Rcd twin switched sockets tripping house cu??

[Hawkpalmer]

Hi all

So I've installed electrics into my new shed but have an issue/query.

I have a rcd wired 13amp plug in device on the internal wall that goes from house plug socket to outside into x2 ip65 rated twin sockets (low voltage LEDs and wall lights, all up rated). From one twin external socket I've run a 13amp fused spur and from this spur I've run 3 core 10mm armored cable clipped to fence upto shed (about 15ft), this goes into a 2 way rcd cu with 63a 30ma rcd and x1 b16 mcb and x1 b6 mcb. The b16 mcb ive used for x2 rcd twin switched sockets on a radial circuit, the b6 goes to a 1 gang switch that feeds a fluorescent strip light and a pir sensor light on shed wall.

So I power it up and all is ok but when I click the "test" button on any of the rcd sockets in the shed it trips out the house mcb (house has a split rcd cu).

Have I gone over the top on rcds or am I missing something else?

My thinking is that if the shed sockets trip it will just trip the shed cu or the 13amp fused spur or the internal rcd wall plug adapter thing and NOT the house mcb?

The twin rcd sockets have a red "on/live" light and when I flick the b16 mcb on shed cu the lights go out. The lights and switch are all fine. I've also plugged in a battery drill charger into she'd sockets and they seem to be fine apart from test button tripping out the house cu.

Any help appreciated

 

[DetlefSchmitz]

If you have two rcds in series you are likely to trip both. It's better to find some safe legal way to have a fault in the shed not affect the house. but as the Irish say, 'I wouldn't have started from here.'

 

[ban-all-sheds]

From one twin external socket I've run a 13amp fused spur and from this spur I've run 3 core 10mm armored cable

Why such a large size, when you're limited to 13A?

How did you terminate the cable into the FCU?

Did you carry out all of the appropriate polarity, continuity and loop impedance tests on the cable before energising it?

clipped to fence

Not good, Fences move in the wind, blow down etc.

this goes into a 2 way rcd cu with 63a 30ma rcd and x1 b16 mcb and x1 b6 mcb.

What on earth is the point of a CU on the end of a 13A supply?

What good will a B16 breaker be downstream of a 13A fuse?

Did you apply for Building Regulations approval before installing the CU?

Do you have a schedule of test results for it?

So I power it up and all is ok but when I click the "test" button on any of the rcd sockets in the shed it trips out the house mcb (house has a split rcd cu).

It trips the MCB in the house?

Have I gone over the top on rcds

Completely.

or am I missing something else?

Quite a lot of skills and knowledge which you should have if you want to do electrical design and installation work.

My thinking is that if the shed sockets trip it will just trip the shed cu or the 13amp fused spur or the internal rcd wall plug adapter thing and NOT the house mcb?

Do you really mean MCB ?

But your thinking is flawed anyway - with RCDs in series there's no guarantee which one(s) will trip, and you don't have any discrimination with your over-current devices.

It's a bodged and incompetent mess.

Any help appreciated

I suggest you get an electrician.

 

[ban-all-sheds]

If you have two rcds in series you are likely to trip both

Two?

He's got four.

 

[DetlefSchmitz]

If you have two rcds in series you are likely to trip both

Two?

He's got four.

Or you could say he has multiple instances of two.

 

[JohnW2]

Did you apply for Building Regulations approval before installing the CU?

I agree wholeheartedly with everything else you write and imply - it sounds like a crazy arrangement. However, on the one issue of notification, I doubt whether the work was actually notifiable in terms of the word of the current legislation in England if it were undertaken after April 5th of this year. It's clearly all an extension to an existing circuit, and installing (as opposed to 'replacing') a CU does not appear to be something in the list of works which are still notifiable - daft though that may be.

Kind Regards, John

 

[Hawkpalmer]

From one twin external socket I've run a 13amp fused spur and from this spur I've run 3 core 10mm armored cable

Why such a large size, when you're limited to 13A?

How did you terminate the cable into the FCU?

Did you carry out all of the appropriate polarity, continuity and loop impedance tests on the cable before energising it?

clipped to fence

Not good, Fences move in the wind, blow down etc.

this goes into a 2 way rcd cu with 63a 30ma rcd and x1 b16 mcb and x1 b6 mcb.

What on earth is the point of a CU on the end of a 13A supply?

What good will a B16 breaker be downstream of a 13A fuse?

Did you apply for Building Regulations approval before installing the CU?

Do you have a schedule of test results for it?

So I power it up and all is ok but when I click the "test" button on any of the rcd sockets in the shed it trips out the house mcb (house has a split rcd cu).

It trips the MCB in the house?

Have I gone over the top on rcds

Completely.

or am I missing something else?

Quite a lot of skills and knowledge which you should have if you want to do electrical design and installation work.

My thinking is that if the shed sockets trip it will just trip the shed cu or the 13amp fused spur or the internal rcd wall plug adapter thing and NOT the house mcb?

Do you really mean MCB ?

But your thinking is flawed anyway - with RCDs in series there's no guarantee which one(s) will trip, and you don't have any discrimination with your over-current devices.

It's a bodged and incompetent mess.

Any help appreciated

I suggest you get an electrician.

The armoured cable was cheap

Fcu? It's terminated using armoured glands.

Nope, no tests done.

Clipped to fence was only option!
My bad, it trips the rcd on house cu, lol.

