RCD wiring top and bottom in consumer unit

[DICEGEORGE]

The 80A Wylex RCD in my new consumer unit
has 2 connections top, and 2 bottom.

Is it OK to wire
the Live input to the top,
the Neutral input to the bottom,
the Live output to the top,
and the Neutral output to the bottom
?
The inputs will come from the main switch in the consumer unit
(there are 2 RCDs in it)
(and there will be a 100ma 100ms RCD before this consumer unit and the others)

thanks
george

[John Rumm]

On 26/09/2016 17:42, DICEGEORGE wrote:
> The 80A Wylex RCD in my new consumer unit
> has 2 connections top, and 2 bottom.
>
> Is it OK to wire
> the Live input to the top,
> the Neutral input to the bottom,
> the Live output to the top,
> and the Neutral output to the bottom

If my understanding of what you describe is correct, then

******* NO ********

Or at least, only if you want to short out your supply when you try to
turn the RCD on!

> The inputs will come from the main switch in the consumer unit
> (there are 2 RCDs in it)
> (and there will be a 100ma 100ms RCD before this consumer unit and the others)

TT install I presume... Does the CU have any non RCD protected ways?
(and if not, what is the 100mA RCD for?)


--
Cheers,

John.

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[tabb...@gmail.com]

On Monday, 26 September 2016 18:03:29 UTC+1, John Rumm wrote:
> On 26/09/2016 17:42, DICEGEORGE wrote:

> > The 80A Wylex RCD in my new consumer unit
> > has 2 connections top, and 2 bottom.
> >
> > Is it OK to wire
> > the Live input to the top,
> > the Neutral input to the bottom,
> > the Live output to the top,
> > and the Neutral output to the bottom
>
> If my understanding of what you describe is correct, then
>
> ******* NO ********

+1. If you understand what an RCD does it will be clear you can't miswire it and have it work.

> Or at least, only if you want to short out your supply when you try to
> turn the RCD on!

Video it from a safe distance.


NT

[DICEGEORGE]

i dont think it would short out -
top left neutral in would go to bottom left neutral out
and bottom right live in to top right live out -
and then on to the mcbs
so when its turned off both would be disconnected.

[g]

100 ma RCD is because there are lots of old circuits and consumer units

[DICEGEORGE]

> +1. If you understand what an RCD does it will be clear you can't miswire it and have it work.
> > Or at least, only if you want to short out your supply when you try to
> > turn the RCD on!
> Video it from a safe distance.
> NT

Why would it short the supply?
I thought that a RCD connects the 2 blues and 2 browns,
and measures that the current is the same in both
and disconnects both if there's an imbalance.

I'm unsure of whether swapping the blues from top to bottom
would short everything out and why?

That's why I asked,
I want to understand electrics more,
and have a better than professional job at the end of it!

(I got my A level physics many decades ago!)

[DICEGEORGE]

ps
I wasnt swapping the wires left and right,
but up and down,
there would still be blue wires on the left and brown on the right
but one input would be on top and the other at the bottom.

Theoretically the RCD would work, wouldn't it?

pps i probably wont do this as its confusing

[George]

[Andy Burns]

DICEGEORGE wrote:

> i dont think it would short out -
> top left neutral in would go to bottom left neutral out
> and bottom right live in to top right live out -

The typical operation of an RCD is that the live poles are wound one way
round a ferrite core, while the neutral poles are counter-wound on the
same core, so cancelling each other out until some leakage happens ...
if the live goes top to bottom while the neutral is bottom to top, I'd
expect the windings would add rather than cancel and the RCB trip instantly?

I'm not familiar with the insides of a modern wylex, can you not feed
one of the wires behind the DIN strip so they both run top to bottom?

[DICEGEORGE]

On Monday, September 26, 2016 at 8:11:10 PM UTC+1, Andy Burns wrote:
xxx

> The typical operation of an RCD is that the live poles are wound one way
> round a ferrite core, while the neutral poles are counter-wound on the
> same core, so cancelling each other out until some leakage happens ...
> if the live goes top to bottom while the neutral is bottom to top, I'd
> expect the windings would add rather than cancel and the RCB trip instantly?
>
> I'm not familiar with the insides of a modern wylex, can you not feed
> one of the wires behind the DIN strip so they both run top to bottom?

yes,
that's the way to do it.
I was thinking of minimising cable wire length
but much simpler to do it your way,
thinking of myself or another trying to understand the wiring ten years later!

