CU change only one lighting circuit ???

[ianphilip007]

hi there

need a little advice when you change a C.U that currently has only one lighting circuit covering the whole property( upstairs and down) this circuit would need to be split into 2 seperate circuits before beeing connected to the new CU is my thinking correct re reg 314??

 

[ianphilip007]

any advice as to where is usally best, minimal dissruption,
to make the split ?

 

[Spazz]

How many points are on that one circuit?
Over how many floors?

It is not always suitable to request a rewire of the property just to have up and down on separate circuits.

All 314.1 stats is that all circuits should be divided into circuits, as necessary

 

[ianphilip007]

so its not a must that the circuit be split when you change the cu ? if that is how the existing wiring is. it would be over 2 floors but not over 1000w

wasnt sure if you had to split the circuits, when you changed the cu and as you stated would require alot of remmedial work to rewire for 2 seperate circuits

 

[RISElectrical]

Regulations aren't retrospective and just changing a CU doesn't mean you need to wire a new circuit to split the lighting. However would be a good idea to have sockets on a seperate RCD or maybe everything on RCBOs and then to a large extent reg 314 is satisfied

 

[ianphilip007]

well im glad that my initial thinking was wrong as seperating could be a problem

 

[Top Cat]

Regulations aren't retrospective and just changing a CU doesn't mean you need to wire a new circuit to split the lighting. However would be a good idea to have sockets on a seperate RCD or maybe everything on RCBOs and then to a large extent reg 314 is satisfied

Good advice!

 

[Spazz]

Dont forget the BS7671 is not law! It is advised - you should follow it as much as possible unless you have a good reason not to - customer would not pay for a rewire is an ok reason

Do an Ohms law if your in doubt:
P=IxV
I=P/V
= 1000/230
=4.35A

Use a 6A MCB and you have more than enough room to move with.

If in doubt change all the bulbs to Energy Saving - you would only get a max of 140w (based on 10 lights at 14w Energy Saving Bulbs - 0.6A

 

[ianphilip007]

thanks guys for all of the advice most appreciated

 

[Mr.Ian]

Trouble with lighting all on one is the safety issue of it ever tripping, the whole house is then in darkness, no lighting at all and not safe. You can get very lucky in as much as to split the lighting to upstairs/downstairs can just be a case of finding where the existing circuit feeds to the upper floor/disconnect it from it's supply from the downstairs lighting/remove it and run a new cable to the upstairs lighting it fed. Lighting is then split up/down, only 1 1.5mm cable run. Still a real big pain in the you know what though.

 

[Knobhead]

So all of downstairs is in darkness. The lights upstairs are fine. Doesn’t help when bumbling in the downstairs cubby hole for the MCB.
If you want to take this to the extreme then every room should have it’s own MCB. BUT a room may have a centre light and wall lights, so that’s two MCB’s. One step further and each room should have it’s own radial for the sockets. We will finish up with every house having to have Sizewell B switching station under the stairs.

For goodness sake apply a bit of common sense, a two up two down only needs one lighting circuit. One or (two ring mains (kitchen separate), if you want to be extravagant). Cooker and shower.

When you’re rewiring the Ritz then think about splitting the lighting.

 

[Rockingit]

As others have said, if it was there before you then it can stay (so long as it's safe etc etc). Presumeably it's been sat there quite happily for years on a 5A rewireable fuse, so logic says that it will also sit for years on a 6A MCB.

If you're fitting a split board and all the sockets are on just one ring final as well then just have them on opposte RCD's, otherwise you'll need to fit RCBO's to achieve discrimination.

The 'Safety Lighting' argument is sometimes a little bit of a red herring - how many lights stay on in a power cut?

 

[Knobhead]

The 'Safety Lighting' argument is sometimes a little bit of a red herring - how many lights stay on in a power cut?

Good analogy, like it.

 

[Rockingit]

Good analogy, like it.

Out of interest, you might be surprised as to the number of times I can easily talk a customer into fitting one of the new led downlight style ENM's over a hall/stairwell. Wire them onto the smoke alarm feed / signal line and more usefully they'll just about last longer than the powercut!!

 

[Mr.Ian]

Well I'm sure we have the reg 'minimise inconvenience in the event of a fault’ and surely no lighting at all is a bit of an inconvenience.