Shed Supply - Upfront Rcd?

[ray-bentos]

Hello

I've got to install an SWA submain to a garden shed.

The house CU is a wylex dual RCD job and doesn't have any facility for unprotected ways.  The outdoor meter box is quite cramped and would be difficult to install henleys and switch fuse to run the submain minus the RCD isn't really an option.

I've never been a fan of running a supply like this due to the issue of the shed/SWA tripping causing the house to trip too.  This is a friend and I was planning to use the job as my next inspection visit for ELECSA but I'm not sure what their opinion of this will be?

The supply is TNC-S, shed is all wooden construction with no extraneous conductive parts.  Will only be running a lighting circuit and a radial supplying a couple of sockets in the shed. 

Would anyone else be happy doing this?  Will just have to have a 'main switch' CU in shed as all final circuits will be RCD protected from house.

 

[steptoe]

where is the CU in relation to the incomer?

BTW

if you want to utilise TNCS [what they class as PME], outside the EZ you need the DNOs permission.

 

[ray-bentos]

Physically? 

Its mounted almost directly behind the meter cupboard on the kitchen wall.  The tails feed straight through the cavity and into the CU.  No chance of diverting the tails into a Henley and mounting another board inside (wouldn't look great neither as its in plain sight on kitchen wall)

 

[steptoe]

personally,

I'd say doesnt comply , even worse than a split board, at least thats only the house circuits,

I deffo wouldnt take an outside feed from an RCD shared with house circuits.

 

[ray-bentos]

Not the answer I was wanting to hear  

Assuming I can squeeze a switch fuse into the meter box how would you recommend I got power from SF to SWA?  I was thinking about an adaptable box on outside wall but can't see a good way of getting cable from SF to adaptable box outside meter box.  I very much doubt a SF with a gland sticking out of it will fit into the box.

Alternatively do you think I might have to put Henley in meter cupboard and run a set of tails into some form of small CU inside the property and back out to SWA?

Nothings easy........

 

[steptoe]

If, there are spare ways in CU,  you could modify the bus bar arrangement for an unprotected way, but, then you have changed the design and again,  it may not comply, 

Easiest way is change the tails and  split them,

Some DNOs take exception to you putting stuff in 'their' cabinet.

 

[apprentice87]

Would it be possible to install either a second meter box if you have the flush with the wall type, or if it is just a surface mounted one, a lockable enclosure next to it?? Install all the bits you like then!!

john...

 

[Murdoch]

If you do feed the shed from the house CU, just make sure you fit a DP isolator in the house, so you can easily isolate the ourside circuit should you or the customer need too.

 

[ray-bentos]

If you do feed the shed from the house CU, just make sure you fit a DP isolator in the house, so you can easily isolate the ourside circuit should you or the customer need too.

I had thought about this, 45A DP cooker switch next to CU to isolate the shed when not in use

 

[SLIPSHOD & SLAPDASH]

personally,

I'd say doesnt comply , even worse than a split board, at least thats only the house circuits,

I deffo wouldnt take an outside feed from an RCD shared with house circuits.

Although i agree with  all your other comments i cant see why this would  not comply ?

 

[steptoe]

Split load boards are at best a compromise as to inconvenience under fault, adding an outside feed is making it worse, imo,  as I said, only my personal opinion, I like to keep outside feeds separate, 

 

[Adrian]

As Murdoch says a dp switch job done

 

[Evans Electric]

The ideal way is a supply through a non- RCD protected breaker and your RCD within the shed .     If you feel you can't alter the consumer bus bar configuration  to give you a unprotected way   ( Personally  I would alter it and risk arrest by the Electric Police ) ....then just get on with it and feed it from a spare way .

RCDs are now with us to stay ...sometimes they cause nuisance tripping ...just swith off the shed until its sorted. 

Remember there are so many regulations now, lurking in the backs of our minds , that , when asked to do a job,  many electricians can produce a thousand reasons how NOT to do it .

Ideal utopian world  ....change the board .

Real world ...just do it .   

 

[brman]

The supply is TNC-S, shed is all wooden construction with no extraneous conductive parts.  Will only be running a lighting circuit and a radial supplying a couple of sockets in the shed. 

So a SFCU off the downstairs ring will do the job fine then? Plus another FCU in the shed to downfuse the lights. 

If you are concerned about the PME then stick a spike in.

Seriously, why over-complicate things? If the sockets and lights are in a shed they are less of a trip risk than an outside light or socket on the house.

 

[SLIPSHOD & SLAPDASH]

Split load boards are at best a compromise as to inconvenience under fault, adding an outside feed is making it worse, imo,  as I said, only my personal opinion, I like to keep outside feeds separate,

Ahh, that is something I have always said. Only 2 days ago whilst improving an installation I thought why am I fitting these 4 MK rcbos @ £33 each + vat when I can get a 2 rcd split board for less than £40.