new consumer unit-do i need an RCD?
 

I;m about to replace my existing metal cased wylex consumer unit,the
one with the big grey RCD on/off switch which has a penchant for
nuisance trippage,with a new unit which will have an isolator and
mcb,s. Do i really need an rcd though ?. My biggest issue is nuisance
trippage once or twice a year leading to fridge /freezer defrost.
There is no apparent fault,it may just be a fault on an adjacent
property or something or just nothing at all. Are newer rcd's less
prone to trippage?

joe

"tarquinlinbin" wrote in message
...
I;m about to replace my existing metal cased wylex consumer unit,the
one with the big grey RCD on/off switch which has a penchant for
nuisance trippage,with a new unit which will have an isolator and
mcb,s. Do i really need an rcd though ?. My biggest issue is nuisance
trippage once or twice a year leading to fridge /freezer defrost.
There is no apparent fault,it may just be a fault on an adjacent
property or something or just nothing at all. Are newer rcd's less
prone to trippage?

CU units are available with mcb on the RCD and other that supply the
freezer, alarm, etc, not on the RCD. get one of these.

I;m about to replace my existing metal cased wylex consumer unit,the
one with the big grey RCD on/off switch which has a penchant for
nuisance trippage,with a new unit which will have an isolator and
mcb,s. Do i really need an rcd though ?

The problem is that whole house RCD units are both prone to trips, and their
consequences, as you've found out.

The best, but most expensive solution, is to use RCBOs instead of MCBs for
socket and exterior electrical circuits. This way, any trip only affects
that circuit, and trips are less likely anyway, because they only measure
leakage on that individual circuit.

The next best solution is to use a split load circuit. This has only a
single RCD, but this only covers high risk circuits, like sockets and
exterior circuits as above. Some circuits (such as lights) are not covered
by the protection.

In either case, a fridge freezer should actually be on a dedicated circuit
and not be RCD protected.

Note that if you have a TT type supply, the circuits MUST be RCD protected.
This is normally achieved using a time delayed 100mA RCD, with 30mA RCD
protection provided as above. Alternatively, RCBOs could be used for every
single circuit without exception.

Christian.

"tarquinlinbin" wrote
| I;m about to replace my existing metal cased wylex consumer
| unit,the one with the big grey RCD on/off switch which has
| a penchant for nuisance trippage,with a new unit which will
| have an isolator and mcb,s. Do i really need an rcd though ?.

You *must* have RCD protection on:
- a TT (earth rod) installation
- sockets likely to be used for appliances out of doors

In practice, it is usually easier to provide RCD protection to all sockets
as this saves proving by calculation that the MCB alone offers sufficient
protection.

You should NOT use a whole-house 30mA RCD main switch. This is contrary to
the Regulations.

If you have a TT installation then use a 100mA Time-Delay RCD main switch
and 30mA RCD on socket circuits (either a split load CU or RCBOs on
individual circuits).

If you do not have a TT installation then use either a split load CU or
RCBOs on individual circuits.

| My biggest issue is nuisance trippage once or twice a year
| leading to fridge /freezer defrost.

You should try to identify which circuit(s) is tripping the RCD. There may
be a fault such as poor insulation or ingress of damp.

If you use a split load CU, then the freezer can be wired on the non-RCD
side, as should be lighting and smoke alarms.

Owain

On Mon, 18 Oct 2004 11:06:00 +0100, "Christian McArdle"
wrote:



Note that if you have a TT type supply, the circuits MUST be RCD protected.
This is normally achieved using a time delayed 100mA RCD, with 30mA RCD
protection provided as above. Alternatively, RCBOs could be used for every
single circuit without exception.

Christian.

Yes the thing is it would be troublesome to provide a dedicated supply
just for the fridge /freezer as its just a typical upright model
plugged into a socket in the kitchen so its a little impractical to
run a separate supply just for this as i;d have to take upstairs
apart(solid floor downstairs).
BTW i have a passing recognition of supply/earthing types. Mine is PME
so is it acceptable for me to have an isolator,no rcd and just mcb's?

ta joe

On Mon, 18 Oct 2004 12:15:08 +0100, "Owain"
wrote:


You should try to identify which circuit(s) is tripping the RCD. There may
be a fault such as poor insulation or ingress of damp.

It only happens about two ccasions a year but inevitably,when it
happens there are usually 2 or 3 offs per occasion then it settles for
another year!!. Tried everything to try and proove a fault on my
installation but I'm now thinking it must be a duff RCD or a fault in
a neighbouring property
If you use a split load CU, then the freezer can be wired on the non-RCD
side, as should be lighting and smoke alarms.

Owain

On Mon, 18 Oct 2004 11:06:00 +0100, Christian McArdle wrote:


In either case, a fridge freezer should actually be on a dedicated circuit
and not be RCD protected.


Not questioning that this is the recommended case - but I've found this
recommendation to be curious...

I *would* put *all* my appliances on RCD just as an extra line of defence in
the case of either multiple mode failure (live to case + case earth
fault) or to cover someone plugging some other appliance into that socket
now or in the future.

I see why the recommendation is the way it is (I think - food going
mouldy?), but I'd rather have a freezer full of mouldy food than a shock.

Is there any other reasoning behind the recommendation that I've missed?

Timbo

tarquin wrote:

BTW i have a passing recognition of supply/earthing types. Mine is PME
so is it acceptable for me to have an isolator,no rcd and just mcb's?

Since you are not on a TT supply, then you don't require RCD protection
for ALL circuits. However, you should have RCD protection (30mA trip) on
any socket circuits that might conceivably supply power to portable
appliances that could be used outdoors.

