What is the difference between MCB, MCCB, ELCB, and RCCB
MCB (Miniature Circuit Breaker)
CHARACTERISTICS • • •
Ra t e dc u r r e ntn o tmo r et h a n1 00A. T r i pc ha r a ct e r i s t i c sn sn or ma l l yn otadj us t a bl e. Th er ma lo rt h er ma l ma gn et i cop er a t i o n. Top
MCCB (Moulded Case Circuit Breaker)
CHARACTERISTICS • • •
Ra t e dc u r r e ntu pt o10 0 0A. T r i pcu r r e ntma ybead j u st a bl e . Th er ma lo rt h er ma l ma gn et i cop er a t i o n. Top
Airr Ci Ai Circ rcui uitt Br Brea eake ker r CHARACTERISTICS • • • •
Ra t e dc u r r e ntu pt o10 , 0 00A. T r i pchar ac t er i s t i c sof t enf ul l yadj us t abl ei nc l udi ngconfi gur abl et r i pt hr es hol dsanddel ay s. Us ua l l yel e ct r o ni c al l yc on t r o l l e d—s omemo mo de l sar emi mi c r o pr o ce ss orc on t r o l l e d. Of t e nu se df o rma i np owe rd i s t r i b ut i o ni nl a r g ei n du st r i a lp l a nt ,wh er et h eb r e a ke r sa r ear r a ng edi nd r a wo ute nc l o su r e sf o re as eo fma i n t e na nc e. Top
Vacuum Circuit Breaker CHARACTERISTICS • • •
Wi t hr a t e dc u r r e ntu pt o30 00A, The sebr e ak er si n t e r r u ptt hear ci nav ac uu mb ot t l e . Th es ec anal s obeap pl i e da tu pt o35 , 0 00V.Vacuum ci r cui tbreakerst e ndt oh av el o ng erl i f ee x pe ct a nc i e sb et we eno v er h au lt h and oa i rc i r c ui tb r e ak e r s . Top
Limitation of RCCB •
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St andar del ect r omechani calRCCBsar edesi gnedt ooperat eonnormalsuppl ywavef ormsa n dc a n no tb egu a r a n t e e dt oo pe r a t ewh er en on e s t a nd a r dwa v e f o r msar ege ne r a t e db yl o a ds .Th emo s tc o mmo ni st h eh a l fwa v er e c t i fi e dwa v e f o r ms o me t i me sc a l l e dp ul s a t i n gd cg e ne r a t e db ys pe e d c o nt r o ld ev i c e s ,s e mi c o nd uc t o r s , c o mp ut e r sa nde v endi mme r s . Sp ec i a l l ymo di fi e dRCCBsa r ea v a i l a bl ewh i c hwi l l o pe r a t eonno r ma la can dp ul s a t i n gd c . RCDsdon’ tofferpr ot ect i onagai nstcur r entover l oads:RCDsde t e cta ni mb al a nc ei nt h el i v ea ndn eu t r a lc ur r e nt s .Ac ur r e nto v er l o ad ,h o we v erl a r g e, c a nn otb ed et e c t e d.I ti saf r e qu en tc a us eofp r o b l e mswi t hno v i c e st or e p l a c ea nMCBi naf u s eb oxwi t hanRCD.Th i sma ybedo nei nanat t e mp tt o i n cr e as es ho ckpr o t e ct i o n.I fal i v e n eu t r a lf a ul to cc ur s( as ho r tc i r c ui t ,o ra no v er l o ad ) , t h eRCDwo n’ tt r i p ,a n dma yb ed ama ge d.I np r a c t i c e,t h ema i nMCB f ort hepr emi s eswi l lp r o bab l yt r i p,ort hes er v i c ef us e,s ot hes i t ua t i o ni sun l i k el yt ol eadt oc at as t r op he;b uti tma ybei n con ve ni ent . I ti sn o wp o s s i b l et oge ta nMCBa nda ndRCDi nas i n g l eu ni t ,c a l l e da nRCBO ( s e ebe l o w) .Re p l a c i n ga nMCBwi t ha nRCBO o ft h es a mer a t i n gi s ge ner al l ys af e. Nui sancet r i ppi ngofRCCB: Su dd ench an ge si nel e ct r i c all o adca nc au seas ma l l ,b r i e fc ur r e ntfl owt oe ar t h ,e sp ec i a l l