So it doesnt matter if both inputs to an RCD are at the top or at the bottom.
That's right isn't it?

[george]

[DICEGEORGE]

Photo of the consumer unit,
i think i've got it right now,
have I ?
http://www.dicegeorge.com/wiring-a-consumer-unit/
[George]

[Andy Burns]

Rather than ramming three thick cables into a single terminal, I'd take
the N output of the main switch up to the right hand neutral bar, them
take individual neutrals from there to each of the two RCDs and then
from the outputs of those to the other two neutral bars.

Looks like the photoshopping accidentally shows the output neutral on
the RCDs coming from the live outputs?

maybe have another stab at drawing it?

[DICEGEORGE]

yes, yes,
(but the end of the 3 blue wires are already squashed together somehow
and were when I got the unit.
But the main swqitch got dust in it,
then i took a few years to replace it
and forgot where the wires had been originally!)

[g]

[John Rumm]

On 26/09/2016 19:38, DICEGEORGE wrote:

> i dont think it would short out -
> top left neutral in would go to bottom left neutral out
> and bottom right live in to top right live out -
> and then on to the mcbs

That is not (how I read) what you described... it seems like you
suggested live in and and out of the top, and neutral in and out of the
bottom.

> so when its turned off both would be disconnected.

Even with the revised wiring it would not work since the RCD would trip
the moment you drew any current through it.

> [g]
>
> 100 ma RCD is because there are lots of old circuits and consumer units

ok makes sense - I sounded like the multi CU was the only one.

> On Monday, September 26, 2016 at 5:42:27 PM UTC+1, DICEGEORGE wrote:
>> The 80A Wylex RCD in my new consumer unit
>> has 2 connections top, and 2 bottom.
>>
>> Is it OK to wire
>> the Live input to the top,
>> the Neutral input to the bottom,
>> the Live output to the top,
>> and the Neutral output to the bottom
>> ?
>> The inputs will come from the main switch in the consumer unit
>> (there are 2 RCDs in it)
>> (and there will be a 100ma 100ms RCD before this consumer unit and the others)
>>
>> thanks
>> george

[John Rumm]

OK that is a 17th edition "high integrity CU"... it provides for three
separate load areas - one without RCD protection, and two further ones
each with their own RCD.

ISTM you want two neutral tails leaving the lower right terminal of the
main switch - one goes to the top right neutral bus bar, and the other
to the top right terminal of the right RCD. Another neutral shares that
terminal and goes to the top right terminal of the left RCD.

The bottom right terminal of the right RCD goes to the middle bus bar,
and the bottom right terminal of the left RCD goes to the leftmost
neutral bus bar.

The bottom left terminal of the main switch feeds the top left terminal
of the right hand RCD (you could also have a live bus bar comb in there
for non RCD protected MCBs or RCBOs). The top left terminal of the right
RCD also connects to the top left of the left RCD.

[tabb...@gmail.com]

On Monday, 26 September 2016 19:58:15 UTC+1, DICEGEORGE wrote:

> ps
> I wasnt swapping the wires left and right,
> but up and down,
> there would still be blue wires on the left and brown on the right
> but one input would be on top and the other at the bottom.
>
> Theoretically the RCD would work, wouldn't it?

definitely not. Go read what RCDs do.


NT

[Roger Hayter]

The other poster misunderstood your proposal. However, the way you
want to do it the balanced currents in the neutral and live wires would
be going in opposite directions so would amount to an imbalance equal to
double the current drawn. That is, the tiniest load would trip the RCD.

--

Roger Hayter

[DICEGEORGE]

yes Roger,
I see that now.

Both input wires, blue and brown,
must either go to the top
or to the bottom of the RCD.

I think thats right!

[g]

[DICEGEORGE]

Apart from using the top right neutral rail
this is pretty much what happens in this video:
Dual RCD Consumer Unit by John Ward
https://www.youtube.com/watch?v=WNe1xHlI5i4

George

On Monday, September 26, 2016 at 5:42:27 PM UTC+1, DICEGEORGE wrote: