electric shock protection

8/2/2019 Electric Shock Protection

1/19

Seite 4 EEV1: Protection against electric shock

3 Preparation of the laboratory experimentThe fundamenta l ru le of protection against electric shock, according to IEC 60364, is thathazardous l ive parts m u s t not be accessible and accessible conductive parts must not be ha-zardous l ive , nei ther under normal condi t ions nor under s ingle fau l t condi t ions .A protective measure shall consist of:- an appropr ia te combination of a provision for basic protection and an independent provi-sion for fault protection, or an- enhanced protective provision which provides both basic protection and fault protection.> = > Please define the terms 'basic protect ion ' and 'fault protect ion ' . 1/iTtrn O-

ce.rrfa ^Wh i c h protect ive m easures are general ly p ermit ted accord ing to IEC 60364-4-41?

3 / ; Q"S- Which protect ive measures shall only be used fo r installations either accessible to orsupervised by skilled or instructed persons?

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"is. Which protect ive measures may be used fo r fau l t protection in TN sys tems?flj oW ^Tt|5cWonol c x j r v i H h x k c x ^ an

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2/19

EEV1: Protection against electric shock Seite 5"s. W hich protective m easures may be used for fault protection in TT systems?

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oWhich protect ive m easu res may be used for fault protection in IT systems?MDnthnm deoio/o

Protection against electric shock may also be provided by means of extra-low voltage (SELVo r P E L V ) .

'S. Which are the requirements fo r protection by means of extra-low voltage?l) Mo J P f V e C J o n J u j i d v w o> JRi; *maif c j ome i ted k >

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3/19

Seite 6 EEV1: Protection against electr ic shock

4 Measurements and InterpretationEach par t of the exper im ent sho uld be executed quickly beca use the eq uip m en t i s s t ressed bycurrents h igh enough to trip the protective devices. Fur thermore , with the exist ing mea-s u r emen t devices , the type of m eas ure m en t (cu rren t or voltage) and -especially for currentmeas ur emen t s - the measur ing range mus t be careful ly cons idered.4.1 Protective measure: automatic disconnection of supply (411)4.1.1 Requirements fo r fault protection ( 411 .3 )W e will investigate at first the requirements for fault protection regarding the protectivemeasure 'automat ic disconnect ion of supply".4.1.1.1 Protective earthing ( 411 .3 .1 .1 )"Exposed-conductive-parts shall be connected to a protect ive conductor under th e specificcondi t ions for each type of system earthing".Connect consumer 1 (just one line) over the overcurrent protective device L SI to a TN-Ssystem (bypass the RCD, R PE /N = iri). Establish a 'dead short-circuit ' to the exposed-conduct ive-parts (a fault of negl igible imp edan ce between the l ine cond uctor and the ex-posed-conduct ive-parts due to insula tion breakdow n, R K = O }). A person is touching the ex-posed-conduct ive-par ts ( t rans i t ion res is tance: Ru=560 H). M e a s u r e the l ine current I L l j thetouch voltage U B , the current through the person IM and the disconnection time taus in caseth e consumer is connected to the protect ive conductor as well as in the opposi te case.(Please pay attention to the proper measuring range for current measurement)

Protect, earthingyesno

I L I in A0-3

U B i n Vii2fi

IM in mA

taus in s

oCO"S. In which case is the person in danger?

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4/19

EEV1: Pro tect ion again s t e lec tr ic shock Sei te 7

4.1.1.2 Protective equipotentional bonding ( 4 1 1 . 3 . 1 . 2 )" J s , W hich cond uct ive par ts should be connected to the protect ive equipo tent ia l bo nd ing ?

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In th e fo l lowing we wil l examine the protect ive equipotent ia l bonding ins ide an ins ta l la t ion ./LSI.

C onnec t c o n s u m e r 1 over t he overcurren t protective device L SZ to a TN-S system (do notforget to connec t the exposed-conduct ive-par t s to the pro tec t ive conduc to r ) . Cons ide r th ecase of a broken PE N c o n d u c t o r ( R P E / N -> ).a) M easure the vo l tage U F between the w a t e r pipe and the exposed-conduct ive-par ts , in caseno protect ive equipotent ia l bonding is g iven.

