Designing Outgoing Feeders in LT Panels

Can you define some of these acronyms, please? What's an "L.T." panel"?

Need some information

Incoming: ampere?

Outgoing: ampre ? how many Mccb? 3 or 4 pole or both

Hello friend,

First of all the concept of LT panel itself is wrong. It creats confusion to understand. When the operating voltage is 415volts we say its MEDIUM voltage. Accordingly we have to name the electrical panel as MEDIUM VOLTAGE PANEL . In short its M.V.PANEL.

The breaker rating has to be the next available higher size of the connected load of the feeder. There is no necessity of neutral cut off, & hence a TP MCB can be used connecting the feeder neutral to the common neutral bus in the panel. This saves the cost.

UNDER NORMAL SITUATIONS WITH VOLTAGES UNDER 600V DICONNECTING THE NEUTRAL IS NOT NEEDED. UNLESS THE EQUIPMENT THE FEEDER IS BEING CONNECTED TO, REQUIRES COMPLETE ISOLATION UPON THE REMOVAL OF THE ELECTRICAL SERVICE. IF THAT IS THE SITUATION THE NEUTRAL MUST BE BROKEN AT THE SAME TIME THE POWER IS REMOVED FROM THE FEEDER.

Klsvp72,

I've looked at your posts. Are you in school? or are you just trying to increase your knowledge on your own? One source I have used many times is the manufacturer's data sheets, catalogs, engineering and application data, and similar materials. Trade handbooks and texts are worth locating and reading. All these will probably give you more information (but possibly less exposure to experience) than CR4.

--JMM

Dear Sir,

Please note that LT Voltage 415VAC derived from secondary of star conneced transformer which is earthed at the neutral end .If we derive LT 415VAC from this secondary voltage of this transformer to LT Board Incomer and this LT Board is required to feed 3-phase load as well as no of also single phase loads P-N (say 240VAC) then the neutral of transformer has to be brought to LT board.This is done by having (3-P+N )or 4-Pole ACB/MCCB as incomer of LT Board.Through fourth pole of this MCCB/ACB neutral is connected to LT Board Bus.(R-Y-B-N).

If you have load which requires 3-P and neutral which in turn distributes as R-N,Y-N,B-N loads as in the case of Illumination system then neutral is required in out going feeder too.

Further 4-P MCCB gives flexibility of isolation of all phases R-Y-B-N at the same time for maintenance purpose instead of having fixed connected nrutral connection.

Hope I have made myself clear

V.Ambarani

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Dear ambarani,

Thanks for the clarification.

Regards,

klsvp72

Hi ambarani

I an not an expert in panel design but i wish to share my little knowledge.

As regards to the selection of feeder breakers, the right choice may be a three pole breaker with an isolatable neutral link for all power loads involving three phase supply such as motors etc.,

For other loads involving sensitive equipment like UPS and other computer related equipment you can go in for a 4 pole version (or) a TP version with a switched neutral. Hope I am some what correct in my logical conclusion.

Ramesh