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Aucom Emx3 - Type 1 Coordination

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#1 MB123


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Posted 02 July 2016 - 07:33 AM

Hi All,


The EMX3 manual states that HRC fuses are required for type 1 coordination to 50kA


Is this really necessary? 


What is the short circuit rating of the starter itself, without any protection? Our prospective fault rating is 20kA, and there will be an MCCB upstream of the drive which will limit the fault current to 7kA. Surely the starter can withstand this without exploding and potentially harming the MCC or persons in the vicinity?


The manual doesn't really give much more than the minimum required information.




Michael Belperio


#2 marke


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Posted 02 July 2016 - 08:57 AM

Hello Michael


Thirty years ago, it was common place to use semiconductor fuses to provide SCR protection.

Today, it is normal to operate the starters without semiconductor fuses. This increases the risk of SCR failure under a short circuit condition, but the cost of replacing multiple fuses is often higher than replacing one or two SCRs.


The SCR fuses begin to melt well below the maximum energy let through of the SCRs, but it is not possible to find fuses where the prearcing I2t is close to the total clearing i2t.


If you really want to use semiconductor fuses under high start duty conditions, you really need to go up another starter size again, just to overcome premature fuse failures.



Best regards,


#3 MB123


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Posted 02 July 2016 - 09:03 AM

Kia Ora Mark


Thanks so much for your quick reply


We have some starters in the MCC which have the semiconductor fuses and are designed for Type 2 Coordination - the starter and fuse combination has been advised by NHP


However most of our starters only have to meet Type 1 coordination, so I am confused if we need to use fuses at all on these - the manual says HRC fuses are required for Type 1 coordination, not the semiconductor fuses - but the resulting withstand values are very high, much higher than we need for this application.

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