yi nol dap pl i a nc es .RCDsar ev er y s en si t i v ea ndo pe r a t ev e r yqu i c k l y ;t h eyma ywe l l t r i pwh ent hemo t o ro fa no l df r e ez ers wi t c he so ff.So mee qu i p me nti sno t o r i o us l y` l e ak y ’ ,t h ati s ,g en er a t e as ma l l ,c on st a ntc ur r e ntfl owt oea r t h .So met y pe so fc omp ut e re q ui p me nt ,a ndl a r g et e l e v i s i o ns et s ,a r ewi d el yr e po r t e dt oca us ep r o bl e ms . RCDwi l lnotpr o t e cta ga i ns tasoc ke tout l e tbe i ngwi r e dwi t hi t sl i v eandne ut r a lt e r mi na l s t hewr ongwayr ound. RCDwi l ln otpr o t e c ta ga i ns tt heov e r h ea t i ngt h atr es ul t swhenco nd uc t or sar eno tpr o per l ys c r e wedi nt ot he i rt e r mi n al s . RCDwi l lnotpr o t e cta ga i ns tl i v ene ut r a ls hoc ks,b ec au set h ecur r e nti nt h el i v eandneu t r al i sbal an ced .Soi fy out ou chl i v ea ndneu t r al c on duc t or sat t h es amet i me( e. g. ,bo t ht er mi n al sofal i ghtfi t t i n g) ,y ouma ys t i l l ge tana st ysh oc k . Top
ELCB (Earth Leakage Circuit Breaker)
CHARACTERISTICS • • • • • • •
Ph as e( l i n e) ,Ne ut r a la ndEa r t hwi r ec on ne c t e dt h r o u ghEL CB. EL CBi swo r k i n gb a s edonEa r t hl e a k ag ec u r r e n t . Oper at i ngTi meofELCB: T hes af e s tl i mi to fCu r r e ntwh i c hHu ma nBo d yc a nwi t h s t a n di s3 0mas ec . SupposeHumanBodyResi st ancei s500Ω andVol t aget ogroundi s230Vol t . T heBo d yc ur r e n twi l lb e50 0 / 2 30 =4 60 mA. HenceELCBmust beoper at edi n 30maSec/ 460mA=0. 65msec Top
RCBO (Residual Circuit Breaker with OverLoad) •
I ti sp os s i b l et oge tac omb i n edMCBa ndRCCBi no nede v i c e( Re s i d ua lCu r r e ntBr e ak e rwi t hOv e r l o adRCBO) ,t h ep r i n c i p al sa r et h esa me ,b utmo r e s t y l e so fd i s c on ne ct i o na r efi t t e di n t oo nep ac k ag e Top
ifference !etween ELCB and RCCB • • •
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EL CBi st h eo l dna mean do f t e nr e f e r st ovo l t a geop er a t e dd ev i c est h ata r en ol o ng era v ai l a bl ean di ti sad vi s edy our e pl a cet he mi fy o ufi ndon e. RCCBo rRCDi st h en e wn amet h a ts p e c i fi e sc ur r e n to pe r a t e d( h en c et h en e wn a met odi s t i n gu i s hf r o mv o l t a g eo p er a t e d ) . Thene w RCCBi sbe stb ec au sei twi l l d et e cta nyea r t hf a ul t .Thev ol t a get y peo nl yde t e ct sea r t hf a ul t st h atfl owb ac kt h r o ug ht hema i nea r t hwi r esot h i si s wh yt h e ys t o pp e db e i n gus e d. Thee as ywa yt ot e l l a no l dv ol t a geo pe r a t e dt r i pi st ol o okf o rt h ema i ne ar t hwi r ec on ne ct e dt h r o ug hi t . RCCBwi l l o nl yha v et h el i n ea ndn eu t r a lc o nn ec t i o ns . EL CBi swo r k i n gb as e do nEa r t hl e ak a gecu r r e nt .Bu tRCCBi sno th av i n gs e ns i n go rc o n ne c t i v i t yo fE ar t h ,b ec a us ef u nd ame nt a l l yPh as ecu r r e nti seq ua l t ot h en eu t r a lc ur r e nti ns i n gl eph as e.Th at ’ swh yRCCBc ant r i pwh ent h eb ot hcu r r e nt sar ede f e r e nta ndi twi t h st a ndupt obo t ht h