4 Feb
2011
4 Feb
'11
12:51 p.m.
On 04/02/2011 19:25, Tony Duell wrote:
The currnet agianst time (I-t) characteristics of
fuses and circuit
breakers are specified i nthe data sheets (and at least over here there
are British Standards giving hte ones ocmmonly used). It's often
important to allow a higher-than-normal inrush current. I am sure we've
all used anti-surge fuses, for example.
Yes... the standard circuit breakers used in homes, offices, etc are
usually A-curve or (more often) B-curve, but for IT installations (lots
of switchmode power supplies) and installations with motors, usually
C-curve or D-curve to handle quite long inrush currents. And they're EN
standards, so international (sorry, I don't remember the EN number).
However, I didn;t think that earth-leakage brekaers
(RCDs, etc) had much
of a time delay as standard. The idea being that there really shouldn't
be an earth leakage current, not even fopr a faraction of a second.
Usually l about one cycle of the mains, 20ms here (with 50Hz mains),
occasionally one half-cycle, though as I may have mentioned when
describing our big RCDs in the data centres, those can be set for longer
times too: up to one second I think.
--
Pete Peter Turnbull
Network Manager
University of York