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.

 

[Midwest]

Firstly I hope you know what you are doing and can carry out safe isolation?

Sounds like you may have a fault. You might have to get that sparky in earlier than you thought. What happens when you disconnect wiring from the load side of the RCD?

 

[Pete999]

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.

A Sparky should have been present / involved at all stages of the installation, for him to issue an EIC. Having two RCDs in series or on the same leg is a no no as well.

 

[Fitzy]

Can you post a photo of the RCD/board please?

 

[John Chalmers]

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.

 

[buzzlightyear]

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.

I had a customer did what the op tried to do ,he came of worse in the end .

 

[John Chalmers]

A Sparky should have been present / involved at all stages of the installation, for him to issue an EIC. Having two RCDs in series or on the same leg is a no no as well.

There are not two RCDs involved. As per the post the shed is being wired to the non-elcb side of the cu. The elcb in the cu protects only the two mcbs for the sockets. Other than the elcb there are only mcbs in the cu.

 

[John Chalmers]

I had a customer did what the op tried to do ,he came of worse in the end .

Sorry don’t understand this short cryptic(?) comment. ‘did what the op tried to do’ ?

 

[Pete999]

There are not two RCDs involved. As per the post the shed is being wired to the non-elcb side of the cu. The elcb in the cu protects only the two mcbs for the sockets. Other than the elcb there are only mcbs in the cu.

Sorry misunderstood your description, my error

 

[John Chalmers]

Can you post a photo of the RCD/board please?

Attached.

 

[Midwest]

As per my previous post; have you tried that?

 

[Pete999]

There are not two RCDs involved. As per the post the shed is being wired to the non-elcb side of the cu. The elcb in the cu protects only the two mcbs for the sockets. Other than the elcb there are only mcbs in the cu.

What you describe as an ELCB what make and type is it

 

[John Chalmers]

Firstly I hope you know what you are doing and can carry out safe isolation?

Sounds like you may have a fault. You might have to get that sparky in earlier than you thought. What happens when you disconnect wiring from the load side of the RCD?

As per my previous post; have you tried that?

yes, I replied above. The RCD stays on. I then reconnected the brown wire and it stayed on. As soon as I tried to connect the neutral the RCD tripped.

 

[MJPD29]

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

 

[John Chalmers]

What you describe as an ELCB what make and type is it

ELHNC 404. By MEM.