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Low-Voltage Power Distribution and Installation Technology

MCCB KA selection

Thread Starter: PISCEAN 2010   Started: 11/19/2010 5:26 AM   Replies: 27

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  11/19/2010, 5:26 AM
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Hello Experts,
I ahve to select 3 pole MCCB at input side of a machine. My question is whether I should go for 25 KA capacity MCCB or 50 KA capacity MCCB?Can any one help me.
Thanks in advance.
DEEP.

Tell me and I will forget. Show me and I will remember. Involve me and I will understand. -Confucius
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  11/22/2010, 10:59 AM
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Hello everybody,
30 views so far but not a single reply. Is it so difficult?
DEEP.

Tell me and I will forget. Show me and I will remember. Involve me and I will understand. -Confucius
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  11/26/2010, 9:53 AM
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Hello Experts,
Ok I will put this in another way. While selecting MCCB which one should be prefered i.e. 25 KA capacity or 50 KA capacity.
Regards,
DEEP.

Tell me and I will forget. Show me and I will remember. Involve me and I will understand. -Confucius
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  12/2/2010, 11:48 AM
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Dear Deep,

          MCCB selection is depends on the Fault level of your Busbar ( or Incoming Transformer KA fault level). Based on your Fault level you can select the MCCB.

Regards,
Srrr
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  12/2/2010, 11:51 AM
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Dear Deep,

          MCCB selection is depends on the Fault level of your Busbar ( or Incoming Transformer KA fault level). Based on your Fault level you can select the MCCB.

Regards,
SrrrRnf:lblSmileyTooltip_
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  12/5/2010, 7:23 AM
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Hello srrr-in,
Thanks for your reply. But we have equipped with Distribution panel board system & in this case e.g. suppose connected load is 70 Kw 3 phase, 415 Volt, 50 Hz. Main supply protection SFU is 160 Amp capacity, aluminium bus bar capacity is 25 mm x 3 mm 1 no per line. In this case what capacity MCCB to be selected means 50 KA or 25 KA? & what are the selection creteria?
Thanks in advance.
DEEP.

Tell me and I will forget. Show me and I will remember. Involve me and I will understand. -Confucius
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  12/16/2010, 1:14 PM
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Dear  Deep,

                What is your LT Transformer Fault Level????

Sridhar          

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  12/20/2010, 1:30 PM
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Hi srrr-in,
Where shall I get that information.
Regards,
DEEP

Tell me and I will forget. Show me and I will remember. Involve me and I will understand. -Confucius
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  2/11/2011, 3:31 PM
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Hello Deep,

As an example you could check the "
Planning Manual - Planning with SIVACON S8, Flexible Low-Voltage Switchboard", available on http://support.automation.siemens.com/WW/view/en/20356391/133300. Chapter 8.10 provides a table showing short-circuit currents of three-phase distribution transformers.

These are maximum values on the transformer output. The longer the cable way from the transformer to your panel the lower this value (impedance of the cable).

Regards,

Sentronix

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  2/12/2011, 7:56 AM
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Hi sentronix,
thank you very much for your valuable information. From the table, existing transformer short circuit current of transformer is 32,791 (tranformer rating is 1500 KVA) But agin my basic question is what capacity MCCB should I select 25 KA or 50 KA? & why?
Thanks & regards,
DEEP. 

Tell me and I will forget. Show me and I will remember. Involve me and I will understand. -Confucius
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