KYORITSU 4116A - Page 15

L1
L2
L3
N
PE
R
R
O
RCD 30mA
― 13 ―
Forthis examplemax value is1667Ω, theloop tester reads12.74Ω, it
meansthatthecondition
RA
＜
50/Ia
isrespected.
Itisfundamentalforthisexample totestalsotheRCDto ensurethat
operationtakesplacequicklyenoughtorespectthesafetyrequirements.In
ordertodoit,canbeusedtheRCDtestermodel5406A.
AccordingtotheinternationalStandardIEC60364forTNsystem the
followingconditionshallbefulfilledforeachcircuit:
Zs
＜
Uo/Ia
Where:
¡
Zs
istheFaultloopimpedance.
¡
Uo
isthenominalvoltagebetweenphasetoearth.
¡
Ia
isthecurrentcausingtheautomaticdisconnectionoftheprotective
devicewithinthetimestatedintableasfollows:
Note:
● Fora distribution circuita disconnection time notexceeding 5s is
permitted.
● Whentheprotectiondeviceisaresidualcurrentdevice(RCD),
Ia
is
theratedresidualoperatingcurrentI
⊿
n.
Uo(Volts)
120
230
400
>400
T(seconds)
0.8
0.4
0.2
0.1
Fig.8
PracticalexampleofverificationoftheprotectioninaTTsystemaccording
totheinternationalStandardIEC60364.