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earth wire size fro motors


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#1 tahira

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Posted 22 October 2002 - 09:41 AM

how to calculate the SWG for earth wire , it also depend on load ?
some body tell me the general rule i.e earth wire size half the cables used for equipment.plz tell me in detail

#2 BigMax

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Posted 23 October 2002 - 06:06 AM

Hello tahira,

In general, the earth conductor should be large enough to 'safely' carry the prospective short circuit current. This really means that the earth conductor must be of sufficient cross sectional area to safely (ie without excessive temperature rise) carry the short circuit current until the branch protection device (ie circuit breaker/fuse) clears.

In practice, how do you apply this information?

Here in Australia, I would refer to Australian Standard AS3000, which lists common Active conductor sizes with minimum applicable Earth conductor sizes. In general, the size ratio varies by between 30-50% or so. Unfortunately there is no simpe fixed ratio.

An alternative (and more complex, as per AS/NZS3008) approach is to calculate the size required based on prospective short circuit currents, expected fault duration and protective device clearing times. Most of this information is not readily available, therefore reference to AS3000 is easier (for me).

My suggestion therefore would be to refer to your local standards.

I hope this is helpfull.

BigMax

#3 grobert

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Posted 24 October 2003 - 03:38 AM

In the USA we call it the "equipment grounding conductor". Its size ,is as stated above, is based on the OCP (over current protection) on the phase conductors serving said equipment. We follow table 250.122 from the NEC to size the ECG.

#4 Guest__*

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Posted 06 February 2004 - 12:18 PM

QUOTE
Originally posted by tahira
how to calculate the SWG for earth wire , it also depend on load ?
some body tell me the general rule i.e earth wire size half the cables used for equipment.plz tell me in detail


#5 jhun

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Posted 06 February 2004 - 12:23 PM

QUOTE
Originally posted by tahira
how to calculate the SWG for earth wire , it also depend on load ?
some body tell me the general rule i.e earth wire size half the cables used for equipment.plz tell me in detail




50% of your current load

#6 Guest__*

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Posted 15 September 2004 - 03:55 PM

the earth as to be half the conductor size over 16mm

#7 porky

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Posted 21 January 2007 - 06:50 PM

I disagree ....the earth wire should be greater or equal to the current carring conductor... It should offer less resistance to the flow of current or the fault current might take a different path ...

#8 AB2005

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Posted 22 January 2007 - 02:13 AM

Hi Tahira;

We are working at a new project and following JAAKKO POYRY standards. We also select the main earth conductor for machines the half size of power cable. If power cable is, for example, 120mm˛, then we select 70mm˛ earth conductor.

"Don't assume any thing, always check/ask and clear yourself".




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