Outdoor and indoor lighting on same circuit

[Ellsa100]

Hi

The ground floor of my house has two lighting circuits which are each protected by an MCB. One of those circuits is just indoor lights. The other circuit covers both indoor and outdoor lights. There is no RCD protection for either of these circuits.

The problem with the circuit that covers both indoor and outdoor lights is that outdoor lights occasionally have issues with water ingress etc which will cause the MCB to trip, but this then trips for the indoor lights on the same circuit too. Not good.

QUESTION 1 - Is it easy for an electrician to effectively separate the circuit which currently has both an indoor and the outdoor circuit on one MCB so that the outdoor circuit is on its own independent MCB and the indoor circuit is on its own independent circuit? By easy I mean something this is not an extensive rewire job etc.

I’m guessing that the house - built in 2006 - originally probably split the ground floor lighting circuits into two circuits, each protected by a 6A MCB, because of the higher power rating of halogen bulbs - say 50W - whereas now all the bulbs are LED.

QUESTION 2 - can the two indoor circuits be combined into one circuit protected by a single 6A MCB given a typical LED consumes roughly a tenth of the power of halogens?

-> the reason I ask this is I’d rather have the whole ground floor indoor lights on one MCB and the outdoor lights on another MCB (than have two ground flood light circuits each occupying an MCB together with an MCB for the outdoor lights)

QUESTION 3 - presumably I should use MCB+RCDs or RCBOs for both indoor and outdoor lighting circuits (rather than just an MCB)?

Thank you!

 

[westward10]

If an mcb is tripping then it is almost certainly a bigger issue than water ingress.

 

[timhoward]

This is difficult to answer on a forum I'm afraid.
As above, for an MCB to trip lots of amps would need to be flowing. While water has a resistance it is quite large (many Mohms per square cm) and it's unlikely this would be the cause.

In general it would probably be easier to fix the issue than start rearranging circuits.
You really need a sparks to have a look and run some tests to find the issue first, and then see what options there are to resolve it.
How many outside lights do you have?

 

[Ellsa100]

The issue with the MCB tripping only seems to happen when I turn on the garden lights, so there is something wrong with that part of the circuit....

Previously the sparky who swapped out the lights suggested it could be a result of water ingress which causes the circuit to short. There are maybe 10 garden lights outside.

The MCB on the ground light circuit has not tripped when the garden lights have been off.

This is one of the reasons why I want to isolate the outdoor lighting circuit from the indoor lighting circuit.

Thanks again.

 

[westward10]

Sounds like you have a live to earth fault.

 

[davesparks]

The issue with the MCB tripping only seems to happen when I turn on the garden lights, so there is something wrong with that part of the circuit....

Thats fairly conclusive that the outside lights are the cause of the tripping. It won't be water ingress alone, but water ingress may have caused other corrosion/damage which has led to the fault developing.

Seperating the external lighting from the internal will likely involve a lot of work in such a modern built house. Probably requiring the lifting of upstairs floors to get a new cable from the consumer unit to the outside lights.

However there may be other options.
It may be possible to install a DP isolation switch so that the external lights can be easily isolated if a fault occurs.

 

[Ellsa100]

Sounds like you have a live to earth fault.

But the circuit doe snot have RCB protection...I thought a MCB would not trip from simply a live to earth fault - wouldn't you need an RCB or RCBO? thanks

 

[Ellsa100]

Thats fairly conclusive that the outside lights are the cause of the tripping. It won't be water ingress alone, but water ingress may have caused other corrosion/damage which has led to the fault developing.

Seperating the external lighting from the internal will likely involve a lot of work in such a modern built house. Probably requiring the lifting of upstairs floors to get a new cable from the consumer unit to the outside lights.

However there may be other options.
It may be possible to install a DP isolation switch so that the external lights can be easily isolated if a fault occurs.

That makes sense re DP isolation.

Guess need to have someone check the outdoor cabling...wonder if I can get this covered by my Homeserve policy!?!?

 

[westward10]

But the circuit doe snot have RCB protection...I thought a MCB would not trip from simply a live to earth fault - wouldn't you need an RCB or RCBO? thanks

A live to earth fault generates fault current and this is one of the principles behind circuit protection.

 

[davesparks]

But the circuit doe snot have RCB protection...I thought a MCB would not trip from simply a live to earth fault - wouldn't you need an RCB or RCBO? thanks

An MCB operates on over-current, it doesn't care where the current is flowing to, if there's too much current flowing the MCB will operate.

MCB's operate on Live to neutral, live to earth and live to live faults.

 

[Ellsa100]

An MCB operates on over-current, it doesn't care where the current is flowing to, if there's too much current flowing the MCB will operate.

MCB's operate on Live to neutral, live to earth and live to live faults.

gotcha,, thank you.

 

[brianmoooore]

The fault current that will trip the MCB is of the order of 1000 times greater than that which would trip a RCD. Or, to put it another way, the leakage in your wiring is at least 1000 times worse than the maximum that is considered safe.

 

[timhoward]

The issue with the MCB tripping only seems to happen when I turn on the garden lights, so there is something wrong with that part of the circuit....

[.....] There are maybe 10 garden lights outside.

Even if you did arrange a new circuit for the outside lights, the fault would need finding anyway as things definitely won't be up to the standards required to sign off a new circuit as it stands.
A decent sparks could do some testing to work out where the issue is and I'd imagine have a good idea what is going in within a couple of hours.

One serious point - they aren't RCD protected, and there's a suspected live-earth fault. I'd suggest leaving them off until this is sorted. If they are metal then one or more of them could be in a condition that if they were touched they would cause an electric shock.

 

[Ellsa100]

Even if you did arrange a new circuit for the outside lights, the fault would need finding anyway as things definitely won't be up to the standards required to sign off a new circuit as it stands.
A decent sparks could do some testing to work out where the issue is and I'd imagine have a good idea what is going in within a couple of hours.

One serious point - they aren't RCD protected, and there's a suspected live-earth fault. I'd suggest leaving them off until this is sorted. If they are metal then one or more of them could be in a condition that if they were touched they would cause an electric shock.

Thanks for this and all replies. I learn a lot posting here (although I’m starting from a low base!).

 

[Calson]

A properly installed outside outlet with a weather cover will not have water leaking inside. It does not hurt to caulk where inside wires enter and leave the box used for the outside outlet.

In the USA there are code restrictions that prohibit doing this but it is not likely to come up in a casual inspection.

 

[PeakSteve]

But the circuit doe snot have RCB protection...I thought a MCB would not trip from simply a live to earth fault - wouldn't you need an RCB or RCBO? thanks

It depends on the type of Earth, but as long as >6A fault current can flow from L to E, it can still trip an MCB!
But as stated above, it is likely to be more than simply damp (which would trip an RCD @ 30mA, but likely wouldn't run to anything like enough to trip an MCB)