typical RCBO for radial light circuit

[heavyduty]

Hi

We are installing new light circuits and I've decided to go with traditional junction box circuit using the new maintenance free boxes from hager.

what is the recommended RCBO (preferably hager) for each lighting circuit using 2.5mm T&E?

Thanks

 

[Taylortwocities]

You need an electrician,mate.

Lighting circuits are not usually run in 2.5mm². You'll never get the conductors in lighting switches & lamp terminals.

Choice of CPD will be a factor in the cable calculations that your electrician will do as part of his/her circuit design.

 

[sparkwright]

In a domestic dwelling it is the norm to use 1.0 or 1.5 mm cable.

Also, junction boxes that are inaccessible are a bad idea, although it was very common practice once.

Why use 2.5 mm? For one thing the connections on lighting accessories are quite small. And I don't think 2.5 mm 3 core and earth is available for 2 way switches.

 

[bernardgreen]

I've decided to go with traditional junction box circuit using the new maintenance free boxes

It cannot be traditional if you are

using the new maintenance free boxes

As they are new then few if any have any life time testing in real enviroments. They probably have had some "accelerated life testing" but that testing method has often failed to find life time problems in other types of new equipment leading to recalls and other inconvenience to end users.

So I would NEVER put any type of junction box in place that it was not EASILY accessible for maintainance, but not so easy that a child with a screw driver could remove the cover.

 

[ericmark]

Because a ceiling rose is rated at 6A in most houses the lighting is protected by a 6A MCB/RCBO. The regulations allow up to a 16A device if the junction boxes and wiring are high enough rated. The trip will also have a letter i.e. B6 and this is the rating for 0.1 ms tripping and is magnetic rather than thermal to select one needs the know the loop impedance. This needs measuring with a loop impedance tester or you may have paperwork with the reading recorded and you can then calculate.

Although nothing to stop using 2.5mm cable you may have a problem with some fittings getting the cable into the terminals.

The RCD rating for bathroom lights is 30mA @ 40ms after fitting it will need testing with a proper tester not just pressing button. The fitting of a RCBO can cause a small malformation of case etc. It is common for them to fail so they do need testing.

Test equipment can be hired about £75

 

[ban-all-sheds]

We are installing new light circuits

When you applied for Building Regulations approval, what did you say would be the way you'd comply with P1?

and I've decided to go with traditional junction box circuit

Why?

what is the recommended RCBO (preferably hager) for each lighting circuit using 2.5mm T&E?

Do you really think that you should be attempting to design and install new circuits if you don't know something as basic as that, and (clearly) don't have any books or guides where you can look it up?