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8 comments
Participant

Join Date: Apr 2008
Posts: 3

Circuit Breaker selection????

05/12/2008 10:14 AM

Hi all,

I am using 15KW 3 phase 380VAC sequiral cage induction motor, which will take aprx 30 Amp. I want to install a Circuit breaker in its circuit for line protection. what should be rating or specs of that Breaker? which things I should note for this selection.

Thanks in advance

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Guru
New Zealand - Member - Kiwi Popular Science - Weaponology - New Member Engineering Fields - Power Engineering - New Member

Join Date: Sep 2006
Location: Auckland, New Zealand
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Good Answers: 29
#1

Re: Circuit Breaker selection????

05/12/2008 3:19 PM

I am always a little disturbed when people ask these sort of questions. The answer is a simple one and if you don't know it you are not qualified to perform the electrical work (especially given your previous posts).

I am hardly going to offer advice that I believe will put either the poster of the question or others that may come into contact with the posters work in potential danger. That would be very unprofessional of me (and others). I advise you to get an electrician or other suitably qualified professional to perform the work for you.

Guru

Join Date: Sep 2006
Location: California, USA
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#2
In reply to #1

Re: Circuit Breaker selection????

05/12/2008 4:09 PM

To clarify that a bit better for the Original Poster, selection of protection devices is a key component of any electrical installation and should only be done by professionals. But it is also something that is very specific to the location you are in, meaning there are codes and governances that vary in each country, state even municipality. So you need a professional IN YOUR AREA who knows how to do this safely, correctly and legally.

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#5
In reply to #1

Re: Circuit Breaker selection????

05/27/2008 1:27 AM

I am sorry to say sir, your comment is not good either. This is a forum where we learn. We are all people in the practical field. May be this is the debue for the person. We cannot imply our own predictions about somebody's qualification. If the person is ignorant then its your duty to expound the matter more than what He needs.

Guru

Join Date: Sep 2006
Location: California, USA
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#6
In reply to #5

Re: Circuit Breaker selection????

05/27/2008 3:10 PM

I think you misinterpreted my comment. The point I was making is that the
"proper selection" is NOT just a purely engineering endeavor, it also involves adherence to local codes and laws in a given country. It would be irresponsible for me to explain how we do it here, because that might be illegal where he is!

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Guru
New Zealand - Member - Kiwi Popular Science - Weaponology - New Member Engineering Fields - Power Engineering - New Member

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#7
In reply to #5

Re: Circuit Breaker selection????

05/27/2008 3:43 PM

Point noted but this is not the cross-stitching or painting forum. The answer to the original post is actually simple and the original poster should know it or at the very least, know where to find it. Remember, as a professional our job is also to protect others. I have answered other questions like this, generally with comments suggesting that they refer to the motor or circuit breaker manufacturer documentation (the answer is in there and should be the first place to look).

Here is a question for you, would you answer this hypothetical question posted on CR4.....

" Hi all, need plans for mercury dispersion and vaporisation system. Also diagram of electric detonator."

The answer is clearly no in this extreme case. The key point is that in the end it comes down to a personal judgement call - what do I think the poster would do with this information if I give it to him/her and will it be used responsibly and not cause harm.

Hopefully this short post clears up a few things for you and gives the original poster a better idea on where they should look for this information if they have not found it already.

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#3

Re: Circuit Breaker selection????

05/12/2008 5:10 PM

I agree with the last two comments....Motor protection should be sized by a professional.....Given this some information for you to know.....Typicall start-up in-rush current can be up to 5 to 6 times the normal running current of the motor...and depending on the ineteria of the load being started the duration of this start-up current varies.....Hence a need to evaluate the I2T requirements to implement proper motor protection....

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Guru
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#4

Re: Circuit Breaker selection????

05/13/2008 8:14 AM

Please consult a competent person on this issue before proceeding with ann installation.

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Member

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#8

Re: Circuit Breaker selection????

05/28/2008 1:05 AM

Vow, Vow. So many comments. It's quite true that such sort of things have to be done by a professional. But how does the professional come into being? Nobody is born professional. He acquires professionalism from various sources. Look , I am also new in the field, so I need help from the experienced guys. I may not do things myself. I just watch the others do that. But the more I go into it, I look for more sources to acquire practical knowledge. This forum happens to be one of those sources.

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