U F i n Vb) Connec t the protect ive conductor and the wate r p ipe to the pro tec t ive equ ipo ten t ia lbond ing . Measure the vo l tage U F i between water p ipe and exposed-conduct ive-par ts as

wel l as the vol tage U F 2 be tween exposed-conduc t ive -par t s and re fe rence ea r th .U F 1 in VU F 2 in V

o va a ^ v a M t T -

"S. W h ic h im p ro v e m e n t is brough t abou t by the protect ive equipotent ia l bonding?

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person

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5/19


c) Connect additionaly the installation earthing to the protective equipotential bonding,R A = 47 ft. M e a s u r e th e voltages Un und UF2 once again.

U F ] in VU F 2 in V

o y3 , / ? v"2s , Draw the equivalent circuit of the fault loop. Which resistances does voltage UF2 de -pend on?

R ,6.

ht inkMbJfc ,and

4.1.2 TN system (411.4)([411.4.1/ "In TN systems the integrity of the earthing of the installation depends on thereTTarJIeand effective connection of the PEN or PE conductors to earth ..."[411.4.2] "Note 1: If other effective earth connections exist, it is recommended tha t th eprotective conductors also be connected to such points wherever possible ..."

W e will investigate at first the requirement for a reliable and effective connection of the pro-tective conductor to earth . C onnect consumer 1 (just one phase) over the overurrent protec-tive device LSI to a TN -S system (bypass the R CD). E stablish a dead shortcircuit to exposed-conductive-parts (R i


6/19

EEV1: Protection against electric shock Seite 9"S. Interp ret the term s "reliable" and "effective" with respect to the con nec tion of theprotec t ive conductor to earth accord ing to the measuremt .

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G U IKC c U v a o V

"S. Draw th e equivalent c i rcui t of the fault loop and calculate th e maximal resis tanceR P E / N , for which the^v^rcurreni,protective device still trips. Further calculate the touch vol t -age for this value of R P E / N - j ^ V o u l d a person touching th e exposed-conduct ive-par t s be in d a n -ger? W hich protec t ive measures can ensure faul t protect ion?

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In the fol lowing we w ill discuss the recom men dat ion for addi t ional connect ion of the pro tec-t ive conductor with other effective earth connect ions according to note 1 411.4.2. C o n -sumer 1 stays one-phase-connected to the TN-S system, however the short circuit now t akesplace over a faul t resistance R K = 1 0 0 0 H. The resistance of the PEN c o n d u c t o r is R P E / N = 470H . M e a s u r e the l ine current IL1 ; the touch vol tage U B j th e current through th e person IM andth e disconnec t ion t ime tau s in case no protect ive equipotent ia l bonding is given and in case aprotect ive equipo tent ia l bo nd ing is given (connect therefore the protect ive c on du cto r, waterand gas pipes as wel l as the installation earthing, R A = 2 2 0 H, to the equipo t en ti a l bond ing ) .(Please pay attention to the proper measuring range for current measurement)

Equipotentialbondingabsentexistent (& 4f

I L I in A

D^&0 - B

U B i n V

M^.< Q o *IM in mA

J\B^4taus in s

ood


7/19

Seite 10 EEV1: Protection against electric shock^s. Interpret th e recommenda t ion fo r addit ional connect ion of the protect ive condu ctorwith other effective earth connections according to the measurent resul ts .

Additional connections of protectivebe

bondtx/ifi and

te-iHvJoouino on

[411.4.5] In TN systems, residual current protective devices (RCDs) may be used fo r faultprotection (protection against indirect contact). ". . .Note 1: Where an RCD is used for faultprotection th e circuit should also be protected by an overcurrent protective device."In th e fol lowing w e will investigate th e fault protection of TN systems by mea ns of residualcurrent protective devices as well as the requi rement fo r addit io nal protec t ions by an over-current protective device. Connect consumer 1 ( just one phase) over the ov ercurre nt protec-tive device L SI and the R C D to a TN-S system (R P E / N -1 ). Establ ish a short circuit to ex-posed-conduct ive-parts ( R K = 6 0 0 2) . A person is touching th e hous ing of the c onsumer(R o = 560 fi). Observe the performance of the R C D .

