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Max Zs @ 80% TN-C-S System

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

16vMatt

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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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westward10

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

PJH2903

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You need to look at appendix B (page 125 in the on site guide)

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

Zs=Ze+R1+R2

Zs/100×80

Arms
Esteemed

Strima

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Arms
Esteemed
Enlightening
It certainly is a long way round of getting the answer...

Ashley-Joseph

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It certainly is a long way round of getting the answer...
Sorry I am currently studying level 2 so this is what I know. There is probably an easier way.

Strima

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Arms
Esteemed
Sorry I am currently studying level 2 so this is what I know. There is probably an easier way.
Zsx0.8

Ashley-Joseph

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I see and you can get all the maximum Zs for each circuit in the osg on the page stated above.

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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