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kuppahalli
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Join Date: Mar 2011
Posts: 22

Air Circuit Breaker

05/12/2011 10:07 AM

What will happen if we connect 3Phase for 4pole Air circuit breaker by keeping nutral open
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kvsridhar
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#1

Re: Aircircuit breaker

05/12/2011 10:16 AM

1. The fact that you have spent extra money for a 4-pole ACB implies that you need the neutral to be switched also.

2. It is not a good practice to keep the neutral open, it may give rise to floating neutral and other undesirable consequences.

3. You can run the neutral through directly, without connecting it to the 4th pole. It will work ok. Except that you cannot open the neutral if required (for switching over to a standby supply for example). But then, why was the 4-pole ACB ordered?

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kuppahalli
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#2

Re: Aircircuit breaker

05/12/2011 10:31 AM

But unfortunatly we got this 4pole breaker because ups require 3pole only. what to do.
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kvsridhar
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#3
In reply to #2

Re: Aircircuit breaker

05/12/2011 10:40 AM

Are you sure about the UPS being only 3 pole? i am surprised. When you have a UPS, my understanding is that you MUST break the neutral. i have not gone into the depth of why, but some experts will doubtless enlighten us.

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electricalexpert65
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#8
In reply to #3

Re: Aircircuit breaker

05/15/2011 10:27 AM

I fully agree with KVS! It is dangerous not to break the neutral. Imagine you have switched off the 3-pole breaker for some maintenance on the UPS! At the same time if there is an earthfault elsewhere in the system, a portion of the earth fault current would circulate thro this unbroken neutral and cause dangerous potential rise inthe UPS neutral thus endangering any person working on the UPS. Please break the neutral for God's sake.
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hien.nguyenquoc
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Engineering Fields - Mechanical Engineering - New Member Engineering Fields - Electrical Engineering - New Member Engineering Fields - Construction Engineering - New Member

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Location: BH, Vietnam
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#4
In reply to #2

Re: Aircircuit breaker

05/12/2011 10:55 AM

What relationship of this 3-pole UPS and the 4-pole breaker?

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KJK/USA
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United States - Member - Member Engineering Fields - Electrical Engineering - Electrical Construction

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#5
In reply to #4

Re: Aircircuit breaker

05/12/2011 11:19 AM

Cousins by marriage

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#6
In reply to #5

Re: Aircircuit breaker

05/12/2011 11:28 AM

Awesome answer to one of the most inane posts i have ever seen

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msamad
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Join Date: Feb 2009
Location: Houston, USA
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#7

Re: Aircircuit breaker

05/12/2011 11:17 PM

This may help:

http://cr4.globalspec.com/thread/53968/Domestic-Installation

- MS

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Users who posted comments:

Anonymous Poster (1); electricalexpert65 (1); hien.nguyenquoc (1); KJK/USA (1); kuppahalli (1); kvsridhar (2); msamad (1)

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