Not all owners of private homes know that sometimes when choosing a lightning protection system for a home, it is not necessary to install lightning rods on the roof. If conditions allow, you can consider another, not the most common, but quite effective way to organize a lightning protection system.
Recently, one of our clients asked the question: “How will the 25-meter-tall trees growing next to me affect my house protection (it is 6 m high) if I install lightning rods on the roof of the house?
Our answer: “In your case, the trees significantly exceed the height of the house, so they can become part of the lightning protection system! According to the current standards, it will only be necessary to install down conductors on the trunks and ground them.”
Let's take a closer look at the technical solution for this problem, which was prepared by the specialists of the ZANDZ Technical Center.
- object - single-family house;
- dimensions of the house: 15x15 m;
- height of the walls: 4 m;
- ridge height: 6 m;
- type of roof: four-pitched;
- the distance from the house to the trees (2 pcs.) - 10 m;
- distance between trees - 3 m;
- tree height - 25 m.
- it is necessary to calculate the probability of a lightning breakthrough into the system using trees as lightning rods;
- calculate grounding device.
The private house belongs to the "ordinary" objects, in accordance with IS 153-34.21.122-2003 and to category III according to AD 34.21.122-87. Required system reliability — not less than 0.9.
As per EIC-7,par.1.7.103the total spreading resistance of the ground electrodes (including natural) of all the repeated groundings of the PEN conductor in each overhead line at any time of the year must not exceed 10 ohms at the line voltage of 380 V for a three-phase power supply or 220 V for a single-phase power source.
AD 34.21.122-87, paragraph 2.30 states: “Small buildings with non-metallic roofs located in rural areas shall be protected from direct lightning strikes in one of the simplified ways:
a) if there are trees at the distance of 3-10 m from the structure and the trees are twice or even more higher, taking into account all the objects protruding on the roof (chimneys, antennas, etc.), a down conductor must be laid along the trunk of the nearest tree the upper end of which protrudes at least 0.2 m above the crown of the tree. The down conductor must be connected to the ground electrode at the bottom of the tree”.
Calculation of the grounding device:
The design resistance of a grounding device is 7,85 Ohms, which is less than the required resistance of 10 Ohm.
Results of the calculation carried out with the software developed by the OJSC "Energy Institute to the name of G.M. Krzhizhanovsky (JSC "ENIN"):
Density of lightning strikes into the ground - 4 strikes / sq. km per year
The total number of strikes into the system is - 0.085 (once in 128 years);
The total number of breakthroughs is 0.0025 (once every 400 years)
Reliability of a lightning protection system using trees - 0,97
Probability of a breakthrough into all the system objects - 0.03.
Location of equipment is shown in figure 1.
Figure 1 - Location of equipment.
Условные обозначения – Type Codes
Проволока стальная оцинкованная – Galvanized steel tape
Полоса стальная оцинкованная сечением – Galvanized steel tape with the cross-section of 40*4 mm
Вертикальный заземлитель - Vertical ground electrode
The list of equipment and required materials is given in Table 1
Table 1 - List of need in materials.
|№||Figure||Product item||Name||Quantity, pcs.|
|1.||ZZ-502-404-38||ZANDZ Copper-bonded steel tape (40*4 mm; coil of 38,5 m)||1|
|2.||ZZ-001-065||ZANDZ Copper-bonded threaded grounding rod (D14; 1.5 m)||4|
|3.||ZZ-002-061||ZANDZ Threaded coupler||3|
|4.||ZZ-003-061||ZANDZ Starting tip||2|
|5.||ZZ-004-060||ZANDZ Driving head for a jackhammer||1|
|6.||ZZ-005-064||ZANDZ Clamp for connecting conductors (up to 40 mm)||5|
|7.||ZZ-006-000||ZANDZ Conductive grease||1|
|8.||ZZ-007-030||ZANDZ Waterproof tape||1|
|9.||ZZ-008-000||ZANDZ Header for a jackhammer (SDS max)||1|
|10.||ZZ-502-008-62||ZANDZ steel galvanized tape (D 8 mm / S 50 mm²; coil of 62,5m)||1|
|11.||GL-11551A||GALMAR Clamp for connecting down conductors (painted galvanized||5|
|12.||GL-11703A||GALMAR Clamp for fixing down conductor (painted galvanized steel)||60|
Do you have questions or do you need to calculate a grounding device or lightning protection system for a single-family house? Send your request to email@example.com.
Video: Can a tall tree replace a lightning rod in a single-family house?