Analysis of Transfer Touch Voltages 200

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Analysis of transfer touch voltages in low-voltage electrical

installations

M Barretta

BSc, K OConnella

BSc MSc CEng and ACM Sungb

BSc MSc PhD CEnga

lecturer in the department of Electrical services Engineering, DIT, Dublin, IrelandbHead of the Department of Electrical services Engineering, DIT, NG Bailey Ltd.

Protection against electric shock in our homes and work places is one of the most important

priorities for electrical services engineers who are now designing electrical installations to

conform to the requirements of the 17th edition IEE Wiring Regulations (BS7671: 2008).

Now Chapter 41 of BS7671: 2008 requires that additional protection by means of a 30 mA

40 ms residual current protection device be provided for final circuits supplying general

purpose socket outlets that are intended for use by Ordinary persons. However, there are

few publications and little information available on the theory describing how touch voltageof a dangerous magnitude could be transferred from a faulty circuit onto the exposed-

conductive-parts of Class 1 equipment of another healthy circuit. This paper summarises the

theory of transfer touch voltage calculations and expands on it to show how to carry out a

sensitivity analysis in relation to the design parameters that are being used by designers and

installers. Based on the results of a real case study, it appears that there is sufficient

evidence to show that it may not be sufficiently safe to use the nominal external earth

fault loop impedance quoted by the electricity utility companies for adopting a low touch

voltage design.

Practical application: The touch voltage sensitivity equation derived in this paper is a

powerful tool for designers and installers of electrical installations to investigate and identify

the sensitivity of resulting touch voltages of any electrical circuits.

Nomenclature

Ut = touch voltage

Uoc = open circuit voltage of the mains supply

R2 = circuit protective-conductor resistance

R1 = phase conductor resistance

Ze = earth fault loop impedance external to

the faulty circuit

Usource = the potential drop ofZe

MET = the main earthing terminal (or mainearth bar) of the electrical installation

Uo = the nominal declared voltage of the

mains supply

1 Introduction

Statistically it has been shown that electricshock is one of the main causes of fatality in

the workplace1 and homes.2 To ensure anegligibly small risk of electric shock in thebuilt environment, designers and installersadopt good wiring practices and abide bythe relevant national wiring rules, e.g. NEC2008,3 BS7671: 20084 or IEC 60364,5 to enablethem to produce a safe electrical installation.It has been agreed universally that for

Address for correspondence: M Barrett, Department ofElectrical Services Engineering, Dublin Institute ofTechnology, Kevin St., Dublin 8, Ireland.E-mail: [email protected] 1, 2 and 48 appear in color online:http://bse.sagepub.com

Building Serv. Eng. Res. Technol. 31,1 (2010) pp. 2738

The Chartered Institution of Building Services Engineers 2010 10.1177/0143624409351796


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general applications, an earthed and poten-

tially equalised (i.e. main-bonded) system will

afford protection against electrical shock

hazards. The circuit-protective-conductor

(cpc) of a final circuit provides a dedicated

low resistance and high efficiency earth fault

current return path to the supply source. An

effective low impedance earth-fault current

return path ensures an almost guaranteed

operation of the overcurrent and/or shock

protection device thus disconnecting the elec-

tric shock energy source under earth-fault

conditions, limiting the duration of the touch

voltage. In addition the main bonding will

limit the magnitude of the touch voltage6 one

can receive across two simultaneously acces-sible bonded conductive parts. Therefore, the

use of proper earthing (i.e. grounding) and

bonding techniques remains the best way to

protect people and equipment against electric

shock hazards. However, when an installation

has a large number of interconnected

circuits and exposed-conductive-parts, a

fault in another circuit can result in a touch

voltage of a dangerous magnitude and

duration being transferred onto a circuitfeeding healthy equipment with exposed-

conductive-parts.

2 Theory of touch voltage

For the purpose of this paper, we shall definetouch voltage as a difference in voltagepotential being experienced by a person who

makes contact simultaneously with more thanone conductive part, which is not normallyenergised.

By this definition, we have excluded thedirect contact electric shock hazard which isdefined as the hazard of electric shock arisingfrom making an unimpeded contact withnormally live parts and we explicitly restrictour discussions to touch voltage arising fromcontact with exposed-conductive-parts andextraneous/exposed-conductive-parts.

The touch voltage Ut of the faulty equip-ment circuit shown in Figure 1 can becalculated using a simple voltage dividercircuit:7

Ut UocR2

Ze R1 R2

1

From the above formula (1) for touchvoltage, it is evident that in practice themagnitude of touch voltage Ut is dependentupon four values U

oc, Z

e, R1 and R2.

(1) The Uoc value will be higher than thedeclared nominal supply voltage Uo.

Usource

Uoct

Dist. board

MET

R2

Ut

R1

Faultyequipment

Ze

240V

Figure 1 Touch voltage concept of a single faulty equipment circuit

28 Analysis of transfer touch voltages


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(2) The external earth fault loop impedanceZe will depend on the system earthingtype,

(3) R1 will depend on the final chosen size ofthe phase conductor (which mainly

depends on the size of the overcurrentprotective device overload protection inparticular), and

(4) R2 will depend of the final installedsize of the cpc (which depends on thestandard twin-with-cpc cable if notsingle-core conductor cables).

It can be seen from Figure 1 that R2governs Ut and the size of the cpc of a circuitcan be designed or selected to provide a touchvoltage that is restricted by the designer orinstaller intentionally. By assigning a bound-ary value to each of Ut, Uoc, Ze, R1 and R2,the size of cpc can be designed using thefollowing expression:

Ut UocR2

Ze R1 R2

Ut

Uoc

R2

Ze R1 R2

2

In the UK and Republic of Ireland, forlocations where low body resistance is notexpected (i.e. normal dry locations) the fol-lowing boundary values are used by designersand installers:

Safe touch voltage value: Ut 50 V Utility supply voltage:

Uoc 240V (16th edition IEE WiringRegulations) or

Uo 230 V (17th edition IEE Wiring

Regulations) where Uo is the declared nom-inal voltage of the mains supply.

For simplicity, this paper assignsUoc 240 V and a safe touch Ut 4 8 V , alimiting value of R2 is found to be:

R2 1

4Ze R1 3

From IEC 60479 part 18 (Effects of currenton human beings and livestock), when thetouch voltage is 50 V a.c. or less under normaldry conditions, the body impedance of aperson is high enough to prevent a touch

current of high enough magnitude to causeany injury. Based on this assumption,Table 41C of the 16th edition of IEE WiringRegulations9 permits the extending of thedisconnection time from 0.4 to 5 s maximum.The use of a safe touch voltage is limited bythe types and rating of a protection deviceand the associated maximum impedance ofthe cpc.

It will be a simple design procedure for thedesigner or installer to apply Equation (3) and

the appropriate value of Tables 41C and 41Dto the required circuit to adopt a safe touchvoltage design with an extended 5 s discon-nection time.

In the UK and Republic of Ireland, R1 andR2 are normally dictated by economics andstandard practice. The standard combinationsof conductor size in twin-with-cpc cables are:16mm2/6mm2, 10 mm2/4mm2, 6 mm2/2.5 mm2, 4 mm2/1.5 mm2, 2.5 mm2/1.5 mm2

and 1.5 mm2/1.0 mm2. These are general pur-

pose wiring cables used for final circuits indomestic type properties. These would beunder the control of the designer and installer.

