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Topic Title: Maximum Zs for BS1361 and BS3871 Type1,2
Topic Summary: could not find a table on 18th edision
Created On: 22 February 2019 08:59 PM
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 22 February 2019 08:59 PM
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aargeitakis

Posts: 162
Joined: 14 July 2005

Hi

I had a look on 18th regs book for maximum Zs values table for BS1361 and BS3871 Type 1,2 but I could not find them.

Any help welcome


Regards

Paul
 23 February 2019 03:32 AM
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Jaymack

Posts: 5571
Joined: 07 April 2004

Originally posted by: aargeitakis
I had a look on 18th regs book for maximum Zs values table for BS1361 and BS3871 Type 1,2 but I could not find them.

BS1361 replaced by ...... on Page 341. Can't see the other but the OSG gives the replacement on Page 79, as BS EN 60898.

Regards

Edited: 23 February 2019 at 03:58 AM by Jaymack
 23 February 2019 04:58 AM
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gkenyon

Posts: 5354
Joined: 06 May 2002

BS 1361 fuses - see Table B5 of OSG. BS 1361 has been replaced by BS 88-3; however, the nominal ratings and loop impedance values differ, so use the values from OSG Table B5.

Similarly, Table B6 in OSG for BS 3871.

The values in Tables B5 and B6 are maximum measured, so if you want the BS 7671 Table 41.2 to 41.4 equivalent, divide by 0.8.

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 23 February 2019 11:09 AM
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Legh

Posts: 4427
Joined: 17 December 2004

BS1361 and BS 3871 last made a showing in the 17th ed, 1st amd, green and 16th ed. 2 amd. yellow, respectively. Not much good if you don't have access to a copy of either.

Legh

-------------------------

http://www.leghrichardson.co.uk

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 23 February 2019 12:07 PM
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gkenyon

Posts: 5354
Joined: 06 May 2002

Originally posted by: Legh

BS1361 and BS 3871 last made a showing in the 17th ed, 1st amd, green and 16th ed. 2 amd. yellow, respectively. Not much good if you don't have access to a copy of either.



Legh
Not completely useless if you use the tables in the OSG that I pointed to earlier.

The reason they're not in BS 7671 now, is that those standards have been withdrawn, see: BS1361:1971 and BS 3871-1:1965

Whereas BS 3036:1958 is still current.

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 23 February 2019 02:40 PM
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Legh

Posts: 4427
Joined: 17 December 2004

Do these obsolete standards sell well across the European Union?
I notice that each tome is over £100 each. In fact the two together adds up to £382!.. At that price for an undersized obsoIete publication I'll demand maximum flippancy....

Legh

-------------------------

http://www.leghrichardson.co.uk

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 23 February 2019 10:37 PM
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Fitzy71

Posts: 311
Joined: 27 February 2018

Originally posted by: aargeitakis

Hi

I had a look on 18th regs book for maximum Zs values table for BS1361 and BS3871 Type 1,2 but I could not find them.

Any help welcome

Regards

Paul


I'll have a look in the 16th edition BS7671 regs I've just acquired and try to post an image of the relevant Zs values.
 24 February 2019 09:37 AM
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AJJewsbury

Posts: 17795
Joined: 13 August 2003

Some care is needed when looking up max Zs values from older editions of the regulations - depending on how far back you go the calculation might have been based on 240V rather than 230V and/or without the Cmin factor - both of which result in larger Zs values than currently permitted.

For MCBs it's relatively easy to calculate Zs values needed for 'instantaneous' operation - if you know the multiple for the type.

B-types operate instantaneously somewhere between 3x and 5x their rating, C-types between 5x and 10x.
Likewise the old type 1s operated between 2.7x and 4x; type 2s between 4x and 7x and type 3s between 7x and 10x.

So for say a 15A type 2 you'd need a fault current of 7x 15A to guarantee instantaneous operation - 105A. By Ohm's Law to get that from a Uo * Cmin = 230*0.95 = 218.5V supply needs a resistance of no more than 2.08 Ohms (BS 7671 value) or after a 0.8 multiplier 1.66 Ohms (to compare with test results on a cold system).

By comparison, previous editions might have calculated it as 240V/105A = 2.29 Ohms (or 1.82 Ohms for cold) or 230V/105A = 2.19 Ohms (1.75 Ohms cold)

(all subject to a little rounding error).

(I've also glossed over D-types, as 5s disconnection can be achieved via the thermal element rather than magnetic, which means that higher Zs values can sometimes be permitted)

- Andy.
 24 February 2019 08:59 PM
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aargeitakis

Posts: 162
Joined: 14 July 2005

Thanks for your help everybody.
Much appreciated!!!
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