Star Delta Cable

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Anonymous Poster #1	Star Delta Cable 09/29/2014 2:50 PM
	I have one question. star-delta starter motor have 2 run cable.if motor full load current is 40A so it will divide in two part i.e 20A in main contactor and 20A in star or delta depend upon running? please confirm
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Crabtree Guru Join Date: Jul 2007 Location: Commissariat de Police, Nouvions, occupied France, 1942. Posts: 2599 Good Answers: 77	#1 Re: Star Delta Cable 09/29/2014 3:14 PM
	I have one question. Why do you want to use underrated contactors? __________________ Good moaning!
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Anupam Diwan Active Contributor Join Date: Sep 2010 Location: India Posts: 11	#4 In reply to #1 Re: Star Delta Cable 09/30/2014 3:04 AM
	its not about contactors its about cable.what i want to know is actual current in both cable ie connected to main contactor and connected to star (starting)/delta (running) contactor.
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wareagle Guru Join Date: Jun 2008 Location: Alabama Posts: 1604 Good Answers: 63	#2 Re: Star Delta Cable 09/29/2014 4:39 PM
	I do not understand your question but if you have 2 cables of the same size and length, they will each carry 1/2 half of the load. Is this what you wanted to know?
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JRaef Guru Join Date: Sep 2006 Location: California, USA, where the Godless live next door to God. Posts: 4665 Good Answers: 804	#3 Re: Star Delta Cable 09/29/2014 8:50 PM
	No, because if you are starting in Star, the current will be 58% of normal at that time, so everything needs to be sized for that as a minimum and in accordance with your local codes for proper sizing (for example here in the US we must over size at 125% of that value). Then it is fine for when it is connected to run in Delta, where yes, the current will be evenly split between the two sets of cables. __________________ All I every really wanted to be, was... A LUMBERJACK!.
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7anoter4 Guru Join Date: Oct 2012 Location: 100 miles North from the World Center Posts: 879 Good Answers: 42	#5 Re: Star Delta Cable 10/01/2014 2:18 PM
	As jraef explained, if we shall follow NEC Art.430.22 Single Motor (C) Wye-Start, Delta-Run Motor then the cable ampacity of the cable in the Wye-Start has to be at least 1.25/sqrt(3)=0.72 *Irated.[Irated as per Table 430.250 Full-Load Current, Three-Phase Alternating-Current Motors]. Since the transit from star to delta is short -usually-the ampacity could be less. IMO NEC considers the ampacity for continuous load [no switch to Delta?]. If there are two parallel cables connected to the main motor terminals-and it is not the cable connecting the star point or the other for delta connection-and if the cable are identical-same conductor, same length [same temperature?]-then the main supply current will split in two equal parts. __________________ Julius
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