However, during the design stage, theearth-fault-loop impedance that is externalto the electrical installation (Ze) is normallyan estimated figure. The exact value cannotbe ascertained until the supply is actuallyinstalled and energised by the utility com-pany. In most cases at the enquiry stage ofa project the utility company will only

provide the designer and installer with aworst case nominal Ze of 0.35X for a TNC-S supply or 0.8X for TN-S supply.However, the actual installed Ze could becompletely different and it is outside thecontrol of the designer and installer. Usingthe typical nominal value quoted by theutility supplier and assigning a boundary

M Barrett et al. 29


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value of Ut 50 V, Equation (2) will give theresult of:

Ut 50 Uoc R2

0:35 R1 R2

It can be seen that the final circuit wasoriginally based on a Ze 0.35X to provide atouch voltage of 50 V under an earth faultcondition, but the actual resulting touchvoltage will be higher than 50 V should theactual Ze be lower than 0.35X. Hence, theconsequence of not knowing the exact valueof Ze means that the actual touch voltageresulting from a faulty circuit could not beaccurately calculated using a nominal Ze

indicatively quoted by the electricity supplier.The indicative Ze is only useful in providingthe designer or installer a frame of referenceto check if the overall fault-loop impedance(Zs) of the circuit is designed correctly toensure operation of the overcurrent or shock

protection device promptly. Unfortunately itwill err on the unsafe side for the touchvoltage value.

To illustrate the deficiency of an indicativeworst case maximum Ze, the results of touch

voltage variations with a decrease in theactual value of Ze and increasing circuitlengths were produced using an Excel spread-sheet for a typical TNC-S supply withZe 0.35X. The outcomes are plotted inFigure 2 for final circuits wired in 1.5 mm2/1.0 mm2 twin-with-cpc cables.

It can be seen from Figure 2 that the touchvoltage Ut will rise from a safe-to-touch value(45 V) to an unsafe value (450 V) withdecreasing Ze and increasing circuit length.

It should be noted that Ut, will be at itsmaximum or worst case when Ze is at itsminimum value. (The minimum valueexpected for each situation was calculatedusing the prospective short circuit current (Ipf)value of the incoming supply.) irrespective of

Touch voltage sensitivity to Ze

for a general TNC-S system, pscc 16kA at 230Vusing a 1.5mm twin and earth cable cpc 1mm

Touc

hvo

ltage

160

140

120

100

80

60

40

20

0

12.44%

0.0

43555

0.0

525

0.0

7

0.1

05

0.1

4

0.1

75

0.2

1

0.2

45

0.2

8

0.3

15

0.3

5

15% 20%

Touch voltage at 5M from dist. board








30% 40% 50% 60% 70% 80% 90% 100%

External impedance Ze ()

Figure 2 Touch voltage plot of 1.5 mm2

/1.0 mm2

twin-with-cpc cable circuits



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the actual circuit length. Most of the resultsplotted indicate a value of Ut well above 50 V.

The new BS7671:20084 was introduced inJanuary 2008, replacing the 16th edition IEEWiring Regulations and Table 41C removed.

However, additional protection by means of a30 mA 40 ms residual current protectiondevice (RCD) will have to be provided forfinal circuits supplying general purpose socketoutlets that are intended for use by ordinarypersons. It should be noted that the use ofRCDs can help to reduce the risk of a hightouch voltage and touch current of theassociated circuit in the event of an earthfault, but it is unable to provide protectionagainst any touch voltage transferred from a

fault arising from another circuit not pro-tected by an RCD within the sameinstallation.

3 Touch voltage transferred from afaulty circuit to a healthy circuit

The above analysis was applied to a singlecircuit. However, within the same building

where a number of circuits with mixeddisconnection times exist, as illustrated inFigure 3,10 it has been shown that theresulting touch voltage from an earth faultof another defective circuit will be transferredto the exposed-conductive-part of a healthycircuit. Clearly, unless every circuit within thesame installation is protected by an individualRCD or the whole distribution panel byone main RCD, touch voltage of an unsafevalue could appear on exposed-conductive-

parts for a short duration until it has beencleared by the associated overcurrentprotection device.

