Bunched 2.5mm2 Swa 4core for garage supply.

[Shorty73]

Some advice please.

I have a length of of 2.5 4core swa which I would like to supply my garage. I will be taking the feed from the non RCD side of an MK Sentry CU via an RCBO.

The route length from C.U to garage C.U is 10 -12 meters. Most of the route will be clipped to a wall. A short run will be buried in ground (possibly ducted).

My question is if I bunch the cores in pairs to give me a single phase 5mm2 supply will the Steel conductors be sufficient to use as an earth conductor? Would it be better to run a serperate 6mm2 earth wire?

 

[PrenticeBoyofDerry]

There is no need to protect the SWA distribution cable with an RCD, at the CU providing it runs the full length to the garage but you can if you wish.
Protecting the installation with RCD within the garage would likely be needed though. So if you are having a CU within garage RCDs can be introduced there.
I would use a core from each cable as CPC earth and the amour as addition earth protection.

 

[xr4x4]

2.5 doesn't get you far these days, your gonna be limted to around 16amps.

As been said, use the three cores, L N E, ignore the 4th.

What's the loading going to be?

 

[Monkeh]

As been said, use the three cores, L N E, ignore the 4th.

No, earth the fourth. Random floating conductors suck, you may as well increase your CPC size.

 

[JohnW2]

2.5 doesn't get you far these days, your gonna be limted to around 16amps.

That's presumably why the OP was contemplating doubling up the conductors to get 5.0mm² total. Unless it's need to fulfill a bonding function, the armour should be OK as the CPC.

Kind Regards, John

 

[Shorty73]

Thanks for the replies.

I will be installing 3 internal double 13a sockets and 1 external double socket. I will have two fluorescent light fittings and one outside LED light on a PIR.
I may fit some heaters on a frost protection stat.

As mentioned above 2.5 mm wouldn't give me much so I was intending to use the 4 core as a single phase with bunched or paired cores and either run a separate 6 mm conductor or use the steel wire conductors as the earth.

I have a background in Distribution so have a sound electrical knowledge but I am unsure of the requirements for installations.

 

[JohnW2]

I will be installing 3 internal double 13a sockets and 1 external double socket. I will have two fluorescent light fittings and one outside LED light on a PIR. I may fit some heaters on a frost protection stat. As mentioned above 2.5 mm wouldn't give me much so I was intending to use the 4 core as a single phase with bunched or paired cores and either run a separate 6 mm conductor or use the steel wire conductors as the earth.

Everything really depends upon what loads you intend to plug into those 4 double sockets. There is no immediately available figure for the current-carrying capacity of 5.0mm² SWA (2x2.5mm², doubled up), since CCC is not directly proportional to conductor CSA, but it will presumably be at least as high as 2-core 4mm² SWA, which would allow you 43A if buried. With only 10-12 metres, voltage drop is not likely to be a limiting factor. What is going to be feeding this cable, and what arrangements for RCD protection of the garage circuits will you have?

The armour of the SWA would probably be adequate to act as CPC for the "5mm²" cable, but if you have a requirement for main protective bonding in the garage, you may well need to run a 10mm² cable (from house Main Earthing Terminal to garage) for that purpose. How do you intend to deal with earthing arrangements (and bonding if required) in the garage?

Kind Regards, John

 

[ban-all-sheds]

A steel cpc would need to be between 9 & 13.6mm² - the actual armour size is 20mm²

 

[JohnW2]

A steel cpc would need to be between 9 & 13.6mm² - the actual armour size is 20mm²

I'm a bit confused by the table in our wiki. The title of the table refers to 'bonding', but I find it hard to believe that it means quite that - since it states the armour (steel) CSA requirement as being a function of the cable size, in particular 7.77mm² for 2.5mm² cable and 4.66mm² for 1.5mm² cable. I therefore presume that, despite it's title,the Table relates to requirements for a CPC, not main bonding.

Kind Regards, John

 

[Spark123]

It is simply just in a sub section called "Earthing, Supply types and Bonding". The tables are under the heading of "SWA earthing."

Unfortunately I don't think that you can setup a URL with a comma, it's that long ago since it was setup!

 

[ban-all-sheds]

The title of the table refers to 'bonding'

No it doesn't.

 

[RF Lighting]

I have a length of of 2.5 4core swa which I would like to supply my garage.....length from C.U to garage C.U is 10 -12 meters.

You can buy enough 6.0mm² SWA for your needs here for under £30, and put in a decent 40A supply.

Is it really worth trying to botch up some unsuitible cable leaving you with an inferior installation for the sake of less then 30 quid?

 

[phatboy]

Urm, 2x 2.5mm cores does not equal a 5mm core, its far less than that......

 

[DetlefSchmitz]

Urm, 2x 2.5mm cores does not equal a 5mm core, its far less than that......

Shya. Right.

 

[EFLImpudence]

2 x 2.5 = 54
1 x 5(6) = 47