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specs of a soft starter


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Hello Uhaykir


The specs really are dependant on what you are looking for. I will cover a few points, and perhaps someone else can fill in the gaps.


Firstly, soft starters com in two control philosophies, open loop and closed loop. Open loop starters do not monitor the current and provide a simple ramping voltage start. It is important to preset the parameters to suit the load. Short ramp time for low inertia and long ramp time for high inertia.

Closed loop starters monitor the current and control the voltage to produce the required current during start. - more sophisticated.


Some starters include motor overload protection, - others don't. The levels of protection range from the very simple inverse time / current overload to the more complex thermal model simulating winding temperatures.


Starters cna control one phase, two phases or three phases. The three phase option gives the best performance, but at the higher price. If you have a high inertia load or frequent starts, then the three phase contorl option is a must. 1 or 2 phase controllers cause more heat rise during start.


Reverse parallel connected SCRs rated at three times line voltage is recommended for three phase usage.


Soft starters are available in chassis mount format which must be mounted inside an enclosure through to totally enclosed high IP units requiring no extra expenditure. - check the total installed cost before buying the cheapest component.


Some manufacturers promote the energy saving option on soft starters. In reality, this will do nothing for you except in a very small number of cases, and can lead to additional problems such as continuous RFI and even increased motor losses. See http://www.lmphotonics.com/energy.htm


Uhaykir, the options are many. If you give more details of your application, perhaps we can help to narrow down what you should be looking for.

You could also have a look at some of the site on soft starters such as AuCom Electronics


Best regards,

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  • 1 month later...

The European standard applying to soft starters is IEC60947-4-2 If the starters are to be used in Europe, then they should comply with this standard and be CE marked.

In the USA they should comply with UL508 and be UL recognised.

In New Zealand and Australia, they should at least have Ctick.


When comparing soft starters, ensure that you are comparing like with like. Ratings are a major area of discrepancy. A starter rated at 200% current for 10 seconds, or even 30 seconds will not start anything because the motor will not produce enough torque.


Some starters are rated to have a very long cool down period before a restart.


AC53a and AC53b are the correct utilization categories for soft starters. Refer to IEC60947-4-2 for details.


[Edited on 12/6/02 by marke]

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  • 4 weeks later...

Hello Uhaykir


IEC 60947-4-2 forms part of a series of standards relating to 'Low Voltage Switchgear & Control Gear'.


The reason I mention this is because it ensures all aspects of the soft starter product comply with other relevant standards.


For example; if the soft starter provides motor protection funtions, then these functions must comply with the standards relevant to motor protection.


It is my opinion that IEC 60947-4-2 identifies the ideal product for current industrial environments, however as suggested by Marke other standards may apply depending upon your location.




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Hello Marke,


My interpretation of your post to our friend Uhaykir is that C-tick compliance is all that is required to satisfy the needs of the Australian soft starter market.


As you may be aware the Australian & New Zealand derivative of IEC 60947-4-2 is AS/NZS 3947-4-2. This standard was published during the month of August 1997 and is now included in most if not all project specifications involving soft starter products.


A soft starter product that carries the CE mark or C-tick logo does not necessarily comply with AS/NZS 3947-4-2!!


I look forward to any further comments you may have on this subject.




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CTick is the minimum standard for any electrical equipment sold in New Zealand and Australia, but I would certainly expect complience with ****947-4-2 as being very much required. Equipment sold in Europe must carry the CE mark. This means that it complies with all relevent standards, not just EMC and so as IEC 60947-4-2 is the Soft starter standard, compliance is required for the CE mark. In New Zealand and Australia, Ctick only refers to part of the EMC specs. i.e. a subset of the EMC part of IEC947-4-2 in the case of the soft starters.

In Europe, beause of CE marking, compliance is mandatory, but in NZ and Aus it is often specified by the end user, but my understanding is that it is not a mandatory standard.

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