Piggybacking onto a MEM QEB fuse??

[piper64]

I have an oldish consumer unit using MEM QEB fuses. I want to put a single light out through to the porch and understand that I could piggyback the wire onto the existing downstairs lighting fuse using the two screws on the fuse.

Is that true?

 

[Adam_151]

Nothing wrong with a circuit branching at the fuse for an outside light as you describe. Are you aware of how to work safely inside a con/unit?

QEB is an MCB range isn't it? not fuses? Not aware of any MCBs that have two terminal screws on, thats normally found on boards which take fuses only. Perhaps you should clarify the situation

 

[piper64]

Thanks for the speedy reply. Perhaps my terminology was wrong in calling it a fuse.

They look like this:
http://www.ebay.co.uk/itm/MEM-M6-TY...UK_BOI_CircuitBreakers_RL&hash=item2a22a60c2d

I'd get a sparky to do it, but if it's only using the screws I could do that myself, once the mains are turned off??

 

[ban-all-sheds]

I don't think you should, as you seem to think you need to connect things to both screws.

 

[Adam_151]

Yes, thats an MCB.

Why do you think you need to touch both screws?

I could piggyback the wire onto the existing downstairs lighting fuse using the two screws on the fuse.

. How exactly are you planning on making the connection?

There are parts within the consumer unit which are always live, its not something to work in unless you know exactly what you are doing

 

[piper64]

Thanks to you both.
I hadn't had a look until just now, but I have removed the plastic cover and can now see why it would be daft to connect to both screws. This idea was suggested to me by a friend that will now be slapped!

Both screws of the MCB are on the live side.

Right?

Regards the connection, I'd switch off the mains, connect brown to the top of the MCB where the red is, blue to the common bar where all the blacks are connected and earth to the earth block in the consumer unit. It's a PME.

 

[Adam_151]

Thats right. We were worried you'd try to connect to the bottom screw of the MCB as well, which is the supply before the MCB protection, this would be a a very dangerous fault, there is a picture on here with a consumer unit connected up as such!

Though you should be aware of the following:

- The incomming tails to the main isolator will be live all the time when when the main isolator is off, some older boards have limited shrouding around terminals. Risks involve catching them with your hands when routing cables, or catching them with a unsheathed earth conductor or any other bit of metal and causing a big bang, loss of power and quite likely burns and arc-eye

- If your board is a split load board you will have two neutral bars

- The neutral and earth of the branch should share the same terminals as the neutral and earth of the existing light circuit

- If any cable is chopped in wall less than 50mm, RCD protection will be required

- If the consumer unit is neat inside, try and bend yours in to match the existing, rather than lashing it in anyhow

- If the cabling is run outside at all other than straight through the wall and into the back of the fitting, then it becomes part P notifiable, the same happens if the inside cabling is in the kitchen. (is the fitting ON the porch, or within the porch?)

 

[piper64]

Thanks. I don't fancy being burned or having arc eye, as I've had arc eye before when I inadvertently glimpsed a weld someone was doing as I lifted my visor up. It was 30 years ago but still remember the pain...

There is one neutral bar, along the bottom of the row of MCBs.
I can follow the wires so using the same earth and neutral as for the existing lights is fine.
The light is INSIDE the porch and the cabling is going straight through the wall, along a joist to the rose.

I intend to fit three downlights though and have been reading about the hazards of such when roof insulation is covering them. A porch shouldn't really need insulation in the roof I know, but it has insulation panels in the floor, the walls and the windows will be A rated, so why not go for it in the roof too?

I'm happy to cut the insulation to leave a void around the lights, if that's OK, but see that there are' loftcaps' available that look like they are made of the same cardboard hospital bed pans are made of!

Best suggestion?

 

[JohnW2]

.... there are 'loftcaps' available that look like they are made of the same cardboard hospital bed pans are made of!

That would be paper mâché !

Kind Regards, John

 

[Adam_151]

You could construct boxes of plasterboard to go over the lights, follow the clearances given in the manufacturers instructions and dont use any combustable materials in the construction of the same, the fibreglass can then be rolled over the top of this construction

The loft caps are intended to restore the fire rating of the ceiling, for example if a fire starts in the room with the lights, the cap swells up and seals the hole in the ceiling to stop it spreading between floors, rightly or wrongly those, most houses are considered one fire compartment (unless three floors or higher) and you dont strictly need to use them even if living space above. But as you can get lights with the fire stopping actually built in these days for not too much more than thsoe without, it is better to use them where there is living space above.

 

[piper64]

Thanks for that.
I've just bought the lights at B and Q - £10 for three. Not fire rated, they come with 50W GU10s, so I'll probably change them for LEDs so they are less hot.

I'll heed your advice about making a box to go over them, but as it's only a porch, would it be OK to simply make sure the insulation is nowhere near the light fitting?

 

[Adam_151]

AFAIK it depends on the how the porch is classificated building regs related, if it is effectivly an outbuilding stuck to the side of your house and you have a proper external door between them, then the situation is different to if you have made it part of your house


In the former instance there is no need to insulate the building and it wont be heated etc. If its the later than it forms part of your hosue and the insualtion will have to comply with part L, and simply rolling it out the way around the fittings will not comply

 

[piper64]

It was an existing pitched roof open porch with a concrete pole in the corner. The pole is gone, a dwarf wall is built, so all I'm doing is effectively filling in an outside shelter.

The existing front door will be retained and a new door added to the porch. It won't be heated and doesn't need heating, but I was just going to put insulation in the roof so it retains any warmth.

As it's not part of the house, it should be OK to lay the insulation with a wide margin around the lights, although insulation is not required.