Starting Current of Ventilation Fan

Once again, the fundamental data for the correct selection of a breaker is missing. It is there to protect the wiring, which the forum is told nothing about. Good grief - the forum is even being denied the supply voltage!

The thing that protects the motor on the fan is the overload unit.

Correct discrimination between them is obtained by following the provisions in British Standard 7671.

choose 25A MCB (thermal + magnetic(9-14 times rated current)) ....its more thn necessary.more preferred is a MPCB instead of MCB.

For what voltage supply? Not 110VAC, surely?

breaker selection is determined by the current drawn and is in place to protect the cable. im judging by the 50 hz that it is 415 volts. inrush current has no effect. i would suggest choosing a 'D' class breaker thermal magnetic which is most common these day. designed to handle a higher inrush

Would that be suitable for a 7/0.29 cable?

The NEC will allow up to 250% of the FLA which you did not list. Wire size is 125% of FLA which you did not list disregarding voltage drop. VD may increase the requirements.

If he is discussing a 63A MCB (Miniature Circuit Breaker), there's about a 99.99% chance he is not in the USA, so our NEC would be meaningless. But you b ring up an excellent point in that the REAL determining factor is whatever is dictated by the LOCAL code wherever you are. That's where you start.

Or better yet as already expressed, if he has to ask he should not be attempting this, he should hire a professional.

Thanks all.

By checking out the tripping curve and characteristic of the CB,

I may use a rate current of 25A (thermal+magnetic) type C/ type D one
which can undertake the starting current around 10times In,
correct me if i am wrong and thanks again.

I belive it is a 15hp motor running on 415 50hz 3 ph rated FL amps at 21A. A 30 OR 40 AMPS MCB would be sufficient with appropriately sized cables to the breaker. The type of starting, a star delta starter or auto transformer starter would be fine.The actual protection for the motor would be from the overload relay.All said very easily but the actual starting current of a fan would depend on the actual condition. Most fans have a long high starting load.

It all depends on the size of your conductors.

Hence #1⇑.

Have you thought about the usage of a variable frequency drive unit? We use these items very much here in the states, they are used to help protect the drive belts on large fans and work on the principle of, as a soft start to the motor and fan relation.

Your informations are not complete.we need to know the fan rated voltage and current.However just to give some useful values,i will assume your voltage to be within 380,400 or 415volts with a 50Hz frequency.

11.2kw motor may give us about21.27 or 22.4amps.lets take 22.4amps multiplied by a factor of 1.8 which gives 40.32amps.21.27 times 1.8 gives 38.29amps.In either case,you may select an MCB of 40amps to protect the fan motor from short cct fault.For overload fault,use thermal overload relay with range up to 25amps and set the relay at21.3amps or 22.4amps respectively.

Your selection of 63amps MCB is over rated

Patrick Whowha

<...selection of 63amps MCB is over rated...>

That depends upon several factors including the conductor size and length, method of installation, etc., which the original poster still hasn't shared with the forum.

The <...overload relay...> will protect the motor, and not the wiring.

If in doubt, consult a qualified local Electrician. This role is there to adequately design, select, install, test and certify as safe the intended installation on completion.