Application Note Earthing and lightning protection tests with MI 3155 A hospital is generally a complex of buildings huddled together, often evolved rather than planned. Constructing, maintaining and testing grounding protection in such an environment is a worthy challenge. The system is complex and filled with redundancy, designed for power reliability and safety of the users. Lightning protection and earthing systems Hospital as a complex is generally a TT earthing system when viewed from the outside. They often have internal transformer substation where earthing for the whole complex is constructed. This system has a particularly low earth impedance. The solution is simpler for earthing electrode maintenance and earth resistance measurements. On the other hand, each building could have its own connection to earth. This can lower interference through earth for sensitive instruments, but it also has higher resistance and makes maintenance more complex with many locations to cover. Courtyards and other open spaces have to be kept on an equalized potential to prevent step voltage hazard in case of a large fault or a lightning strike. Earth electrode should be a wide underground device like a loop, mesh or a plane with multiple parallel connections to it. There should be a lattice of conductors throughout the foundations with its own way to earth, keeping the base potential of each building constant. The ground electrode is usually a loop or a mesh and covers most of the area under the building. Lightning protection design depends on the roof of the buildings’ and grounds shape. Inside, the critical rooms must have full Faraday cage protection both to limit the disturbances and to keep them safe from overvoltage. Machines like MRI are very

sensitive to electromagnetic radiation that other devices, like RTG, can produce. Designer has to keep that in mind. Operating theatres have their own insulated networks that need to be grounded as a whole. Lightning strike is a very extreme case for the installation. There is no absolutely guaranteed protection, only some measures that can help limit the damage. System of heavy conductors leading directly to the ground is the main one, but it cannot prevent voltages inducing anywhere in the installation or side flashes from one conductor to the other. Similar effects can be caused by lightning...

electrode would be 100 m and to C electrode 200 m from the electrical centre of the object, which is not always known. In urban areas, it is not common to have this much space available. 2 clamps method Methods with clamps are much quicker and easier to perform. They do not require disconnecting the earth electrode or special instruments, only a current clamp and a current generator. Current is injected into the earthing leg as close to the electrode as possible. A voltage-inducing clamp can be used, or any kind of connector that can be applied to the wire without disconnecting it. The measurement...

2-clamp method A pair of clamps is also a part of the standard set for MI 3155. They are mainly different in connectors: A 1018 has integrated test wire for connection to the instrument, and A 1019 has connectors for standard test leads. The only settable parameter is maximum acceptable resistance for pass/fail indication. The measurement is entirely automatic, and it is not important which clamp comes top or bottom. Use the threewire test lead and insert it into the test connector on the top of the instrument. Connect the banana connectors one on top of the other and insert into the clamp. Use...