Medical centers are equipped with precise and highly sensitive equipment that needs the toughest support and protection means for their good operations. These means include providing power supply system that meets all factors affecting the power quality, such as no voltage imbalance, harmonic distortions, electromagnetic compatibility, etc., as well as power supply system protection against surges.
A measure to implement the support and protective function for the medical equipment is a properly organized functional and protective grounding. According to the HEALTHCARE INSTITUTION DESIGN GUIDELINES to SNiP 2.08.02-89, an independent operational grounding with the allowed resistance not more than 2 Ohm shall be provided. It is especially difficult to achieve such resistance in high-resistance soil, such as gravel, with the resistivity reaching 1,000 Ohm∙m. However, efficient grounding means exist today, which allow providing the grounding arrangement with the resistance 2 Ohm. The electrolytic grounding provides a larger contact area of the grounding arrangement with the soil significantly reducing resistance, and preserves the desired resistance level even in winter, when the soil is frozen.
Let's consider the example of calculation of a grounding arrangement with the resistance 2 Ohm which was made by the ZANDZ.com Technical Center for a medical center in Samara Region.
Grounding is made in accordance with the EIC, Rev. 7, Chapter 1.7. Grounding arrangement should be provided with a resistance not exceeding 2 Ohm.
According to the customer's information, soil is represented by gravel and construction debris. The estimated soil resistivity is taken to be 1000 Ohm ∙ m.
Warning! In case the Customer provided erroneous and limited soil data, the above calculation of a grounding arrangement is considered incorrect. If the soil resistivity differs from the calculated one, it is necessary to perform computations with a real value. If rated resistance of the grounding arrangement is exceeded, the design corrections shall be introduced.
A set of measures to ensure the requirements for the grounding arrangement is based on the following solutions:
- To provide the rated resistance of the grounding device, electrolytic grounding ZANDZ ZZ-100-102-6МВ is proposed for use;
- 23 sets of 6 m vertical electrolytic grounding, ZANDZ ZZ 100 102-6МВ, combined by a horizontal ground terminal made of corrosion-resistant steel copper plated bar 4 x 30 mm (ZZ-11075);
- the sets were placed at a distance of 6 meters with a parallel arrangement to achieve the acceptable utilization rate and an optimal volume of electrolyte distribution in the soil;
- the ground terminals are connected using clamps ZZ-005-064.
Grounding arrangement resistance calculation
Resistance of set ZZ-100-102-6МВ:
Верт - Vert
where in C is a dimensionless ratio describing the electrolyte content in the surrounding soil;
Lvert is ground terminal, m;
d is ground terminal diameter, m;
ρ is soil resistivity, Ohm·m.
Resistance of a horizontal electrode:
Гор - Hor
where ρ is soil resistivity, Ohm*m;
b is horizontal electrode width, m;
h is horizontal electrode depth, m;
Lhor is horizontal electrode length, m.
Electrical impedance of the grounding arrangement:
ЗУ - GA Исп гр - Util
where n is number of sets;
kutil is utilization ratio;
Estimate resistance of the grounding arrangement is 1.97 Ohm, which is less than the required value 2 Ohm.
Grounding arrangement diagram for a medical center
Условные обозначения: - Legend:
- горизонтальный заземлитель - horizontal grounding terminal
- комплект электролитического заземления - electrolytic grounding set
- зажим для подключения проводника - clamp for connecting conductors
List of required materials
|Item No.||Fig.||Part number||Product||Amount|
|1||ZZ-100-102-6МВ||ZANDZ Electrolytic grounding kit (vertical; 6 meters)||23|
|2||ZZ-11075-50||ZANDZ Copper-plated bar (30 x 4 mm)||3|
|3||ZZ-005-064||ZANDZ Clamp for connecting conductors (up to 40 mm)||25|
|4||ZZ-007-030||ZANDZ Waterproofing tape||9|
Do you have any questions regarding lightning protection for the cadet school or other facilities? Please, contact the ZANDZ Technical Center!