Tripping? V e .'s. Draw the equivalent circuit of the fault loop including the fault resistance R K . Calcu-late the l ine current Iu, the residual current AIF over the faul t impeda nc e RK , the touch volt-ag e U B and the current through th e person IM . Interpret the performance of the R CD accord-in g to you r ca lcula tion.RU

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8/19

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9/19

EEV1: Protection against electric shock Seite 11In order to demonstrate the requirement for addit ional protection by an overcurrent protec-tive device in case a residua l cu rrent protective device is use d for fault protection, we shallinvestigate following circuit: remove the short circuit to exposed-conduct ive-par ts and estab-lish a short circuit between l ine and neutral conductor at the consumer terminals instead.Observe the perfo rma nce of the RC D once again.

Tripping? N o L S I D"S. Draw th e equivalent circuit of the fault loop and calculate the line current IL 1 and theres idua l current A IF . Interpre t the pe rform anc e of both protective devices accord ing to yourcalculation.

14-1

- 0

oo

[411.4.5] "A residu al cu rrent protective device (RC D ) shall not be use d in TN-C systems.""is. Explain why RCDs may not be used in TN-C systems.In ~T N C &ujz,\no f cluJrtfÂ ôuuJJ" dtKc.

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TT4-


10/19

Seite 12 EEV1: Protect ion aga inst electr ic shock

4.1.3 TT system (411.5)[411.5.2] "Generally in TT systems, R C D s shall be used for faul t protect ion"

Connec t consumer 1 (one phase) over the overcurrent protect ive device LSI and the R C D toa TT system. Establish a complete protective equipotential bonding as well as a short circuitto exposed-conductive-parts (over the fault impedance R K ) . M e a s u r e the current IA throughthe installation earthing resistance RA for fo l lowing valu es of R A and R K and observe the per-formance of the R C D .The res is tande of the PEN conducto r is R P E / N = 1 ft.

RAin ftR K i n f t1A in ATripping?

220ftO f t

Y p * /RC&

1500ft1000ft

.Y & o f R ^ O .

" 2 S , Calcu la t e in accordance to 411.5.3 the maximal resistance R A ,ma x of the instal lat ionearthing, which would stil l lead to t r ipping of the R C D .

[411.5.2] ". ..A l ternatively, overcurrent protect ive device s may be used for fault protect ionprovided a su i tab ly low value of Z s is permanen t ly and re l iab ly assured .",

Remove t h e R C D from the circui t (consu me r 1 is now prote cted only by the o vercurrent pro-tective device L S I ) . T he consumer has a short circuit to exposed-conduct ive-par ts over thefault resistance R K =1000 f t . A person is touching the consumer 's housing (R u = 5 6 0 ft).Measure the current through the installation earthing 1A , the touch vol tage U B , and the cur-rent through the person IM for following values of the installation earthing resistance R A .(Please pay attention to the proper measuring range for current measurement)

RA4 7 f t220ft1500ft

1A in A0 / 0 2 4 -O f 2-0,'}

UBin V$ r34-/ ^ad aIM in mA

J/(< 1/ " 4 / 0 %f i / j L

Tripping?A / ofiJ0A /o .


11/19

EEV1: Protection against electric shock Seite 13's. Calculate according to 411.5.4 the maximal installation earthing resis tance R A ,max,which generally still ensures faul t protection by an overcurrent protective device.

