Help identify breakers

[ezekiel]

was looking at old fuse box and have:
main switch is cv1339-4
circuit breakers are bs3871

now im stumped no info for theses types of devices in regs, or am i missing something, quite old installation prob about 30 years how do i go about finding zs values for something like this?

 

[Spark123]

I take it they are type 1, 2, 3 or 4 as opposed to type B, C or D?
There are some max measured values for these in the back of guidance note 3.
The maximum permitted value required to trip the device can be calculated by Uo/Ia. Uo is the line to earth voltage (230v), Ia is the curent causing operation within specified time.
We use the maximum instantaneous trip current for the device Ia which can be calculated by:
Type 1, In x 4
Type 2, In x 7
Type 3, In x 10
Type 4, In x 50
In is the nominal rating of the device.

For example, if you have a type 2, 5A MCB, the maximum permitted efli value for a 230v circuit can be calculated by 230/(5 x 7) = 6.57ohms

 

[ezekiel]

dont know how i would survive without you

very clear explanation many thnx