• metal installations,

• internal systems,

• external conductive parts and lines connected to the structure.

When lightning equipotential bonding is established to internal systems, part of the lightning current may flow into such systems and this effect shall be taken into account.

Interconnecting means can be

• bonding conductors, where the electrical continuity is not provided by natural bonding,

• surge protective devices (SPDs), where direct connections with bonding conductors are not feasible.

• isolating spark gaps (ISGs), where direct connections with bonding conductors are not allowed.

The manner in which lightning equipotential bonding is achieved is important and shall be discussed with the operator of the telecommunication network, the electric power, gas pipes operator, and other operators or authorities concerned, as there may be conflicting requirements.

SPDs shall be installed in such a way that they can be inspected.

NOTE 1 When an LPS is installed, metalwork external to the structure to be protected may be affected. This should be considered when designing such systems. Lightning equipotential bonding for external metalwork may also be necessary.

NOTE 2 Lightning equipotential bonding should be integrated and coordinated with other equipotential bonding in the structure.

In the case of an isolated external LPS, lightning equipotential bonding shall be established at ground level only.

For an external LPS which is not isolated, lightning equipotential bonding shall be installed at the following locations:

1. in the basement or approximately at ground level. Bonding conductors shall be connected to a bonding bar constructed and installed in such a way that it allows easy access for inspection. The bonding bar shall be connected to the earth-termination system. For large structures (typically more than 20 m in length), a ring bonding bar may be used or more than one bonding bar can be installed, provided that they are interconnected;

2. where insulation requirements are not fulfilled (see 6.3).

Lightning equipotential bonding connections shall be made as direct and straight as possible.

NOTE When lightning equipotential bonding is established to conducting parts of the structure, part of the lightning current may flow into the structure and this effect should be taken into account.

The minimum values of the cross-section of the bonding conductors connecting different bonding bars and of the conductors connecting the bars to the earth-termination system are listed in Table 8.

The minimum values of the cross-section of the bonding conductors connecting internal metal installations to the bonding bars are listed in Table 9.

Table 8 - Minimum dimensions of conductors connecting different bonding bars or connecting bonding bars to the earth-termination system

Table 9 - Minimum dimensions of conductors connecting internal metal installations to the bonding bar

If insulating pieces are inserted into gas lines or water pipes, inside the structure to be protected they shall, with the agreement of the water and gas supplier, be bridged by ISGs designed for such an operation.

ISGs shall be tested according to the future IEC 62561-3 and shall have the following characteristics:

• /_imp> k_cI where k_cI is the lightning current flowing along the relevant part of the external LPS (see Annex C);

• rated impulse sparkover voltage t/_RIMP lower than the impulse withstand level of insulation between parts.

For external conductive parts, lightning equipotential bonding shall be established as near as possible to the point of entry into the structure to be protected.

Bonding conductors shall be capable of withstanding the part /_F of the lightning current flowing through them evaluated in accordance with Annex E of IEC 62305-1:2010.

If direct bonding is not acceptable, ISGs with the following characteristics shall be used:

ISGs shall be tested according to the future IEC 62561-3 and shall have the following characteristics:

• /_imp > /_F where /_F is the lightning current flowing along the considered external conductive part (see Annex E of IEC 62305-1:2010);

• the rated impulse sparkover voltage t/_R|_MP lower than the impulse withstand level of insulation between parts.

NOTE When equipotential bonding is required, but an LPS is not required, the earth-termination of the low- voltage electrical installation can be used for this purpose. IEC 62305-2 provides information on the conditions where an LPS is not required.

It is imperative that lightning equipotential bonding is installed in accordance with 6.2.2 a) and 6.2.2 b).

If cables of internal systems are screened or located in metal conduits, it may be sufficient to bond only these screens and conduits (see Annex B).

NOTE Bonding of screens and conduits may not avoid failure due to overvoltages of equipment connected to the cables. For protection of such equipment refer to IEC 62305-4.

If cables of internal systems are neither screened nor located in metal conduits, they shall be bonded via SPDs. In TN systems, PE and PEN conductors shall be bonded to the LPS directly or with an SPD.

Bonding conductors shall have the same current withstand as indicated in 6.2.2 for ISGs.

SPDs shall comply with IEC 61643-1 and IEC 61643-21 and shall have the following characteristics:

• tested with У, > k_cI where k_cI is the lightning current flowing along the relevant part of the external LPS (see Annex C);

• the protection level Up lower than the impulse withstand level of insulation between parts.

