Garden power regulations

[michaelsf90]

Hello all. I'm wondering whether the power in my garden complies or not. I have a consumer unit in the shed. Fed via a 2.5 ring main from the consumer unit in twin and earth to a Wiska box outside. From there it's a 4mm swa to the shed. On a 32a rcbo. The shed has a 40a mains rcd with 3 circuits. One socket in the shed. One light. And then a 2.5 swa to the pond at the back feeding a pump and filter

First of all should the supply to the shed be 6mm instead of 4mm? Secondly do I need an earth rod outside. No extraneous conductive parts. No metal. Wooden shed and wooden decking round the pond. Also the cable run from the consumer unit in the house to the shed is 50 metres. Its obviously downrated half way at the shed consumer unit to 20A. The pond pump and filter is pulling about 50W. So the load is tiny

 

[Murdoch]

Your post raises a number of questions.

are you a spark or DIYer?

 

[michaelsf90]

An electrician who has never done domestic. Commercial and industrial. When it comes to domestic I panic even tho every job we work to the same regs

 

[Fleeting]

Domestic, commercial or industrial circuit principles are the same although additional rcd protection is more reinforced in a dwelling.
Volt drop is calculated from the origin to the furthest point of any circuit, current carrying capacity of conductors and selectivity of protective devices is applicable throughout the circuit/s and ADS must be considered. There is obviously more to it than that but if you are an electrician then circuit design shouldn't be too much of an issue.

 

[Andy™]

and how is this supply to shed connected to the ring?

 

[Speed]

You should not be feeding the shed, a garage, or any outside equipment from a domestic ring. As you have already broken the regulation about the floor area a ring can serve, which is only 100 sq. m. That is only an area of 10m x 10m and the 100 sq. m must be within the confines of fixed barriers like houses walls. That is also the reason why you cannot use 13A socket outlets on a ring in factories. Because there are no physical barriers like walls to prevent users exceeding the 100 sq. m rule or loading and volt-drop requirements for domestic ring circuit. In factories you must use radial circuits with BS4343 socket outlets, which have no floor area limitations.

Any circuit that is fed outside of the Earthed protection zone (i.e. the house), must be feed via a RCD with 30mA tripping current. That is why most houses wired after 1980s that do not have RCD protected rings, must have at least one RCD socket intended for outside electric tools (i.e. lawnmower, hedge trimmers, etc.).

However, the shed should be fed from a separate circuit in your Consumer Unit preferably on a RCBO. Since it outside the Earth protection zone and it likely electric tools will be fed from the shed for use in garden.

 

[Fleeting]

You should not be feeding the shed, a garage, or any outside equipment from a domestic ring. As you have already broken the regulation about the floor area a ring can serve, which is only 100 sq. m. That is only an area of 10m x 10m and the 100 sq. m must be within the confines of fixed barriers like houses walls. That is also the reason why you cannot use 13A socket outlets on a ring in factories. Because there are no physical barriers like walls to prevent users exceeding the 100 sq. m rule or loading and volt-drop requirements for domestic ring circuit. In factories you must use radial circuits with BS4343 socket outlets, which have no floor area limitations.

Any circuit that is fed outside of the Earthed protection zone (i.e. the house), must be feed via a RCD with 30mA tripping current. That is why most houses wired after 1980s that do not have RCD protected rings, must have at least one RCD socket intended for outside electric tools (i.e. lawnmower, hedge trimmers, etc.).

However, the shed should be fed from a separate circuit in your Consumer Unit preferably on a RCBO. Since it likely electric tools will be fed from the shed for use in garden.

You cannot use 13A sockets on a ring final circuit in a factory, they must be radials using BS4343 sockets. Where is this pearl of wisdom quoted in BS7671.

 

[Speed]

If you check, a 13A socket domestic ring circuit can only be used to fed a maximum area of 100 sq, metres. No factory has a floor area that is only 10m x 10m. As for the sockets to BS4343. It in the Appendix under standard circuits. If not it in the 'On Site Guide'. Clearly you don't know the Regs as well as you think.

