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Discuss Max Zs @ 80% TN-C-S System in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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Morning all,

I'm currently finishing off my Lvl 3 C+G and I just need to finish off my design spreadsheet then I'll have completed it. I've one last column to fill in "Max Zs @80%" the design is based on a hotel using a TN-C-S supply. I'm just wanting to know where I can find this information in the On Site Guide.

Thanks
 
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You can use the values from Tables 41.2 to 41.4 in BS7671. Just calculate the 80% value from those.
 

H

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Arms
The values in the OSG for max Zs are already adjusted. As Westy said regards BS7671 you have to multiply those by 0.8
 

Strima

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Arms
Esteemed
I see and you can get all the maximum Zs for each circuit in the osg on the page stated above.
The figures in BS7671 are the maximum permitted, the ones in the OSG have been adjusted to 80% for ease.

These also take into account Cmin.
 
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