Lightning Protection and Grounding

Planning and configuring lightning protection systems primarily is about keeping dangerous strikes of lightning specifically away from building structures, thus protecting them against damage or destruction.

Since microprocessor technology has entered our build-ings, it is no longer sufficient to keep strikes of lightning

“merely” away from building structures. It is equally impor-tant to protect technical installations in buildings against the effects of lightning current during its way through the lightning protection system.

Ground electrode

Besides its function to improve protective equipotential bonding, ground electrodes are an important element of lightning protection. The grounding system takes over the task to discharge the lightning current fed from the arrest-ers via the grounding system to the soil. The more low-ohmic the ground contact resistance can be made, the less installation parts or people in the vicinity are affected. If the grounding electrode and the equipotential bonding conductor are altogether conductively connected, they form an important protection system. Such a system can reduce the effects of faults between electrical and other mechanical, conductive equipment (e.g. gas and water sys-tems, central heating syssys-tems, electronic and IT systems).

9.3.1 Basics of Planning and Definitions

The basics of planning regarding concrete-footed ground electrodes are described in the DIN 18014 standard. In this standard, explanations on the most important terms relating to grounding systems can be found.

Ground

Part of the soil which is in electrical contact with a ground electrode and whose electric potential does not necessarily equal to zero.

Ground electrode

Conductive part which is embedded in the soil or in another conductive medium, e.g. concrete, which itself is in contact with the soil. The following ground electrodes are distinguished:

.

Buried ground rods which are driven vertically into the soil

.

Strip electrodes which are laid horizontally

.

Concrete-footed ground electrodes as a special

Owing to the humidity in the soil, ground electrodes run the risk of being destroyed by corrosion or by forming a galvanic cell with other metal parts. This must be taken into consideration when a material is selected.

Note: Piping networks of the public water supply used to be used as ground electrodes. According to

DIN VDE 0100-410, this is now forbidden.

Concrete-footed ground electrode

Conductive part which is buried in the concrete of a build-ing foundation, generally as a closed rbuild-ing.

Ring ground conductor

Conductive part which is buried in the soil or in the bed-ding as a closed ring and not insulated against the soil.

Grounding system

All electrical connections and appliances used for ground-ing a network, an installation or an item of equipment (e.g. mast foots, reinforcements, metal cable sheaths) and grounding conductors.

Grounding conductor

Conductor which makes a current path or part thereof between a given point in the network, an installation or an item of equipment and a ground electrode or the ground electrode network (e.g. the connection line between the equipotential bonding bar and the grounding system).

Connection part

An electrically conducting part of a concrete-footed ground electrode / ring ground conductor which enables it to be connected to other conductive parts, for example with

.

the equipotential bonding bar (main grounding busbar) for protective equipotential bonding

.

the down leads of a lightning protection system

.

other constructional parts made of metal

.

additional equipotential bonding bars.

Connection lug

Connecting conductor between a concrete-footed ground electrode and other conductive parts outside the foundation.

Connection plate (e.g. grounding fixpoint)

A electrically conducting constructive component buried in

9

Equipotential bonding

Interconnection of conductive parts providing equipoten-tial bonding between those parts.

Protective bonding conductor

Protective conductor provided for protective equipotential bonding.

Main grounding busbar

Connection point, terminal or busbar which is part of the grounding system and enables the electric connection of several conductors for grounding purposes.

Sealed tanking

A tanking made of bitumen or plastic, enclosing the build-ing from all sides in the area with earth contact (also called black tanking) or a construction made of water-imperme-able concrete (also called white tanking) as well as com-bined tankings (e.g. a foundation slab made of water-im-permeable concrete in combination with tanking on the basement walls.)

Perimeter insulation

Heat insulation which encloses the parts of the building with earth contact from outside.

Movement joint

Joint between two structural components which enables expansions, settlements and the like so that no damaging mechanical stress arises at these structural components.

9.3.2 Concrete-footed Ground Electrode

Functions of the concrete-footed ground electrode according to standards

.

Ground fault and protective conductor currents are conducted to earth (DIN VDE 0100-540,

IEC 60364-5-54)

.

Grounding system for external protection against lightning (DIN EN 62305-3, IEC 62305-3)

.

Effectivity increase of protective equipotential bonding (DIN VDE 0100-410, 60364-4-41)

.

Overvoltage protection (DIN VDE 0100-444, IEC 60364-4-444)

.

Protective grounding of antenna systems (DIN VDE 0855-300)

Concrete-footed ground electrode – design

Ground electrodes are part of the electrical installation behind the building's service entrance facility (service entrance box or equivalent provision). A connecting line must be laid from the concrete-footed ground electrode to the main grounding busbar which is usually laid in the service entrance equipment room. Additionally, lightning protection systems require terminations for the down conductors of external lightning protection at the

con-Concrete-footed ground electrodes must be placed in the outer foundations of the building as a closed ring. If there are foundation slabs, the concrete-footed ground electrode must be laid in the vicinity of the outer walls as a closed ring. The concrete-footed ground electrode must be in-stalled in the foundation slab in such a way that it is em-bedded in concrete at all sides. This protects it against corrosion, giving it a nearly endless service life. Ring ground conductors – as the name tells – are also ring-shaped, they must, however, be installed outside of foun-dations with no insulation against the soil. For larger build-ings, the concrete-footed ground electrode / ring ground conductor should be divided by cross-joints and the mesh width must not be greater than 20 m × 20 m. If concrete-footed ground electrodes / ring ground conductors are also used for protection against lightning, smaller mesh widths may possibly be required.

