ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Motor control centers

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!