So in answer to your question, the strict answer is likely to be "no".
Whether you need RCD protection for the particular circuit in question
however will depend on the layout of your house etc.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Tim wrote:


I *would* put *all* my appliances on RCD just as an extra line of defence in
the case of either multiple mode failure (live to case + case earth
fault) or to cover someone plugging some other appliance into that socket
now or in the future.

I see why the recommendation is the way it is (I think - food going
mouldy?), but I'd rather have a freezer full of mouldy food than a shock.

That's a decision for you to make - when Christian wrote that freezers
"should" be on a non-RCD circuit, he wasn't expressing a Regs
requirement, just a trade-off which most households would find
appropriate: the multiple-mode failure you mention is pretty unlikely,
while the spoiling of food is a pain in the fundament to many. But it's
your choice to make. For those who go for the non-RCD option, the
possibility of other stuff being plugged into the socket can be
eliminated by supplying the freezer & fridge through FCUs, or through
non-standard sockets, e.g. 15A round-pins, Schuckos, IEC-320s,
Powercons: there's a shedload of safe, approved connectors you can
choose to use, mostly unfused - with a dedicated 10A or 16A radial for
the fridge-n-freezer supply you can usually readily demonstrate that the
flex to the appliance is adequately protected by the MCB; if you want
the reassurance of an appliance-specific fuse, you can use an FCU to
feed the non-standard socket of your choice, possibly using a
cable-mounted rather than a wall-mounted one, so you have a way of
wheeling the fridge/freezer out of the way for the once-every-four-years
clean-behind-the-fridge session ;-)

Yet another possibility, if you want RCD protection on the
fridge-n-freezer but not lose power to them unless there's a fault in
those appliances themselves, is to feed them with their own
RCBO-protected circuit, or on a circuit fed without RCD protection but
to use a plug or socket incorporating RCD protection.

HTH - Stefek

Stefek

"John Rumm" wrote in message
...
tarquin wrote:

BTW i have a passing recognition of supply/earthing types. Mine is PME
so is it acceptable for me to have an isolator,no rcd and just mcb's?

Since you are not on a TT supply, then you don't require RCD protection
for ALL circuits. However, you should have RCD protection (30mA trip) on
any socket circuits that might conceivably supply power to portable
appliances that could be used outdoors.

So in answer to your question, the strict answer is likely to be "no".
Whether you need RCD protection for the particular circuit in question
however will depend on the layout of your house etc.

As it is not a TT supply then what about no RCD on the CU and have a couple
of these http://tinyurl.com/47q2b

Adam

On Mon, 18 Oct 2004 17:13:40 GMT, "ARWadsworth"
wrote:


"John Rumm" wrote in message
...
tarquin wrote:

BTW i have a passing recognition of supply/earthing types. Mine is PME
so is it acceptable for me to have an isolator,no rcd and just mcb's?

Since you are not on a TT supply, then you don't require RCD protection
for ALL circuits. However, you should have RCD protection (30mA trip) on
any socket circuits that might conceivably supply power to portable
appliances that could be used outdoors.

So in answer to your question, the strict answer is likely to be "no".
Whether you need RCD protection for the particular circuit in question
however will depend on the layout of your house etc.

As it is not a TT supply then what about no RCD on the CU and have a couple
of these http://tinyurl.com/47q2b

link not active...?
Adam

BTW i have a passing recognition of supply/earthing types. Mine is PME
so is it acceptable for me to have an isolator,no rcd and just mcb's?

Provided you wouldn't conceivably use any outside appliances (i.e. you don't
have a garden). The provision of some outdoors sockets with RCD could
support you not providing RCD protection on socket circuits inside. However,
you should realise that you are greatly increasing electrocution and fire
risk by not RCD protecting all socket circuits.

Christian.

Yes the thing is it would be troublesome to provide a dedicated supply
just for the fridge /freezer

There can be ways. Do you have a cooker circuit, for example? A quick
diversity calculation might allow you to use this for the fridge/freezer.

Christian.

In article ,
Christian McArdle wrote:
The next best solution is to use a split load circuit. This has only a
single RCD, but this only covers high risk circuits, like sockets and
exterior circuits as above. Some circuits (such as lights) are not
covered by the protection.

You make it sound like this is fixed. On mine, you decide the combination.

--
*A picture may be worth a thousand words, but it uses up a thousand times more memory.

Dave Plowman London SW
To e-mail, change noise into sound.

Some circuits (such as lights) are not covered by the protection.

You make it sound like this is fixed. On mine, you decide the combination.

OK, "should not be be covered by the protection, as doing so is more
dangerous than providing shared RCD protection with other circuits."

Christian.

On Tue, 19 Oct 2004 09:30:06 +0100, "Christian McArdle"
wrote:

Yes the thing is it would be troublesome to provide a dedicated supply
just for the fridge /freezer

There can be ways. Do you have a cooker circuit, for example? A quick
diversity calculation might allow you to use this for the fridge/freezer.

Christian.


Thanks to all for your feedback,i'll give it some thought.
Coincidentally i have had a plug socket that hasnt worked more or less
since i moved in the house (new build about 20years ago). It was one
that was little used anyway and i suspected a duff switch. I bought a
new socket yesterday and on taking the old one off,it became apparent
that the earths from the ring main were not connected!. They had never
been in place because the earth screw was fully home and had never
been in contact with the socket connector!. I'm just wondering now if
this has been the cause of my spurious trippages,time will tell..night
just do the consumer unit anyway.

thanks,,

joe

They had never been in place because the earth screw was fully home
and had never been in contact with the socket connector!.

Sounds like you could do with a full system electrical test. This will test
continuity, insulation resistance, polarity, earth loop impedence etc.

That RCD tripping might have actually been saving your life all these years.
People who want to remove RCDs are often those most likely to be protected
by them! My RCDs never trip. (Unless I'm using my RCD tester to **** off my
TV watching daughter!)

Christian.