Dorman Smith mcb's

[Hp1]

Hi,

Could anyone please advice me which Maximum earth fault loop impedance tables are to be used for the Dorman Smith mcb's. The mcb's do not have anything witten on them apart from the ampage ratings. They are fitted in a Dorman Smith CU, which is metal and very old. The consumer unit has a label which says "Dorman Smith, Series 15, BS 5486 part 13". I think the mcb's are the Loadmaster Type LM series 15.

Any help would be appreciated.

Harry

 

[securespark]

Try removing the mcb to see if there is any info on the other faces of the breaker.

There should be a BS number (probably 3871).

You also need to know the type and the current rating.

 

[horaceg]

Hi,

Could anyone please advice me which Maximum earth fault loop impedance tables are to be used for the Dorman Smith mcb's. The mcb's do not have anything witten on them apart from the ampage ratings. They are fitted in a Dorman Smith CU, which is metal and very old. The consumer unit has a label which says "Dorman Smith, Series 15, BS 5486 part 13". I think the mcb's are the Loadmaster Type LM series 15.

Any help would be appreciated.

Harry

Harry,
As you are no doubt aware, these are very old and now obsolete.
The LM range of Loadmaster Series 15 MCB's were rated as a Type 4 3kA (M3) which probably equates to a 'D' rated breaker. You would need to contact Dorman Smith and ask them the question.
For your info:
10 Amp = LM10
40 Amp = LM40 et al!

HoraceG

 

[plugwash]

type 4 is far nastier than type D.

iirc gauranteed fast trip on a type 4 is 50 times rating! you'll need some seriously low EFLI to make that comply.

 

[Hp1]

Hi Chaps,

Did as securespark advised and removed breaker. The details were embossed on the side.

The breakers are Loadmaster, series 15 and type 3. Cat M3 BS3871.

Maximum measured earth fault loop impedance for mcb's to BS3871, type 3 is shown on page 114 (table 2D 11) of the current Guidance notes 3.

Thank you everyone (securespark,horaceg & plugwash)for your help.

Kind Regards

Harry