230 V

L

N

E

Earth

Distributionboard

Circuit AExposed-conductive-part

Circuit BFixed

load B

Protective

conductorin cord

Load A

(indoors)

Main earthingterminal

Extraneous-conductive-part

Main equipotential

bondingconductor

Further equipotential

bonding conductor(if necessary)

Rc

Uf

If

Figure 3 Transferred touch voltage appearing on healthy equipment (source: IEE Guidance Note 5)

M Barrett et al. 31


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Figure 4 is a generic diagram illustratingthe concept of how touch voltages Vtouch1 andVtouch2 can appear on healthy equipment. The

diagram illustrates three separate electricalcircuits of an electrical distribution system,which at some point defaulted to utilising acommon earthing riser as part of its earthreturn path. As equipment B develops anearth fault, an earth fault current Ifault flowsin the cpc resistances, and by Ohms law,results in transfer touch voltages Vtouch1 andVtouch2 appearing on the exposed-conductive-parts of equipment in locations A and C.

4 Touch volatge practical case study adomestic property

This section outlines a method of simulatingan electrical fault in the built environment.50 Hz a.c. currents up to 20A were circulatedthrough the cpc of several electrical circuits in

a domestic property to simulate earth faultconditions. The resulting transfer touch vol-tages in the dwellings were measured and

recorded.The electrical installation tested is a domes-

tic property in Dublin built around 1980.The supply is single-phase 230 V 50 Hz a.c.TNC-S. A new consumer unit has recentlybeen installed to meet ET10111 (equivalent toBS7671: 2008). The meter board has recentlybeen re-housed outside the dwelling for easeof access. At the meter board the measured Zewas 0.37X at a Uo of 233 V and frequency of50.1 Hz.

The practical measurements were carriedout as illustrated in Figure 5. A variac acted asthe source of supply. One of the outputterminals of the 225 VA Variac, which can bevaried from 0 to 14V was connected to theassociated cpc at the chosen fault locations andthe other terminal was connected to the mainearth terminal at the main distribution board.

MET.

Extraneous-conductive-parts

Vtouch1

Vtouch2

Rcpc2

Rcpc4Rcpc3

Rcpc1.2Rcpc1.1

Rcpc1.3

Vtouch2Ifault

Ifault

Healthyequipmentlocation A

Healthy

equipmentlocation C

Faulty

equipmentlocation B

Figure 4 Touch voltage is transferred from location B to locations A and C in the same building



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The characteristics of the simulated fault wererecorded using a voltmeter and ammeter. Thetemperature of the associated cpc wasrecorded using a digital thermometer beforeand during each simulated fault.

Figure 6 illustrates the circuits present inthe test dwelling. During the simulation of the

fault, transferred touch voltages thatappeared in various locations were recorded.The test was setup to study in particular whatmagnitude of transfer touch voltage can existin a location (i.e. bathrooms) where low bodyresistance would be commonly encountered.

There are a number of countries wheresupplementary bonding in bathrooms maynot be required but the main equipotentialbonding should be correctly installed. It is forthis reason that the new 17th edition of IEE

Wiring Regulations requires that all electricalcircuits supplying appliances or equipment inthe bathroom be protected by RCDs so thatany touch voltage originating from within thebathroom will be automatically disconnectedwithin 40 ms.

This particular test has deliberately discon-nected the supplementary bonding in the

bathroom to study the magnitude of transfertouch voltage in the particular location.

For such a case, the results are shown inFigure 7 with an earth fault in the light fittingin the attic.

Simulation results At the faulty light priorto simulation, the impedance of the cpc was

recorded at 0.18 X. Under test conditions, thevoltage and current were recorded at 6.4 Vand 15 A, respectively. Using the recordedvalues (6.4 V/15 A 0.4266X) and subtract-ing the impedance of the variac/ammetercombination and the earth wire from thevariac to the MET, the impedance of the cpccan be calculated to be 0.196X. The increaseof resistance is due to copper having apositive temperature coefficient.

Under test conditions, the touch voltage

recorded between the light and earth in theattic was 2.95 V, while in the bathroom thetouch voltage was 2.95 V between the heaterand the cold-water copper pipe and shower.

