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Associate

Join Date: Oct 2009
Location: kuruman NC. SOUTH AFRICA
Posts: 51

# Neutral

03/23/2012 4:00 PM

Hi Guys

there is alot of confusion regarding the term flowding neutral.

can somebody please explain the flowding neutral in detail please.

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Dan Segami
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Guru

Join Date: Apr 2010
Location: Mid Western USA - The Corn Belt
Posts: 1439
#1

### Re: Neutral

03/23/2012 4:22 PM

Hi Danny,

I assume you are referring to a "floating" neutral.

If that is the case have a look at some of these.

Regards - KJK

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Power-User

Join Date: Nov 2011
Posts: 171
#2

### Re: Neutral

03/23/2012 4:31 PM

If your neutral is disconnected from ground or not connected to the ground, it is called that your neutral is a floating neutral.

Analysis of a floating vs. grounded output

Power-User

Join Date: Apr 2010
Location: Dominican Republic
Posts: 189
#3

### Re: Neutral

03/24/2012 8:06 AM

A floating neutral can be a serious problem. Suppose you have a breaker panel with 2 Line inputs and a neutral. The voltage between each line is 240 and the voltage between each line and the neutral is 120. You have single breakers feeding loads that require 120Volts. These 120Volt loads have one line fed by the breaker and a neutral. The double breakers have 2 lines and no neutral for 240Volt loads. Now suppose the Neutral gets loose or oxidized or somehow disconnected in the panel or maybe even out where the power comes from. The 240Volt loads will be unaffected however the 120V loads can be in serious trouble. With this Floating neutral condition you will discover that one of the two lines will go from 120Volts up to 180 or 190 and the other line will go down to 50 or 60 volts. Half of your 120Volt equipment will go up in smoke and the other half will not function due to a low voltage condition.

So, be careful with floating neutrals.

John

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Commentator

Join Date: Jul 2010
Location: North West Province, South Africa
Posts: 67
#4

### Re: Neutral

03/24/2012 4:15 PM

Hi Danny,

You are 100% right - in South Africa there seems to be a lot of confusion regarding the cause and effects of a floating neutral.

As you are aware, in SA our supply line voltage is phase to phase 400v and phase to neutral 230v (may vary slightly from area to area). The supply comes from the secondary of the stepdown transformer where the output is connected in Star where the Star point becomes the Neutral and this is earthed at this point.

Now in order to explain the phenomenon of a 'floating neutral' we should look at a building which is supplied by from a three phase + neutral + earth supply connection - everything would operate correctly if the neutral remained connected.

Should the neutral be disconnected (in SA usually stolen) the building wiring system would now be effectively connected in Star (all the neutral wires from the various 3 phase circuits taken to a common neutral bar). So long as the three phases are balanced (equally loaded) the neutral would be stable but as soon as an unbalanced load is connected the unbalance affects the voltage at the Star point (the neutral bar) and this is your 'floating neutral' which would continually vary according to the unbalance across the three phases.

The practical effect of this is that instead of the phase to neutral voltage being 230vac you are likely to measure between 280 & 320vac which is why so much damage is done to appliances etc. connected to a system where the neutral has been disconnected.

In other countries where I have worked a Protective Multiple Earthing (PME) system is used where the neutral line is earthed at multiple points e.g. at every distribution board and this helps to overcome this problem.

In SA the cable theft problem (in a lot of cases just the neutral & earth wires) has become a major problem not only because of the loss of cable but also the resultant damage to the end user's appliances.

Hope this helps you!

Regards, Keith

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