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**latafat junaid said: **

Dear Sir,

Q1: during making a single line diagram,when i calculated the the total load,then which approperciate cable size i will select,means formula

Q2: For example: f the load s 40 A,Then how i will select MCCB, means i can use the 60A MCCB 3-Phase,but s there s any special arrangement to calculate for MCCB.

Q3: Cable size let say ” 3C,185 mm2″ how capacity of current it will take,any possible formulas r tables for all cable sizes and required MCCB?

A good /satisfaction answers & prompt response will be highly appreciated.

Thanks

Dear ;

**Q1 :**

To do the correct choice of cable, we do as following :

– We calculate the load's current that we called ” Ib “.

– We define the ” Kind ” and the ” Ibtallation Methode ” of cable, then define the correction factors, and multipy them to have the total factor correction ” k “

– We calculate the carrying of current for cable in standard conditions that is ” Iz = Ib / k “.

– Then by the tables of ” IEC 60364-5-52 ” we can do the coorect choice of cable's section.

**Q2 :**

To de define the specification of Circuit Breaker that shpould be installed, we should do our choice of the main specifications of CB that are : ” Nomber of Poles ; Thermal Protection – Ir ; Magnetic Protection – Isd or Im ; The breaking Capacity “, so, we do as following :

– The nomber of poles will be defined accordongly to the ” kind of circuit & Earthing System used “.

– After doing the above methode to define the Cable's Section, we can define de value of ” Ir ” accordingly to ” Ib ≥ Ir ≥ Iz . k “.

– To define the value of ” Isd or Im “, we should calculate the ” minimum short circuit current – Isc1min ” between ” phase & neutral ” at the end of cable, and calculate the ” Earth Fault – If ” also at the end of cable, then the value if ” Im ” should be msaller than the smalest calculated value.

– To define the ” Breaking Capacity “, we should calculate the ” maximum short circuit current – Isc3max ” at the begining of cable, then the value is ” Breaking Capacity ≥ Isc3max “.

**Q3 :**

We can know the capacity of current or the carrying of current of cable from the tables of ” IEC 60364-5-52 ” after define the kind of cable that means : Single or Multi ; Cu or Alu ; PVC or XLPE ” and also the ” Methode of Installation ” . Noting that value is in Standard Conditions that means the total correction factors is ” 1 “.

Regards.