Hence, under true fault conditions, if afault occurred at the light in the attic and atouch voltage developed, a voltage of thesame magnitude would develop on the heater

Ammeter

Voltmeter

Distributionboard

Variac

Phase

NeutralEarth

E N P

Figure 5 Circuit diagram of the test setup

M Barrett et al. 33


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in the bathroom where there was no supple-

mentary bonding present.Using the recorded values an approximated

value for the touch voltage can be calculated.Fault loop impedance at distribution

board 0.42 XResistance of R1 is approximately 0.12 XResistance ofR2 is approximately 0.1966 X

(both R1 and R2 will vary depending on the

temperature of the copper under fault condi-

tions). Using Equation (1):

Ut 64 V 2400:1966

0:42 0:12 0:1966

It was found that a touch voltage istransferred into the bathroom where theexposed-conductive-part of a heater, although

Fau

lt2downs

tairssoc

ke

tsno.

8

Downs

tairssoc

ketsno.

5

Ups

tairssoc

ke

tsn

o.

5

Immers

ion

hea

ter

Fau

lt5a

ttic

Lights

Lights

Ups

tairs

Downs

tairs

Downs

tairssoc

ketsno.

7

Fau

lt1

Fault 4 bathroom

Bar heater

Fault 3 oven

Hob

Oven

20A MCB B type

30mA RCD

board

Distribution63A switch

Fuse

Main incomingsupply

33A MCB B

type

Main earth bar

10A MCB B type

Main gasEarth

electrode

Figure 6 Single-line diagram of the test dwelling



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it was not switched on, has attained a value of64 V, which is considered a dangerous voltagefor people with low body resistance.

In addition to using Earthed EquipotentialBonding by Automatic Disconnection of

Supply (EEBADS) as the primary methodof protection against electric shock faults,IEE Guidance note 510 suggests that addi-tional supplementary equipotential bondingconductors can be installed at strategiclocations so that any touch voltage Utoriginating from outside the particular loca-tion is lowered to a safe-touch-value. This was

implemented as a control comparison and theresults are shown in Figure 8.

Simulation results, supplementary bondingrestored With a fault simulated on the lightin the attic, touch voltages were recorded at

the fault location and in the bathroom. Thevoltage and current were recorded at 4.35 Vand 15 A, respectively. The reduction in thevoltage required to drive 15 A through thecircuit dropping to 4.35 V due to the parallelpaths back to the MET as shown in Figure 8.

10A of the 15 A was recorded flowingtowards the bathroom and the remaining

Bathroom

MET

Fault at light in attic-Nosupplementary bonding in bathroom

AtticFault location

Consumer unit

Light

Heater

Cold watercu. pipe

Showers earthSocket

Extraneous conductive part

Ut=64 V Ut=64 V

Figure 7 Presence of dangerous touch voltage in bathrooms with no supplementary bonding

Bathroom

MET

Fault at light in atticsupplementary bondingin bathroom restored

Consumer unit AtticFault location

Light

Heater

Cold watercu. pipe

Showers earthSocket

Extraneous conductive part

Ut=24 V

Ut=3.6 V

Ut=1.56 V

Figure 8 Elimination of presence of transfer touch voltage in bathrooms by mandatory supplementary bonding

M Barrett et al. 35


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5.0 A was recorded flowing from the faulttowards the distribution board. In the bath-room the 10A split in two directions, 7 Aflowed through the electric showers earthcircuit and 3 A flowed through the copper

pipes.The touch voltages recorded under simula-

tion were as follows, 0.96 V at the faulty lightin the attic, 0.144 V between the heater andelectric shower in the bathroom and 0.066 Vbetween the heater and cold-water copperpipes.

From the recorded values it was possible tocalculate the resistance R2, 4.35/15 A 0.29X resistance of circuit under fault con-ditions. 0.290.23X (impedance of earth wire

and variac) 0.06X R2. Also, the resis-tances of the supplementary bonding in thebathroom could be calculated, 0.144 V/7 A 0.02X and 0.066 V/3 A 0.02X.

