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What Would Be the Fault Clearing Time of a Motor (415V)

11/19/2012 1:57 AM

if no data is provided then we assume the fault current of a motor (415V) as 20 times the FLC, but how to calculate the fault clearing time. is there any standards?

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#1

Re: what would be the fault clearing time of a motor (415V).

11/19/2012 2:10 AM

It depends on what fuses and/or circuit breakers there are. They have charts or tables that tell how fast they will open at various fault currents.

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#2

Re: what would be the fault clearing time of a motor (415V).

11/19/2012 3:11 AM

British Standard 7671.

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#3

Re: what would be the fault clearing time of a motor (415V).

11/19/2012 5:23 AM

The clearing time has to be less than maximum stalling time[cold].But the maximum current -temporized-has to be starting current-6-8 times rated full current[see also Manufacturer catalogue or instructions].Usually maximum stalling time 6-8 sec.

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Julius
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#4

Re: what would be the fault clearing time of a motor (415V).

11/19/2012 7:01 AM

Motors don't clear faults. Circuit breakers and fuses clear faults.

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#5

Re: What Would Be the Fault Clearing Time of a Motor (415V)

11/19/2012 1:01 PM

In the open post it is required the "fault clearing time" for the inrush current[20 times FLC]. For this current no need a clearing time

since after half of a wave [1/60 or 1/50 seconds]the phenomenon disappears alone. But if one need a motor protection against overload,

rotor locked, voltage unbalance, one phase disconnected and short circuit at terminals the protecting time is not connected-directly-with the

fault clearing at breaker or fuse level .That will be the last stage of very limited time. Usually the breaker "clear" the fault in about 100 milliseconds and the fuse[rapid one] in less time.

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