2 Lighting Circuits on one 6A CB

[Snapester]

I take that the porch light is on adequate sized cable for the breaker? I thought you need more than one for assessment? A few big jobs and one small or something, at least when i joined it was......... i think i might sell my test gear.....

 

[sparks1973]

It has , but there can be more than one feed for each circuit.

so what if the neutral was shared then......each on its own MCB then eh?...lol....

 

[Strima]

You can also run a spur from the origin of the circuit...

 

[sparks1973]

You can also run a spur from the origin of the circuit...

such as smokes n heats..through their own means of isolation (FCU)...

 

[Guest55]

so what if the neutral was shared then......each on its own MCB then eh?...lol....

Well thats not the same as 2 cables sharing a mcb is it ?
which is the issue being discussed isnt it ?

 

[sparks1973]

Well thats not the same as 2 cables sharing a mcb is it ?
which is the issue being discussed isnt it ?

just another scenario BIFF...just another scenario.....

 

[Guitarist]

It is always a good idea to split the lighting if possible, 1 onto each RCD, so that you don't lose everything if 1 trips. The problem arises if the 2 circuits share a neutral (I think this is what sparks1973 was getting onto), as you will end up with an imbalance. Have you checked for shared neutrals? If you have, and the 2 circuits are completely separate, then I would split them across the RCD's. This is, after all, the reasoning behind dual RCD boards.

 

[NewbieRuffy]

I did do a IR test between N/E and this what confirmed that they were separate. To be sure (as i am still a Newbie) i removed one of the circuits in the CU from CB, connector blocked it, and then energised (after replacing cover of course!) Then simply turned on the lights down stairs and just a case of elimination, i repeated for other circuit to confirm. I guess long way round but had time and didnt take too long.

I also do have a number of spare ways in the CU, I have just thought though i am installing a new kitchen (i also fit kitchens with my bro, so pretty handy) and think i am going to put in downlighters, so will more likely have to upgrade to a 10A CB so thinking leaving the one porch light circuit on 6A and moving the rest of the downstairs and new kitchen lights to 10A CB.

 

[richy3333]

In the house we are in there are 5 lives stuffed in to a rewirable fuse, CU! Landlords agreed to let me sort the mess that are our electrics out though and pay for it

 

[NewbieRuffy]

Totally agree Guitarist, the upstairs lights are already on the other RCD, I now plan to move the porch light circuit on to the upstairs RCD and put in a new 10A CB for the downstairs, as mentioned before, installing downlighters in kitchen very soon. I was taught that it was always best practice to have all circuits on separate CB where possible, hence i asked this original question.

 

[Deleted member 26818]

At the moment, it is one circuit.
A circuit is defined as: "An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s)."
The fact that there are two conductors in one MCB is immaterial, it is one circuit.

 

[Jonny66]

I would leave it as is, cant see anything wrong with the porch light added via MCB, and agree with spinlondon that this is one circuit.
IMO, I would rather do it this way (at MCB) than hidden junction box under floor/ above ceiling.

 

[ackbarthestar]

That's my thinking as well.
I would have wanted to know what each lighting leg fed and whether they could be separated or whether they shared a neutral. If the latter then they would have to be regarded as one circuit and kept together in the same breaker.

With these new 16 - 20 way CCUs you can have lots of separate circuits without the need for sharing.

One quick way to check besides IR testing across the neutrals would be to place one leg on one RCD and the other leg on another RCD. If both RCDs trip out when a light is switch on then you have a neutral across the two legs

- - - Updated - - -

That's my thinking as well.
I would have wanted to know what each lighting leg fed and whether they could be separated or whether they shared a neutral. If the latter then they would have to be regarded as one circuit and kept together in the same breaker.

With these new 16 - 20 way CCUs you can have lots of separate circuits without the need for sharing.

One quick way to check besides IR testing across the neutrals would be to place one leg on one RCD and the other leg on another RCD. If both RCDs trip out when a light is switch on then you have a neutral across the two legs

- - - Updated - - -

That's my thinking as well.
I would have wanted to know what each lighting leg fed and whether they could be separated or whether they shared a neutral. If the latter then they would have to be regarded as one circuit and kept together in the same breaker.

With these new 16 - 20 way CCUs you can have lots of separate circuits without the need for sharing.

One quick way to check besides IR testing across the neutrals would be to place one leg on one RCD and the other leg on another RCD. If both RCDs trip out when a light is switch on then you have a neutral across the two legs

 

[ackbarthestar]

Its gone bonkers again ! Updating...... Its gone bonkers again ! Updating ....... etc.

 

[Risteard]

As others have said we should be clear that there is ONE circuit supplied by the protective device. By definition you have one circuit (and indeed there can be good reasons for designing this way e.g. to limit Zs/volt drop).