If protection of internal systems against surges is required, a coordinated SPD system conforming to the requirements of Clause 7 of IEC 62305-4:2010 shall be used.

Lightning equipotential bonding for electrical and telecommunication lines shall be installed in accordance with 6.2.3.

All the conductors of each line should be bonded directly or with an SPD. Live conductors shall only be bonded to the bonding bar via an SPD. In TN systems, PE or PEN conductors shall be bonded directly or via an SPD to the bonding bar.

If lines are screened or routed into metal conduits, these screens and conduits shall be bonded. Lightning equipotential bonding for conductors is not necessary, provided that the cross-section S_c of these screens or conduits is not lower than the minimum value S_CM|_N evaluated in accordance with Annex B.

Lightning equipotential bonding of the cable screens or of the conduits shall be performed near the point where they enter the structure.

Bonding conductors shall have the same current withstand as indicated in 6.2.3 for ISGs.

SPDs shall comply with IEC 61643-1 and IEC 61643-21 and shall have the following characteristics:

- tested with /_im > Ip where /_F is the lightning current flowing along the lines (see Annex E of IEC 62305-1:2010)

;- re selection level Up lower than the impulse withstand level of insulation betwee" cs".s

■ z'c'eotion against surges of internal systems connected to lines entering the st^ct-'e s 'ec- "ec a coordinated SPD system conforming to the requirements of Clause "

EC 52305-4:2010 shall be used.

SC"t Лrer equipotential bonding is required, but an LPS is not required, the earth-termira?c* o' fe =»- *o tage e ectrical installation can be used for this purpose. IEC 62305-2 provides information or t~e co-:-;-s л-е'е ar _PS is not required.

Electrical insulation between the air-termination or the down-conductor and the structural metal parts, the metal installations and the internal systems can be achieved by providing a separation distance, s, between the parts. The general equation for the calculation of s is given by:

(4)

where

A, depends on the selected class of LPS (see Table 10);

k_m depends on the electrical insulation material (see Table 11);

k_c depends on the (partial) lightning current flowing on the air-termination and the down-

conductor(see Table 12 and Annex C);

I is the length, in metres, along the air-termination and the down-conductor from the point, where the separation distance is to be considered, to the nearest equipotential bonding point or the earth termination (see E.6.3 of Annex E).

NOTE The length I along the air-termination can be disregarded in structures with continuous metal roof acting as natural air-termination system.

Table 10 - Isolation of external LPS - Values of coefficient k_t

Table 11 - Isolation of external LPS - Values of coefficient k_m

In the case of the lines or external conductive parts entering the structure, it is always necessary to ensure lightning equipotential bonding (by direct connection or connection by SPD) at their point of entry into the structure.

In structures with metallic or electrically continuous connected reinforced concrete framework a separation distance is not required.

The coefficient k_c of the lightning current amongst the air-terminations/down-conductors depends on the class of LPS, on the overall number n, on the position of the down­conductors, on the interconnecting ring conductors and on the type of earth-termination system. The necessary separation distance depends on the voltage drop of the shortest path from the point where the separation distance is to be considered, to the ground electrode or the nearest equipotential bonding point.

In typical structures for the application of Equation (4), the following conditions have to be considered:

k_c depends on the (partial) lightning current flowing on the down-conductor arrangement (see Table 12 and Annex C);

I is the vertical length, in metres, along the down-conductor, from the point where the separation distance is to be considered, to the nearest equipotential bonding point.

Table 12 - Isolation of external LPS - Approximated values of coefficient k_c

Further information on partitioning of the lightning current amongst down-conductors is given in Annex C.

NOTE The simplified approach usually leads to results being on the safe side.

In an LPS with a meshed air-termination system or interconnected ring conductors, the air­terminations or down-conductors have different values of current flowing down their lengths due to current division. In these cases a more accurate evaluation of the separation distance s may be performed by the following relationship:

^s = )Г^Х(^кс1 ^X/1 ^+/(c2 ^x/2 ⁺ - ^+/<cn^x/n) (5)

When the air-terminations or down-conductors have different values of current flowing down their lengths due to interconnecting ring conductors, Figures C.4 and C.5 apply.

NOTE 1 This approach is suitable for evaluation of the separation distance in very large structures or in structures with complex shape.

