Can/should I open consumer unit to replace a wire

[Safety First]

Hi all,
I have a question please.

Just had PME fitted and black main cable re-routed through wall.

There's a 2.5mm T+E cable still going through the door frame. Door and frame due to be replaced. It is as red arrow, and feeds exterior light.

The cable goes into the CU.

I want to open CU and replace cable with clean new 2.5mm T+E, clean as in when going through the wall and once outside it will run across mortar join and blend in.

Current cable is covered in paint and yuk.

Any thoughts on switching over old for new.

Never seen inside a CU..... behind the wizards curtain!

Thanks for any input.

Image

 

[ban-all-sheds]

First of all, inside a CU there are still live parts, even with the main switch off, so you do need to take care. A photo showing the inside, and how much of a mess it is (or not) and how much room there is to work would be useful.

Secondly, it's a BGI to have external lights going through a double-pole switch so that they can be completely isolated if they develop a fault which trips the RCD.

Thirdly, T+E outside is not a good idea - it is not stable under UV radiation. Use something different, e.g. black tough rubber sheathed cable, or ideally not have any exposed cable outside at all.

Lastly, I hope the wizard doesn't have lace curtains.

 

[plugwash]

Remember the incoming terminals will be live even with the main switch off. The live parts SHOULD be shielded so they can't easilly be touched but damaged parts, poorly terminated conductors or with some CU designs (I don't think yours is one of them) missing covers can result in live metal on the incoming side of the main switch being exposed once you take the CU lid off.

Work slowly and carefully with the main switch off, don't touch anything metal unless you are sure it's dead and be especially careful to stay clear of the incoming connections.

 

[JohnW2]

I want to open CU and replace cable with clean new 2.5mm T+E, clean as in when going through the wall and once outside it will run across mortar join and blend in. ... Any thoughts on switching over old for new. ... Never seen inside a CU..... behind the wizards curtain!

You have received good advice about the hazards, and cautions/ precautions that would be necessary, as well as some good advice about other aspects of the circuit.

However, I have to say that, in view of the potential hazards involved, if someone needs to ask the question "Can/should I open consumer unit to ....", my inclination is to say that the wise (and safe) answer probably should be 'no'. It would not be a very big job for an electrician to do.

Kind Regards, John

 

[AndyPRK]

2.5mm cable is also overkill if its connected to a 6A MCB. Is it ? or what is it connected to? which one makes the light stop working ?

 

[sparkwright]

If you are uncomfortable about connecting to a consumer unit, why not use a junction box just next to the consumer unit?

Leave a nice neat loop of slack in the new cable, so the cable can be connected to the consumer unit at a later date.

 

[Safety First]

2.5mm cable is also overkill if its connected to a 6A MCB. Is it ? or what is it connected to? which one makes the light stop working ?

Thanks for post and question. Do you mean which of the MCB's when off, turn off the light? I don't think it has it's own, but then thinking about it, as it's only a single line out, it can't be on a ring. Do they have akin to junction boxes in the CU, so that it might be a spur off a ring?

[/b]

 

[Safety First]

A right thank-fest; cheers all for the advice/info/warnings. Really appreciated

Combining all input...

I think I will fit:
- 32 amp junction box with
- spare (for when sparky is on another job) loop of wire (T+E) that is
-painted (acrylic, very shaded spot under porch)
-with 2 pole surface mounted isolation box.

Will stay out of the CU. Pretty sure I would not balls it up, but given that it's all going to live in a boxed in space, the risk/benefit seems a no-brainer.

Wondering why not 3 pole isolation. 3 pole is for bathrooms, no, so why not 3 for outdoors?

 

[EFLImpudence]

It could be spurred off the Ring circuit MCB although...

... that would be silly as the Lighting circuit is there too.

Just find out which MCB switches off the light.


Bathroom fans can have three live conductors; your light will only have two so a double pole switch would be a good idea.
The CPC, earth conductor, must never be switched.

 

[JohnW2]

Will stay out of the CU. Pretty sure I would not balls it up, but given that it's all going to live in a boxed in space, the risk/benefit seems a no-brainer.

That probably is sensible. Inside a CU is not a good place to be unless one has all the necessary knowledge and is confident/comfortable about what one is doing (and what the hazards are).

Wondering why not 3 pole isolation. 3 pole is for bathrooms, no, so why not 3 for outdoors?

Because there are usually only two things (line/live and neutral) to isolate [one doesn't (and mustn't) switch/isolate the earth/CPC]. Bathroom timer fans are one of the few exceptions - there are then two lines/lives (one permanently live, and the other live when lights are on) plus a neutral - hence three things to 'isolate'.

Kind Regards, John
Edit: typed too slow, yet again!!!

 

[AndyPRK]

You probably want to fit a fused switch with 3A fuse

 

[Safety First]

You probably want to fit a fused switch with 3A fuse

Thanks,...

Why add fuse when its on MCB? Wouldn't a MCB trip quicker than old-school (melting) fuse?

 

[JohnW2]

You probably want to fit a fused switch with 3A fuse

Why add fuse when its on MCB? Wouldn't a MCB trip quicker than old-school (melting) fuse?

Even if they are the same 'rating', there's a fair bit of 'hit and miss' as to whether a fuse or MCB will 'operate' first. However, in this case a 3A fuse would have an appreciably lower 'rating' than the MCB - which would probably be 6A if its from s lighting circuit (we don't seem sure about that), or more likely 32A if it's derived rom a sockets circuit - and so would stand a better change of blowing before the MCB tripped.

Kind Regards, John

 

[AndyPRK]

Most double pole isolators come with a fuse built in anyway.

 

[JohnW2]

Most double pole isolators come with a fuse built in anyway.

Well, FCUs and switch-fuses do, but I think what we were talking about here was just a DP switch, to enable the outside wiring to be isolated (e.g. if it got water-ridden), and that wouldn't have a fuse.

Kind Regards, John