Regs regarding CU fuse to MCB?
 

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?
If they are required does anyone know where to get a deep one for a Volex
CU?

Regs regarding CU fuse to MCB?
 

On Mon, 8 Jun 2009 10:52:34 +0100, "dennis@home"
had this to say:

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?
If they are required does anyone know where to get a deep one for a Volex
CU?

I think that Volex used to make a deep cover, but I've never seen nor
used one.
As long as you're not likely to bump into the trips you shouldn't have
any problems. My last setup was like that.

--
Frank Erskine

Regs regarding CU fuse to MCB?
 

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?
If they are required does anyone know where to get a deep one for a Volex
CU?

the cover is normally left off. Be aware that there are downsides to
fitting these 3kA MCBs as well as the easy reset advantage.


NT

Regs regarding CU fuse to MCB?
 

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?

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).

--
Cheers,

John.

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Regs regarding CU fuse to MCB?
 

"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?

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).

Never mind fuses these replace re-wireable fuse holders!

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

Regs regarding CU fuse to MCB?
 

dennis@home coughed up some electrons that declared:


Never mind fuses these replace re-wireable fuse holders!

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

Measurement is the only way.

If you ask your supplier, they'll just say 16kA which is the maximum.

How close are you to your nearest transformer?

Mine's a fair way away and my PFC is about 2kA (measured by me).

OTOH, I had more than 5kA at a flat that has a transformer outside.

Cheers

Tim

Regs regarding CU fuse to MCB?
 

Tim S coughed up some electrons that declared:

dennis@home coughed up some electrons that declared:


Never mind fuses these replace re-wireable fuse holders!

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

Measurement is the only way.

If you ask your supplier, they'll just say 16kA which is the maximum.

How close are you to your nearest transformer?

Mine's a fair way away and my PFC is about 2kA (measured by me).

Brain fart - it's 1.2kA

OTOH, I had more than 5kA at a flat that has a transformer outside.

Cheers

Tim

Regs regarding CU fuse to MCB?
 

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]

Regs regarding CU fuse to MCB?
 

dennis@home wrote:


"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?

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).

Never mind fuses these replace re-wireable fuse holders!

Yup - "semi-enclosed" is the posh name for a rewireable fuse (or
BS3036). The traditional fuse carrier with coloured dots on the back
produced by the shed load by wylex etc.

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

Most modern test meters will read it directly. However you can make a
decent stab at it with a clamp meter and a DVM.

If you have clamp meter stick it round a meter tail, and put a voltmeter
somewhere where you can see the mains voltage. Then you can measure the
voltage drop against current drawn (although as Andy said - draw the
power from a different circuit to the one you are measuring the voltage
on). Once you have a couple of readings you can just use V/I=R to get
the supply impedance. Anything less than about 0.25 ohms is starting to
get boarderline for a rewireable fuse. A 3kA MCB ought to be ok down to
0.08 ohms - which you are unlikely to meet unless you are in a densely
populated area or sat right on top of a substation.



(if you have not got access to a clamp meter, then you can still get a
feel for it with just a volt meter and a known load - say a 3kW kettle)



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/