What is the contact voltage? -Solutions - Huaqiang Electronic Network

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When the electrical device M is damaged and the case is short-circuited, the short-circuit current flowing through the ground electrode is Id. For example, the grounding resistance force Rd of the grounding pole, the grounding voltage Ud = Id·Rd generated at the grounding pole, usually called Ud is the fault voltage, and the corresponding potential distribution curve is the curve C in Fig. 2. In general, the impedance of the ground line can be ignored, and the potential presented on M is Ud. When the person is in the divergence zone, the curve C shows that the ground potential of the person is Uφ. At this time, if a person touches M, the fault voltage Ut = Ud - Uφ generated by the contact. The person stands on the ground, and the shoes, socks and ground resistance of one foot are Rp, when the person touches M. The two legs are connected in parallel and their combined resistance is Rp/2. Under the action of Ut, Rp/2 is connected in series with the human body resistance RB, and the current flowing through the human body is IB = Uf/(RB+Rp/2), and the voltage that the human body is subjected to is Ut = IB·RB = Uf · RB / (RB +Rp/2). When the insulation of the electrical device is damaged, the contact voltage Ut between the hand touching the electrical device and the foot touching the ground is related to the distance between the M and the ground. It can be seen from Fig. 2 that when M is closer to the grounding pole, the larger Uφ is, the smaller Uf is, and the smaller Ut is. When the person is outside the range of the divergent zone, Uφ = 0, Uf = Ud, Ut = Ud·RB/(RB+Rp /2), and Ut is the maximum value. Since the position in which the person stands in the scatter zone is related to Uφ, the contact voltage is usually calculated by standing at a distance of 0.8 m from the horizontal direction of the electric device and 1.8 m in the vertical direction of the hand contacting the electric device. If the electrical device is outside the dying zone, the above horizontal and vertical distances need not be taken into account when calculating the contact voltage Ut.