Using the recorded values an approximatedvalue for the various touch voltages can becalculated. Using Equation (1):

Touch voltage at faulty light Ut 24 V

240 0:06=0:42 0:12 0:06

To determine the touch voltages developedin the bathroom, the prospective fault current(Ipf) at the fault location was calculated:

Ipf 233V

0:6 388A

Two-thirds (259 A) of the total faultcurrent flows towards the bathroom underfault conditions. The current that would flow

to earth via the cold water copper pipes isgiven by (3/10) 259A 78 A. Hence thetouch voltage between the heater and coldwater copper pipe would be approximately78 0.02 X 1.56 V.

Therefore the touch voltage between heaterand the shower would be approximately be259 A (7/10) 0.02 X 3.6 V.

The findings demonstrate that with supple-mentary bonding, the transfer touch voltagewas reduced to less than 4 V within thebathroom. Therefore it appears that there issufficient evidence to show that with supple-

mentary bonding in place, even in the event of adefective RCDa or a sluggish overcurrentprotection device such that the faulty circuitmight remain in an energised state for quitesome time, a person in the bathroom wouldonlybe exposed toa touch voltage of4 V orless.

Alternatively, a designer or installer can optfor making sure that all the circuits within thesame dwelling will have a very low safe touchvoltage value in the event of a fault. Forexample, to have a transfer touch voltage not

exceeding 12 V4

maximum to provide protec-tion against electric shock for a person withvery low body resistance in the special loca-tion. This requires the designer and installer tohave a good understanding of the sensitivity ofthe resulting touch voltage in relation topercentage changes of Uoc, Ze, R1 and R2between design and as-installed phases.

5 Touch voltage sensitivity analysis

In this section, the technique of partial dif-ferentiation for small percentage changes wasused to determine the sensitivity of touch vol-tage in relation to the four design parameters:

Equation (4) is obtained by applyingpartial differentiation to Equation (1):

Ut @f

@UocUoc

@f

@ZeZe

@f

@R1R1

@f

@R2R2 4

aFrom the ERA Technology Report In-service reliability ofRCDs published in Italy in May 2006 electromechanicalRCDs have an average failure rate of 7.1%. If RCDs are testedregularly this figure falls to 2.8%. RCD reliability is improvedif the test button is operated regularly. However, the report hasindicated that RCDs with an inadequate IP rating subjected todust and moisture could have a 20% failure rate.



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where f Ut Uoc R2=Ze R1 R2and Ut is the small change in touch voltage,giving the result of (For simplicity, we havelet Ze, R1 and R2 be summed directly. Theactual Ut can vary significantly when com-

plex quantities are used.):

Ut R2

Ze R1 R2Uoc

Uoc R2

Ze R1 R2 2Ze

Uoc R2

Ze R1 R2 2R1

Uoc R2

Ze R1 R2 2

Uoc

Ze R1 R2

R2

Ut R2 Uoc Uoc R2

Zs w Zs 5

where Zs Ze R1 R2, w Uoc R2=Z2s ,

and Zs Ze R1 R2

U0t Ut Ut 6

where Ut0 is the final touch voltage after

changes ofUoc, Ze, R1 and R2 been accounted

for.Equations (5) and (6) allow the designerand installer to investigate the resulting mag-nitude of the change in touch voltage Ut forany combination of percentage changes of thefour design parameters Uoc, Ze, R1 and R2.

