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Posted to uk.d-i-y
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Do circuit breakers die of old age?
wrote:
The breakers are all Type 2 - i'm not aware what this signifies but it
did cross my mind that they might be simillar to standard fuses
insomuchas they can be slow blow, quick blow etc
Yes, that's the idea. MCBs have two distinct tripping mechanisms -
magnetic for "instant" tripping at high current, and thermal for smaller
overloads. The "Type" determines where the transition between the two
lies. Type 2 (now obsolete) will trip instantly at somewhere between 4
and 7 times the nominal current, so a minimum of 120 A for a 30 A unit.
The current Type B will go at between 3 and 5 times then nominal
current, are more sensitive to inrush surges. For your office a Type C
might be appropriate (5 to 10 times).
might have 10 workstations plugged in but not powered up - however i
assume power is still going to their power supplies - i would imagine
there to be a bit of a "peak inrush" (i forget the exact term) - demand
if all of them had powered applied at the same time (this is what
happens when i try to reset the trips) - maybe i need a slow blow type
breaker?
Yes, see above. Even then, switching that lot on in one go might
continue to be a problem. Big CRT monitors - any of those? - add to the
inrush current, due to the degaussing coils. Staggered switching is the
name of the game here. You can buy multi-way IEC distribution blocks
with built-in staggered turn-on - they're used in the broadcast industry
for switching banks of TV monitors.
Do all new installations/upgrades include RCD main breakers ?
No, a split-load board has a main switch, then a bank of MCBs for the
circuits that don't need RCD protection, then an RCD that only protects
selected circuits. The selected circuits should be only those which
feed socket outlets for general use (in particular those likely to be
used for portable appliances outdoors) and, if you want to pre-empt the
new 17th edition regulations coming in in 2008, everything in a bathroom.
--
Andy
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