Thanks you all but I have more questions.
Thanks you all but I have more questions.
Hi PVH
In any case, even the 4.4A would fall below the rating of the minimum cable size we would use so, as far as cable rating is concerned, it's a bit academic. I agree with Crionics in the last post - the motor overloads should be sized for the nameplate current otherwise they won't be protected.
But do you design the supply based on 4.4A or 2.2A....
Here, I would use the 2.2A per motor and rate the supply accordingly. Otherwise you'd end up providing a supply operating at a maximum of 50% of its rating.
Another observation/question. At 2.2A per motor, the supply will have to provide around 50kVA. Do you intend to use a 4-wire three phase 380/220V system?
And a final question. I don't know where you are from - for some reason I have it in mind that it is Malaysia and specifically KL. Whether or not that's correct, I note that your motors are 50Hz. That suggests a country with links to Europe rather than North America. If that's the case, is the NEC code the applicable standard?
Hi Besoeker,
I am from Vietnam where European standard appllied. I tried to search for some helpful instructions from IEC/IEEE but no success. I found in NEC clear instructions and think that I should follow. Would be grateful if you can show me where to find equivalent instructions on how to design my circuit following International/European standards. I am an electrician and this is the first time I got an assignment to do this task.
Yes I use 4 wire 3 phase 380V/220V system.
I use FLC of 4.4A to size the ground fault and short-circuit protection device, and use FLA of 2.2A to size the motor overload protection device. All are clearly stated in NEC.
The results is as follows:
- for 1 motor: overload ratings is FLA x 1.15 = 2.2A x 1.15 = 2.53A and take the lower number of 2.5A (NEC 240.6 (A))
On the other hands, NEC 430.52 specifies selection of overload device ratings as FLC x 1.75 = 4.4A x 1.75 = 7.656A and take the upper number of 8A.
So there is difference btw 2.5A and 8A ratings, but 8A seems more resonable as it is higher than mortor stating current of 7.2A, while I am also concerned if 8A overload device can protect the motor overload of, for example, 5A? My answer would be not, the motor may burn out before overload device can react. For overload, I intend to use time-delayfuse.
I do not know what is guided in IEC?
Any helps are highly appreaciated.