As an example: for a final circuit with aUo 230 V, Uoc 240 V TNC-S system,R1 0.1X and R2 0.15X, during thedesign stage Ze 0.35X and Ipf 16kAwere obtained from the electricity supplierby enquiry.b Using Equation (1), the esti-mated touch voltage Ut can be evaluated

equal to 60 V. However, the actual touchvoltage will change due to the percentagevariation of the four parameters for reasonsbeyond the control of the designer as below:

Uoc changes by 6%c due to the variationof the utility supply, Uoc 2406% 14:4 V

Ze changes by 35% due to the location ofthe utility supply transformer, Ze 0:35 35% 0:1225

R1 changes by 15% due to shorter cableruns in the construction stage,R1 0:1 15% 0:015 and

R2 changes by 15% due to shorter cableruns in the construction stage,

R2 0:15 15% 0:0225

Using Equation (5), the change of touchvoltage will be:

Ut 3:6 9 16V 10:6 V

Hence, U0t 60 10:6V 70:6 V,approximately. The actual Ut is 73.72 V ifthe exact value of R1 0.085X, R2 0.1275X, Ze 0.2275X and Uoc 254.4 Vwere applied to Equation (1). The discrepancyof (73.72 70.6) V 3.12V is mainly due tothe large percentage change of Ze but theoverall result is still within an acceptablemargin.

It can be seen from the above, the touchvoltage sensitivity equation (5) derived in thispaper is thus a powerful tool for designersand installers of electrical installations toinvestigate and identify the sensitivity ofresulting touch voltages of any electricalcircuits.

bBS7671: 2008, Regulation 434.1 suggests determinationof prospective short circuit current (Ipf) at the relevant pointof the installation may be done by calculation, measurement orenquiry.

cThe UK ESQC Regulations state that the declared nominalvoltage on LV networks is 230 V 10%, the open circuitvoltage at the DNO supply transformer is normally set at240V, hence 240 V 6% is used in the analysis.

M Barrett et al. 37


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6 Conclusion

The underpinning basic theory of thesafe touch voltage design equation has

been explained and illustrated with anexample. A generic circuit diagram is presented

illustrating how a touch voltage of adangerous magnitude could be transferredfrom a faulty circuit onto healthyequipment located elsewhere within anelectrical installation.

A touch voltage case study has been used todemonstrate that a dangerous touch voltagecould be present in locations where extreme

low body resistance may exist. It has been demonstrated that by the use oflocal supplementary bonding, the danger ofany touch voltage transferred from a faultarising from outside the bathroom canalmost be completely eliminated even inthe event of a fault of long duration.

A set of touch voltage sensitivity calcula-tion equations has been developed and usingan example, the authors have demonstratedthat the equations can be used by installation

designers and installers to investigate andidentify the range of resulting touch voltagevalues that might be the consequence ofvariation of the four main design parametersUoc, Ze, R1 and R2.

References

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2 Pointer S, Harrison J. Electrical injury anddeath. Flinders University, South Australia[Online]. 2007 [Cited April 2008]. Available at:http://www.nisu.flinders.edu.au/pubs/reports/2007/injcat99.php accessed April 2008.

3 NFPA. NEC 2008 National Electrical Code.USA, NFPA, 2008.

4 BSI/IET. BS7671: 2008 Requirements forElectrical Installations IEE Wiring Regulations,17th edn. London, UK, BSI/IET, 2008.

5 IEC. IEC60364: 200206 Electrical installa-tions of buildings, 2nd edn. Geneva,

Switzerland, IEC. 2001.6 Cook P. Commentary on IEE wiring

regulations (BS7671: 2001), 16th edn.Stevenage, UK, The IEE, 2002.

7 Jenkins BD. Electrical installation calculations.UK, Blackwell Scientific Publications Ltd, 1993.

8 IEC. IEC 60479 part 1: effects of current onhuman beings and live stock. Geneva,Switzerland, IEC, 2007.

9 BSI/IET. BS7671: 2001 Requirements forelectrical installations, including amendmentsNo 1 and No 2, 16th edn. London, UK,

BSI/IET, 2004.10 IET. IEE Guidance Note 5, Protection againstelectric shock. London, UK, IET, 2005.

11 ETCI. ET101: 2006 National rules forelectrical installations, 3rd edn. Ireland,Electro-technical Council, 2006.


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Analysis of Transfer Touch Voltages 200