In article ,
"dennis@home" writes:


"John Rumm" wrote in message
o.uk...
dennis@home wrote:

I want to fit some GE minitrips to a CU that has wired fuses in it.
The trips just plug into the existing slots.
However they are too deep to fit the cover.
Is the cover a requirement or even necessary once the minitrips are in
place?

For the Wylex CUs, you could get covers with openings for the breakers.

The lack of a cover is unlikely to be a problem as long as they are
unlikely to be physically abused in their present location.

These plug in MCB often only have a maximum breaking capacity of 3kA (less
than the 6kA or better typical of modern MCBs), but one could argue that
is a non issue since BS3036 semi-enclosed fuses often have an even lower
breaking capacity. Since you are making the change it would be worth
checking your supply impedance to make sure that 3kA is adequate (if its
not, then your existing fuses would almost certainly be inadequate as
well).

The original ones with a pair of circular push buttons were even
less, IIRC.

Never mind fuses these replace re-wireable fuse holders!

How do you find the supply impedance without resorting to measuring the
short circuit current?

You should use a calibrated tester.

You can probably get a good idea for a max value on a single phase
supply by measuring the voltage drop at the CU* when you switch on a
known load, such as a 2kW heater or kettle. (That's no good for earth
fault loop impedance measurement for checking disconnect times though.)
The voltage drop divided by the load current will be the supply
impedance.

* Don't stick test meter probes into your CU. Measure the voltage on
different circuit (with no varying loads at the time) from the one
with the test load, and you should use fused test meter leads.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]