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Switchgear selection

7/11/2013 12:57 PM	Rate (1)
kinjalpatel1899 Posts: 61 Rating: (15)	Hello everybody, If i have HP rating of any motor then can how can i calculate the ratings of Switchgears(e.g. SFU/MCCB, contactor, OLR) without using the selection chart?
kinjalpatel1899 Posts: 61 Rating: (15)
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7/11/2013 9:03 PM	Rate (0)
Nicky123 Posts: 59 Rating: (2)	You just calculate first the current rating from HP by using below equation. 1HP = 0.746 KW I = P/V Here I is current, V is voltage & P is power which is in kw. Once u get current from above just calculate 20% higher rating from the value got from above equation.
Nicky123 Posts: 59 Rating: (2)
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7/12/2013 8:41 AM	Rate (0)
PISCEAN 2010 Posts: 8092 Rating: (884)	Nicky123 You just calculate first the current rating from HP by using below equation. 1HP = 0.746 KW I = P/V Here I is current, V is voltage & P is power which is in kw. Once u get current from above just calculate 20% higher rating from the value got from above equation. If it is DC above is ok. For AC I =P/(1.732Vcos phi)
PISCEAN 2010 Posts: 8092 Rating: (884)
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7/12/2013 2:35 PM	Rate (0)
CS Moderator Moderator Joined: 9/1/2005 Last visit: 10/31/2025 Posts: 4114 Rating: (195)	new question split to type-2 Selection chart for 380V AC. Best regards CS Moderator
	My Forum is the place to personalize your profile, track your topics, and maintain content that interests you. Best regards CS Moderator
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7/13/2013 7:43 AM	Rate (1)
jeet2907 Posts: 235 Rating: (52)	kinjalpatel1899 Hello everybody, If i have HP rating of any motor then can how can i calculate the ratings of Switchgears(e.g. SFU/MCCB, contactor, OLR) without using the selection chart? Dear kinjal First of You have to convert HP to KW for finding current easily. 1HP=0.746KW, After that using below formula you can find the current P=1.732 x V x I x cosPhi so, I= P/1.732 x V x CosPhi for AC THREE PHASE AND I=P/ V X CosPhi FOR AC SINGLE PHASE AND I= P/V FOR DC . After getting current you can select switchgera 1rating higher then its actual requirement . i hpoe u will got it. Regards
jeet2907 Posts: 235 Rating: (52)
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This contribution was helpful to 1 thankful Users kinjalpatel1899

7/13/2013 8:57 AM
jeet2907 Posts: 235 Rating: (52)	kinjalpatel1899 Hello everybody, If i have HP rating of any motor then can how can i calculate the ratings of Switchgears(e.g. SFU/MCCB, contactor, OLR) without using the selection chart? Dear kinjal First off all you have to convert HP to KW so you can easily find out the current, 1) 1HP= 0.746KW 2) P=1.732 x V x I x Cosphi for AC three phase system. 3)P=V x I x Cosphi for AC single phase system. 4) P=V x I for DC system, where P= power in kw V= voltage in volt I = current in ampere Cosphi= power factor now after finding current you can select switch gear 1 rating higher then actual current vallue for stable working I hope you will got it.
jeet2907 Posts: 235 Rating: (52)
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