On 29/03/2021 13:41, Robin wrote:
On 29/03/2021 12:45, Roger Hayter wrote:
On 29 Mar 2021 at 10:15:39 BST, ""Brian Gaff \" Sofa\)"
wrote:

Which reminded me, why is it that a breaker of any type often seems,
maybe
through never having been tripped for years can take too long to trip
when
it finally does have a fault to protect against which can often mean
a whole
fitting needs to be replaced due to overheating. Is it just build up
of crud
or whatever, and should one say every few months manually trip these
one at
a time to make sure they keep healthy?

Brian

It is normally printed on the front of them that they should be tested
periodically.Â* But you are not alone in not seeing that!


I think Brian might be referring to how MCBs (and RCBOs) perform with
over current rather than how RCDs (and RCBOs) perform with an imbalance.
Â*Testing how breakers perform with stable, over & short-circuit
currents requires special kit.Â* I'd be interested to know if even Adam
carries it routinely.

Testing is currently carried out with no load. I think the behaviour of
the MCB would be the arbiter of what happens in an over-current or fault
condition.

Perhaps in future, as we have a number of different RCD characteristics,
some cope with DC, others with HF currents etc, there is a chance that
testing will require tests performed under these conditions?