2-20 M - 3 T tI 2.6} J L _

4.1.4 ITsystem (411.6)In IT sys tems th e fau l t current is low in the event of a single fault to an exposed-conduct ive-part or to earth and au tom atic disconn ection is not imperative provided the condition in411.6.2 is fulfilled.In the following we will investigate fault protection in IT systems. Connec t consumer 1 (allthree phases) over th e overcurrent protective device L SI to an IT system (bypass th e R C D ) .Also include the insulation resis tance R iso (connect the neutral point of the insulation repro-duc t ion to refere nce earth) and e stablish a comp lete protective equ ipote ntial bon ding . T heconsumer has a dead short circuit to exposed-conduct ive-par ts (R K = 0 ii). A person is touch-ing the consumer 's housing (R u= 5 6 0 Q). Measure the current IA through the installationearthing resistance R A j the touch vol tage U B and the current through th e person IM for follow-ing values of R A und R iso. T he resis tance of the PEN conductor is R PE /N= 1 &

Jl

R A47 ft2 2 0 Q1500 Q .

Riso220 kli2 ,2 kfl2,2 kQ

IA in mA[ Z D i i j4mU B i n V0,04S[170' f o

IM in mA0,04- > , r %&hi&3 .

"s. Interpret th e r equ i rement in 411.6.2 according to the measurement above.\yaAu0

1 4 -" fo ke&P % F >


12/19

Seite 14 EEV1: Protection against electric shock" 2 3 . Draw the one-phase equivalent c i rcui t of the faul t loop inc luding the insulat ion resis-tances (neglect both the consumer and the person) . Calculate the maximal instal la t ionearthing resistance R A , m a x for R i so=2,2 kQ in accordance wi th 411.6.2.

u

R ./ s oAfrit o

[411.6.3] "Note : Whe re a res idu a l cur ren t ope ra t ing device (RCD) i s used , t r ipping of theRCD in event of a first faul t cannot be excluded due to capaci t ive leakage currents ."In the fol lowing we wil l examine the t r ipping performance of RCDs in the event of a firstfaul t in IT sys tems. Consumer 1 is now three-phase connected both over the overcurrent pro-tective device LSI and the RCD to an IT system (RP E /N=1 Q, R A = 2 2 0 ft). The consumer has adead short c i rcui t to ex posed -condu ct ive-par t s ( R K = O 1). Observe the t r ipping performanceof the RCD for following values of the insulation resistance.

Riso220 kft2,2 k^

Tr ipp ing?N oX e o" J S - Calculate in accordance with the previous equivalent c i rcui t th e value of the insula-t ion resistanc e, which st i ll leads to tripping of the RC D.

si


13/19

EEV1: Protection again st electr ic shock Seite 15[411.6.3.1] "... an insulation monitoring device shall be provided to indicate the occurrenceof a first fault from a live part to exposed-conduct ive-par ts or to earth. This device shall in -i t iate an audible and/or visual signal which shall continue as long as the f au l t persists."Connect consumer 1 (one phase) over the overcurrent protective device LSI and the RCD toan IT system (R P E / N = 1 Q). Also include the insulation resistances (^0=220 kT). Furtherconnect the insulation monitoring device (IMD) to the system conductors (prior to the pro-tective devices). Consumer 1 has a short circuit from the phase condu ctor to the exposed -conductive-parts . Observe the IMD signals for the following faul t resistances RK . The con-sum er is either in service or out of operation accord ing to the following table (disc onn ect theconsumer by operating the overcurrent protective device L S I ) .

R K i n 1consumersignal

DO

in/out of servicer f oO f tin seviceV t o

1 kftin service

Yco1 kftout of servicefi

"2s. The insulation monitor ing device ( IMD) is cont inuously measur ing th e insulation re -sistance of the system active parts to system earth and signals an earth fault in case of a s u d -den resistance decrease. Draw the complete equivalent circuit (one-phase, also include theovercurrent protective device L SI in the circuit) of the system and calculate the insulationres is tance between line and protective conductor both prior to failunTas well as~after failureoccurance (R K = 1 kf t ) . How would th e result change if the consumer w as disconnected (pro-tective device L SI open)?


