New build, garage sockets... where to start...

[ninnage]

OK, where to start... I'm in a new build and to cut a long story short want to add some extra sockets in the garage for a small workshop - the only high power item I occasionally use is a 2kw heater, everything else is relatively low power - battery chargers, drills etc.

While I'm at it though, I have 'concerns' about the electrics in this place. It's all signed off of course so ticks all the Part P boxes. Anyway, I'll not open that can of worms . But to give you an idea...

Shortly after moving in I noticed one of the smoke alarms hanging off the ceiling - it was 'secured' to a standard metal backbox using plasterboard screws. I put the proper screws in but noticed sparks coming out of the smoke alarm - significant arcing from the cheapo choc block connector they used to wire the thing up - the screws were all threaded and the wires were basically just resting on each other. I fixed this.

I've also noticed many walls where cables are running outside safe zones - i.e. cables running down the middle of a stud wall where there are no fittings on the wall at all. I'm sure that's not allowed but hey, it's signed off Part P so must be fine.

Also, the circuit arrangement just seems bizarre in my book. It's a 3 storey town house with a detached garage:-

RCD 1 (63A):-
Smoke Alarm - 6A
Floor 1 Lights - 6A
Lights (?) - 6A
Water Heater - 16A
Ground Floor Sockets - 32A (spur to garage)
RCD2 (80A):-
Central Heating - 6A
Floor 2 Lights - 6A
Ground Floor Lights - 6A
Floor 1 & 2 Sockets - 32A
Cooker - 40A

So 4 lighting circuits but no separate circuit for the garage? (the CU is full btw)

The garage is fed from a (non-fused) spur from a kitchen socket - so it goes:-
Kitchen Socket -> DP Switch in Kitchen -> DP Switch in Garage -> Garage Socket and Fused Spur to lights (the socket isn't off the fused spur). So technically the garage socket is a spur off the kitchen socket that then has a spur to the lights. Oh, and the armoured cable runs through a 1.5" plastic pipe roughly 2" below the soil surface in the garden, over to the garage.

SO, sorry for rambling. My questions are:-

1. Adding sockets in the garage. There's no easy way to add a dedicated circuit from the CU. What would you suggest for adding more sockets in the garage? Install a mini CU with 16A RCBO and then just keep radial for the sockets? I'm happy to do a ring but seems pointless? I'll probably keep the fused spur for the lights off the 16A circuit. I also plan to use one of these for the sockets: http://www.screwfix.com/p/mk-20a-dp-secret-key-switch-metal-clad/29973
2. Does the general state of the electrics in this house seem unusual / worrying? I mean, it's all signed off and Part P so must be fine, right?!

Thanks in advance!

Andy

 

[Lectrician]

CU is laid out with thought. If an RCD trips, you only loose lights, but retain sockets on that floor and visa versa.

Cables in stud walls, less than 2" deep doesn't comply, but we assume mains wiring here?

Cheaply choc blocks not great. Come across those quite often.

Two spurs from kitch socket poor. Best way to sort this is to replace the DP switch in kitch with an unswitched FCU. Everything after is then compliant, and you can spur and add sockets to your own content.

Why would you add a 16amp RCBO? Pointless. You already have RCD protection.

 

[ninnage]

I could understand 3 lighting circuits but 4? I need to double check what the Lights (?) circuit actually is. To me it would have made more sense to free up a space for a dedicated circuit for the garage, but such is life.

Yes, cable in stud wall is grey mains - looks like 2.5mm T&E.

16A RCBO in garage - I'm just thinking of something to protect the stretch of cable between the garage and the kitchen from potential overload.

Cheers for help!

 

[AndyPRK]

The extra light circuit could be for the light by the CU so you can see to work there.


The fcu in the garage could be 3a to allow 1mm cable to be used for the lights.

Be interesting to know what size cable runs to the garage.

 

[ninnage]

Cable run to the garage is 2.5mm 3 core armoured.

 

[AndyPRK]

Although not to the latest regulations, if it were me I would fit a 16 or 20a MCB in the garage for a radial for the sockets.

This will allow you to draw a sensible amount from garage sockets while not overloading the house ring.

Leave the garage lights off the new MCB so you still have garage lights if the MCB trips.
Or if fitting a dual mcb garage cu connect the lights off the 6a

 

[AndyPRK]

Two spurs from kitch socket poor. Best way to sort this is to replace the DP switch in kitch with an unswitched FCU. Everything after is then compliant, and you can spur and add sockets to your own content.
.

Loosing neutral disconnection would be a significant disadvantage to me, say if the garage were to get wet , you wouldn't be able to disconnect the garage easily to keep the house elec working

 

[ninnage]

Andy - I was thinking the same, to put in a separate 6A RCBO/MCB for the lights but that would then potentially allow 22A down the 2.5mm run back to the house... not sure if that's a problem or not - I think 2.5mm armoured handles about 40A anyway... I think?!

 

[yorkspark]

You could remove the kitchen dp switch and fit a 2mod grid with a 20a dp switch and a 13a fuse carrier.
this would allow safe isolation and will also fuse the garage supply down to allow extra sockets to be added

 

[Lectrician]

Of just fit a SWITCHED FCU in place of the DP switch if you really want isolation.

To be fare, I assumed attached garage.

RCBOs would be silly.

 

[winston1]

You don't need a dedicated MCBs for central heating and smoke alarm. Put them both on one 6A MCB which will then free up a space for the garage on a new 20A MCB.

 

[ninnage]

Why would RCBO's be silly? It protects the cable run between the house and garage and also allows trips to be reset from the garage instead of the house. Don't see a problem with this but I might be missing something?

Winston1 - if I was going down that route I'd put the smoke alarms on one of the many lighting circuits but the cable run from the garage to the CU would be a nightmare.

I think my preference is leave the DP switch in the kitchen and add a 16A RCBO in a mini CU in the garage with a FCU for the lights.

Thanks for all the pointers guys - appreciated!

 

[AndyPRK]

For earth leakage faults both the rcd in the house and rcbo in the garage would trip. Therefore it doesn't make it easier to reset or prevent nusent trips.


They do give clues where the fault was though

In any case garage CUs often come with an rcd in.

 

[Lectrician]

Adding an RCBO would not only be silly, it would be non compliant, due to discrimination.

With an RCBO and an RCD in the same circuit there is no guarantee which woud trip first. It would be hit and miss. Having two 30mA device on the same circuit is stupid and non compliant.

 

[ninnage]

Why would it be non-compliant? The regs say you need discrimination where discrimination is needed to prevent danger. In this situation discrimination doesn't prevent danger - just inconvenience if both trips go. As mentioned surely it's better to have an RCD or at least *something* in the garage to prevent overload of the cable run back to the start of the spur in the kitchen?