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Motor control centers #135552
01/15/03 08:19 PM
01/15/03 08:19 PM
K
kitha  Offline OP
Member
Joined: Nov 2002
Posts: 12
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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Re: Motor control centers #135553
01/16/03 01:31 AM
01/16/03 01:31 AM
Trumpy  Offline

Member
Joined: Jul 2002
Posts: 8,231
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.

Re: Motor control centers #135554
01/16/03 10:56 AM
01/16/03 10:56 AM
L
lighthouse  Offline
Member
Joined: Jan 2003
Posts: 134
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.

Re: Motor control centers #135555
01/16/03 12:01 PM
01/16/03 12:01 PM
P
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
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.

Re: Motor control centers #135556
01/16/03 07:52 PM
01/16/03 07:52 PM
K
kitha  Offline OP
Member
Joined: Nov 2002
Posts: 12
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.

Re: Motor control centers #135557
01/17/03 03:19 AM
01/17/03 03:19 AM
C
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
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. [Linked Image] (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).]

Re: Motor control centers #135558
01/17/03 07:05 AM
01/17/03 07:05 AM
P
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
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.

Re: Motor control centers #135559
01/17/03 10:48 PM
01/17/03 10:48 PM
L
lighthouse  Offline
Member
Joined: Jan 2003
Posts: 134
philadelphia pa 19125
pauluk..i just check out the link you posted.an like i said.i don't know. [Linked Image] boy what a differance.the nec is so much easier.


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

Re: Motor control centers #135560
01/18/03 06:27 AM
01/18/03 06:27 AM
P
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
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.

Re: Motor control centers #135561
01/31/03 11:10 PM
01/31/03 11:10 PM
Trumpy  Offline

Member
Joined: Jul 2002
Posts: 8,231
SI,New Zealand
kitha,
Did you finally get the answer, you were looking for?. [Linked Image]

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