Connecting a second consumer unit

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I have an existing consumer unit connected as normal to the meter and need to connect a second unit located in another building at the end of my garden. I understand that the meter tails need to be split to feed the second unit and have an electrician coming in to sort this out but have a question in relation to where RCD protection should be.

My options are:

meter tails to inline RCD connected to SWA cable running to outbuilding

meter tails connected to SWA cable running to outbuilding which has standard DP isolating switch on a split load board with RCD protection.

Thanks for your advice

Chris
 
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Any good spark will tell you when he comes to do the estimate.
 
You'll have to provide overcurrent protection at the orgin for the SWA cable, if you have sufficent capability on your current CU it can be connected there, if not a separate switch fuse (or I suppose a 'switch mcb' to coin a term!) can be fitted and the meter tails split to it.

Generally I'd say to put the RCD protection in the sub-board down in the outbuilding, but there may be occasions where it should end up at the orgin end
 
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I have plenty of spare capacity in my existing CU on both the switched and RCD protected circuits but was unsure as to whether these could be used as the highest capacity mcb I can get is 40A which I didn't think was big enough given that the new CU will be running a 32A ring, 6A lighting circuit and a 16A exterior radial.
 
itll have to be rcd protected if the new board doesnt have an rcd as its ground level and can be assumed it could be used externally. If your putting in another rcd itll have to be a time delay at the other board.

if you ever damaged the cable in the garden before the new CU, then thatd mean it wasnt rcd protected
 
main cu is an mk split load 17way with 5 spare 2 of which are rcd protected. the new cu is a wylex 5 way with optional rcd protection
 
kevinspark said:
itll have to be rcd protected if the new board doesnt have an rcd as its ground level and can be assumed it could be used externally. If your putting in another rcd itll have to be a time delay at the other board.

if you ever damaged the cable in the garden before the new CU, then thatd mean it wasnt rcd protected

There is no need to RCD protect the underground cable. It is only socket outlets which could supply equipment for use outdoors which need to be RCD protected.

It is best to keep the RCD as local to the point of utilisation as practaicable.




By the way, cralph, MK do a 50A MCB


http://www.tlc-direct.co.uk/Products/MK5950.html
 
so here's the daft question....

If I connect the swa into the existing cu with the rcd at the new cu what rating should the mcb in the existing unit be and what rating should the rcd be in the new cu.

SWA is 10mm betwwen buildings

chris
 
Really depends on what load you think you are likely to use. Just because you are going to fit a 32amp circuit for sockets (doesn't have to be a ring you know) and a 6amp lighting circuit and a 16amp radial (usually 20amp....), this doesn't mean you are going to use 54amps!

What is the outbuilding for? What kit are you going to have? What about the future?

Is the 10mm already in? I would not go higher than 40amp on a 20mm TBH, but could calc to find the exact limit on current carrying capacity. Have you got PVC or Thermosetting SWA?





I would also go for RCD protection at the out building end, and not neccessarily for the lighting cct.




Also need to consider earthing systems....it can be prudent to leave the PME earth at the origin for certain types of outbuilding structure....
 
I'm going to be using the outbuilding as an office for one - so typically a couple of desktops, screens and a laptop on most of the time, maybe an oil heater in the winter or a portable aircon unit in the summer.

I already know that my usage is well below 32amps as everything is on an existing upstairs ring in my house which has never tripped and I have meters on each circuit. In fact I originally had my office in the loft and only found out after I moved to a spare room that the ring up there was tapped of the upstairs lighting circuit which also never tripped (obviously I have disconnected this ring!)

The lights will hardly ever be on as I always use a desk lamp and the outside circuit is going to be for low voltage deck lighting.

The 10mm SWA is PVC and already installed

My original option was to use a 40A mcb at the original CU with the rcd protected circuits mentioned above in the outbuilding. Does this still sound acceptable?

Thanks

Chris
 
the connection to the original cu can be installed onto the the existing RCD protected section (its already there for the original buildings that I removed for the new outbuilding) - my main concern is making sure I get the mcb and rcd ratings correct
 

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