!3A sockets are for Domestic and Commercial (i.e. Offices) use only. Not industrial (i.e. Factories).

 

[Fleeting]

If you check, a 13A socket domestic ring circuit can only be used to fed a maximum area of 100 sq, metres. No factory has a floor area that is only 10m x 10m. As for the sockets to BS4343. It in the Appendix under standard circuits. If not it in the 'On Site Guide'. Clearly you don't know the Regs as well as you think.

!3A sockets are for Domestic and Commercial (i.e. Offices) use only. Not industrial (i.e. Factories).

So no factory has a floor area at any part of its site not exceeding this 100m sq. I have installed multiple ring final circuits in factories using BS1363 accessories. Can you tell us where it is quoted in the Regulations that 13A socket outlets cannot be used in factories, we are all willing to learn.

 

[Speed]

In that case you have broken the regulations. As 100 sq. metres is only 10x10 metres (i.e. 10 stride x 10 strides) and must be within physical boundaries like walls. Most 4 bed house exceed 100 sq. m, which is why have two rings these days. So there is no way a factory floor will comply. A 100 sq. metres is not an area that measures 100x100 metres. As that would be a 1000 sq. metres. Where you learn your maths?

 

[Fleeting]

In that case you have broken the regulations. As 100 sq. metres is only 10x10 metres (i.e. 10 stride x 10 strides) and must be within physical boundaries like walls. Most 4 bed house exceed 100 sq. m, which is why have two rings these days. So there is no way a factory floor will comply. A 100 sq. metres is not an area that measures 100x100 metres. As that would be a 1000 sq. metres. Where you learn your maths?

There is absolutely no Regulation in BS7671 which states a ring final must not exceed a floor area above 100m sq, that is a fact.
As for your maths 100×100=10000 and not 1000.

 

[michaelsf90]

The shed is supplied via a dedicated circuit. It's a 32A rcbo in the consumer unit. The 2 2.5mm twin and earth's run under the floor to the utility room which is an extension and a concrete floor. From there it's in a mini trunking sat above the skirting that can't be seen due to storage, fridge, freezer etc. Then in the corner it's drilled through the wall to a wiska box outside. From there it's jointed onto a 4mm swa which goes under the flags and is buried to the shed. About a 7 metre length of cable. That then feeds the shed consumer unit. I did it in 2.5 so the cpc was slightly bigger and as a ring as to be able to put it on a 32A RCBO. A 4mm or 6 mm twin has only 2.5 cpc. I'm considering upgrading it to 6mm twin and then the swa to 6mm. The load is negligible outside tho. If it was possible to run the swa straight to the mains I would. The armored is a 3 core so has a cable earth and has been glanded off properly with a banjo so good earthing outside

 

[binky]

floor area for a cct was ony ever a meaningless recommendation, your ctt limitation is, and will always will be Zs for the cct

 

[Fleeting]

The shed is supplied via a dedicated circuit. It's a 32A rcbo in the consumer unit. The 2 2.5mm twin and earth's run under the floor to the utility room which is an extension and a concrete floor. From there it's in a mini trunking sat above the skirting that can't be seen due to storage, fridge, freezer etc. Then in the corner it's drilled through the wall to a wiska box outside. From there it's jointed onto a 4mm swa which goes under the flags and is buried to the shed. About a 7 metre length of cable. That then feeds the shed consumer unit. I did it in 2.5 so the cpc was slightly bigger and as a ring as to be able to put it on a 32A RCBO. A 4mm or 6 mm twin has only 2.5 cpc. I'm considering upgrading it to 6mm twin and then the swa to 6mm. The load is negligible outside tho. If it was possible to run the swa straight to the mains I would. The armored is a 3 core so has a cable earth and has been glanded off properly with a banjo so good earthing outside

Why did you feel the 1.5 cpc of a 4.0 cable or 2.5 of a 6.0 was not large enough?

