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Mohamed Akram Khan
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Join Date: Mar 2012
Posts: 48

LV Bus Bars For Switchboard

06/11/2014 1:16 AM

I need to specify bus bars in a switchboard for LV. The design current is 200 A. I read somewhere that the short circuit rating for up to 400A should be 25 kA for 1 sec. What should be the rated current? 2x200 = 400A?

Thank you
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silverfox
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Join Date: Nov 2011
Posts: 286
Good Answers: 15
#1

Re: LV Bus Bars for Switchboard

06/11/2014 2:42 AM

suggest you don't specify these bars. Without an understanding of the supply to the board, without an understanding of the protection serving the board, without knowing the cables supplying the board and without knowing you need to know these my suggestion is hand this job over. It will make sense in the long run and save on fire extinguishers.
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Mohamed Akram Khan
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Join Date: Mar 2012
Posts: 48
#2
In reply to #1

Re: LV Bus Bars for Switchboard

06/11/2014 2:52 AM

Please note that all the factors which you are stating are known and have been taken into consideartion before the question was asked
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silverfox
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Posts: 286
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#3

Re: LV Bus Bars for Switchboard

06/11/2014 4:36 AM

at only 200A do you even need a fault rated board?

25kA at 1 sec is a typical type of spec for a switchboard usually hung off the end of a 1MVA transformer. You make no mention of the transformer, where the board is fed from. What is the PSCC at the board? Without this sort information you can't begin to get to the right answer.
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Blackpaper
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Join Date: Mar 2014
Posts: 75
#4
In reply to #3

Re: LV Bus Bars for Switchboard

06/11/2014 12:50 PM

Only typical. Not always.
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silverfox
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Join Date: Nov 2011
Posts: 286
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#8
In reply to #4

Re: LV Bus Bars for Switchboard

06/13/2014 2:33 AM

Typical - depends whether there are current limiting fuses - there might be a huge run of cable reducing the fault, it migt be close coupled. Like I said typical only but in the right ball game. There are lots of variables that must be taken into account and we have been given none of them to play with. I'm thinking our original poster is really looking for an LV panelboard - 8 way TP&N type of thing with a 200A incomer.
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pnaban
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Join Date: Jun 2010
Location: srilanka
Posts: 2725
Good Answers: 5
#5

Re: LV Bus Bars For Switchboard

06/11/2014 11:11 PM

consider the fault/short circuit level at the switchboard

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DHARAMRAJSINH
Active Contributor

Join Date: Feb 2014
Posts: 10
#6

Re: LV Bus Bars For Switchboard

06/12/2014 1:13 AM

Regarding bus bar size only:- you need to specify actual current drawn by panel. i.e. in panel rating, design ambient temperature, material of bus bar and its density and Fault level at bus bar.

based on that vendor shall give you final size / cross sectional area of bus bar with considering de rating factor of temp. and other factors.
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beentheredonethat
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Join Date: Sep 2011
Location: Durban South Africa
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Good Answers: 2
#7

Re: LV Bus Bars For Switchboard

06/12/2014 4:57 AM

I don't know.
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Blackpaper
Commentator

Join Date: Mar 2014
Posts: 75
#9

Re: LV Bus Bars For Switchboard

06/13/2014 4:22 AM

Where did you read that?
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Jignesh Shah
Associate

Join Date: Mar 2014
Location: Mumbai, India
Posts: 25
#10

Re: LV Bus Bars For Switchboard

07/30/2014 8:42 AM

Unless fault level at this switchboard is known, there is no point in specifying what kA for what time level (0.5, 1, 3 s). Better do fault level calculation upto the point specified.
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Users who posted comments:

beentheredonethat (1); Blackpaper (2); DHARAMRAJSINH (1); Jignesh Shah (1); Mohamed Akram Khan (1); pnaban (1); silverfox (3)

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