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Topic Title: Earthing Conductor Installation / High Zs
Topic Summary:
Created On: 21 January 2019 08:53 AM
Status: Read Only
Linear : Threading : Single : Branch
 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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 21 January 2019 02:35 PM
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OMS

Posts: 22864
Joined: 23 March 2004

It would be worth looking at the potential to replace the standard thermal/magnetic trip unit with a micrologic electronic unit (they are usually interchangeable on the particular MCCB

There is certainly something adrift in the measured Zs (unless the Ze is particularly high) - and it should be perfectly reasonable to adjust a 250A MCCB with electronic tripping to have a much lower earth fault pick up threshold to accommodate a circa 180m run of 120mm2 SWA (you might need to pick a 200A unit to go in the 250A breaker frame

I suspect the original install would probably have never achieved 5s disconnection under earth fault condition

Regards

OMS

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