ec ur r e nt sa r es ame .Bo t h t h en eu t r a la ndph as ecu r r e nt sar edi ff er e ntt h atme an scu r r e nti sfl owi n gt h r o ug ht h eEa r t h . Fi n al l ybot har ewor k i ngf ors ame,bu tt het hi ngi scon ne ct i v i t yi sdi ff er en ce. RCDdoe sno tn ec es sa r i l yr e qui r eane ar t hc onne ct i oni t s el f( i tmoni t or sonl yt h el i v ean dneu t r a l ) . I nad di t i oni tde t e ct scur r e ntfl owst oe ar t he veni n e qu i p me ntwi t h ou ta ne ar t ho fi t sown . Th i sme an st h ata nRCDwi l l c o nt i n uet og i v es h oc kpr o t e c t i o ni ne qu i p me ntt h ath asaf a ul t yea r t h .I ti st h es ep r o pe r t i e st h ath av ema det h eRCDmo r e p op ul a rt h ani t sr i v a l s .Fo re x a mp l e ,e ar t h l e ak ag ec i r c ui tb r e ak e r s( EL CBs )we r ewi d el yu se da bo utt e ny e ar sa go .Th es ede v i c esme as ur e dt h ev ol t a geon t h ee ar t hco nd uc t o r ; i ft h i sv ol t a gewa sn otz er ot h i si n di c at e dacu r r e ntl e ak ag et oea r t h .Th epr o bl e mi st h atEL CBsne edas ou ndea r t hco nn ec t i o n,a s d oe st h ee qu i p me nti tp r o t e c t s .Asar e s u l t ,t h eu s eo fEL CBsi sn ol o ng err e c omme nd ed . Top
MCB "election •
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Thefir s tc har ac t er i s t i ci st heov er l o adwhi c hi si nt end edt opr e ventt heac ci d ent al o ver l oa di ngoft h ec ab l ei nanof aul ts i t u at i on.Thesp ee doft heMCB t r i p pi n gwi l l v ar ywi t ht h ed eg r e eo ft h eo v er l o ad .T hi si sus ua l l yac hi e v edbyt h eu seo fat h er ma ld ev i c ei nt h eMCB. These co ndc ha r a c t e r i s t i ci st h ema gn et i cf a ul tp r o t e ct i o n,wh i c hi si n t e nd edt oo pe r a t ewh ent h ef a ul tr e ac he sap r e de t e r mi ne dl e v el a ndt ot r i pt h eMCB wi t h i nonet en t hofase co nd .T hel e vel oft hi smag ne t i ct r i pgi v est h eMCBi t st y pech ar ac t er i s t i casf ol l o ws :
Ty pe
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Tr i ppi ngCur r ent
Oper at i ngTi me
TypeB
3To5t i mef ul ll oadc ur r ent
0. 04To13Sec
TypeC
5To10t i mesf ul l l oadc ur r ent
0. 04To5Sec
TypeD
10To20t i mesf ul l l oadc ur r ent
0. 04To3Sec
Thet h i r dc har ac t e r i s t i ci st hes hor t c i r c ui tpr o t ec t i on ,wh i c hi si n t e ndedt opr o t ec tag ai ns th ea vyf au l t sma ybei nt hou sand sofamp sc aus edb ys hor t c i r c ui t f aul t s . Theca pa bi l i t yoft h eMCBt oope r a t eund ert h es ec ond i t i onsgi v esi t ss ho r tc i r c ui tr a t i ngi nKi l oamp s( KA) .I nge ner al f orc on sumeru ni t sa6KAf au l tl e vel i sad eq ua t ewh er e asf o ri n du st r i a lb oa r d s10 KAf a ul tc ap ab i l i t i e so ra bo v ema yber e q ui r e d. Top
#use and MCB characteristics •