14/19

Seite 16 EEV1: Prote ct ion against ele ctr ic shockIn IT systems "provisions shall be t aken [ . . . ] to avoid risk of harmful pathophysiological ef-fects on a person in contact with simultaneously accessible exposed-conductive-parts in theevent of two faults exis t ing s im ultaneously ." [411.6.1].In the following we will investigate the case of exposed-conduct ive parts interconn ected by apro tec t ive conductor and collectively earthed to the same earthing system (411.6.4a). Con-nect consumer 1 (one-phase) over the overcurrent protective device LSI (bypass the RCD)and consumer 2 over the overcurrent protective device LS 2 (bypass the isolating trans-former) to an IT system (RA^_47 H ). Neglect the insulation resistances. Establish a short cir-cuit to expose-conduct ive-parts over th e faul t impedance RK600 Q . at consumer 1, as wel l asa dead short circuit between neutral con ductor and hous ing at consum er 2. A person istouching the housing of consumer 1 (Ro560 H). Measure the current through the installa-t ion earthing IA ; the current through the fault impedance I K and the touch voltage U B for fol-lowing resistance values of the PEN conductor . Also observe th e t r ipp ing performance of theovercurrent protect ion devices.(Please pay attention to the proper measuring range for current measurement)

R P E / N in Q1 Q .22 & .470 &

I A in A000

I K in A

^H


15/19

EEV1: Protection aga inst electr ic shock Seite 17W e will now investigate the case of exposed-conductive-parts being earthed individually .C o n su m e r 1 stays one-phase connected to the IT system over the overcurrent protective de-vice L S I ( R p E / N ^ l f t ) with a short circuit to exposed-conductive-parts ( R x ^ G O O ft) . Cons umer2 also stays conne cted to the IT system (over LS2 and w ithout the isolating transform er) witha short circuit between neut ra] conductor and housing. However , the hous i ng of consumer 2is no more connected to the protective conductor but directly to reference earth. The insula-tion resistances can fur ther on be neglected. A person is touching th e housing of consumer 1Measure th e current through the installation earthing IA, the current through the fault im -pedance IK , the touch vol tage U B and the current through the person IM for following resis-tance values of the installation earthing R A.(Please pay attention to the proper measuring range for current measurement)

R A i n f t47ft220 ft1500 ft

I A in A0*330-1$

> /

I K in Ao < 3 70-32^PjL/l

UBin V1 4 o3HL[* ^

IM in mA5-S-50*9-?~o- 6 ."S. Is fault protection in this case given? Which requirement ensures fault protection inth e event of two faults existing simultaneously, when the exposed-conduct ive-par ts areear thed in groups or individual ly?

" 2 s . Draw th e equivalent circuit of the fault loop (neglect th e person) and calculate th emaximal resistance of the installation earthing R A , m a x according to 411.6.4b. Further calcu-late th e touch voltage U B in case RA-Rvmax-


16/19


4.2 Protective measure: electrical separation (413)[413.1.1] "Electrical separation is a protective measure in which [...] faul t protection isprovided by simple separation of the separated circuit from other circuits and from earth."Connec t con sum er 2 (without the diod e) over the overcurrent protective device LS2 and theisolating t rans fo rmer Tl to a TN-S system (RPE/N=! & ) Expo sed-conductive-parts shall notbe connected to a protective conductor or to earth when th e protect ive measure 'electricalseperation' is applied (413.3.6). The consumer has a dead short circuit to exposed-conduct ive-par ts and a person is touching its housing (R.0^560 H ). Measure the touch volt-age U B and the current through th e person I M -

U B i n VIM in mA

00

[413.3.3] "Live parts of the separated circuit shall not be connected at any point to anothercircuit or to earth or to a protective conductor."In the following we will investigate the requirem ent in 413.3.3. The expe rim ent layout s taysunmodi f i ed , however, an additional earth fault between neutral cond ucto r (at the consum er)and referenc e ear th occurs . M easure the touch voltage U B and the current through the personIM once again .

