Division of Installation

[imroberts]

Division of installation requires that every installation shall be divided into circuits, as necessary, to:
- avoid hazards and minimize inconvenience in the event of a fault
- facilitate safe inspection, testing and maintenance
- take account of danger that may arise from the failure of a single circuit such as a lighting circuit
- reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced

Let's take a CU change on an existing installation in a flat with the following circuits:

- 1 x 32A cooker circuit
- 1 x 32A ring main
- 1 x 20A socket circuit covering part of kitchen
- 1 x 6A lighting circuit

It's easy to minimise inconvenience and reduce unwanted RCD trips either by splitting the circuits across two RCDs or by a full RCBO setup.

However, single lighting circuits are generally frowned upon due to the potential danger of losing all lighting within the property. How does one resolve this?

- Putting the lighting on a seperate RCD to the ring main, for example, would presumably reduce unwanted RCD trips taking out the lighting
- Putting the lighting on an RCBO would achieve this potentially to a greater extent

My personal opinion is that the installation will be "no less safe" than it was prior to the CU change, therefore would be acceptable. But ultimately, the lighting is still a single circuit which does not fully meet this requirement of BS 7671?

What are your thoughts?

 

[EFLImpudence]

I would/do put the lighting on an RCBO and RCD the rest of the circuits.
It's down to what the customer wants to pay.

If you are only changing the CU and there is only one lighting circuit then there is only one lighting circuit.

 

[sparkwright]

You must remember you're not rewiring the place.

Using a high integrity board, and putting the lighting on the unprotected side with an RCBO as suggested is one solution.

If using a dual RCD board, it could be argued put the lighting on one RCD, and the main sockets on the other RCD, as portable lights can be plugged in.

 

[AndyPRK]

When I was faced with this, I put the lights on a C6 RCBO.

An RCD for the rest.

 

[ericmark]

I have said before it's all down to a risk assessment. With a street light outside which would mean there is always some light in the house then a single lighting circuit is not a problem.

In the middle of nowhere with no outside lighting then you may need to split the circuits.

However I would say my single 6A lighting circuit RCD protected with same RCD as sockets is safe because I have two emergency lamps one which lights the stairs and landing the other in the garage above the consumer unit. (Which reminds me must change the batteries)

There are touches which clip into a charger and auto light once the supply fails these do the same job as emergency lights.

The point is if there is a general power cut then all the RCBO's in the world will not stop lights failing so emergency (battery backed) to me is the way to go.

 

[PrenticeBoyofDerry]

What are your thoughts?

Let's take a CU change on an existing installation in a flat with the following circuits:

- 1 x 32A cooker circuit
- 1 x 32A ring main
- 1 x 20A socket circuit covering part of kitchen
- 1 x 6A lighting circuit

The way you split the circuits would depend on the type of board you fitted.
You would need to consider at least dual RCD.
Having lighting circuit on different split to ring final circuit.
Then split the other two radial/power circuits either side.
or the use of RCBOs as stated

It's easy to minimise inconvenience and reduce unwanted RCD trips either by splitting the circuits across two RCDs or by a full RCBO setup.

However, single lighting circuits are generally frowned upon due to the potential danger of losing all lighting within the property. How does one resolve this?

There are options to resolve this:
*Divide the lighting circuit
*install additional lights, maybe wall lights from new circuit or using FCU from RFC.

- Putting the lighting on a seperate RCD to the ring main, for example, would presumably reduce unwanted RCD trips taking out the lighting
- Putting the lighting on an RCBO would achieve this potentially to a greater extent

Indeed it would

My personal opinion is that the installation will be "no less safe" than it was prior to the CU change, therefore would be acceptable. But ultimately, the lighting is still a single circuit which does not fully meet this requirement of BS 7671?

Indeed it is no less safe and does not fail to meet requirements.
If you take in to account the hazards that may arise to lighting failure by having a source or a potential source of power that can supply lighting.
ie RFC on separate split.