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F us e sa ndMCBsar er a t e di namp s .Th ea mpr a t i n gg i v e no nt h ef u s eo rMCBb od yi st h ea mo un to fc u r r e nti twi l l p as sc on t i n uo us l y . Th i si sn or ma l l y c al l edt her at edc ur r en to rn omi n al c ur r en t . Man ypeo pl et hi n kt ha ti ft h ec ur r e nte x cee dst h enomi nal c ur r en t , t hede vi c ewi l l t r i p ,i ns t a nt l y .Soi ft her at i ngi s30amps ,ac ur r entof30. 0 0001amp swi l l t r i pi t ,r i ght ?Thi si snott r u e. Thef u sean dt h eMCB,e v ent h ou ght h ei rn omi n al c ur r e nt sa r es i mi l a r ,h av ev er yd i ff er e ntp r o pe r t i e s. F ore x a mp l e ,F or3 2 AmpMCBa nd30AmpFu s e ,t obes ur eoft r i p pi n gi n0. 1s ec o nd s ,t h eMCBr e q ui r e sac u r r e n to f1 2 8a mp s ,wh i l et h ef u s er e q ui r e s 300a mps . Thef u s ec l e ar l yr e q ui r e smo r ec ur r e ntt ob l o wi ti nt h att i me ,b u tn o t i c eh owmu chb i g ge rb h es ec ur r e nt sar et h ant h e’ 3 0a mp s ’ma r k e dc ur r e ntr a t i n g. o t ht The r ei sas ma l l l i k e l i h oo dt h ati nt h ec ou r s eof ,s a y ,amon t h ,a3 0a mpf u sewi l lt r i pwh enc ar r y i n g3 0a mp s.I ft h ef u seh asha dac ou pl eo fo v e r l o ad s b ef o r e( wh i c hma yno te v enh av eb ee nn ot i c e d)t h i si smu c hmo r el i k e l y . Th i se x pl a i n swh yf u s esc ans o me t i me s‘ b l o w’ f o rn oo bv i o usr e as o n I ft hef us ei smar k ed’ 30amps ’ ,b uti twi l l ac t ua l l ys t and40amp sf o ro v eranhou r ,ho wc anwej u st i f yc al l i ngi ta’ 30amp’f u se?Th ean swe ri st hatt he o v e r l o adc h ar a c t e r i s t i c soff u s esar ed es i g ne dt oma t c ht h ep r o pe r t i e so fmo de r nc ab l e s .F o re x amp l e ,amo de r nPVCi n s ul a t e dc a bl ewi l l s t a nda5 0% o v er l o adf o ra nh ou r ,s oi ts ee msr e as on ab l et h att h ef u sesh ou l daswe l l .
RC (Residual Current evice $ RCCB(Residual Current Circuit Breaker)
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Ph as e( l i ne )a ndNe ut r a lb o t hwi r e sc o nn e c t e dt h r o u ghRCD. I tt r i pst h ec i r c ui twhent her ei sear t hf aul tc ur r ent . Theamo un to fc ur r e ntfl owst h r o ug ht h ep ha se( l i n e)s ho ul dr e t u r nt h r o ug hn eu t r a l. I td et e c t sb yRCD.a nymi s ma t c hb et we ent woc u r r e nt sfl owi n gt h r o u ghp ha s ea ndn eu t r a ld et e c tb yRCDa ndt r i pt h ec i r c u i twi t h i n3 0Mi l i s e c on ed . I faho us eh asanea r t hs y st e mc o nn ec t e dt oanea r t hr o dan dn ott h ema i ni n c omi n gc a bl e ,t h eni tmu s th av eal l c i r c u i t sp r o t e c t e db yanRCD( b ec a us eu mi t eno tb ea bl et oge te no ug hf a ul tc ur r e ntt ot r i paMCB) RCDsar eanex t r e me l yeff ec t i v ef o r mo fs h oc kpr o t e c t i o n
Th emo s twi d el yus e da r e3 0mA( mi l l i a mp )a n d1 00mAd ev i c e s .Ac u r r e ntfl o wo f3 0mA( o r0 . 0 3a mp s )i ss uffic i e nt l ys ma l lt h ati tma k esi tv e r yd i ffic u l tt or e c e i v e ada ng er o uss ho c k.Ev e n1 00mAi sar e l a t i v e l ys ma l l fi g ur ewh enc omp ar e dt ot h ec u r r e ntt h atma yflo wi nanea r t hf a ul twi t h ou ts u c hp r o t e c t i o n( h un dr e do f amps ) A3 00 / 5 0 0mARCCBma ybeus edwh er eon l yfi r epr o t e ct i o ni sr e qu i r e d.e g. ,o nl i g ht i n gc i r c ui t s ,wh er et h er i s kofe l e ct r i cs ho cki ss ma l l .
