can i add more than one circuit to mcb

[veedee]

Sparky who wired the consumer unit put smoke alarm on separate circuit.

I find this to be unnecessary and would like to combine this circuit with lighting circuit on 6AMP MCB.

Question:

1. Is it okay to add more that one circuit to MCB?

2. If so, is there a limit on how many you can add?

3. Is better to have separate circuits for smoke alarm and lighting circuits? Or is it better to have both lighting and smoke alarms on the one circuit

 

[EFLImpudence]

1. Is it okay to add more that one circuit to MCB?

Not possible - everything on a MCB is by definition one circuit.

2. If so, is there a limit on how many you can add?

No.

3. Is better to have separate circuits for smoke alarm and lighting circuits? Or is it better to have both lighting and smoke alarms on the one circuit

Opinions vary but if the alarm is on another circuit, you will more likely notice if the circuit switches off.

 

[oldbutnotdead]

Pace on all the previous threads about this CU swap.
Yes you can have more than one cable fed from an MCB but make sure the cores are the same type (solid/stranded) and the same size otherwise they tend not to get gripped very well by the terminal screws in the MCB.
If that's a problem, just put a junction box outside the CU and do your joining there (Wagos or terminal block).
There's a physical limit to how many cores you'll get into each hole (the neutral and earth bar holes tend to be smaller than MCB). It's also not a brilliant idea having loads of devices on 1 MCB (if one device fails you lose all the items. Makes faultfinding very tedious).
Alarm on separate circuit or on lighting circuit- depends on the alarm.
There's pros and cons with both setups;
Lights and alarm on 1 MCB.
PRO
If the lights stop working you'll investigate straight away
CON If the alarm is causing an electrical fault or needs some work you'll be doing it in the dark
Lights and alarm on 2 MCB
PRO
A faulty light won't knock the alarm out.
If you are working on the alarm you'll have electric light available
CON UNLESS there's an audible/visible powerfail warning on the alarm you might be unaware that supply has failed to it for some time

 

[veedee]

Pace on all the previous threads about this CU swap.

No Mate, this is another consumer unit (pic below)

Yes you can have more than one cable fed from an MCB but make sure the cores are the same type (solid/stranded) and the same size otherwise they tend not to get gripped very well by the terminal screws in the MCB.

I don't get it..

Didn't @EFLImpudence say that what I am proposing is not possible?

Or did I just not use the correct terminology?

To clarify, I want to take the wire (smoke alarm) which comes into the the MCB and add this wire to the MCB which currently has the cable for the lighting

This is perfectly fine as long as the cores and sizes are the same as you advised?

If that's a problem, just put a junction box outside the CU and do your joining there (Wagos or terminal block).
There's a physical limit to how many cores you'll get into each hole (the neutral and earth bar holes tend to be smaller than MCB). It's also not a brilliant idea having loads of devices on 1 MCB (if one device fails you lose all the items. Makes faultfinding very tedious).
Alarm on separate circuit or on lighting circuit- depends on the alarm.
There's pros and cons with both setups;
Lights and alarm on 1 MCB.
PRO
If the lights stop working you'll investigate straight away
CON If the alarm is causing an electrical fault or needs some work you'll be doing it in the dark
Lights and alarm on 2 MCB
PRO
A faulty light won't knock the alarm out.
If you are working on the alarm you'll have electric light available
CON UNLESS there's an audible/visible powerfail warning on the alarm you might be unaware that supply has failed to it for some time

That's brilliant - thanks for the pros and cons.

A smoke alarm could save a life. Potentially being unaware of a defective smoke alarm because they are on separate circuits is a flaw for me. Like you said, if the lights go out, you'll notice this immediately and investigate.

 

[pete01]

I would always put the smoke detector circuit with the lighting circuit, reason being if a seperate smoke circuit ever tripped you may not notice, if the smoke circuit trips and effects the lights you will definitely notice.

 

[EFLImpudence]

I don't get it..

Didn't @EFLImpudence say that what I am proposing is not possible?

No - you asked if you can have two circuits in one MCB - you can't; it is not possible.

You can have two (or more) wires in the MCB but they will then be ONE circuit.

 

[EFLImpudence]

From the regulations:

 

[veedee]

No - you asked if you can have two circuits in one MCB - you can't; it is not possible.

You can have two (or more) wires in the MCB but they will then be ONE circuit.

Oh come on @EFLImpudence you knew what I meant

A school boy error on my part and a teachable moment..

 

[EFLImpudence]

Oh come on @EFLImpudence you knew what I meant

I did but you obviously did not read all of my reply.