Extending Supply from Garage to Summer house

[Flinstone]

For reference I have a radial circuit in my detached garage fed from a 2 way FCU (20A/5A). This FCU is fed by 4mm SWA connected from a dedicated FCU and 80A 30mA RCD in the house (cable run is approx 15mtrs). Three sockets and a fluorescent lamp are installed.

I would also like to have power in my summer house so I can have a ceiling fan/light combination and a socket for the occasional use of a radio or portable television. The distance between summer house and garage is approx 17mtrs

Is it reasonable to extend the existing 4mm SWA that feeds the garage, further on to the summer house? And by joining the extended SWA at the incoming terminals of the Garage FCU? Hence total cable run from the house to the summer house will be 32mtrs.

Is it also reasonable to have a garage CU (16A/6A MCBs c/w 63A 30mA RCD) installed in the summer house despite having a RCD back at the house? I had assumed that there should be separate MCB circuit protection for each outbuilding. While noting comments in the forum for and against additional RCDs, I thought a garage CU would be the most convenient all-in-one unit to have installed.

I am much obliged for any friendly advice.

Fred

 

[Steve]

For reference I have a radial circuit in my detached garage fed from a 2 way FCU (20A/5A). This FCU is fed by 4mm SWA connected from a dedicated FCU and 80A 30mA RCD in the house (cable run is approx 15mtrs). Three sockets and a fluorescent lamp are instaled.

FCUs???? do you mean consumer units? I hope the 4mm² cable is protected by a 32A MCB somewhere, not just this 80A RCD.

Is it reasonable to extend the existing 4mm SWA that feeds the garage, further on to the summer house? And by joining the extended SWA at the incoming terminals of the Garage FCU? Hence total cable run from the house to the summer house will be 32mtrs

Do you have a spare MCB/fuse way on the garage consumer unit? If so, use this, and fit a 20A MCB, run 2.5mm² SWA from this to the summer house, and fit a consumer unit at the summer house.

If practical, this feed for the summer house should come straight from the house, using the same protection and cable as the garage.

Is it also reasonable to have a garage CU (16A/6A MCBs c/w 63A 30mA RCD) installed in the summer house despite having a RCD back at the house? I had assumed that there should be separate MCB circuit protection for each outbuilding. While noting comments in the forum for and against additional RCDs, I thought a garage CU would be the most convenient all-in-one unit to have installed.

No, it is not acceptable to have 2 RCD of the same trip ratings in a row. By the way, do you know the difference between an RCD and a MCB???

Think about how an RCD works: It has a trip rating - 30mA. If you have 3 of these in a row, they will all trip at 30mA - what's the point? You gain no additional protection by doing this.

Buy a 2-way consumer unit and use this in the summer house, with 2 MCBs, and no RCD unless there isn't one already protecting this circuit.

 

[Flinstone]

Yes, I'm sorry - please excuse my ignorance.

To clarify, inside the house there is a RCD connected to a 2-way consumer unit fitted with a 30A cartridge fuse which connects to a 2-way consumer unit in the garage using 4mm² SWA cable. The garage consumer unit is currently fitted with a 20A and 5A cartridge fuse.

I'm afraid a separate feed from the house is impractical since there is a conservatory and block paving in the way.

So, based on on your advice, I thought I should now replace the garage consumer unit with a new 3-way, fitted with an additional 20A MCB, and fit the old 2-way at the summer house.

The garage CU is located at the front of the building and I need to take the new summer house SWA out through the back of it. So I thought I could run 2.5mm² T+E near the top of the garage wall alongside the existing garage wiring (for neatness and to avoid using bulkier SWA), terminating it in a junction box on the back wall. Then run 2.5mm² SWA cable from that point to the summer house consumer unit.

Have I understood the requirements properly?

Out of interest, would you happen to know if my existing garage consumer unit, a Wylex model 206, can be fitted with MCBs?

Thanks again.

Fred

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Out of interest, would you happen to know if my existing garage consumer unit, a Wylex model 206, can be fitted with MCBs?

Sorry, just did another search and found out the answer is yes.
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moderator

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[Steve]

wylex do make plug-in MCBs for old boards:

see here

general electric also make them.

The way you propose to do the work now sounds fine, as long as you aren't going to be running a pottery kiln / hot tub / particle accelerator in your summer house

Make sure you terminate the SWA properly - do you know how? Its sheath must be earthed, this is part of its protection characteristics.

 

[Flinstone]

Thanks Crafty1289, your replies are most helpful and much appreciated.

I assume that the Wylex 306 is the obvious choice of 3-way CU to replace the old 2-way CU in the garage:-
e.g., http://www.tlc-direct.co.uk/Products/WY306.html

Could I ask for a recommendation on the choice of CU for the summer house?
I don't fancy putting the old garage 2-way CU (Wylex 206) in there anymore since it looks a bit bulky and industrial as well as a little rusty.
So can you recommend a brand/model of CU that's any smarter and perhaps smaller in appearance so that it looks less obvious in the top corner of a T&G wall? And does it have to have a ON/OFF switch, particularly if MCBs are fitted?

Thanks,
Fred

 

[Steve]

All the wylex old-style ones have a master on/off switch, and its good practise to have a master switch in each CU, not sure if it's required though in your situation. As for what looks good - its personal im afraid, they are all just as ugly as each other . They are all pretty much the same inside too.

Rather than the Wylex, why not buy a newer type of consumer unit, that looks better and more modern?