Hi,

I recently had the 5A lighting fuse go in our household fusebox. This
fusebox takes household plug style fuses in the holders.

Except the sizes seem different. When I tried putting in a spare 5A
fuse, it was too long, and therefore did not fit. Thankfully, a
neighbour had a spare.

I want to order some of my own, but am trying to find the right ones!
I've measured the required 5A one at a length of 22mm.

Are these the ones I need? ...

http://www.maplin.co.uk/Module.aspx?...&ForceUpdate=Y

Annoyingly, Maplin don't list the physical dimensions.

Thanks in advance,

Tris.

Are these the ones I need? ...

http://www.maplin.co.uk/Module.aspx?...&ForceUpdate=Y

They're certainly the type you are supposed to use. The last time I had a
fused consumer unit, it could take plug top fuses instead, though. It
depends on the design of the holder.

Christian.

They're certainly the type you are supposed to use. The last time I had a
fused consumer unit, it could take plug top fuses instead, though. It
depends on the design of the holder.

I should say that you should use the BS1361 HRC fuse in preference even if
both types fit. I don't know if BS1362 (standard plug fuses) have sufficient
breaking capacity.

Christian.

Christian McArdle wrote:

I should say that you should use the BS1361 HRC fuse in preference even if
both types fit. I don't know if BS1362 (standard plug fuses) have sufficient
breaking capacity.

The rated breaking capacities are 16.5 kA for BS 1361 consumer unit
fuses and 6 kA for BS 1362 plug fuses.

In principle you shouldn't use the BS 1362 fuse in a consumer unit, but
since only the 5 amp types are interchangeable, the chance of the 6 kA
breaking capacity being exceeded in practice is very very small. I'd
have no hesitation of using a 5 A plug fuse as an temporary replacement,
until a round tuit allows a BS 1361 fuse to be fitted.

--
Andy

I should say that you should use the BS1361 HRC fuse in preference even
if both types fit. I don't know if BS1362 (standard plug fuses) have
sufficient breaking capacity.

The rated breaking capacities are 16.5 kA for BS 1361 consumer unit fuses
and 6 kA for BS 1362 plug fuses.

6kA is normally enough. Most MCBs are 6kA anyway, with some 10kA. A quick
check with a loop tester should indicate compatibility, if you happen to
have one lying about...

Christian.

Christian McArdle wrote:

6kA is normally enough.

Agreed. Although the fault level (PSSC) on a house service can be as
high as 16 kA, it's rarely anywhere near that.

Most MCBs are 6kA anyway, with some 10kA.

Yes, but the complete MCB CU system will have been type tested to BS EN
60439-3 at 16 kA and given a conditional rating - conditional, that is,
on the presence of the supplier's 100 A (BS 1361 Type 2) fuse to provide
backup protection. IOW even when the MCBs' breaking capacities are
exceeded you have an assurance that the supplier's fuse will clear the
fault without the CU blowing itself apart (at 16 kA the magnetic forces
are huge) or catching fire. You can't necessarily assume that this will
be the case with an old Wylex board fitted with the wrong type of fuse.

A quick check with a loop tester should indicate compatibility, if
you happen to have one lying about...

Of course I do :-). The lowest impedance domestic mains supply I've
ever encountered was about 0.05 ohm (phase-neutral loop) so c. 5 kA
fault level.

--
Andy

Of course I do :-). The lowest impedance domestic mains supply I've ever
encountered was about 0.05 ohm (phase-neutral loop) so c. 5 kA fault
level.

Mine is certainly much lower, despite living in an urban area. I can't
remember the figure, but it is less than 2kA. Not that you are allowed to
rely on it, in case of upgrading in the supply somewhere.

Christian.

On Sat, 19 Aug 2006 12:44:02 +0100 someone who may be Andy Wade
wrote this:-

Of course I do :-). The lowest impedance domestic mains supply I've
ever encountered was about 0.05 ohm (phase-neutral loop) so c. 5 kA
fault level.

At the risk of being thought to be a fan of "mine's bigger than
yours" discussions, the highest I have found in a house is 12,000A.
The house concerned is perhaps 10m from the transformer which
undoubtedly feeds the house. That is fed by I guess less than 100m
of 11kV cable, which is fed by less than 2km of 33kV overhead, which
comes from a large compound into which a number of pylon runs of
132kV size congregate.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

Christian McArdle wrote:

Mine is certainly much lower, despite living in an urban area. I can't
remember the figure, but it is less than 2kA.

Mine's very similar at about 0.16 ohm, or 1.5 kA. These seem to be very
typical figures.

Not that you are allowed to rely on it, in case of upgrading in the
supply somewhere.

You are allowed to rely on the attenuation of the PSCC due to the
impedance of your service cable. The idea is to assume that the fault
level on the main distributor cable in the street is 16 kA at 0.55 PF at
all points (since in principle they could drop a new transformer in at
any point) and then calculate the reduction due to adding the impedance
of the length of service cable between the street cable and your supply
intake.

16 kA at 0.55 PF corresponds to a source impedance of 8.25 + j12.53
milliohm, to which add about 1.4 + j0.06 milliohm per metre of service
cable (for the usual 25 mm^2 Cu or 35 mm^2 Al cable). So a 10 m long
service will give a PSCC of 9.3 kA at 0.86 PF, an so on. (These numbers
are for single-phase supplies, of course.)

--
Andy