Can someone please refresh me where I find the efli values of the wretched 3871's, either they are just staring me in the face or im losing it rapidly.

On Site Guide or GN3.

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John Peckham

http://www.astutetechnicalservices.co.uk/

Thanks John, that explains it as I've lost my OSG.

There are % corrected values in the Green OSG page 119.

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http://www.niceic.biz

Regarding 3871 type 4 mcb's

Can any one tell me any history about these ie when they were in manufacture and when they were phased out etc?

The Zs on these are very low, as low as modern mccb's.

Type 4 devices were manufactured at the same time as type's 1,2 and 3; they had shock protection characteristics similar to a six inch, (sorry) a 150mm nail, so were only suitable for industrial applications. Unfortunately many of the earlier devices had this characteristic and were mis-used by the ill-informed installer, even in public buildings.

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http://www.niceic.biz

-- i always refer to manufacturers data "wiring regs" stuff is only general
info.

Regards

I have found plenty of DBs full of Type 4s either Dorman Smith or Square D. I think they were fitted in complete ignorance without any consideration for Zs values. I looked at a large building this year with another forum member and every board was fitted with Type 4s and Zs values well in excess of that required for ADS. We had a look at the current PIR for the building and the the MCBs were incorrectly stated as being 60898 types. The supply fuses were stated as 100A 1361s but we found 2 x 400A heads fitted with BS88s. I think the clowns that did the PIR just wrote what they always write for a 8 way board in the cupboard under the stairs! Oh yes they put down 2 ohms for a Ze without comment. All signed off by the QS who should have spotted the very obvious errors throughout the report.

I understand from another forum member that he visited one circuit breaker manufacturer as an NICEIC engineer as they were flooding the market with cheap Type 4,s which the contractors were buying to cut costs, to dissuade them from doing so.

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John Peckham

http://www.astutetechnicalservices.co.uk/

As a rule of thumb without manufactuer's info you can use the calc Uo/ITCxIn.

The values are at normal working temperture.

Circuit breaker InstantaneousTrip current (ITC)
Type (0.1-5s)

1 2.7 to 4In
B 3.0 to 5In
2 4.0 to 7In
C 5.0 to 10In
3 7.0 to 10In
4 10.0 to 50In
D 10.0 to 20In

Use the worst case ITC value.


Regards

And exactly what is wrong with a 150mm nail ??? Often seen on the odd farm

Stu