Lots of conflicting info on the web saying use a 13amp fused spur, I was reading that some suggest go direct into back of house 13amp plug socket which I could do but decided to go into the external sockets instead!

Thanks for the help!

 

[ban-all-sheds]

Nope, no tests done.

Unacceptable.

Clipped to fence was only option!

No it wasn't.

My bad, it trips the rcd on house cu, lol.

4 RCDs in series.

FFS.

 

[EFLImpudence]

It's clearly all an extension to an existing circuit, and installing (as opposed to 'replacing') a CU does not appear to be something in the list of works which are still notifiable - daft though that may be.

Have we discussed this before? I don't recall.

How can you install a CU without creating new circuits?

 

[Hawkpalmer]

Nope, no tests done.

Unacceptable.

Clipped to fence was only option!

No it wasn't.

My bad, it trips the rcd on house cu, lol.

4 RCDs in series.

FFS.

Lmfao

Yes it is!!

So, I swap out the rcd sockets in shed for normal twin sockets, and fused spur into back of house socket on inside/outside wall??

 

[JohnW2]

Have we discussed this before? I don't recall.

Yes, at length There have actually been whole threads which were essentially about the question of 'what is a circuit' and 'what is a new circuit'.

How can you install a CU without creating new circuits?

It totally depends upon how one defines 'a new circuit' (which, in turn, depends upon the definition of 'a circuit'). The Building Regs don't help. The BS7671 definition of 'a circuit' is in terms of wiring/equipment which shares a common OPD. I suggested that the only realistic way of interpreting this was in terms of the 'primary' OPD' - i.e. that in a CU or switch-fuse supplied directly from the installation's meter - and that any further OPDs downstream of that 'primary' one did not create separate (hence 'new' when first installed) circuits.

If you don't accept my 'interpretation' then you are probably in the position of having to say that any OPD (whether MCBs/RCBOs in a CU, an FCU or whatever) creates a 'new circuit' (hence needing notification) - but that would mean that a fused spur from a ring or radial circuit (explicitly non-notifiable even under the old rules) would now be notifiable - which I don't think any of us believe is the case.

Kind Regards, John

 

[EFLImpudence]

Have we discussed this before? I don't recall.

Yes, at length There have actually been whole threads which were essentially about the question of 'what is a circuit' and 'what is a new circuit'.

I remember the 'new circuits' thread(s) but don't recall it being proposed that although the new rules state 'replacing a CU' is notifiable therefore 'fitting a new one' would not be.

Can't argue with the logic, I suppose.

HOWEVER, aren't CUs supplied with sub-mains which lead to new circuits?
That would be different than FCUs etc.

Or did I miss that as well.

Ignore if all said before and I will search.

 

[JohnW2]

I remember the 'new circuits' thread(s) but don't recall it being proposed that although the new rules state 'replacing a CU' is notifiable therefore 'fitting a new one' would not be. ... Can't argue with the logic, I suppose.

... that's a different issue, but we did touch on that one before as well. The wording of the legislation is clear - it is only 'replacement' of a CU that is notifiable. However, as we discussed, it is rarely going to be possible to 'install a new CU' (apparently non-notifiable) without creating 'new circuits' (either to feed it, or for it to feed), so the job would end up being notifiable, anyway. However, that only applies to what I called 'primary' CUs.

HOWEVER, aren't CUs supplied with sub-mains which lead to new circuits? That would be different than FCUs etc.

If, as will usually be the case, it is a new submain, then that is clearly a 'new circuit' and, in any event, that CU would probably qualify as a 'primary' one as I have called it.

The situation discussed in this present thread is very different. The shed CU appears to get its power from an existing sockets circuit, via what is probably at least two 13A fuses (and some RCDs!). That sounds like 'extending an existing circuit to me'. For whatever reason, the OP has got a CU on the end of all that. Had it been just a socket or two, and maybe an FCU for some lighting, I don't think you would have argued with the notion that the whole lot was merely an extension to an existing circuit (hence non-notifiable), would you? If so, it wouldn't make sense (to me) if ('unnecessarily') installing a CU in the shed (instead of just socket(s) and FCU) would suddenly make it notifiable - would it to you? In this case, I guess it's a question of 'when is a CU a CU?'. This one is totally unnecessary, and could be replaced with sockets and FCUs, so I really don't (personally) feel that it deserves to be notifiable, do you?

Kind Regards, John

 

[EFLImpudence]

I can't argue with that.

Installing unnecessary parts would, I agree, not affect the notification process.

 

[JohnW2]

I can't argue with that. Installing unnecessary parts would, I agree, not affect the notification process.

IMO, it certainly shouldn't - which is the basis of my argument. Glad you agree.

However, you need to understand that I am inclined to extend my argument to situations in which the CU is not quite so (if at all) 'unnecessary'. We had a thread recently in which there was a 'proper' exsting supply to a CU in one outhouse. This was 'extended' to a second outhouse, where another (new) CU was installed. I would again be inclined to interpret that as 'extending an existing circuit' and installing (not replacing) a new CU - hence, again, arguably all non-notifiable. What would you say about that?

In fact, I suppose that almost any CU in a location such as a shed or garage could be argued to be 'unnecessary', since it could be replaced by a series of FCUs (one for each socket if necessary, and one for the lights).

Kind Regards, John