Touch Current Basics.ppt - ifmqs.com.au

1 Touch Current Basicsprepared for CTL PTPW orkshop May 2010 Ronald VaickauskiSenior Staff EngineerUnderwriters Laboratories Response-Electric Shock Charles F. Dalziel,University of California Berkeley W. E Hart, Fluke Corp.,IEC 66E CommitteePerception/Reaction FindingsIEC TR 60479-5:2007 Table 1 Let-Go FindingsIEC TR 60479-5:2007 Table 1 Values for Current are in FibrillationIEC TR 60479-5:2007 Table 1 Current is in Touch Current NetworkIEC 60990:1999 Figure 3 Threshold of PerceptionFigure 1 of IEC TS 60479-2:2007 Perception/Reaction NetworkIEC 60990:1999 Figure 4 Let-Go NetworkIEC 60990:1999 Figure 5 Calculated Impedance Perception/Reaction NetworkIEC 60990:1999 Table of NetworkIEC 60990.

2 1999 Table Range of Design and Calibration Frequency of Touch Current 50 and 60 Hertz Sinusoidal Electronic circuitry Non-Sinusoidal wave forms Fourier expansion Higher frequency componentsReferences IEC 60990:1999, Methods of measurement of Touch Current and protective conductor Current IEC/TR 60479-5:2007, Touch voltage threshold values for physiological effects IEC/TS 60479-1:2005, Effects of Current on human beings and livestock-Part 1: General aspects Measuring Touch Current Resolving the Controversy About Peak versus RMS; Hart, ,Perkins, , Skuggevig, W., Response-Electric Shock:Charles F.

3 Dalziel, a professor of electrical engineering at the University of California Berkley, did research on human response to electric shock and wrote a book, The Effect of Electric Shock on Man. Much of the requirements in place for Touch Current are based on his major contributor was Walter E. Hart, Fluke Corporation who was a member of the IEC 66E committee and IEC TC 74 Working Group F. Dalziel, a professor of electrical engineering at the University of California Berkley, did research on human response to electric shock and wrote a book, The Effect of Electric Shock on Man.

4 Much of the requirements in place Another major contributor was Walter E. Hart, Fluke Corporation who was a member of the IEC 66E committee and IEC TC 74 Working Group Findings:Perception/reaction Current flowing through the body is just enough to cause involuntary muscular contraction to the person through which it is flowing3 Perception/reaction Current flowing through the body is just enough to cause involuntary muscular contraction to the person through which it is flowingLet-Go Findings:Let-Go Current flowing through the body is just enough to cause involuntary contraction of a muscle, such as inability to let gofrom an flowing through the body is just enough to cause involuntary contraction of a muscle, such as inability to let goVentricular Fibrillation:Ventricular fibrillation Current flowing through the body is just enough to cause ventricular fibrillation of the heart.

5 Human heart is in danger of failure to function. 5current flowing through the body is just enough to cause ventricular fibrillation of the heart. Ventricular fibrillation is where the human heart is in danger of failure to function. Elementary Touch Current Network:The three component combination of the 500 parallel combination of the 1500 resistor and the body impedance model. It represents handelectrical impedance of a person touching a conductive part. The 1500 resistor in parallel with the F capacitor represents the combined impedance of the entry and exit skin contacts (wet skin, not immersed) with a conductive surface of equipment and ground, or with two equipment contacts.

6 The 500 resistor represents the internal body resistance, less the skin, and serves as the Current -sensing resistor in the measuring circuit since all of the Current that flows through the body impedance model flows through this three component combination of the 500 resistor in series with the resistor and F capacitor comprises the body impedance model. It represents hand-to-hand or hand-to-feet electrical impedance of a person touching a conductive part. The 1500 F capacitor represents the combined impedance of the entry and exit skin contacts (wet skin, not immersed) with a conductive surface of equipment and ground, or with two equipment resistor represents the internal body resistance, less the sensing resistor in the measuring circuit since all of the Current that flows through the body impedance model flows Threshold of Perception:The human bodies response to Touch Current varies with frequency.

7 The threshold of perception increases with frequency. The graph shown is figure 1 of IEC 60479-2 human bodies response to Touch Current varies with frequency. The threshold of perception increases with frequency. The graph shown is figure 1 of IEC TS Perception/Reaction Network:The Touch Current network for perception/reaction is a frequency weighted network. This network is the one most often referenced I product safety testing standards. by a voltage-divider consisting of the resistor and capacitor connected across the 500 Current -sensing resistor. The frequency-weighting network is essentially a lowdesigned to attenuate the voltage signal from the 500 of the body Current .

8 The voltage transfer characteristics of the network is designed from Dalziel's data describing human responses for perception or startle frequency weighting network causes the instrument to have an indication that is related to the expected level of physiological response, independent of frequency. A Touch Current measuring instrument is not a substitute for an ammeter. The Touch Current measuring instrument's response is not necessarily equal to the number of millithrough the body impedance model. The reading of a Touch Current measuring instrument is adjusted by the frequency-weighting network for variations in human response due to frequency.

9 Therefore, the reading can be compared to the limit value in the requirements without knowing the frequency, and allowing a single numerical value for the Touch Current limit for the physiological effect to be RMS Current measured through the 500 Weighted Current indicated by the voltage after the reaction is related to the body muscular response to the Touch Current independent of frequency. Weighted Current is useful to evaluate Current comprised of combinations of frequencies, including nonshapes. The weighted Current is referenced to the 50/60physiological Touch Current network for perception/reaction is a frequency weighted network.

10 This network is the one most often referenced I product safety testing standards. The frequency-weighting is done divider consisting of the resistor and capacitor connected across the 500 weighting network is essentially a low-pass filter designed to attenuate the voltage signal from the 500 resistor according to the frequency of the body Current . The voltage transfer characteristics of the network is designed from Dalziel's data describing human responses for perception or startle frequency weighting network causes the instrument to have an indication that is related to the expected level of physiological response, independent of frequency.