6. NOTE 2 For the calculation of the coefficients, k_c on the individual conductors numerical network programs may be used.Maintenance and inspection of an LPS

   1. General

The effectiveness of any LPS depends on its installation, maintenance, and testing methods used.

Inspections, testing and maintenance shall not be conducted during threat of thunderstorms.

NOTE Detailed information on the inspection and maintenance of LPS are provided in Clause E.7.

The objective of the inspections is to ascertain that

1. the LPS conforms to the design based on this standard,

2. all components of the LPS are in good condition and capable of performing their designed functions, and that there is no corrosion,

3. any recently added services or constructions are incorporated into the LPS.

Inspections should be made according to 7.2 as follows:

• during the construction of the structure, in order to check the embedded electrodes;

• after the installation of the LPS;

• periodically at such intervals as determined with regard to the nature of the structure to be protected, i.e. corrosion problems and the class of LPS;

NOTE For detailed information see Clause E.7.

• after alterations or repairs, or when it is known that the structure has been struck by lightning.

During the periodic inspection, it is particularly important to check the following:

• deterioration and corrosion of air-termination elements, conductors and connections;

• corrosion of earth electrodes;

• earthing resistance value for the earth-termination system;

• condition of connections, equipotential bonding and fixings.

Regular inspections are among the fundamental conditions for reliable maintenance of an LPS. The property owner shall be informed of all observed faults and they shall be repaired without delay.

6. Protection measures against injury to living beings due to touch and step voltages

   1. Protection measures against touch voltages

In certain conditions, the vicinity of the down-conductors of an LPS, may be hazardous to life even if the LPS has been designed and constructed according to the above-mentioned requirements.

The hazard is reduced to a tolerable level if one of the following conditions is fulfilled:

1. under normal operation conditions there are no persons within 3 m from the down­conductors;

2. a system of at least 10 down-conductors complying with 5.3.5 is employed;

3. the contact resistance of the surface layer of the soil, within 3 m of the down-conductor, is not less than 100 kQ.

NOTE A layer of insulating material, e.g. asphalt, of 5 cm thickness (or a layer of gravel 15 cm thick) generally reduces the hazard to a tolerable level.

If none of these conditions is fulfilled, protection measures shall be adopted against injury to living beings due to touch voltages as follows:

• insulation of the exposed down-conductor is provided giving a 100 kV, 1,2/50 ps impulse withstand voltage, e.g. at least 3 mm cross-linked polyethylene;

• physical restrictions and/or warning notices to minimize the probability of down-conductors being touched.

Protection measures shall conform to the relevant standards (see ISO 3864-1).

8.2 Protection measures against step voltages

In certain conditions, the vicinity of the down-conductors may be hazardous to life even if the LPS has been designed and constructed according to the above-mentioned rules.

The hazard is reduced to a tolerable level if one of the following conditions is fulfilled:

1. under normal operation conditions there are no persons within 3 m from the down­conductors;

2. a system of at least 10 down-conductors complying with 5.3.5 is employed;

3. the contact resistance of the surface layer of the soil, within 3 m of the down-conductor, is not less than 100 kQ.

NOTE A layer of insulating material, e.g. asphalt, of 5 cm thickness (or a layer of gravel 15 cm thick) generally reduces the hazard to a tolerable level.

If none of these conditions is fulfilled, protection measures shall be adopted against injury to living beings due to step voltages as follows:

• equipotentialization by means of a meshed earth-termination system;

• physical restrictions and/or warning notices to minimize the probability of access to the dangerous area, within 3 m of the down-conductor.

Protection measures shall conform to the relevant standards (see ISO 3864-1).Annex A

(normative)

Positioning the air-termination system

A.1 Positioning the air-termination system when utilizing the protection angle method

A.1.1 General

The position of the air-termination system is considered to be adequate if the structure to be protected is fully situated within the protected volume provided by the air-termination system.

For the determination of the volume protected only the real physical dimensions of the metal air-termination systems shall be considered.

A.1.2 Volume protected by a vertical rod air-termination system

The volume protected by a vertical rod is assumed to have the shape of a right circular cone with the vertex placed on the air-termination axis, semi-apex angle a, depending on the class of LPS, and on the height of the air-termination system as given in Table 2. Examples of the protected volume are given in Figures A.1 and A.2.

IEC 2649/10

Key

A tip of an air-termination rod

В reference plane

ОС radius of protected area

h₁ height of an air-termination rod above the reference plane of the area to be protected