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Question
how to calculate cable size, olr rating, contactor rating 
and mccb rating,to below given details three phase motor
75 kw,415 v,.85 pf,50 hz?
 Question Submitted By :: Sakkaravarthi Soganur Arakonam
I also faced this Question!!     Rank Answer Posted By  
 
  Re: how to calculate cable size, olr rating, contactor rating and mccb rating,to below given details three phase motor 75 kw,415 v,.85 pf,50 hz?
Answer
# 1
motor rating 75kw,so it taken full load p=1.732*v*I*cosfy
i= p/1.732*v*cosfy
=123 amp. so we requared a cable to carry 123 amp
contonious rating. so require to run motor in star delta
starter . in star delta connection load current is 58% of
line current. we require 58% of 123 amp carring capasity
cable.it is around 71 amp.generly copper cable taking 4
times current of cable rating and alluminium cable taken
1.5 times of cable ratting .so for 71 amp carring alu.
cable 50mm2 suffisent but due to high starting curent its
take 70 mm2 cable ib best.
its overload relay ratting is in range to 71 amp. it to be
60-80 amp,and mccb rating is 2.5 times of full load =300amp
is best.
 
Is This Answer Correct ?    33 Yes 32 No
Rsbangra
[Grasim Ind.(birla White)]
 
  Re: how to calculate cable size, olr rating, contactor rating and mccb rating,to below given details three phase motor 75 kw,415 v,.85 pf,50 hz?
Answer
# 2
motor rating 75kw,so it taken full load p=1.732*v*I*cosfy
i= p/1.732*v*cosfy
=123 amp. so we requared a cable to carry 123 amp
contonious rating. so require to run motor in star delta
starter . in star delta connection load current is 58% of
line current. we require 58% of 123 amp carring capasity
cable.it is around 71 amp.generly copper cable taking 4
times current of cable rating and alluminium cable taken
1.5 times of cable ratting .so for 71 amp carring alu.
cable 50mm2 suffisent but due to high starting curent its
take 70 mm2 cable ib best.
its overload relay ratting is in range to 71 amp. it to be
60-80 amp,and mccb rating is 2.5 times of full load =200
amp
is best.
 
Is This Answer Correct ?    24 Yes 16 No
Brakadeesh
 
 
 

 
 
 
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