B2 Tripping curve?

[gazj82]

Hi Guys,

I cannot see B2 in the tripping curves for 60898 in the BGB, any of you guys know the answer before I ask the manufacturer.

Thanks in advance

Gary

 

[telectrix]

page 301in bgb. look at the ones there. for 2A start at the bottom at 10A. draw vertical line to 10sec, then sketch curve parallel to the 6A curve to give a pretty accurate guide.

 

[gazj82]

Oh I see, we are presuming all is linear, i.e every B type MCB needs 5x it's rated current to trip in 0.1 to 5 seconds. So I need 10A of fault current for a 5 second disconnection time.

230v / 10A = 23 ohms as a maximum Zs.

Sorted. Can't believe I didn't see the correlation, Thanks telectrix

 

[extec]

Oh I see, we are presuming all is linear, i.e every B type MCB needs 5x it's rated current to trip in 0.1 to 5 seconds. So I need 10A of fault current for a 5 second disconnection time.

230v / 10A = 23 ohms as a maximum Zs.

Sorted. Can't believe I didn't see the correlation, Thanks telectrix

Type B 60898 MCB 32A or less = 0.1 Seconds disconnection time
Type B 60898 MCB more than 32A = 5 Seconds disconnection time

Type B will require 3 to 5 times load to trip always work on worst case so x5 and so for a 6A 60898 MCB 30A is required for 0.1 second disconnection time as for ZS it will be 230/30 (the 30 being 6A X 5 =30A) = 7.66 and then rule of thumb for temperature rise so 7.66 x 0.8 = 6.13 ZS=6.13 for a 6A circuit. The disconnection times only apply to TN systems.