Replacing Wylex wired fuses

[HarryM]

I have a TT installation, the power coming from an oversail, and consisting of a 100A fuse, an 80A RCD, and an 8 way Wylex CU with wired fuses, each with a colour-coded replaceable base. All circuits are radial.

I am considering replacing the fuses with Wylex type B MCBs, and bought a 20A (BSEN60898) on spec. It works OK, but it sticks out a lot further and means the cover over the fuses no longer fits, although this shouldn't be a problem as the whole board is enclosed in a box with a lid.

However I am not so sure about the contacts. The prongs on the MCB are narrower and closer together than those on the fuses. The MCB has 8mm wide prongs 17mm apart, and the fuse has 9mm prongs 25mm apart. Although the females are much larger, it looks as if one of the MCB prongs possibly does not make contact with the socket across its whole width. Does this sound normal?

Would I be better off buying replacement plug-in cartridge fuse holders? Or are they likely to have the same problem?

I know the ultimate solution would be to replace the complete CU, but apart from the cost, the mains board is close to a ceiling and
the wiring is difficult to get at.

 

[Lectrician]

Photo?? These retro-fir plugins come with a new base, and to my knowledge, make perfect contact, although a little out of allignment with the 3036 fuses you removed.

The fusecover has a weakened section on the inside to allow you to 'knockout' the fron of it, allowing the MCB's to show through.

Personally, I would prefer a new CU, as this would also give you 30mA RCD protection to sockets if fitting a split loader. (assuming your current RCD is a 100mA).

 

[JohnD]

I recently fitted these Wylex MCBs (you can pick them up very cheap on Fleabay) for a relative, was annoyed that they stuck out so far, and could be knocked by coats etc in the cupboard.

I managed to find a plastic (sandwich) box in Wilkinsons that I could trim down; the sides now fit into the CU where the old cover used to fit. Sadly I couldn't manage to use a retaining screw, but it grips well and you have to flex the sides in to pull it out.

It is transparent so you can see which MCB has popped.

I think it's very annoying that Wylex sell MCBs to fit their standard range (and they are more expensive than DIN-rail MCBs) and dont sell a plastic cover that fits.

 

[HarryM]

Photo?? These retro-fir plugins come with a new base, and to my knowledge, make perfect contact, although a little out of allignment with the 3036 fuses you removed.

Sorry, don't have a camera.

I have swapped the base over with no problems, but it's very difficult to tell if the MCB makes perfect contact. Each of the fuse prongs sits well within the width of the socket contacts, but the MCB prongs are right on the inside edges. Also one of the prongs possibly has about 1mm which is overhanging the edge of the socket contacts, but I haven't yet taken the cover of the CU to really check.

Is it possible to adjust the female contacts?

Personally, I would prefer a new CU, as this would also give you 30mA RCD protection to sockets if fitting a split loader. (assuming your current RCD is a 100mA).

My RCD is 80A. Is that OK for a split loader? And does a split loader work on type TT?

 

[ban-all-sheds]

A split load board is the commonest way to meet the requirements of the regulations for TT installations:

Main incomer - 100mA time-delayed RCD, then at the split a normal 30mA RCD.

 

[Pensdown]

A split load board is the commonest way to meet the requirements of the regulations for TT installations:

Main incomer - 100mA time-delayed RCD, then at the split a normal 30mA RCD.

Does he need a time delay RCD? they cost a packet

 

[Spark123]

It is advisable for discrimination between the RCDs.

 

[Pensdown]

It is advisable for discrimination between the RCDs.

I've only ever seen them to discriminate between two 100mA RCD's, never as a main switch with 30's but I can see the logic

 

[HarryM]

I have had the cover off the CU. The distance between the female sockets and the distance between the male prongs on the new MCB is identical, but the slots in the colour-coded removable base are slightly misplaced with regard to the sockets, which means that part of one of the prongs does not make contact.

I won't be following the MCB route with this CU.