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.

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.

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.

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.

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.

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).]

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.

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).]

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.

kitha,
Did you finally get the answer, you were looking for?.

No Trumpy. I could not find the answers for all. For example I don't know how they take service factor into account, the basis for continuous and non continuous operation(based on duration of operation). I noted one thing, for most of the times they use dual element breakers for branch circuit protections which give overload protection capabilities as well. Additionally they use separate overloads for all the motors above 0.37 kW(IEE 16th edition). Therefore the dual element breaker acts as a back up protection for the overload. Further if the motor consumes say 12 amperes they select the next(15A) breaker with type 3 (or Type D if BSEN) characteristics where their magnetic settings are around 10-20 times their ratings. Therefore those breakers are capable to be used for motor starting. Most of the breakers they use have dual elements and short time long time pickups can be adjusted. When the feeders or branch circuits are calculated what I have noted is, they derate for the ambient temperature correction, grouping, insulation correction. I could not find any article how they classify the motors based on their duty ratings and use the factors like 1.25(as used in NEC and Canadian standards). I appreciate If somebody could give me the hints.

Hi guys!

Been following your discussions for a while. Very interesting stuff. One particular part in the discussions about motors caught my eye.

C-H: ”The smallest standard 3-ph circuit is 16A (using 2.5 mm2) as this is the smallest IEC 60309 plug.”

Maybe I don’t understand what you mean. But If you take a smaller 3-ph motor, let’s say it’s labeled 1,35A. I would use 1.5 mm2 and 10 A fuses.

Kent, in your particular example you know how to select the breaker and the conductors, seems to me by a rule of thumb. My question to you guys is, if there's any properly laid out procedure showing motor calculations and specially feeder and feeder protective devices ratings for couple of motors. I have IEE 16th edition, IEE On site guide, Construction industry training board publications. But could not find answers.

Hurra! En svensk elektriker! Jag vet att du varit här tidigare, men det var ett bra tag sedan du skrev något sist. Rackarns att du skulle fastna på just det jag skrev

Resten av Europa verkar inte dela den svenska förtjusningen för 10A ledningar, kanske främst för att kabel är så mycket billigare. Nu får jag väl byta språk så att våra utrikes vänner förstår...

Back to English:

Indeed, it is possible also to use 1.5 mm2 for small loads. What I meant was that a small load can simply be plugged into one of those standard 3-ph 16A sockets which seems to be everywhere.

Kitha:

"I could not find any article how they classify the motors based on their duty ratings and use the factors like 1.25"

Are you refering to the American practice of sizing to 125% of the continuous load and 100% of the non continuous load? (With non-continuous being less than three hours, IIRC)

BTW. I found an article comparing NEMA and IEC motors at:
http://www.iprocessmart.com/leeson/leeson_iec_article.htm

[This message has been edited by C-H (edited 02-01-2003).]

Tjena C-H! Ja, det var ett tag sedan jag var här sist. Kul med en landsman på forumet. Jobbar du inom branschen eller?

Okay, I understand what you mean.

Ingenjör(snart i alla fall) men i en annan bransch. El verkar vara mycket roligare, så jag funderar allvarligt på att byta.

Guys,
Maybe it's me or my computer, but I have got a large number of Japanese/Chinese characters,preventing me from reading your replies properly.
Sorry about this, I can't help it,.

Chinese/Japanese???? Looks like Swedish to me!

It's really freaky, man!

I think that it's just my computer, in the text, there are Japanese characters where there should be letters.
I don't know how this happened or why,but my God, it's annoying!

Does it look better if I write the characters like this?

&Aring &aring &Auml &auml &Ouml &ouml



[This message has been edited by C-H (edited 02-14-2003).]