RCD refuses to switch on (up)

[John Chalmers]

I’ve run a 2.5mm t&e cable from a 16a cu in the house to the shed all in 20mm plastic conduit - say 7m. The shed has a BG garage unit with RCD and two ways, 5 and 16a.
In the shed is a final ring circuit with a spur for a fan and a LED style fluorescent fitting. The RCD refuses to switch on. Even with both ways switched off the RCD will not switch on.
I have checked all connections and can find nothing. I checked the mcb, previously used for an immersion heater, by connecting the lights wire into it and everything was okay.
Wired brown into mcb, blue to neutral bar and earth to earth bar all on the non-elcb side of a MEM cu. Other end as per instructions into RCD.
Any ideas please? I simply wanted this up and working before bringing a sparky in to test and certify.

 

[KEV 1 N]

I am 100% sure it's a DIY who thinks he knows more than he does. Mind you, he's served his time...…….working in a wholesalers.

That’s why there’s a 32A mcb in his garage DB, ordered a 16A but wholesalers had none in stock, so they sent a 32A instead!
Anyone else notice that? You order something from wholesaler, it’s not in stock so they send something else instead

 

[KEV 1 N]

I am 100% sure it's a DIY who thinks he knows more than he does. Mind you, he's served his time...…….working in a wholesalers.

That’s why there’s a 32A mcb in his garage DB, ordered a 16A but wholesalers had none in stock, so they sent a 32A instead!
Anyone else notice that? You order something from wholesaler, it’s not in stock so they send something else instead

 

[Rpa07]

That’s why there’s a 32A mcb in his garage DB, ordered a 16A but wholesalers had none in stock, so they sent a 32A instead!
Anyone else notice that? You order something from wholesaler, it’s not in stock so they send something else instead

And they always send you double!

That’s why there’s a 32A mcb in his garage DB, ordered a 16A but wholesalers had none in stock, so they sent a 32A instead!
Anyone else notice that? You order something from wholesaler, it’s not in stock so they send something else instead

And they always send you double!

 

[ipf]

And they always send you double!

And they always send you double!

No worries…….as long as you only pay for the one.

 

[richy3333]

Worked for a wholesaler but bought a CU from Screwed fix or Tool station I bet? (Do any wholesalers sell BG?) No testing, poor installation method and we have to guess in the dark to resolve the fault as the bang test failed.

Although to be fair to the OP the wiring in the BG board is neater than some I see

 

[ChrisElectrical88]

Newey and Eyre or Rexel whatever they are called these days sell BG.... Although if i had to choose someone from a wholesaler to install something in my house, the lads at my local neweys would be bottom of the list. Good on the computer, ----ing useless at getting up serving.

 

[GeorgeCooke]

I worked for years in electrical wholesalers and understand matters fine.

You clearly don't. Why have you got a 32a MCB in the shed being fed from a 16a one in the house?
Why are you feeding a 32a ring in the shed with 2.5mm cable from the house?
Where is the RCD protection for the cable from the house to the shed?

OK. The RCD would be better at the house end. At the shed you don't need the mini CU. Run the sockets direct as a radial (protected by the 16a MCB in the house). Lights via a switched FCU with a 5 amp fuse.

 

[alasdairp]

Insulation resistance test cable from old board to new board, failing that do you have a n-e fault in New wiring? Would explain why it trips with mcbs off

This (a n-e fault) in the shed is almost certainly the cause (in my experience). Maybe on the Fan circuit?

The supply cable should be protected by an RCD at the house end (as I understand it this is a legal requirement for a new external circuit, though some protection is provided by the ELCB - if that has been checked and found to work correctly). The 32A MCB is just nonsence. If you want a separate MCB in the shed, then I would make that one 16A and the one in the house CU as 20A one. I can't see the current set-up being signed off by anybody qualified to do so.

 

[Midwest]

The supply cable should be protected by an RCD at the house end (as I understand it this is a legal requirement for a new external circuit

Not necessarily, it would depend on the installation method and/or the cable. I can't be bothered to scroll back thru the thread now.

 

[a-z electrics]

think you need a 2nd N bus bar or terminal block in the BG box.. one for incoming, one for the loads.

 

[a-z electrics]

oh its my eyes now, looks ok as was.

 

[dksanders]

I worked for years in electrical wholesalers and understand matters fine.
I reckon I do have a fault, however I cannot understand where. I tripped the in-house mcb and then disconnected the RCD, now when switched up it stays up.
Surely this means the fault is between the cu and the RCD, as I have thought until now, it’s simply a single length of cable within plastic conduit, even through the wall and right into the RCD! Thanks.

How does the cable get from the house to the shed i.e. is that 20mm conduit buried, in the air, on a fence, catenary, what?

You stated the shed CU had a 5 and 16A mcb, it has a 32A and a 6A!

You've got a N-E earth fault, unless you've mixed the neutral wires at the busbar, it's difficult to see what goes where as the shed CU is a mess.

The verification and testing required BEFORE energising would have found that out.

You don't 'understand matters fine', you're dangerous plain and simple of the worst kind. I.e. someone who thinks they know what they're doing, but don't.

 

[Norah Nabino]

Why a 16A radial to the shed then a ring main on a 32A in the shed, wheres the thinking in that?

Also why have you energised before initial verification was carried out?

Anyone mentioned exporting the earth to the shed yet

Correct me if i am wrong but remember a radial is meant to be on a 20a mcb.
The design of this shed installation is not well thought .It is a bad design.

 

[richy3333]

Correct me if i am wrong but remember a radial is meant to be on a 20a mcb.
The design of this shed installation is not well thought .It is a bad design.

No. The protective device relates to the load, cable size and installation method to name but three. Lighting is normally a radial circuit and you wouldn’t stick that on a 20A breaker?

 

[Norah Nabino]

You clearly don't. Why have you got a 32a MCB in the shed being fed from a 16a one in the house?
Why are you feeding a 32a ring in the shed with 2.5mm cable from the house?
Where is the RCD protection for the cable from the house to the shed?

OK. The RCD would be better at the house end. At the shed you don't need the mini CU. Run the sockets direct as a radial (protected by the 16a MCB in the house). Lights via a switched FCU with a 5 amp fuse.

What is wrong with wiring a 32a ring circuit with 2.5mmm T&E??