27.10.15 , , ,
Usually we publish the actual calculations of grounding and lightning protection for the objects, which are located on firm ground: loam, clay loam, stone, sand and so forth. And what about the restaurants, cafes and other entertainment and residential establishments, located on the water? Is grounding necessary for such objects? And if it is, then how to make it? The question is interesting and we decided not to wait for a customer or designer to ask us to carry out a similar calculation. We imagined such a facility ourselves and made calculation of grounding for it, which can be used as a guide. I am pleased to share it with you!
Firstly, it is worth saying a few words about why grounding is really necessary. Nowadays, any structure, be it a restaurant, a shop, a house, a residential house or any other object, are full of lots of electrical equipment, with which a person is in contact one way or another. And the fact that the site is on the water, it is possible to talk about the availability of additional specialized equipment (pumps, clean-up systems, etc). Such "epicenters" of power networks are particularly vulnerable to the risk of fire and equipment failure. To avoid this, you need to take care of "health" of electric wiring and individual equipment in advance. For that, it is necessary to arrange a reliable grounding, which directly affects the quality and stable performance of everything described above. We hope that our guide will help you with the calculations and the design of grounding for such objects.
The object of the protective grounding installation is a restaurant on the water. Screw piles 4.5 m long and 0.133 m in diameter are the foundation. The length of a pile, submerged in the sand - 3 meters, in the water - 1 m.; the total estimated length of the pile is 4 m.
Screw piles of the foundation of the restaurant are used as ground electrodes of protective grounding. The resistivity of strongly humidified sand, into which the piles are submerged, is taken equal to 50 Ohm * m, water resistance of the plain river is taken equal to 50 Ohm * m according to the reference da
In accordance with the EIC p. 1.7.103 the total resistance of spreading of ground electrodes (including natural) of all repeated groundings of the PEN conductor of every overhead transmission line at any time of the year should be not more than 10 ohms, respectively, with line voltages of 380 V of a three-phase power source or 220 V of a single-phase power source.
The set of measures to ensure the necessary requirements for the grounding device is represented by the following decisions:
- Interconnection of 20 foundation piles of the restaurant by a stainless steel copper tape with the cross section of 30x4 mm. The connection is made by welding. Screw piles are 4.5 m long and 0.133 m in diameter. The length of a pile, submerged in the sand - 3 meters, in the water - 1 m.; the total estimated length of the pile is 4 m.
- Interconnection of piles may be made not in the water, that is why the resistance of spreading from the tape is not considered.
Calculation of resistance of a grounding device:
1) Pile resistance:
Where ρ - soil resistivity, Ohm*m;
Lсв. - Pile length, m.
β - Reinforcement cage ratio;
dсв. - pile diameter, m.
2) The impedance of the grounding device:
Where n - the number of ground electrodes;
kисп - Utilization ratio;
The design resistance of the grounding device is 2.68 ohms, which is less than the required impedance of 10 Ohm.
The layout chart of ground electrodes:
Условные обозначения - notions
Винтовая свая длиной 4,5 м, диаметром 133 мм – crew pile 4,5 m long, 133 mm in diameter
Коррозионностойкая полоса – corrosion-resistance tape
The list of required materials:
In this case, the use of separate vertical or horizontal ground electrodes is not required. For the organization of grounding at the site, a tape is enough. The material of the tape will ensure reliable operation of the whole grounding for many years.
Dear friends! If you have questions about how to properly calculate grounding or lightning protection for your property, please send us these questions and we will surely answer them!