Any healthcare institution requires a high-quality lightning protection and grounding systems. If a hospital is equipped with a high-precision equipment such as a mammography machine, then the systems providing safety should be designed more thoroughly.
To provide lightning protection of the hospital with the mammography machine considered herein, a lightning grid is used that is installed on a high-rise building. The lightning protection of a single-story part is made through several low-rise lightning rods, while the remaining area is covered by a protection zone created by the high-rise building.
The resistance of the grounding device of the mammography machine should be as low as possible; the preferred value is 1 Ohm. A functional grounding with this resistance will be sufficient to provide safe functioning of all the remaining hospital equipment.
Let's study the design of the lightning protection and grounding for the hospital with the mammography machine in more details.
Task
To perform calculations of the lightning protection and grounding system for the hospital with the mammography machine.
Solution
Calculations of the hospital lightning protection are made in conformity with the following documents:
- "Electrical Installations Code" (hereinafter referred to as the EIC), 7th edition.
- "Instructions for the installation of lightning protection of buildings, structures, and industrial communications" SO 153-34.21.122-2003 (hereinafter referred to as SO).
- "Instructions for mounting the lightning protection of buildings and structures" Working Documentation 34.21.122-87 (hereinafter referred to as the RD).
The lightning arresters are used to protect the hospital against lightning strikes. Lightning discharger consists of an interception rod, intercepting a lightning discharge, the main conductor cable, and the ground electrode. All these elements let us divert lightning current into the ground safely, without any damage to the protected facility.
The hospital belongs to conventional facilities in terms of lightning protection according to SO and to Category 3 according to RD.
Description of the lightning protection system for the hospital with the mammography machine
A set of arrangements ensuring compliance with the lightning protection requirements is based on the following solutions:
- The facility's lightning protection is made as a lightning grid using a steel zinc-coated wire having diameter 8 mm, which is installed with the step not more than 12 x 12 m. The grid is made such that the current would have at least two different paths to the grounding arrangement.
- The grid is not installed on a low-rise building. It is protected by the high-rise building being a natural lightning arrester, and 6 lightning rods 1.5 m high installed on the wall (it is taken into account that 0.5 m of the rod length is used for securing).
- The main conductor cables are mounted (installation step 0.6-1 m):
- to the walls using clamps GL-11703A;
- to the roof using clamps GL-11711.
- Multifunctional clamp GL-11551A is used to connect rolled products over the length and in assemblies.
A set of measures to ensure the requirements for the grounding arrangement is based on the following solutions:
- Installation of a grounding arrangement consisting of a horizontal electrode (steel zinc-plated bar with cross-section 4 x 30 mm), depth 0.5 meter, laid as a circuit around the building.
- As per clause 2.13 WR, only a circuit, without the installation of vertical electrodes is considered as sufficient.
- The horizontal electrodes are connected to each other using clamp ZZ-005-064.
- The connection of the current collector with the terminal of the zinc-plated ground bar is performed using control clamp GL-11562A.
- The design of the grounding arrangement corresponds to clause 1.7.55 of EIC Grounding arrangements for protective grounding and grounding for lightning discharges are common.
The location of the elements of the lightning protection system and the grounding arrangement is shown in Figure 1. The depicted protection area corresponds to area B, constructed as per Appendix 3 of WD.
Picture 1. Layout of the lightning protection elements and ground electrode of the hospital a with mammography machine
Calculation of the grounding arrangement for the mammography machine
The estimated soil resistivity is taken to be 90 Ohm ∙ m.
The calculation is made using formulas provided in the Grounding Calculation page.
The calculation formulas with the completed data are shown below.
Estimated resistance of the grounding arrangement is 0.98 Ohm, which is less than the required value of 1 Ohm.
Components for lightning protection and grounding for a hospital with the mammography machine
| № | Part number | Name | Quantity, pcs. |
| Lightning protection system | |||
| 1. | GL-21134 | GALMAR Interception rod tower (1.5 meters; for vertical surfaces; galvanized steel) | 6 |
| 2. | ZZ-502-008-125 | ZANDZ Galvanized steel wire (D 8 mm/ S 50 mm²; wire bundle 125 m) | 6 |
| 3. | GL-11551A | GALMAR Terminal for main conductors connection (painted galvanized steel) | 30 |
| 4. | GL-11711 | GALMAR Flat roof terminal for the main conductor cable (D8 mm; plastic, concrete) | 370 |
| 5. | GL-11703A | GALMAR Terminal for fastening the main conductor cable with elevation (15 mm height; galvanized steel with painting) to the facade/wall | 320 |
| 6. | GL-11562A | GALMAR Control terminal wire + strip (painted galvanized steel) for main conductors connection | 9 |
| Grounding arrangement | |||
| 7. | ZZ-005-064 | ZANDZ Conductor connection terminal (up to 40 mm) | 15 |
| 8. | ZZ-502-304-52 | ZANDZ Galvanized steel strip (30 * 4 mm; 52 m-bundle) | 6 |
| 9. | ZZ-007-030 | ZANDZ Waterproofing tape | 5 |
Do you have questions regarding lightning protection and grounding of the hospital with the mammography machine? Please, contact the ZANDZ Technical Center!
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