On 22/11/2016 23:25, Roger Hayter wrote:
ARW wrote:

On 22/11/2016 20:23, Roger Hayter wrote:
Andy Burns wrote:

Andy Burns wrote:

Jack Lawson wrote:

MCB swapped for Type C 32 Amps

32A? Properly you should use 4mm^2 with that.

Or make it a very short ring with 2.5mm^2

We've established upthread that the 2.5^2 is short enough.


Not short enough for a C type 32A MCB on a TN-S supply that is at the
upper limits of it's maximum allowed Zs.

Sorry I missed we'd changed from type B to type C. That makes a
dfference I suppose?

The C type has the same overload protection (i.e the thermal part of its
response is the the same) as the type B, but its magnetic response is
less sensitive. A type B will open "instantly" on fault currents of 5
times the nominal current, so 160A for a B32. The C type devices require
10 times the nominal current to open instantly, or 320A for a C32

The effect is to make them far more tolerant of high inrush currents,
but at the expense of possibly lowering the protection for fault
currents, so in some cases one will need to check (by measurement or
calculation) if a C type is safe to use on a particular circuit.

With my limited knowledge I think I just know
that ordinary circuits will be all right with 20A type B and if I want
anything more unusual I'll ask.



--
Cheers,

John.

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