Running supply to shed

[Innominata]

Hi Guys,
I have been asked to quote for running a supply to to a garden shed/workshop.The shed is at the bottom of the garden so approx 40 metres of SWA will be required.The existing house CU is quite old with rewirable fuses.The customer wants to use various tools in the shed including a lathe.Total wattage of all tools/machines = approx 8Kw but all will not be used at the same time.The house is supplied via a TN-S system.I was thinking of leaving the house CU alone and use a Henley block via a fuse to connect the swa.I would then install a an RCD protected garage CU in the shed.Would this installation require an earth rod or is connection to the main MET ok.Any suggestions on size of SWA.
many thanks.

 

[Jason Smith]

TT keep earths joined at both ends, i.e house and garage.- rod it.- insulated cu in garage/shed required, as opposed to metal.

TNCS run earth to garage but do not join to garage circuit garage-rod it

TNS As above.- rod it.

Dashing out now m8, you should get afew more answers tonight.

 

[bugsy]

If your linking out of a henly install 32a switched fuse , run you SWA to C.U. and install a rod

 

[Jason Smith]

Lathe ? hell of a start up current, find out what it is from the manufacturer.

 

[Deleted member 9648]

At the risk of repeating myself why the need to rod it?....I'ts TNS so no problem with using that...and if it were TNCS as long as there were no other services requiring bonding in the shed there's nothing wrong with using the TNCS.

I cant see this constant insistance on rodding outbuildings. Consider this.....

You are installing some outside lights around a house,with a couple of lamposts and an external socket or two for the lawnmower. All fed from and switched from the house which is on a TNCS...(or TNS) supply.....Do you....
1.Run all these points back to a separate DB and run out a spike.
2.Separate the earth to each point and put a separate spike in for each point.
3.Do what everyone else does and use the earthing system for the house your points are fed from.

If the answer is no 3 this obsession with separating the earth on an outbuilding makes no sense at all.

 

[Innominata]

Hi Wirepuller,
Are you pretty sure that a rod is not needed?Any ideas on size of SWA.
thanks

 

[Sintra]

TN-S no rod needed.

 

[Jason Smith]

I was taught this way so that faults are not transported from one building to another. I agree if something is attached to a house, its on that houses circuit. Thats it.
However, a shed or garage is a seperate building, and should be treated as such.
Thisis my opinon only wirepuller, I will always bow down to experience though so can you expand on your reasons apart from a rod kit is about £22, plus fitting.

 

[Deleted member 9648]

Sorry ,my post probably sounds somewhat sarcastic which wasnt what I intended. I just wanted to make the point that many people who insist on rodding outbuildings so they dont export the earth will happily install other outdoor electrics such as lights and sockets direct to a TN earth.It doesnt make sense to me.
Of course if you feel happier rodding then we are all free to make our own decisions on such things. But the facts are there are no restrictions on using a TNS for external supplies.There are also no restrictions on using a TNCS supply for external supplies providing the installation is not a special location as defined in bs 7671. When using a TNCS supply for an outbuilding if there are any services which require main bonding it must be run back to the MET...not to the DB in the outbuilding....so in those circumstances it is often more practical to rod.

 

[Sav]

Hi,
I agree with wirepuller,

I did a similar set up for my in laws and I ran a swa 16mm 3 core.
The swa is fed from a 60amp isolator inside the main building. This in turn has 25mm tails into henley blocks with the 25mm to the house c/unit.
The house is a TN-S system .
Used the house m.e.t for earth and obviously earthed the swa as well.
In the new outbuilding (approx 45meters away) I installed a dual RCD board which supplies sockets and lighting (main switch is 100amp BSEN61008). The earth core is more than adaquate (16mm), so no additional earthing required.

Hope this helps,
Sav

 

[Jason Smith]

Dont worry mate, It is sometimes hard to put into words without sounding like we having a pop. There are some major learning points from your post for me which have been written down. The no regs bit is what alows so many different ways of skinning a cat out there. Have taken on board what you say, and will be reviewing my standard practices. Summers coming and the shed manufacturers are on overtime !!

 

[Adam W]

BRB allows a TNS supply for a caravan, boat, site cabin etc, so I would have thought it would be OK for a shed or outbuilding, unless as mentioned bonding would be an issue.

 

[mattcos1972]

Hi all,
If its any help, I have spoken with NICEIC about this very issue and they said that with TN-S there is no need to rod the shed end. Use the house earth via one of the cores in the armoured, and the armour if required.
With PME there are a few more considerations but TN-S is fine to share earths. My college tutor is DEAD against it...but I get the impression he'd rod every room in the house, given half the chance!!

Matt

 

[Deleted member 9648]

The TNCS 'considerations' are special locations as defined in the BRB....which do not include bog standard garden outbuildings,and the requirement that services in the shed which require bonding must go back to the MET.
None of those requirements apply to TNS.

 

[martysparky]

How many times do you come across the words 'drove a rod in for good measure'.

Sometimes I think its a case of pride and not wanting to look like your showing a builders bum.