Wylex type 2 MCB's

steve6501 · 24 Nov 2015

Hi.

The MCB on my shower has started to trip. The shower has been installed for years with no problems. When I checked the MCB I noticed it was a 30A. The shower is 8.5kW the cable is 6mm.

Now with further investigation I have discovered that the MCB is a type 2 (Wylex) so replacing with a 40A is not straightforward as with the more modern consumer units.

Are the MCB's replaceable without dismantling the consumer unit.

I am asking cos it looks like a longer job than plugging in a new 40 unit.

Steve

EFLImpudence · 24 Nov 2015

steve6501 said:
The MCB on my shower has started to trip. The shower has been installed for years with no problems. When I checked the MCB I noticed it was a 30A. The shower is 8.5kW the cable is 6mm.

It has probably worn out with the overloading over the years.

Now with further investigation I have discovered that the MCB is a type 2 (Wylex) so replacing with a 40A is not straightforward as with the more modern consumer units.
Are the MCB's replaceable without dismantling the consumer unit.

Not all.

flameport · 24 Nov 2015

The fact the existing MCB is a type 2 doesn't really matter - although they are not made any more, newer types can probably be fitted instead.

There are many varieties of Wylex consumer units and MCBs, a picture of it would be helpful.

ban-all-sheds · 24 Nov 2015

steve6501 said:
I am asking cos it looks like a longer job than plugging in a new 40 unit.

Do you actually have plug-in ones in your CU?

ericmark · 24 Nov 2015

It is likely the MCB is a plug in type like this

as to if you can replace with this

depends on how the cable is run. 6mm² thermoplastic insulated and sheathed flat cable with protective conductor Reference Method C* (Clipped direct) is 47A however Reference Method 103# (in a stud wall with thermal insulation with cable not touching the inner wall surface) is just 23.5A so it is not as simple as saying 6mm² cable is rated X amps. In the main we consider it is good for 34A i.e. Reference Method 100# (above a plasterboard ceiling covered by thermal insulation not exceeding 100 mm in thickness) but there is no simple answer until inspected.

However simply replacing with a B32 will likely mean it will run for another good few years. Although the shower will be an overload what is important is the MCB trips before the wiring gets too hot and because the B32 will trip before wires get too hot even if technically overloaded it is still safe. This may not be the case if you change to a 40A.

Although in my house the two old fuse boxes now with MCB's fitted are protected by two RCD's that is not normal with old fuse boxes. In the main a RCD will need adding.

PBC_1966 · 24 Nov 2015

ericmark said:
It is likely the MCB is a plug in type like this {.....} as to if you can replace with this {.....} depends on how the cable is run.

And on whether it's a Wylex board which will accept an MCB rated over 30/32A. Some have only one slot for >30/32A, some are 30/32A max. in any position.

ericmark · 24 Nov 2015

On my Wilex board the spring clips which grip the MCB are the same for every position. The colour coded base masks part of the spring clip so a 6A (white) will fit in a 32A (red) and not vice versa but one screw which does not require main cover removal allows the changing of the mask although it does expose live parts. As to if there is a difference between red 32A and red 40A I don't know. I don't have any 40A trips in my board. I would not consider an electric dribble system I want a proper shower so it's a mixer unit powered from a 25kW gas boiler.

PBC_1966 · 24 Nov 2015

Up to 30/32A there's no problem, but the coded base for higher ratings has a restricting lug and will fit only in positions designated for those higher ratings.

Adam_151 · 24 Nov 2015

PBC_1966 should have said:
Up to 30/32A there's no problem, but the coded base for higher ratings has a restricting lug and will fit correctly only in positions designated for those higher ratings.

Seen a good few sat at an angle due to being installed in an incorrect board

steve6501 · 24 Nov 2015

This is the board

Steve

ban-all-sheds · 24 Nov 2015

steve6501 said:
I am asking cos it looks like a longer job than plugging in a new 40 unit.

Those MCBs do not plug in.

If you can find a 40A Type 2, or a B40 which is compatible, I'm pretty sure (but welcome to be corrected) that that CU would support it.

But then there are these issues:

1) What is the current carrying capacity of the cable given its size and installation method?

2) Testing.

steve6501 · 25 Nov 2015

The term 'plugging in' was a reference to installing a new mcb. As you see the mob is NOT a plug in type

Steve

Taylortwocities · 25 Nov 2015

ban-all-sheds said:
steve6501 said:

I am asking cos it looks like a longer job than plugging in a new 40 unit.

Click to expand...

Those MCBs do not plug in.

If you can find a 40A Type 2, or a B40 which is compatible, I'm pretty sure (but welcome to be corrected) that that CU would support it.

But then there are these issues:

1) What is the current carrying capacity of the cable given its size and installation method?

2) Testing.

I agree, you cannot just upgrade a protective device without first checking all of those items.
My other concern would be the capability of the (63A rated) RCD. I see that current for all of the circuits, with the exception of the lighting, is through that one RCD.

seasickstevie · 25 Nov 2015

Looks like three x 6mm², two ring finals plus immersion heater (?), all on 63A RCD.

steve6501 · 25 Nov 2015

SNM said:
Looks like three x 6mm², two ring finals plus immersion heater (?), all on 63A RCD.

Yes, but it was OK'd when we bought the house five years ago so it may be 'on the edge'.

My original question though was .....it it easy to replace the 30A MCB with a 40A. It looks like you have to remove the bottom busbar but there don't appear to be any screw and it looks to be all in one piece. Or do you have to unscrew all the lower MCB connectors

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Wylex type 2 MCB's

steve6501

EFLImpudence

flameport

ban-all-sheds

ericmark

PBC_1966

ericmark

PBC_1966

Adam_151

steve6501

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ban-all-sheds

steve6501

Taylortwocities

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