OP
nick611
rcd get stuck if you dont test them regular. i,ve been bit by one myself.but the fact remains 1667 ze 0.2 disconnection.who are we to judge
Discuss Zs values? in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
1667 is for TT systems.
On a TNS system the mcb or rcbo is your method of complying with 411.3.2.2 & you use table 41.3
The rcd is for additional protection so 1667 does not come into it.
Table 41.5 is for TT systems.
It is alo for TN system Reg 411.4.9 comes under TN. Under this reg table 41.5 can be used in a TN
Well I am just waiting for the first test case for a fatality due to an RCD not operating and saving a life, I fitted a Power breaker RCD/FCU the other day, guess what >400ms over range about as much use as a fridge to an Eskimo, if a domestic inspect is 10 Years on a new install with the lower lethal level of 50ma what's the chances of it operating in <30ma 9 years time ?..None.
I retested mine at home today all come in at under <19ms @ x5
b=5x c=10x d=20x
zs = nominal voltage/Ia (current causing automatic disconnection) x0.8
examples of making disconnection times with various mcb types
eg b32
b x 5=160 230/160=1.43 x 0.8 = zs max of 1.15ohms
eg c20
c x 10=200 230/200=1.15 x0.8 = zs max of 0.92ohms
eg d16
d x 16=320 230/320=0.71 x 0.8 = zs max of 0.57ohms
c and d type breakers are used for circuits with high inrush currents
ive gotta get out more!
max Zs= U0/Ia (x0.8) only works for B C D mcbs 60898 rcbos 61009. (table 41.3) makes life easier to work out max zs without looking it up... fuses i look up. ;-)
That's a great formula but would it still apply to bs88 fuses?
Obviously, Ohm's law applies to everything but -So yes, it does apply to BS 88 fuses.
...there is no one value which applies throughout the amperage range of BS88s to calculate the maximum Zs for each.It's just easier to work out for 60898 and 61009 breakers because it's just 5 x In (type B), 10 x In (type C) and 20 x In (type D).
Soooo - Smiffy is right then.
Obviously, Ohm's law applies to everything but -...there is no one value which applies throughout the amperage range of BS88s to calculate the maximum Zs for each.
max Zs= U0/Ia (x0.8) only works for B C D mcbs 60898 rcbos 61009. (table 41.3) makes life easier to work out max zs without looking it up... fuses i look up. ;-)
Yes, I know but smiffy's thread is about the fact that you don't need the graphs for 60898s because the relationship between Ia and In is linear,
i.e. 5, 10, 20 for B, C, D respectively.
This is not the case with BS88s and, indeed, other fuses.
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