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Member

Join Date: Aug 2012
Location: coimbatore
Posts: 6

20 hp Motor Connection Circuit

06/18/2013 8:31 PM

Dear sir ,

i am using 20 hp compressor .motor to be connect on star - delta wiring .3nos ML2 Power contactor used contactor coil as 440 v supplied .additionaly using there single phase preventor & 2 phase off delay timer . how to given supply ? how is working ML2 power contactor ?

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Guru

Join Date: Jun 2007
Location: chennai,India
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Good Answers: 19
#1

Re: 20 hp Motor Connection Circuit

06/19/2013 3:03 AM

ML2 contactor is L&T Make. AC 3 duty is 32 Amps.But L&T has introduced new range of contactors.

Please contact L&T or their dealer request them to provide you Star Delta Starter wiring diagram. You can follow the wiring diagram and wire the starter.

The OFF delay timer is not required, however ON delay timer is required.

I have basic doubts about your requirement.

Generally for compressor it is preferable to use DOL starter as against Star Delta starter.

If you are using MCCB /MPCB for controlling the incoming supply for the 20 hp motor 32 Amps Contactor will be under rated. You should use 38/40 Amps Contactor.

If you use Fuse switch unit with HRC fuses, then 32 Amps Contactor will be in order.

I would advise you to get help of qualified experienced Engineer for this task.

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Guru

Join Date: Jul 2005
Location: Stoke-on-Trent, UK
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#2
In reply to #1

Re: 20 hp Motor Connection Circuit

06/19/2013 4:24 AM

Generally for compressor it is preferable to use DOL starter as against Star Delta starter. That's right, unless the compressor is unloaded for starting there is not enough torque to start it in star.

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Member

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Posts: 6
#4
In reply to #1

Re: 20 hp Motor Connection Circuit

06/19/2013 11:30 AM

thank u sir

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Anonymous Poster #1
#7
In reply to #1

Re: 20 hp Motor Connection Circuit

06/23/2013 12:49 PM

"If you are using MCCB /MPCB for controlling the incoming supply for the 20 hp motor 32 Amps Contactor will be under rated. You should use 38/40 Amps Contactor.

If you use Fuse switch unit with HRC fuses, then 32 Amps Contactor will be in order."

What is the reason sir...?

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Guru

Join Date: Oct 2009
Posts: 2061
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#8
In reply to #7

Re: 20 hp Motor Connection Circuit

06/30/2013 7:11 PM

The sizing of the contactor is done based on short circuit withstand too. If a HRC fuse is used as an SCPD (Short Circuit Protective Device), its clearing time for a heavy short circuit would be lesser (about 4 to 5 milliseconds). So, a contactor has to withstand carrying the short circuit current only for a lesser duration; and, thus a smaller siae contactor would suffice.

Whereas, if an MPCB or MCCB is used as an SCPD, the fault clearing time is slightly higher at 8 to 10 milliseconds. Thus, the I2t withstand requirements of the contactor goes up. Hence, go for a higher sized contactor in this case.

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Guru

Join Date: Oct 2008
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#3

Re: 20 hp Motor Connection Circuit

06/19/2013 11:15 AM

Do as ramvinod said, HIRE A COMPETENT, QUALIFIED ELECTRICIAN.

You are not qualified.

No offense, but that's the truth.440 volts can be lethal!

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Member

Join Date: Aug 2012
Location: coimbatore
Posts: 6
#5
In reply to #3

Re: 20 hp Motor Connection Circuit

06/19/2013 11:47 AM

i learn quickly sir .

thank u

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Guru

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Posts: 42369
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#6
In reply to #5

Re: 20 hp Motor Connection Circuit

06/19/2013 12:03 PM

You get no second chances when learning about 440volt power at somewhere around 30 AMPS.

You will lose arms and feet if you mess up.

Don't do it.

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Users who posted comments:

Anonymous Poster (1); Codemaster (1); electricalexpert65 (1); lyn (2); palanisamy (2); ramvinod (1)

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