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# calculating csa of earthing conductor with BS1361 fuse

Discuss calculating csa of earthing conductor with BS1361 fuse in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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#### knasher

Welcome to ElectriciansForums.net - The American Electrical Advice Forum

Maybe I'm overlooking the obvious but how would you calculate the min. csa of an earthing conductor of say a tn-s system when there is no time/current graph for a 1361 fuse in the BGB? Do you just obtain If from Uo/Ze and then use this in the adiabetic equation. Ta

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#### i=p/u

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keep it simple and use same size as line conductor... but yes adiabatic is your friend

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#### Deleted member 26818

Look in a copy of the BRB, or obtain the information from the fuse manufacturer.
You would not be able to conduct the adiabatic equation without this information, as you require a value for 't'.

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#### knasher

Thanks Spinlondon, ive still got BRB somewhere, so will dig it out.

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#### knasher

As a matter of interest, what is the logic behind IET not bothering to do time/current graphs for certain fuse types?

#### ruston

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From the BGB -1361 spec for cartridge fuses for ac in domestic or similar premises replace by BS 88-3: and withdrawn 1/3/2010.

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#### knasher

Hi rushton, are you saying BS88-3 is now the replacement for the 1361 fuse? or that BS88-3 replaced the BS1361 fuse but now not deemed as a suitable replacement? Just trying to get this clear in my head please

#### chocca

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So, to satisfy an old man's confusion, if the installation has a BS1361 fuse and it's now been turned into a BS88 type 3 by the magic of the BGB, do you use the info for BS88 fuses in the tables?

#### ruston

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Yes as understand it the spec for BS 1361 has been removed and replaced by BS88 -3: 2010 . It's on page 277 of the green book. and the book will only list the current standards. Appendix 1 on the top of the page gives the criteria.

#### ruston

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So, to satisfy an old man's confusion, if the installation has a BS1361 fuse and it's now been turned into a BS88 type 3 by the magic of the BGB, do you use the info for BS88 fuses in the tables?
I would still use the old specs its as clear as mud.

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#### Deleted member 26818

It's the same as with the old BS3871 MCBs.
Still in use, but the time current curves are no longer in BS7671.

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