Another Shed Supply Question With A Twist

[Darrenm200]

I never knew my question would spark!!! of a sparky bun fight.

Would anybody like to comment on the original question (cable sizing etc).

I've got the option to do either I could fit an additional MCB to the RCD protected side of the house CU, but as I've bought a garage CU with an RCD included i'm going for the RCD at the shed end.

If some numb nuts sticks a spade through this cable they deserve all they get as it is quite clear where it enters and exits the ground (only 1M apart) and it's about 450mm down under tarmac, concrete and hardcore. Oh and it's inside some damm heavy duty conduit. Also my views is that you want the protective device as close to the circuit it's protecting as possible - just a simplistic view.

You really would struggle with a spade even a stainless one.

I think I can sleep easy on this decision. Oh and why is it everybody assumes electric shock equals death !!! I like 3 phase it tickles and makes your ears buzz, try it some time.

 

[holmslaw]

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[DIYANIMAL]

We always feed outbuildings from the non RCD side of the board and fit an RCD in the outbuilding.

It's our preference, in that if there is leakage in the garage, you don't loose the whole house.

Re the submain, bearing in mind that the submain is classed as fixed equipment it only needs a 5 second disconnection time, RCD protection of the submain is overkill IMO.

Providing your new Zdb will disconnect the supply mcb within 5 seconds in the event of a short circuit

We always use 3 core SWA and use the braid and one conductor in parallel for the cpc, as it helps keep the loop impedances lower.

 

[ban-all-sheds]

If mcb's do not fail then theres not much sense in testing them is there.

How do you test MCBs?

 

[DIYANIMAL]

with a nail, rubber wellies and rubber gloves

 

[ban-all-sheds]

No 'scope?

 

[holmslaw]

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[DIYANIMAL]

on an MCB?

I doubt many domestic sparks would have the gear to do that test.

I've only ever seen it done in hager's MCCB factory in france!

 

[jason1958]

Personally, I fit RCBO at the head end to protect the SWA-shed cable run in the house. Sticking a shed on a split-load would not be a good idea, re reg 314.

Thinking... CPD discrimination...
- House - Type-B MCB
- Shed - Type-B MCB with RCD
- You might not have CPD discrimination

Under high fault currents you might actually trip both shed & house CPD.

One solution would be to use a BS1361 fuse in the house CU, MK do not list them, Hager & MEM might subject to them fitting. Using Type C characteristic would work, 10*In, but that imposes stricter EFLI requirements that may require a large CSA SWA etc.

 

[ban-all-sheds]

Its called a primary injection test - better get googling. or ask an electrician

Oh, OK - I'll try that. Any suggestions on who I could ask "How do you test MCBs?"?

If you can think of anyone, I'd also like to ask him who tends to run these tests, and when/where and in what context.

 

[ban-all-sheds]

One solution would be to use a BS1361 fuse in the house CU, MK do not list them, Hager & MEM might subject to them fitting. Using Type C characteristic would work, 10*In, but that imposes stricter EFLI requirements that may require a large CSA SWA etc.

I've always liked the idea of

Tails => Switchfuse = SWA => Outbuilding CU.

 

[holmslaw]

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