BS 3871

[oldspark]

Hi: testing a job and came across a CU with BS 3871 type 3 breakers in it can anyone tell me what the Max Zs is and the (KA ) capacity would be for them.

thanks

OS

 

[luminaire]

Table 41B2(a)?

 

[Spark123]

Table 2D, p144 in GN3 outlines the maximum measured value. Alternatively you can work it out. A type 3 requires X10 current for an instantaneous trip (same as type C). If you divide the open circuit voltage of the supply transformer (Uoc=240v) by the current required to operate the MCB then you have the maximum Zs required to operate the MCB. Multiply this by rule of thumb for max measured.

Example for a 5A type 3 it will be 240/(10x5)=4.8 ohms. 80% for temp correction gives 3.84 which is the figure given in GN3 table.

 

[oldspark]

Thanks for that info anything on the (Ka) value

 

[Spark123]

Does it have an M rating on it? I.E. M3 (3KA), M6 (6KA) etc?

 

[oldspark]

Yip thats what I have to look for M1 M1.5 etc
Thanks