Have I got 2 x mains switches?

[Forty_Two]

What have I got in there? Is that white (100amp) unit next to the large black original mains switch another mains on/of switch i.e. have I got two switches doing the same job?

Note: We had a 2 room extension built about 20 years back and the Wylex CU box (in the pic) in the meter cupboard in the garage supplies the 13amp plugs and lighting for that extension. The main house fuse board is inside the house (under the stairs in the hall)

 

[ImpededLoop]

The new, white switch is provided by the electricity board so that you can connect to their supply without opening the meter or pulling their main fuse.

The dark coloured MEM switch fuse will also probably also isolate your entire installation (depending on how the white wylex board below it has been connected).

From the look of the photo the main earthing conductors are inadequate and you should consider asking an electrician to have a look as a matter of urgency.

 

[Forty_Two]

The new, white switch is provided by the electricity board so that you can connect to their supply without opening the meter or pulling their main fuse.

The dark coloured MEM switch fuse will also probably also isolate your entire installation (depending on how the white wylex board below it has been connected).

From the look of the photo the main earthing conductors are inadequate and you should consider asking an electrician to have a look as a matter of urgency.

Thanks . . . the large on/off switch does isolate the whole house but it look it is supplied from the white box i.e. if the white box is switched off will that not isolate the whole house? Hence my question - have I got two switches doing the same job?

 

[timhoward]

Thanks . . . the large on/off switch does isolate the whole house but it look it is supplied from the white box i.e. if the white box is switched off will that not isolate the whole house? Hence my question - have I got two switches doing the same job?

It's actually not possible to say for certain. A number of questions need confirming:
a) Do the black and red tails pass behind, around the side, and then into the MEM from behind or is it two pairs that go in and out to somewhere else
b) are the tails coming from the MEM box on the supply or load side
c) does the black SWA cable pass behind everything and the MEM box is actually a fuse for a sub-main (another consumer unit possibly in shed or garage)

In other words, it's not a clear cut setup and even a sparks would have do do a little digging to be sure.
What we can say for sure is that the new white isolator turns off the lot.

And please get that earthing looked at! My initial reaction is that a dead short would melt that earth before the main supplier fuse popped, leaving a very dangerous situation.

 

[ImpededLoop]

Thanks . . . the large on/off switch does isolate the whole house but it look it is supplied from the white box i.e. if the white box is switched off will that not isolate the whole house? Hence my question - have I got two switches doing the same job?

Yes, in functional terms, you have. In practical terms you are likely to need both as one belongs the the electricity board, the other is to provide fused protection to the cabling to your consumer unit in the house.

 

[timhoward]

Ah, I've now read the original post again, the main pertinent question is whether the MEM switch isolates the garage as well as the house. Forgive me for being very careful before declaring anything about isolation over the internet!

 

[Forty_Two]

My reason for asking this is because I am going to get that 3 way Wylex box replaced to cater for a later installation of an EV charger and to make some room in there I am asking myself should I replace that large mains on/off with a smaller one or do away with it altogether?

 

[timhoward]

While you could get a smaller one fitted, I don't see a reason to.
I wouldn't do away with it altogether as a fuse is the best way of protecting a mechanically protected sub-main, ensuring that devices the far end in the other consumer unit trip/blow first.
It technically could become a final circuit from the new consumer unit but to my thinking this would be an inferior circuit design as a circuit breaker would not provide the same degree of discrimination.

I'd probably just fit some Henley blocks between the brand new isolator and the large MEM switch, and run new tails from the Henley blocks to your new consumer unit. It's then totally obvious to anyone how it's arranged. The MEM switch could do with a label on it saying "House Supply".

 

[Forty_Two]

That large MEM is 200mm x 140mm . . . the below (150mm x 78mm) would that do the same job?

100A DP Isolator with 2 Module Enclosure

Slimline double pole 100A supply authority isolator in a 2 module enclosure

www.cef.co.uk

I understand and accept that this large and old MEM does not need replacing as it meets current regs but as I will be paying someone for their time fitting a new CU my thinking is that (whilst he's here) adding an extra 30 mins to fit a new MEM isn't going to add much to the bill? Is that sensible or silly?

 

[timhoward]

That large MEM is 200mm x 140mm . . . the below (150mm x 78mm) would that do the same job?

No, it does a totally different job. That one you linked to is just an isolation switch.

The current MEM unit also has a fuse in it; this is required as you exceed the maximum length of meter tails and because the smaller cable running to the other consumer unit needs appropriately rated protection to prevent it catching fire/melting under overload or fault conditions.

Smaller units are available, this is a modern functional equivalent though I don't believe you could gland SWA cable to this one:

80A Fused Main Switch

Click essentials profile

www.cef.co.uk

This is probably what I'd use:

Wylex 60A DP Domestic Switched Fused Unit - Screwfix

Order online at Screwfix.com. Robust all-metal enclosure with a rated operational current of 100A and supplied with a 60A fuse. Designed for easy installation and connection of sub-mains or system extensions. Features an easy to open rotary fuse drawer that automatically disconnects the fuse...

www.screwfix.com

(I think it's bigger than your current one!)

 

[loz2754]

The large dark coloured unit appears to be a 4 way fuse box, not a switch fuse.

 

[westward10]

The large dark coloured unit appears to be a 4 way fuse box, not a switch fuse.

I concur and that dates to around the 1950s so it is possible the cabling may also date to this.

 

[7029 dave]

The large dark coloured unit appears to be a 4 way fuse box, not a switch fuse.

Yep had a MEM 4 way fuse box in my old house, grey metalclad, porcelain fuses.
To note had the asbestos heat arresters in the fuse holders.

 

[timhoward]

Sorry for the confusion caused.
I think it's similar to this one:

MEM 4 way enclosed grey metal fuse box

Old completely enclosed 4 way MEM metal fuse box containing 4 ceramic rewireable fuses

www.flameport.com

Really it needs an in-person inspection, particularly to discover how the CU under the stairs is supplied, what that SWA is doing, and whether there are in fact outgoing tails as I wondered in post #4.

 

[westward10]

Sorry for the confusion caused.
I think it's similar to this one:

MEM 4 way enclosed grey metal fuse box

Old completely enclosed 4 way MEM metal fuse box containing 4 ceramic rewireable fuses

www.flameport.com

Really it needs an in-person inspection, particularly to discover how the CU under the stairs is supplied, what that SWA is doing, and whether there are in fact outgoing tails as I wondered in post #4.

It is like that but a lot older.