Lightning protection of medical establishments is an integral part of electro and fire-security. It is important to note that when designing lightning protection of hospital complexes it is necessary to protect all the objects included into this complex.
Recently, the ZANDZ Technical Center received a request for the development of lightning protection system for a hospital complex of 12 buildings. We will study the solution for the main building, which was offered by our specialists.
- object: main building of a hospital complex;
- sizes: 48m x 22m x 8.9 m;
- ridge height: 10,1 m;
- the power supply is fed along overhead lines;
- soil resistivity - 100 Ohm * m.
Calculate external lightning protection and grounding system for the main building of a hospital complex.
Lightning protection and grounding of a hospital complex are performed in accordance with:
- Electrical Installation Code EIC 7th ed., hereinafter - EIC;
- IS 153-34.21.122-2003 "Instructions for lightning protection of buildings, structures and industrial communications", hereinafter IS;
- AD 34.21.122-87 "Manual on arrangement of lightning protection of buildings and structures", hereinafter AD.
The object refers to III category of lightning protection in accordance with AD and to "ordinary" in accordance with IS. Required lightning protection system reliability – at least 0.9.
According to EIC-7, p. 1.7.103. The total speading resistance of the ground electrodes (including natural) of all repeated groundings of the PEN conductor of each overhead line at any time of the year should not exceed 10 ohms at line voltage of 380 V of the three-phase power supply or 220 V of a single-phase power source.
The set of measures on the provision of required lightning protection measures to lightning protection and grounding systems for a hospital complex is presented by the following solutions:
Lightning protection is carried out with the help of air terminals masts 4,7 m high (GL-21104G) which are installed on the walls of bay windows (distance for installation - up to 1 m) and ridge lightning rod 2 m high (GL-11521SS).
Copper-bonded steel wire is used as down conductor (thickness of the copper coating not less than 70 mcm), d8mm wire (GL-11149).
To connect rolled metal over the length and in the nodes, a universal clamp GL-11551A is used.
Copper-coated steel electrodes 3 m long are used in places of downdrops as a vertical ground electrodes. Copper-bonded steel tape with the cross-section of 30x4 mm (GL-11075) uniting all vertical electrodes is used as a horizontal ground electrode system. The distance to the object foundation- not less than 1 m. Burial depth of the tape 0,5 - 0,7 m.
In accordance with the EIC-7 ed., P.1.7.55 - Grounding devices for protective grounding of electrical installations of buildings and structures and lightning protection of the 2nd and 3rd categories of these buildings and structures, as a rule, should be common.
If there are metal reinforce concrete framings, they must be connected to down conductors/ grounding device.
Connection to the grounding device is carried out with the help of clamps ZZ-005-064.
The density of lightning strikes into the ground - 4 strikes / sq. km per year;
The total number of strikes into the system in: 0.039 (once in 26 years);
The total number of breakthroughs (strikes directly into the object passing lightning rods) - 0.0037 (once in 270 years).
System reliability – 0,906.
Grounding device resistance calculation:
The design resistance of the grounding device is 6,58 Ohm, which is less than the required resistance of 10 Ohm.
Location of equipment is shown in figure 1.
Figure 1 - Arrangement of lightning protection and grounding equipment of the main building of a hospital complex.
The list of equipment is given in Table 1.
Table 1 - Materials requirement list.
Do you have questions or you need to calculate lightning protection and grounding for a hospital complex? Send your request to firstname.lastname@example.org.