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#135552 - 01/15/03 05:19 PM Motor control centers
kitha Offline
Member

Registered: 11/12/02
Posts: 10
Loc: Hamilton, ON, Canada
Can anybody guide me how to calculate the feeder, branch circuits(final circuits) sizes and respective protective devices as per BS or IEC standards. I am familiar with NEC/Canadian standards only. But I know the current carrying capacity tables from IEE 16th edition and european standard fuse/circuit breaker ratings etc. I do not know how they calculate feeders/branch circuits based on continuous/non continuous mor operations. If you need I can give a problem as follows.

10hp -2 motors(continuous operation)-direct online start
60 hp-1 motor(non continuos operation-less than 3 hrs) and star delta start.

Guide me how to calculate the feeder/branch circuit cables/protective devices(fuses or circuit breakers). How do you take the Service factor into account? Where do you find the locked rotor currents etc. etc. Appreciate your detailed response.

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#135553 - 01/15/03 10:31 PM Re: Motor control centers
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Welcome to ECN, mate!.
Just a few questions regarding your Motor Installation:
What are these motors to be used for?
What Brand are the motors?
Will any other equipment be affected by the Voltage Drop, caused by starting 2 10 Horse motors?, will they start at the same time?
Have you considered using Electronic starters/controllers on these, they are a lot "easier" on the supply.
Look forward to your reply.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#135554 - 01/16/03 07:56 AM Re: Motor control centers
lighthouse Offline
Member

Registered: 01/02/03
Posts: 141
Loc: philadelphia pa 19125
kitha...sorry i can't help you per BS or IEC standards....nec would be no problem.i do think you do need some more info on the motors.
the voltage of the motors.single phase,3 phase.ac/dc.etc and is it fuses or circuit breakers.is it one feed to all 3 motors or 3 seperate feed to each motor.and as far as the service factor of the motor that for sizing the overload/heater.like i said i don't know what the BS or IEC standards are.

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#135555 - 01/16/03 09:01 AM Re: Motor control centers
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
I have to confess that I'm on shaky ground a little here, as I've never really been involved much with big motor wiring.

One of our U.K. industrial guys is probably in a better position to give some guidance on this one.

On the subject of continuous vs. non-continous loads, the IEE Regs. makes less distinction between them, at least not with respect to your specific questions.

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#135556 - 01/16/03 04:52 PM Re: Motor control centers
kitha Offline
Member

Registered: 11/12/02
Posts: 10
Loc: Hamilton, ON, Canada
All these motors are manufactured to IEC standards. All of them are 3 phase 400V, 50Hz. All the motors will not start at the same time but will run at the same time. There is no specific brand name. No need to worry about the voltage drop for other equipments. I need to know the exact procedure to be followed or where I can find the exact procedure etc.

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#135557 - 01/17/03 12:19 AM Re: Motor control centers
C-H Offline

Member

Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
The procedure is probably laid out in some BS and/or IEC standard. (Much of the information contained in the NEC is found in various standards in Europe) If you are unable to find any standard or other information, it can be that the "intuitive" approach is used.

I'm not going to pretend that I know anything about motor sizing, but I did think about one thing that might help you. (Separate circuits for the three motors would seem to be sensible.)

10 hp ~ 7 kW ==> 10A @ 400V 3ph

I expect that you know the power factor and inrush current? The smallest standard 3-ph circuit is 16A (using 2.5 mm2) as this is the smallest IEC 60309 plug. For a 16A type C breaker, the maximum current should stay below 80A.

As for the larger motor: Calculate it as per the NEC and see what numbers you come up with. The laws of physics are the same on both side of the pond. (Although motors are often sized in kW rather than hp on this side.)

[This message has been edited by C-H (edited 01-17-2003).]

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#135558 - 01/17/03 04:05 AM Re: Motor control centers
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
You might find this link useful:
http://www.tlc-direct.co.uk/Book/4.3.9.htm

It's a page on general sizing of cables under BS7671 (IEE Regs.), but if you scroll down to near the bottom you'll see a 3-ph motor example.

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#135559 - 01/17/03 07:48 PM Re: Motor control centers
lighthouse Offline
Member

Registered: 01/02/03
Posts: 141
Loc: philadelphia pa 19125
pauluk..i just check out the link you posted.an like i said.i don't know. boy what a differance.the nec is so much easier.


[This message has been edited by lighthouse (edited 01-17-2003).]

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#135560 - 01/18/03 03:27 AM Re: Motor control centers
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
It used to be easier here too, if you go back to say the 14th edition of the IEE Regs. It started getting complex with the move toward IEC standards in the 15th (1981) edition.

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#135561 - 01/31/03 08:10 PM Re: Motor control centers
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
kitha,
Did you finally get the answer, you were looking for?.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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