 

[AJS87]

The shed is supplied via a dedicated circuit. It's a 32A rcbo in the consumer unit. The 2 2.5mm twin and earth's run under the floor to the utility room which is an extension and a concrete floor. From there it's in a mini trunking sat above the skirting that can't be seen due to storage, fridge, freezer etc. Then in the corner it's drilled through the wall to a wiska box outside. From there it's jointed onto a 4mm swa which goes under the flags and is buried to the shed. About a 7 metre length of cable. That then feeds the shed consumer unit. I did it in 2.5 so the cpc was slightly bigger and as a ring as to be able to put it on a 32A RCBO. A 4mm or 6 mm twin has only 2.5 cpc. I'm considering upgrading it to 6mm twin and then the swa to 6mm. The load is negligible outside tho. If it was possible to run the swa straight to the mains I would. The armored is a 3 core so has a cable earth and has been glanded off properly with a banjo so good earthing outside

Providing your Zs is acceptable a 1.5mm cpc is perfectly fine on a 32A OCPD. Just to note a 4mm PVC/PVC contains a 1.5mm cpc, a 6mm contains a 2.5mm.

 

[michaelsf90]

I just figured a 3mm cpc would be better

 

[Speed]

There is absolutely no Regulation in BS7671 which states a ring final must not exceed a floor area above 100m sq, that is a fact.
As for your maths 100×100=10000 and not 1000.

You right, I missed a zero off. lol.

The IET Wiring Regulations (BS 7671) permit an unlimited number of 13A socket outlets (at any point unfused single or double, or any number fused) to be installed on a ring circuit, provided that the floor area served does not exceed 100 square metres. In practice, most small and medium houses have one ring circuit per storey, with larger premises having more.

 

[Fleeting]

You right, I missed a zero off. lol.

The IET Wiring Regulations (BS 7671) permit an unlimited number of 13A socket outlets (at any point unfused single or double, or any number fused) to be installed on a ring circuit, provided that the floor area served does not exceed 100 square metres. In practice, most small and medium houses have one ring circuit per storey, with larger premises having more.

Which Regulation cites 100m sq.

 

[Speed]

Providing your Zs is acceptable a 1.5mm cpc is perfectly fine on a 32A OCPD. Just to note a 4mm PVC/PVC contains a 1.5mm cpc, a 6mm contains a 2.5mm.

You have complicated the installation.

For a start, if you run two cables. Unless you tapping off cables at multiple locations along the cables it is NOT called a ring circuit. It just called a parallel circuit. A installation method often used in Industry if a circuit's demand falls between two cable sizes and it cheaper to run two smaller cables than one large cable. Once you get to 400 sq. mm SWA cables they get very expensive.

A 3 core SWA is not necessary on a single-phase TN-S system. A 2 core SWA would do. Since the armouring is the earth, provided it terminated with the appropriate SWA gland with an Earth Ring (CW SWA gland if outside). Otherwise manufactures would not make 2 core SWA cables. As no one would buy it.

Plus, if you think I'm wrong. Then you better tell the Electricity Suppliers as well. Since they use only 2 core to your house (i.e. Earth concentric cable). Where the armouring is the PEN conductor (TN-C system). The Earth and Neutral only separate after the meter. Making it a TN-C-S system.

All SWA cables made to British Standards comply with the requirements in the Regs for earthing. There was a period once many decades ago between Editions of Regs, when the armouring did not comply and additional earth cable was run outside cable. However, that was only for a short period until old stock used up. Since then ALL SWA cable's armouring complies with Regs for use as the Earth. Yet some electricians seem to still think you need a separate earth core in SWA cable.

 

[Fleeting]

The PEN conductor of a concentric cable is not the armour. The earthing conductor and neutral conductor are derived from the service head, not after the meter.