【正文】 through two thorough fares of earth body and human body at the same time in earth, I =IL + IP, we know: In a parallel circuit, the electric current value of passing each branch road is in inverse proportion to size of the resistance.In the type: I Electric current total value in the earth return circuitIL Electric current flowing through along the earth body IP Flow through electric current of the human body　Have type can find out earth resistance little , flow through to little electric current have human body, human resistance usually is it ground than earth resistance through electric current of human body electric current of body have several hundred less flowing through too to have several hundred heavier. When earth resistance is extremely small, the electric current that remakable body flows nearly equals zero. Namely I≈IL. In fact, because earth resistance very little, earth short out electric current flow out of date produce press and lower very lightly, so equipment outer cover voltage in earth high. People stand while going to touch the outer cover of the equipment on the earth, the voltage that the human body bears is very low, it can not be dangerous.　Is it protect earth device and reduce earth resistance of it to install additional , not only ensure the electric security of system of intelligent building, the effective measure operated effectively, it is not the essential means of equipment and personal security in the intelligent building that ensure too. current is grounded: In a block of intelligent building , include a large number of puters , munication apparatus and automation equipment of building with puter. Importing to information in these electronic equipment, transmission information, change energy , amplify signal, logic movement, output information a series of course go on through little electric potential or little electric current fast, and will often carry on the work through the internet between the equipment. So in order to make its accuracy high, the stability is good, besides needing to have a steady power supply power, must also possess a steady basic electric potential . Can adopt bigger and sectionaller insulating copper core line as the lead wire , one end is connected with basic electric potential directly, another end support electronic equipment direct current earth. It is unsuitable to connect with PE line to deserve and go between , forbid connecting with N line. shielding earth defend static earth: In the intelligent building, it is very important to design electromagnetic and patibly, in order to avoid the dysfunctions of the equipment used, equipment can appear evenned to prevent from damage, form equipment of wiring system should can prevent inside oneself conduct and extraneous interference from. Or because of the coupling phenomenon between the wire in these production that interfere, or because of the electric capacity effect or inductance effect. Main source its superelevation voltage, highpower pieces of radio magnetic field, strike by lightning naturally and static discharge. Phenomenon these will is it send or receive very high to transmit equipment of frequency produce heavy interference very to used for designing. Is it must take the protective measure to equipment the to connect up , avoid the interference from various kinds of respects. Shielding and correct earth to prevent electromagnetic best protection method that interfere. Can connect the equipment outer cover with PE line 。t connect with PE line either.　In highpressure system , adopt neutral some person who connects place can make earth relay protection accurate movement and dispel singlephase electric arc earth overvoltage. Can prevent the skew of voltage of zero preface , keep the threephase voltage in a basic balance in some neutral earth, this is very meaningful to lowvoltage system, can be convenient to use the singlephase power. protection is grounded: Safe protection earth metal part and earth body with electricity make good metal join electric equipment. Namely power consuming equipment and some metal ponents near the equipment of building, join with PE thread, but forbid connecting PE line with N line.t with other earth system, such as direct current earth, shielding earth, defend static earth is it is it connect to mix to wait for。Job earth mean voltage transformer neutral a bit or neutral line (N line ) earth mainly. N line must spend copper core insulating line. There is wiring end son of the electric potential such as being auxiliary in the distribution , wait for the wiring end son of the electric potential generally in the case cupboard. Must notice , should wire the end son and can expose ?！here are a large amount of electronic equipment and wiring system in the intelligent building, such as the munication automated system, the fire reports to the police and fire control link the control system , the automated system of the building , monitoring systems of security personnel, office automated system, the closedcircuit TV system,etc., and their corresponding wiring system. By the look of building built, the roof of every storey in the building, the baseplate, the side wall, hang and is nearly covered with by various