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Starter Ratings to IEC60947-4-2


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Hi All,


As it has been a long time since my last post or response, I thought I might ask a couple of questions that may generate some interest and on-going discussion. These relate to starter ratings presentied in the format described by IEC60947-4-2.


Consider the following example.


125A: AC53a: 3.5 - 10: 70 - 10


125A implies starter rating expressed in Amps


AC53a implies starter is suitable for driving a squirrel cage motor and that the amps rating is based on continuous (non-bypassed) operation.


3.5 - 10 implies a maximum starting current of 3.5 x starter amps for a period not exceeding 10 seconds.


70 - 10 implies an on-load factor of 70% and 10 starts per hour equally spaced.


My questions are as follows:


1. Assuming we are able to start the driven machine within 5 seconds at a starting current not exceeding 3.5 time the starter rating, can we achieve 20 starts per hour (equally spaced and at 70% on-load factor) without compromising starter service life?


2. An on load factor of 70% and 10 starts per hour equally spaced implies a period of 350 seconds between completion of 1 start (ramp) and commencement of the next. What is the affect on starter ratings if the soft stop function is enabled?


I look forward to your responses.




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  • 8 months later...
  • 1 year later...

Hello Schow,


Breakdown of IEC 60947-4-2 is as follows;


IEC 60947 is the standard applicable to Low-voltage Switchgear & Controlgear.


Part 4 of that standard relates to contactors and motor-starters.


Section 2 relates to AC Semiconductor motor controllers and starters.


Hope this helps.




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Thanks for the info but I need details of all sub-clauses, eg. for AC Drive EMC test IEC-61800-3, there are a few tests such as ESD, THD, conducted and radiated immunity, surge etc....If I remember correctly, there are about 7 or 8 tests altogether but for IEC/EN60947-4-2, how many are there?


I tried to check from our local test lab and most of them do not know details about this test. Pls can you tell me what are they? I need to look for a lab who can conduct tests required for IEC/EN60947-4-2.


Cheers! ;c;

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