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Topic Title: Earthing Conductor Installation / High Zs
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Created On: 21 January 2019 08:53 AM
Status: Read Only
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Earthing Conductor Installation / High Zs   - PWatts - 21 January 2019 08:53 AM  
Earthing Conductor Installation / High Zs   - AJJewsbury - 21 January 2019 12:20 PM  
Earthing Conductor Installation / High Zs   - gkenyon - 21 January 2019 01:56 PM  
Earthing Conductor Installation / High Zs   - chrispearson - 21 January 2019 01:59 PM  
Earthing Conductor Installation / High Zs   - OMS - 21 January 2019 02:35 PM  
Earthing Conductor Installation / High Zs   - PWatts - 21 January 2019 03:56 PM  
Earthing Conductor Installation / High Zs   - Alcomax - 21 January 2019 04:21 PM  
Earthing Conductor Installation / High Zs   - PWatts - 21 January 2019 04:24 PM  
Earthing Conductor Installation / High Zs   - Alcomax - 21 January 2019 05:37 PM  
Earthing Conductor Installation / High Zs   - chrispearson - 22 January 2019 09:48 AM  
Earthing Conductor Installation / High Zs   - AJJewsbury - 22 January 2019 11:01 AM  
Earthing Conductor Installation / High Zs   - mapj1 - 22 January 2019 11:06 AM  
Earthing Conductor Installation / High Zs   - John Peckham - 22 January 2019 11:06 AM  
Earthing Conductor Installation / High Zs   - PWatts - 22 January 2019 04:21 PM  
Earthing Conductor Installation / High Zs   - mapj1 - 22 January 2019 04:27 PM  
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22 January 2019 04:21 PM
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PWatts

Posts: 5
Joined: 05 June 2015

Hi Many thanks again for all of your replies. To Recap the SWA cable run starts at 120mm ad after around 50m it is jointed with torpedo type joint underground in a large pit /Manhole. The joint is totally encapsulated .It would not be possible to rejoint the cable as there is not enough slack and it would cost a lot of money to then put in a new piece of SWA (120mm or 185mm) back to the supply MCCB.The cable is jointed to a 185mm 4 core then travels around 140m to a pump house where it is glanded off into a spreader box below a switch Fuse which then feeds a bus bar which various Supplies then branch off of . There is not a Banjo present or Flying earth lead at either end which we are obviously going to rectify. Having a high Zs of 2.38 ohms of course I am hoping fitting Banjos and flying leads will bring the Earth Loop down but I cannot see it going down to 0.121.I phoned Schneider today and even fitting a Micro Logic electronic trip unit would not bring down the Maximum permitted Zs that much .They explained that setting the Short time trip to 6 would only give a Max Zs of 0.17 at 1200A.Is a right pain but at the end of the day the Earth Loop is too high for a 5 second disconnection time so we are looking at the option of running a separate earth conductor which a contractor has calculated at 120mm.Thats a large Earth to run under the ground for over 180 metres. My calculations were coming out at 95mm but as you can see they were not calculated using a computer program. It might be an idea to fit the banjos , clean up the metal plates and fit flying leads and then take another reading Zs reading before committing to a big spend for the 120mm .Thanks again guys
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IET » Wiring and the regulations » Earthing Conductor Installation / High Zs

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