U B i n VIM in mA 1 9 9 * 7X A - 3 L

"S. In te rp re t th e requ i rement of live parts being isolated from other circuits an d fromearth according to 413.3.3 on the basis of the measurement (key-word: float ing potent ia l) .

front rfwn9a

1

1 4 d t K i x t io

a


17/19

EEV1: Protection again st electric shock Seite 19

4.3 Protective measure: extra-low-voltage provided by SELV and PELV[414.2] In SELV and PELV systems "basic protection and fau l t protection is d e e m e d to beprovided when- the nom inal voltage ca nno t exceed the upper l imi t of voltage Band 1,- the supply is from one of the appropr ia te sources , and- the condit ions of 414.4 are fulfilled.Connect th e extra-low voltage transformer T2 over th e overcurrent protective device L S3 to aTN-S system ( R P E / N =!0- Extra-low voltage consumer 3 is connected to a SELV system (noconnection of the exposed-conductive-par ts to the protective conductor or to ear th) . Estab-lish a de ad short circuit to the exp osed -cond u ctive-parts at the co nsu m er. A person is tou ch-ing th e consumer 's housing (R o = 560 1). M e a s u r e th e line-to-earth voltage of the SELV sys-tem U 0, the touch voltage U B and the consumer voltage U v (between l ine and neutra l conduc-tor a t the consu mer 's terminals) .

U 0 in VU B i n VUvin V

00wIs the person in danger of electric shock? Does the protection tr ip? Please jus t i fy y o u ranswer .ihi 01?

o 0

In th e fol lowing we will investigate th e r equ i r emen ts for SELV and PELV sys tems . The ex-per iment layout s tays as is , however, an additional short circuit between primary and secon-dary winding of the extra-low voltage transform er T2 now occurs. Measu re the touch voltageU B, the consumer 's voltage U v as well as the current through the person IM .

U B i n VUvin VIM in mA

1,05"Vteca

"s. Is fault protection by extra- low voltage given? Which requirements for the supp lysources of SELV and PELV systems ensures f au l t pr o tec t ion?an ChotUd Jb t fr&m


18/19

Seite 20 EEV1: Protect ion against electr ic shock

4.4 Test procedures for earth electrodesParticularly in the m ost common TN systems doe s the earthing of the exp osed -condu ct ive-parts (andconsequent ly the faul t protect ion) depend on a rel iable and effective connect ionof the PEN cond uctor to earth.

14.4.1 Meauring the earthing impedanceIn the following w e will m easu re the resistance of the inst allatio n earth electrode and inves-tigate the influence of the measuring electrode on the measurement . Connect the installationearth electrode R A over the measuring resis tance R P and the overcurrent protect ive deviceL S2 to the l ine conductor L I . M easure the vol tage between the instal la t ion earth electrodeand reference earth U F, the vol tage between the instal la t ion earth electrode and the measur-ing electrode (R A /R H ) U E, as well as the current through the instal la t ion earth electrode IA .W e will investigate at first the case of a low ear thing impedance (R A = 220 2 ) . The resis tanceof the measuring electrode RA/RH equals 1 k2.(Please pay attention to the proper measuring range for current measurement)

R p i n Q .22 kfi2,2 kfi22022 Q .

IA in A

A0,56

UEin V

v -

UFin V

UA1Calculate th e installation earthing impedance R A on the basis of the measu rement s .

A = Oe/Uo- 2.2-1 Kto"3!/!-"O " 2 - 2 - \ w * I*o_- *"2s. Did you notice an y influence of the measuring electrode's impedance on the meas -urement of the earth electrode's impedance? Interpret the measurement on the basis of anequivalent c ircui t. Inclu de also the internal imp eda nce of the m easuring devices.

> ( J L m^lngrxj-^S

_ >nof

n

,, c fi -6eirvno


19/19

EEV1: Protection against electric shock Seite 21

"S. Which conclusions regarding low values of the measuring resistance R P can you drawon th e basis of the me a su re me n ts a bove ?

to u valuu rtttfen*

o < j

4.4.2 Voltage gradient - Step voltageM e a s u r e the voltage U B e z - s o n d e between reference earth and measur ing e lec t rode for followingdistances to the earth electrode (R P = 2200 Q).

0 m 1 m 2m 5 m 10m 20 m 30 mUfiez -iez-Sonde

Draw the vol tage U B e z - s o n d e in the fo l lowing graph .

20 10 5 21 12 5 10 20 m 30A b s t a n d E rde r -Sonde

H ow wou ld you explain the vol tage U B e z . s 0 n d e for d = 0 m?

electric shock protection

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