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Anonymous Poster

using mcb / isolator

11/16/2009 12:14 PM

how do we select between mcb and isolator for a incomer in distribution board?

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#1

Re: using mcb / isolator

11/16/2009 1:12 PM

question is not clear .mcb and isolatore has different application.

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Participant

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#3
In reply to #1

Re: using mcb / isolator

11/16/2009 9:38 PM

I want the difference in application

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Active Contributor

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#2

Re: using mcb / isolator

11/16/2009 3:32 PM

HI,

I guess that mcb means Main Circuit Breaker. I also guess that isolator means Main Isolator.I also guess that you are dealing with an AC Distribution Board. My final guess is that you are referring to an existing distribution board, and you want to select between a MCB and an Isolator for the main disconnect. If all my guesses are correct, then you can use the following method:

A MCB and an isolator can isolate the supply and can also tripp but you will have to sustain an overcurrent. In some main circuit breakers you can replace the tripping mechanism in order to adjust current rating of the MCB. You can also remove the tripping mechanism and now you have an on/off switch.

If your load is highly inductive, an isolator is your preffered choice. This is so because the speed of the "break" is much faster than a cb. This must be so in order to Quench the arc. Some isolators are fully imersed in oil in order to quench the arc.

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#4

Re: using mcb / isolator

11/17/2009 3:04 AM

An isolator is a manually operated switch.

A miniature circuit breaker can do this, though in addition it has an automatic trip function based upon the current flowing through it and the time that the current flows through it.

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Power-User

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#5

Re: using mcb / isolator

11/17/2009 8:19 AM

guest; i believe an isolator is the same as a open switch. perry

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Guru

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#6

Re: using mcb / isolator

11/17/2009 10:06 AM

MCB is Miniature Circuit Breaker and it has Overcurrent Release and Short Circuit Release in built. It is capable of breaking any current upto its rated breaking capacity (say, 10kA).

Isolators are plain switching devices capable of breaking currents only upto their rated current. They do not have a release (either for over current or for short circuit). They are cheaper when compared to MCBs.

There is no hard and fast rule that you should go only for MCB or Isolator as Incomer. The choice is yours. Economy would call for an isolator and good engineering practice would call for an MCB.

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Participant

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#7
In reply to #6

Re: using mcb / isolator

11/18/2009 10:56 AM

thanks for your clear reply and right under standing of my question.

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Anonymous Poster
#8
In reply to #6

Re: using mcb / isolator

01/03/2011 8:10 PM

Dear electricalexpert65,

what about the rating of isolator and MCB? Is it OK if I have an upstream MCB rated at 25A and a downstream isolator (with earth leakage 100mA) rated at 40A? Meaning to say the rating of isolator is higher than the incoming MCB.

Thank you.

Regards,

Yusri

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Users who posted comments:

Anonymous Poster (1); electricalexpert65 (1); ganeshrethinam (2); JOSHIKD (1); perry (1); PWSlack (1); Taslim (1)

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