Question on sub-distribution boards

[richards1978]

Hi All,

I'd like to run power to a shed, and have a quick question on whether something is allowable under the various electrical regulations.

We currently have a consumer unit pretty much in the centre of the downstairs floor of the house (under the stairs). This then has a thick 16mm2 SWA cable running to the garage, where it connects to a distribution board for garage lights, sockets etc, and has 4 unused ways - apparently a thick SWA cable was used for the garage and a larger than necessary distribution board was fitted as the original house owner wanted to put in a hot tub and outside lighting/sockets in at some point, but never got round to it.

I'm keen to try and get power to a shed that is outside in the garden at some point, but really don't want the floors of the house cut up and a new connection laid from the consumer unit. Would it be allowable to use one of the spare ways on the garage distribution board to run a smaller SWA to the shed and power a second sub-distribution board there (for shed lighting, shed sockets and possibly outside lighting and outside sockets)?
Pretty much creating a "daisy chain" of connections i.e. consumer unit -> distribution board garage -> distribution board shed

Just trying to get an idea of whether this is something that is doable. If we have to use a connection from the main consumer unit, then I'll just abandon the idea.
I'd obviously let an electrician fit it and figure out how the RCDs, MCBs and how everything would fit together to work properly in such a set-up, but don't want to waste anyone's time if something like this can't be done.

Thanks

 

[Harry Bloomfield]

Would it be allowable to use one of the spare ways on the garage distribution board to run a smaller SWA to the shed and power a second sub-distribution board there (for shed lighting, shed sockets and possibly outside lighting and outside sockets)?

Basically, yes! You may not even need to install the extra 'distribution board'.

 

[pete01]

Yes that's exactly the way to do it.

 

[richards1978]

Thanks guys - that's good news!

 

[SUNRAY]

Or you could run 16mm² cable from the garage directly off the existing 16mm² (the live side of the garage distribution board) to have the full capacity at the shed.
That way a problem in the garage won't affect the shed and vice versa.

 

[morqthana]

Sounds like a good idea, but how would you "split" the SWA?

Add a 2nd one into the garage CU with the armours linked, and 2 x 16mm² into each IN terminal on the main switch/RCD?

Or put in a box with SWA from the house, SWA to the shed, and something (wouldn't need to be armoured) to the garage CU? What would be inside to join the cables?

 

[ebee]

Yes it sounds doable and there are a few different ways do do it as has been suggested already.
Perhaps now is the time to get your Electrician and discuss the various options

 

[SUNRAY]

Sounds like a good idea, but how would you "split" the SWA?


Add a 2nd one into the garage CU with the armours linked, and 2 x 16mm² into each IN terminal on the main switch/RCD?

Or put in a box with SWA from the house, SWA to the shed, and something (wouldn't need to be armoured) to the garage CU? What would be inside to join the cables?

Both of those are possibilities

In a safe and professional manner which I'd leave up to the professional who is doing the job and able to do a proper survey of the site and will have his or her preferred solutions.

There are so many options it's not really worth discussion here.

 

[richards1978]

Thanks all - it sounds like my plan is definitely possible, so I will reach out to someone and see which approach they recommend.

 

[Ragnar_AT]

Depending on what you want to power in the shed, the easiest way might be an RCBO in the garage CU (20 A), sockets in the shed powered directly, light via a 5 A FCU. Just something to suggest to your electrician.

 

[richards1978]

I was thinking this originally, but when I ran it through my head in terms of what would happen under a fault, I was worried this could leave me stranded in a dark shed without an easy way of restoring power.

Ideally, I'd just want a minimally protected SWA cable (not sure what protection legally has to be on this) running to the shed. Then have the shed lights and sockets on 2 or more separate RCD protected circuits with a small fuse box in the shed itself. Then if I have a power tool problem that trips the sockets, it would be less likely to plunge me into darkness surrounded by sharp tools, chemicals and other nasties.

Not sure if this is possible, so will see what the electrician suggests.

 

[bernardgreen]

Non-Maintained Emergency Lighting

• Only on in Emergencies:
  These lights remain off during normal operation and only activate using their backup battery when the main power supply fails.
  
  
• Energy Efficient:
  They consume less energy than maintained lights because they are not continuously illuminated.
  
  
• Battery Charging:
  They use a trickle of mains power to continuously charge their backup batteries.
  
  
• Common Uses:
  Often used in workplaces, factories, and offices where artificial lighting is normally present, but a backup is needed for safe evacuation.
  
  
• Integration:
  These units are linked to the building's standard lighting circuit,

 

[AndyPRK]

Is there currently an RCD protecting the garage supply in the house? As that will trip if you have a fault in the shed.

It could get annoying. having to reset a house RCD, goto the garage and reset RCD, and then back to the shed. Only to find out it trips again. That could get really annoying trying to work out what is causing the trip

If the shed has no windows, and emergency light doesn't sound that OTT after all.

I was worried your shed would get wet, and that cause your garage to be without a supply until fixed by a spark. (if the garage in and out SWA's were joined)

 

[richards1978]

There's a 100mA Type-S (time delay?) RCD in a small box with the main isolation switch right next to the electric meter in the outside meter box, with a big chunky SWA cable running into the house and under the floors for a few metres straight to the consumer unit under the stairs.

The main house consumer unit (from right to left) then has an mcb next to the main switch for the garage, then a 30ma rcd followed by 5 mcb protected circuits, then another 30ma rcd followed by another 5 mcb protected circuits. Base on thr labels and layout, I don't think the garage has an rcd protecting it, other than the 100ma type S one near the main isolation point.

The garage supply is also directly connected to the house consumer unit by another big chunky swa.

The shed has windows and is quite new, dry and a reasonable size, so I wanted to use it as a workshop (man cave) throughout the year including during dark winter nights when there's very little light.

I have someone coming out next week, so will see what they say. But if anyone sees any obvious horrors with the existing setup please let me know, so I can prepare myself.

 

[AndyPRK]

Arh. Sounds all good then regarding my worries. They aren't valid.
Bit surprised there is no 30mA RCD in the garage protecting the garage sockets.
Do you plug anything interesting into the garage sockets? Lawn mower, extension leads etc....