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

Sparkingchip

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/.../

  • 0 in reply to Sparkingchip

    Were the B.S. 3871 breakers types 1, 2 or 3?

    Z.

  • 0

    Were the B.S. 3871 breakers types 1, 2 or 3?

    I thought some brands at least did B/C/D types under the BS 3871 banner for a while just before/during the transition to BS EN 60898.

       - Andy.

  • 0

    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. 

  • 0 in reply to AJJewsbury

    Early tech. info. But this may be a red herring.

    http://dormansmithswitchgear.com/wp/downloads/discontinued_products/mcb/loadmaster_mcb_datasheet.pdf

    Z.

  • 0 in reply to Sparkingchip

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

    Z.

  • 0 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

  • 0

    As per usual I am wandering off topic.

    I have to alter and add some lighting, the existing circuit now seems to be protected by a BS3871 D16 MCB without RCD protection, so I am going to run the new lights from the new consumer unit which has RCD protection from a B6.

    However having thought a bit more about the original lighting circuit it does actually comply with 559.5.1.204 which says the maximum OCD rating for lighting circuits with B15, B22, E14, E27 or E40 lamp holders is 16 amps, so when it was originally installed it could have complied with the regs, but I suspect due to alterations it may well be an issue now plus there’s not 30 mA RCD protection.

    It is easier to work from the new additional consumer unit that has a Type A 30 mA RCD and a B6 MCB in it and not get over involved with the existing installation.

    If there were banks of fluorescent lights or similar I would not be surprised to see a D16 on the lighting circuit, but this is only a flat with a few lights in each room.

  • 0 in reply to Sparkingchip

    The need for R.C.D. protection for domestic lighting circuits is possibly overkill in most cases. But perhaps it protects the amateur D.I.Y. installer who shouldn't be meddling with stuff where his knowledge is insufficient.

    Additional protection (415.1.1) to protect users from carelessness. But I can't see a big issue with ceiling lighting which is out of reach in most cases.

    Z.

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