Max Zs values of bs 3871

[Sparkydan]

Hi

Is the max Zs values of a bs3871 the same as a BS 60898 mcb as 60898 replaced the 3871?

thanks

 

[Guest123]

No.

They are essentially 2 different breakers. 3871's were type 1,2 & 3 whereas 60898's are B,C & D. The only ones that are the same are type 3/C. Page 103 in the OSG has the info you need.

 

[pevvers]

No.

They are essentially 2 different breakers. 3871's were type 1,2 & 3 whereas 60898's are B,C & D. The only ones that are the same are type 3/C. Page 103 in the OSG has the info you need.

Or in the event of having no tables to hand, use simple Ohms Law!

We all know that R = V/I, and know that V is 230V.

Type 1 MCB's trip instantaneously (0.1 s) at 4 times the rated current, type 2 trip at 7 times the rated current and type 3 trip at 10 times.

Therefore, if we had a 10A type 1, we would have R=V/I=230/(4x10)=230/40=5.75 ohms maximum earth fault loop impedance.

Always worth knowing the maths if you don't always have the tables, although it's not so easy with fuses as you need the current curve graphs....

 

[pevvers]

And remember that the OSG and GN3 values are at the 80% values, not necessarily the maximum permitted by BS7671... Although that point is still quite contentious!

 

[oldtimer]

Print this laminate it and put it in you folder

Ok what happened to the attach option

 

[oldtimer]

Here it is