The connection lug of the concrete-footed ground electrode must be led out of the service entrance wall or niche. The length of the connection lug as of entrance into the room shall be a minimum of 1.5 m. In addition it must be en-sured that all connection parts have a low-ohmic continuity (guide value less than 1 Ω) among themselves and at the concrete-footed ground electrode or ring ground conductor.

Materials

The following materials can be used for concrete-footed ground electrode and connection parts in compliance with DIN 18014 (Table 93/1):

.

Round steel with a minimum diameter of 10 mm (galvanized or ungalvanized)

.

Strip steel, dimensions 30 mm × 3.5 mm (galvanized or ungalvanized)

.

Connection parts must be designed in durable corrosion-protected materials.

In addition, connection parts at concrete-footed ground electrodes must be made of hot-galvanized steel with additional plastic sheaths or of non-corroding stainless steel, material number 1.4571 or at least equivalent.

DIN 18014 intends the following materials for ring ground conductors and their connection parts:

.

Massive round steel with a minimum diameter of 10 mm (galvanized or ungalvanized)

.

Massive strip steel, dimensions 30 mm × 3.5 mm (galvanized or ungalvanized)

.

The material must be corrosion-proof, e.g. made of stainless special steel, material number 1.4571 or at least equivalent.

.

Hot-galvanized material is not permissible in this case If the concrete-footed ground electrode is part of the lightning protection system, materials must be selected in

9

9.3.3 Ground electrodes outside foundations

A ring ground conductor is required in buildings for which heat insulation measures or provisions against the ingress of water are provided in the basement; this conductor must be laid below the foundation without insulation against the soil.

.

Perimeter insulation at the enclosing walls: A mesh width of 20 m × 20 m is sufficient for the concrete-footed ground electrode, since sufficient non-insulation against the soil is provided here.

.

Perimeter insulation on the walls and below the foundation slab: When lightning strikes, there must be no flashover from the foundation through the insulation to the grounding system. Therefore, a maximum mesh width of 10 m × 10 m must be provided.

Responsibility for installation

The concrete-footed ground electrode is part of the electri-cal installation. The developer / owner or architect has to

initiate its installation. As early as in the tendering process for construction work on the shell, the concrete-footed ground electrode must be considered. Concrete-footed ground electrodes must be erected by an electrically skilled person or a person skilled in construction.

Further standards to be considered for concrete-footed ground electrodes

For buildings with special requirements, e.g. with exten-sive IT systems: DIN EN 50310 (VDE0800-2-310)

.

For power installations above 1 kV: DIN VDE 0101

.

Corrosion protection of ground electrodes:

DIN VDE 0151

.

Documentation

In compliance with the new standard DIN 18014:2007-09 the grounding system must be documented. This includes plans, photographs and measurement results.

Material Form

Minimum dimensions¹⁾

Comments Ground rod Ground

conductor Ground plate

Copper

Rope ²⁾ 50 mm² Minimum diameter per single wire 1.7 mm

Round ²⁾ 50 mm² 8 mm diameter

Strip ²⁾ 50 mm² Minimum thickness 2 mm

Round 15 mm ø

Pipe 20 mm ø Minimum wall thickness 2 mm

Massive plate 500 mm × 500 mm Minimum thickness 2 mm

Grid plate ⁸⁾ 600 mm × 600 mm 25 mm × 2 mm for flat material and 8 mm

diameter for round material

Steel

Galvanized round ³⁾ 16 mm ø ⁴⁾ 10 mm ø

Galvanized pipe ³⁾ 25 mm ø ⁴⁾ Minimum wall thickness 2 mm

Galvanized strip ³⁾ 90 mm² Minimum thickness 3 mm

Galvanized plate ³⁾ 500 mm × 500 mm Minimum thickness 3 mm

Galvanized grid plate ³⁾ 600 mm × 600 mm 30 mm × 3 mm for flat material and

10 mm diameter for round material

Coppered round ⁵⁾ 14 mm ø ⁴⁾ Minimum 250 μm layer with 99.9 %

copper content

Bare round ⁶⁾ 10 mm ø

Bare or galvanized strip ^6),7) 75 mm² Minimum thickness 3 mm

Galvanized rope ^6),7) 70 mm² Minimum diameter per single wire 1.7 mm

Galvanized cross profile ³⁾ 50 mm × 50 mm

× 3 mm Stainless

steel

Round 16 mm ø 10 mm ø

Strip 100 mm² Minimum thickness 2 mm

1) Permitted tolerance – 3 % 2) Can also be tin-plated

3) The coating must be smooth, continuous and free from fluxing agent and have a minimum weight of 350 g/m² for massive round material and 500 g/m² for massive flat material. In compliance with EN ISO 1460, coating can be measured using a sample which is about 200 mm long.

4) Threads must be applied prior to coating.

5) Copper must have a self-adhesion on the steel. Coating can be measured using a electronic paint inspection gauge.

9

9.4 Integration of Regenerative

In document SIEMENS Application Manual Part 1 - Basic Data and Preliminary Planning (Page 173-176)