disconection time and max zs

Postby davino » Tue Aug 26, 2008 7:07 pm

can someone please tell me what the max disconnection times for 17th edition regs for the following
6amp mcb
16amp mcb
32amp mcb
40amp mcb

and also the max zs for a bs60898 mcb on a t n c s system

i :wink:
Last edited by davino on Thu Feb 10, 2011 8:21 pm, edited 1 time in total.
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Simply Build It

Postby ericmark » Wed Aug 27, 2008 10:13 am

MCB come in Type Numbers or Letters 1 to 3 or B to D and these refer to the magnetic part of the trip and how many times the thermal rating it will instant trip at Type1= 4x, Type2= 7x, Type3= 10x, TypeB= 5x, TypeC= 10x, TypeD= 20x if you take voltage and divide by this number you come up with a number that when divided in turn by the current will give max Zs for example for a type B MCB at 230 volt we get 46 as number to divide by the amps so a 16 amp B type MCB will be 2.875ohms using same example with 240 volt will give 3ohms since you don’t give type letter or number on MCB can’t give you values only how to work it out.
6 For B Type 7.666666667 Ω For C Type 3.833333333 Ω For D Type 1.916666667 Ω
16 For B Type 2.875 Ω For C Type 1.4375 Ω For D Type 0.71875 Ω
32 For B Type 1.4375 Ω For C Type 0.71875 Ω For D Type 0.359375 Ω
40 For B Type 1.15 Ω For C Type 0.575 Ω For D Type 0.2875 Ω
This at 230 volt as 17th Edition the old 16th was at 240 volt all values calculated so slightly different to book values as not corrected to 3 significant figures.
Does help Eric

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