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Name the breaker. (Dorman Smith BS3871 Type D).

I an trying to determine the maximum Zs for the spare 16 amp MCB with a 5 second disconnect time.

The maximum Zs of the SWA distribution circuit will be less than 1.4 ohms using a third core as the CPC not including the armour, so it will be lower.

Edit- taking Ze as 0.8 ohms TNS.

professional-electrician.com/.../

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0 Sparkingchip over 3 years ago

I can’t see it was ever a consumer unit suitable for a flat, particularly as it appears to have a D16 MCB on the lighting circuits, there will be a recommendation to replace.

The commercial premises the flat is over is a dentists, so I can see why some of the circuits downstairs could need Type D MCBs, but the flat actually has a separate DNO supply and suppliers meter, so is a completely separate installation, I just suspect the same electricians wired the whole building and wired the flat the same as downstairs.
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0 Zoomup over 3 years ago in reply to Sparkingchip

https://www.diynot.com/diy/threads/old-doran-smith-3871-mcb-and-how-to-determine-type-and-zs.144897/

Z.
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0 Zoomup over 3 years ago in reply to Sparkingchip

https://www.diynot.com/diy/threads/old-doran-smith-3871-mcb-and-how-to-determine-type-and-zs.144897/

Z.
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0 John Peckham over 3 years ago in reply to Zoomup

Zoom

Many thanks for the link as it is a very fine example of persons carrying out EICRs who do not know their amp from their elbow! They then go on to post their pearls of wisdom to others on forums, thus perpetuating the lack of competence.

I think I have Dorman Smiith data in the Great Book of Circuit Protection. They are BS 3871 devices so standard tables can be used. However a lot of them are Type 4 so the OEMs data sheet must be used.

JP
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Name the breaker. (Dorman Smith BS3871 Type D).

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