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pss
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Join Date: Mar 2012
Posts: 2

Neutral Isolation

03/25/2012 9:59 AM

Dear All,

I am working with one of the contracting firm

Our Electrical consultant has indicated TPN breakers (4000A, interlocked) for connecting to load. (No isolation of the neutral)

The system has two source of supply.

A. First sources, is from 2 transformers of 1250 KVA,11kv/415V. Both the transformers have Incomer of 2000A connected to a common Bus. This Bus is inturn, connected to Incoming of 4000A TPN ACB.

B. Second source is from the Generators. 3 Generators of 1000KVA (LT) running in parallel & have their own brekaer. These 3 Generators are also connected to another common bus. This common bus is inturn, connected to incoming of 4000A TPN.

In PCC, these two 4000Amp ACB are on either side & at the centre all loads are connected.

Both these TPN 4000Amp ACB are interlocked. only one will "ON" at a time.

Both neutral are connected.

My question is : Is it right thing to use TPN ACB instead of 4 Pole ACB, where we are using two source of supply?

I feel we should go for 4 Pole ACB instead of TPN ACB for safety. But I dont have any evidence to proove it. I request professional advice, is there any guide line or mandatary rule, insisting for 4 pole breaker for neutral isolation in such condition?

Regds.
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Pathfinder Tags: 4 pole ACB neutral isolation
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msamad
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#1

Re: Neutral Isolation

03/25/2012 9:34 PM

There is some useful discussion on this topic in this forum. You can search for it. Here is one you may get helpful: http://cr4.globalspec.com/thread/53968/Domestic-Installation

- MS

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yooogs
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Join Date: Mar 2012
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#2

Re: Neutral Isolation

03/26/2012 12:21 AM

A small hand sketch of SLD will help in answering your query...

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Mohamed Akram Khan
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Join Date: Mar 2012
Posts: 48
#3

Re: Neutral Isolation

03/26/2012 2:36 AM

Are 4P ACB and TPN ACB not the same?

What I know is that it is general parctice to break the neutral also when a generator is put on line as a standby source. I actually do not know the reason for this.
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manindra
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Join Date: Jun 2010
Location: Kolkata, West Bengal, India
Posts: 172
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#4

Re: Neutral Isolation

03/26/2012 9:34 AM

You are absolutely right to go for 4 Pole ACB instead of TPN for safety reasons as stated below:

Suppose, there is power failure and your DG sets are in running condition to feed the loads; if there is some unbalance in loads(which is unavoidable in L.V. distribution system ), depending of quantum of unbalance, there will be flow of current thro' Neutral. During this time, if Power Supply Utilty's engineers/ technicians are working, and if they touch the neutral conductors(which is earthed at their point ) they will likely to get electric shock depending on the potential rise in common neutral due flow of current thro' Neutral conductor as stated above.Even fatal accident may occur due the above reason.

As such, it is a mandatory practice to isolate the two Neutrals.

Manindra

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electricalexpert65
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Join Date: Oct 2009
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#5

Re: Neutral Isolation

03/26/2012 9:51 AM

It is mandatory that at least either of the Incomers or the buscoupler MUST be 4-Pole Breaker when you have a transformer and a stand-by generator feeding a bus. Pl. refer IS 3043.
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pss
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Join Date: Mar 2012
Posts: 2
#8
In reply to #5

Re: Neutral Isolation

03/26/2012 11:40 AM

Mandataory means by law from Government ? Is it any where specified in any of the regulatory authority guide lines such as I.E rules or Act ? OR IEC code.
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PWSlack
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#9
In reply to #8

Re: Neutral Isolation

03/26/2012 12:25 PM

In this instance, IS stands for Indian Standards.

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electricalexpert65
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#10
In reply to #8

Re: Neutral Isolation

03/26/2012 8:15 PM

Yes, Sir! Pl. refer to the BIS (Bureau of Indian Standards) Code of Practice for Earthing - IS3043. It is very clearly depicted in pictorial form that at least one of the breakers is 4 Pole.
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1capybara
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#6

Re: Neutral Isolation

03/26/2012 10:05 AM

Manindra, that was an excellant explanation. Thank you Sir

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manindra
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#7
In reply to #6

Re: Neutral Isolation

03/26/2012 10:10 AM

Thank you for your compliments.

Manindra.

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1capybara (1); electricalexpert65 (2); manindra (2); Mohamed Akram Khan (1); msamad (1); pss (1); PWSlack (1); yooogs (1)

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