Wiring of external lights on to which MCB?

[Cordless Crazy]

Simple question .........

3No. external PIR lights on 2 seperate spurs i.e. one spur running t front of house supplying 2 lights and one to rear supplying one light both with internal switches. Previous owner wired them in to th lighting circuit.

In rationalising the wiring in my house, should they be wired in to th ground floor lighting circuit, the ground floor RM (on the RCD side o the CU), the kitchen RM (on the RCD side of the CU) or a seperate RC protected MCB?

Note that latter is not possible as no spare MCB's availabl

-- Cordless Crazy

[David Hansen]

On Fri, 1 Dec 2006 08:32:58 +0000 someone who may be Cordless Crazy wrote this:-

Simple questions sometimes don't have simple answers.

That is an option, provided the circuit would not be overloaded. Quite often a downstairs lighting circuit is more heavily loaded than an upstairs one.

Wiring lights into ring mains is undesirable.

Why use an RCD protected one?

Do you have a split board and is there a spare way on the non-RCD side? If so that is ideal.

[dcbwhaley]

Insufficient data.

What wattage are the lamps? Is the lightiing circuit wired in 1mm^2 or 1.5mm^2? What size are the breakers for the lighting circuits?

Dave

[robgraham]

Why ?

rob

[gort]

I assume he meant straight in without any overload or isolation protection ie a Switched FCU.

Dave

[Cordless Crazy]

-- Cordless Crazy

[Christian McArdle]

Good solution, provided the current capacity of the circuit is appropriate.

Both acceptable, provided you use an FCU, although not the preferred method, as you could have nuisance RCD trips.

Also a good solution, particularly if the existing lighting circuit is already highly loaded. No need for an RCD, though, unless you have TT earthing.

Christian.

[Andrew Gabriel]

I don't know what David had in mind, but I keep indoor and outdoor circuits separate. This prevents damage such as water ingress or vandalism from being able to knock out any indoor circuits.

For outdoor lighting, I have a separate MCB. Outdoor fixed lighting does not need to be RCD protected (although apparently the 17th Edition Wiring regs proposes to change this).

A circuit for several outdoor halogen lamps might need to be design for more than 6A protection, due to inrush current.

[Andy Wade]

That's not 100% right. The summary now published[1] says this:

"Chapter 41 now requires that for the protective measure of automatic disconnection of supply for an a.c. system, additional protection by means of a residual current device with a rated residual operating current (I?n) not exceeding 30 mA and an operating time not exceeding 40 ms at a residual current of 5 I?n be provided for socket-outlets with a rated current not exceeding 20 A that are for use by ordinary persons and are intended for general use, and for mobile equipment with a current rating not exceeding 32 A for use outdoors. This additional protection is now to be provided as additional protection in the event of failure of the provision of basic protection and/or the provision for fault protection or carelessness by users of the installation. Note that certain exceptions are permitted ? refer to Regulation 411.3.3."

So fixed equipment outdoors appears to continue not to need RCD protection (unless TT etc.).

[1]

[Andrew Gabriel]

[David Hansen]

On 1 Dec 2006 04:51:44 -0800 someone who may be "robgraham" wrote this:-

Many reasons. These boil down to faults in one sort of circuit affecting another sort of circuit, which is undesirable. For example external circuits are generally more likely to water penetration. Is it sensible that water penetration of an outside light should cause the television set or the microwave to go off? Far better to have them on a separate circuit.