Garage Power fed via SWA from the back of a 13amp double socket to a DB in Garage

[Stuartnt]

I'm hoping some of you guys out there on the forum can perhaps provide the benefit of your experience with the below issue:-

Currently working on a job where the garage which is approximately 25 - 30 feet away and adjacent to the house, has its power fed to it via SWA connected off the back of a 13amp double socket located in the utility room off the kitchen.

House is a new build, built in 2010 and power to garage installed by the builders. The owners have requested to have additional circuits installed in the garage for which an upgrade to the existing DB is required; however before I get into that I wanted to ask some advice.

The SWA is terminated within the garage to a 2-way 63mA DB, protected via a double pole 30mA RCD with 2 MCB's of 6A & 16A respectively. Obviously the cables and circuits within the garage are protected by the RCD in the DB, however my concern is the SWA cable is coming off the RFC [from the socket in the utility room] and the SWA is therefore in my mind not protected fully other than via the main RCD in the main CCU as a result of being connected to the RFC in the main house, so any fault in the SWA will cause potential problems not just with the cable itself, but potentially with the RCD in the main CCU and that of the RFC it is fed from.

To get round this I was wondering whether one of the following options might be a better approach

1. Connect the SWA to a separate FSU so as to provide a level protection if a fault occurred in the cable, by way of discrimination

2. Or use an FSU that has inbuilt RCD protection, but I'm not certain an FSU of this type is available as I have never come across one

3. Run the circuit directly back to the CCU, however this will pose a real headache as there is no easy route, if any from what I can see, to the CCU at the front of the property

4. Leave it and do nothing and hope that the SWA cable is never compromised, ending up in further faults occurring

Any ideas greatly appreciated.

Stuartnt

 

[markyboy2782]

Hi Stuart

Funnily enough I am currently installing a garage circuit for a friend of mine and i am using exactly the same setup. However I have been fortunate enough to rewire the Kitchen RFC so i have incorporated a FSU into the RFC which will have a 13Amp fuse. From this I will be running approximatley 5 metres of 2.5mm SWA to the garage into an RCD protected DB which will have 2 MCB's 6A and 16A. I have done this as his main consumer unit is around 35m away from the entry point of the SWA and would require me to run a cable through 4 rooms and the best thing is he has just had his house redecorated. This was the simplest and most cost effective option for him.

The only thing i am curious about is why if the customer is requiring extra circuits are you thinking of doing this as the loadings would most likely be too high and you will need to go back to the Main Consumer Unit anyway?

 

[Sharpend]

You will not have any discrimination between rcd in main house and the one in the garage as it is effectively an extension of the rfc? Can you not trench around the outside of the property to a point nearer main board?

 

[Zeespark]

What about your Equipotential Zone?

AndyGuinness

 

[Stuartnt]

Thanks for the comments, much appreciated.

The loadings are one thing, but my curiosity was more with the set-up as it comes off the back of a double socket on the RFC not off an actual FSU. My thinking was to insert an FSU on the RFC and then reconnect the SWA to the FSU so as to provide protection to the SWA.

Running back to the main CU is going to pose problems as the flooring is less than two years old and hence would cause all manner of issue if I was to start pulling sections of this up and there is just no simple route back to the CU either via the house or via a trench etc.

The loads and circuits are something I will tackle in due course, however I want to be sure the SWA is protected as it shoudl be and not cause issue with the main RFC and associated RCD its connected to as a result.

Seems FSU is the way forward.

Thanks

 

[M107]

what csa is the swa?

what is the ocpd rating for the kitchen ring?

you might not need to fuse down the swa, you could change the garage rcd for a main switch if the kitchen ring is rcd'd at the house cu.

Failing all that run swa surface around the outside of property to the house cu & put swa on it's own circuit, design it so as no rcd is required or use 100mA s type rcd if property is a TT supply

---------- Post Auto-Merged at 18:48 ---------- Previous post was made at 18:45 ----------

The loads and circuits are something I will tackle in due course,

:C

I would do this first what if the swa isnt sized for additional loads.

 

[adammid]

I understand why you would want to install a fused spur. That will provide protection to the armoured but will only protect against a short and overload. If anything faulty was plugged into the garage and there was no rcd in the garage, the rcd in the house would still trip. A fsu won't protect against earth leakage. Install a fused spur next to the socket for the armoured purely as a means of isolation, then fit an rcd protected 3 way board in garage.

 

[M107]

Install a fused spur next to the socket for the armoured purely as a means of isolation, then fit an rcd protected 3 way board in garage.

adammid you will still not get discrimination between the garage rcd or the house rcd

 

[adammid]

M107 you would if you put a time delay on the house rcd but guess that will involve more work. It may be by chance that the garage rcd will be more sensitive and get discrimination that way.

 

[welchyboy]

Why would you bother with any rcd in the garage??

Just fit a standard spur at the kitchen end of the swa

Job done!

You can't fit a time delayed rcd !!

! It doesn't provide additional protection required for your kitchen ring circuit

 

[Steve3948]

At least if the RCD trips in the house they know to rush from the house to garage to make sure whoever's in there is ok.

Now I'm saying its right, but on my estate there's 87 houses, 13 years old, all with a 3-6M of 4mm 3 Core SWA off back of socket in dining room to garage and into twin socket, with fcu adjacent fused at 5A feeding switch in garage to light. All socket outlets with 30mA protection.

 

[philbas]

I'm sure Steps will be on soon soon, but i will ask first, earthing system ?

 

[PC Electrics]

If the swa comes straight out of the back of a sso which is part of an RCD protected RFC, then:

1. the swa is a spur and may only feed one outlet. If it is required to feed more than one outlet then the swa should have an FCU at it's origin.

2. there is no need for any more RCDs, you already have one and there would be no discrimination

Also watch out for where on the rfc this spur is taken and any possibility that the garage usage might result in an unbalanced ring.

Don't forget that a 13A 1362 will pass 20A continuously!

 

[adammid]

Some good pointers the PC electrics!

 

[SLIPSHOD & SLAPDASH]

If the swa comes straight out of the back of a sso which is part of an RCD protected RFC, then:1. the swa is a spur and may only feed one outlet. If it is required to feed more than one outlet then the swa should have an FCU at it's origin.

!

Not if its wired in 4mm or larger

 

[adammid]

Slipshod wiring a 4mm armoured with stranded conductors into the back of a socket along with 2 x 2.5mm might be difficult.

 

[steptoe]

I dont think the earthing or the fact of exporting even matters here,

Its a half done job that will never be right, so why even worry about anything else?

 

[Stuartnt]

Its wired in 4mm 3 core SWA and feeds a single 63mA DB with a single 30mA RCD with 2 MCB's 6A & 16A.

From a load perspective their will be 3 x 36w fluro's plus 2 x 42w securoty lights on the lighting circult and a upgrade to a 20A radial circuit with 4 double sockets ont he radial. Lo9ad wise I don't see a problem.

There are many options here but I am satisfied that the circuits within the garage are protected via their own RCD and that the RFC in the main house is connected via RCD, however its the SWA that itself in my view was not connected and whilst it will be connected via the RCD in the house, I wanted to ensure there was sufficient protection of the actual cable itself, which woudl seem that the FSU route is the best route to provide an added level of protection to the cabel itself.

Thansk for all the comments, they are all very useful.

 

[steptoe]

:shakehead

 

[Sharpend]

:shakehead

I'm with you Steps, it's too hot for this!!!! :shakehead :shakehead