I've just rewired my house and was using the old consumer unit with
some aftermarket MCBs. I'm pleased to say everything has been working
fine. I decided I should go for a new consumer unit to give me more
control over my circuits and safety. I've bought an already populated
Volex CU from Screwfix. This has a 63A RCD (VR63) which trips at 30mA.
I installed the unit and wired everything up (no instructions came with
it), with the busbar not cut so (presumably) everything is protected.
With everything connected I can switch on really low current devices
like lamps plugged in to sockets or mobile phone chargers absolutely
fine. The second I try and switch on something more hungry, like a TV,
fridge, freezer DVD player or computer the RCD trips out. This doesn't
happen EVERY time, just most of the time. I've tried this with all the
lighting circuits off and every other ring circuit off and it does it
on all three (kitchen, downstairs and upstairs). I can't understand why
this happens, so I've been reading up on circuit capacitance and TNC /
TNCS supplies, but as I'm not a sparky by trade I've just got confused.
On top of this, with the mains on and some lamps switched on or even
off, when I press the "T" button to test the RCD, nothing happens.
Shouldn't it trip itself? I'm thinking (hopefully) that I haven't done
anything stupid, and that the RCD is in fact faulty out of the box. Can
anybody help me with this? I've gone back to the old consumer unit for
now, and I'm not happy! (though at least I can watch TV and have a cup
of tea).
Thanks,
Skote

wrote:

On top of this, with the mains on and some lamps switched on or even
off, when I press the "T" button to test the RCD, nothing happens.
Shouldn't it trip itself? I'm thinking (hopefully) that I haven't
done
anything stupid, and that the RCD is in fact faulty out of the box.
Can

thats right.


But I would also rewire the new CU differently next time. Running a
whole house off an RCD is just asking for ongoing trouble.

If you can spring another =A3100 or so, your best bet is to:
1=2E use a split CU
2=2E put each power socket circuit on its own RCBO,
3=2E have the lights with no RCD anywhere
4=2E Use type C mcb for lights, not type b.

And if you have the opportunity, put the fridge freezer and boiler on a
circuit with no RCD.

I'm assuming you dont have TT system, if you do you'd need to add a
100mA time delay RCD in front of that CU configuration.

If you cant afford another penny, at least use a split CU with RCD only
covering things that need the RCD. Lights should not be on RCD, nor
immersion heater and cooker.


NT

wrote:


If you cant afford another penny, at least use a split CU with RCD only
covering things that need the RCD. Lights should not be on RCD, nor
immersion heater and cooker.


NT


Is it unwise or prohibited to run heavy loads such as immersion heater
and oven via an RCD?

This is how things were installed in my place when we bought it. NB the
previous owners did no DIY! FWIW



TIA Richard.


--
Real email address is RJSavage at BIGFOOT dot COM

The information contained in this post
may not be published in, or used by

http://www.diyprojects.info

Thanks for the information. I had a feeling I was right about the RCD
being faulty. I'm going to split the circuits for now then and run the
upstairs and downstairs sockets on a new RCD and run the kitchen
(boiler, fridge, freezer; I don't have an electric cooker or an
immersion heater) and lights without. I don't have any spare cash at
the moment as I'm doing up a house that time forgot. Before I put the
new wiring in, I had one spur circuit for lights and one spur circuit
for sockets. There was one surface mouted socket in each room, and a
few round pin type bakelite sockets too, to go with the bakelite light
switches. Nasty. Once it's all in I'm going to get it certified.
On top of this, there wasn't any earth at all until I put one in. The
mains supply is labelled as being PME but there was no connection for
earth. At the moment I've earthed the CU via the cold water inlet,
which is cast iron and the gas inlet (which I have just had replaced)
which is now copper. Presumably then, my system is acting as a TT
system? The regs say a 30mA RCD though and don't mention a time delay
for a TT system.....?
Thanks for the advice. Much appreciated.

wrote in message
oups.com...
Thanks for the information. I had a feeling I was right about the RCD
being faulty. I'm going to split the circuits for now then and run the
upstairs and downstairs sockets on a new RCD and run the kitchen
(boiler, fridge, freezer; I don't have an electric cooker or an
immersion heater) and lights without. I don't have any spare cash at
the moment as I'm doing up a house that time forgot. Before I put the
new wiring in, I had one spur circuit for lights and one spur circuit
for sockets. There was one surface mouted socket in each room, and a
few round pin type bakelite sockets too, to go with the bakelite light
switches. Nasty. Once it's all in I'm going to get it certified.
On top of this, there wasn't any earth at all until I put one in. The
mains supply is labelled as being PME but there was no connection for
earth. At the moment I've earthed the CU via the cold water inlet,
which is cast iron and the gas inlet (which I have just had replaced)
which is now copper. Presumably then, my system is acting as a TT
system? The regs say a 30mA RCD though and don't mention a time delay
for a TT system.....?
Thanks for the advice. Much appreciated.

1. That is SO bad I would like to point out today is NOT the 1st of april.
2. TURN IT OFF at the mains, you need a tested earth spike if you are going
down the TT route.
3. You can't install a consumer unit unless you inform building control or
otherwise comply with part P, in other words get a propper sparky in

In article .com,
writes
I've just rewired my house and was using the old consumer unit with
some aftermarket MCBs. I'm pleased to say everything has been working
fine. I decided I should go for a new consumer unit to give me more
control over my circuits and safety. I've bought an already populated
Volex CU from Screwfix. This has a 63A RCD (VR63) which trips at 30mA.
I installed the unit and wired everything up (no instructions came with
it), with the busbar not cut so (presumably) everything is protected.
With everything connected I can switch on really low current devices
like lamps plugged in to sockets or mobile phone chargers absolutely
fine. The second I try and switch on something more hungry, like a TV,
fridge, freezer DVD player or computer the RCD trips out. This doesn't
happen EVERY time, just most of the time. I've tried this with all the
lighting circuits off and every other ring circuit off and it does it
on all three (kitchen, downstairs and upstairs). I can't understand why
this happens, so I've been reading up on circuit capacitance and TNC /
TNCS supplies, but as I'm not a sparky by trade I've just got confused.
On top of this, with the mains on and some lamps switched on or even
off, when I press the "T" button to test the RCD, nothing happens.
Shouldn't it trip itself? I'm thinking (hopefully) that I haven't done
anything stupid, and that the RCD is in fact faulty out of the box. Can
anybody help me with this? I've gone back to the old consumer unit for
now, and I'm not happy! (though at least I can watch TV and have a cup
of tea).
Thanks,
Skote


Bet U as much as U like you've got a neutral/earth short somewhere on
the "consumer" side of the RCD, sounds just typical of what would happen
when you have that. Small loads cause no tripping until the in-balance
gets too much for it to bear!.

It may well be that this has been there for somewhile and the RCD has
started to show it up!.

Get a test meter and disconnect your wiring from the incoming supply and
check for any shorts or low ohms between the earth and neutral
conductors, and then disconnect each circuit in turn till you have found
it. In fact it should read totally open circuit any resistance here
shouldn't be there! .

The object of the RCD is to monitor the current "into" your system on
the live and match it going "out" on the neutral any "leaking" away to
earth will cause an in-balance and hence the tripping. Check also things
like immersion heaters they can and do cause this.....
--
Tony Sayer

Hmm..... Does that mean that I could have a good RCD and just a bad
connection somewhere? The devices I was connecting, like TV, DVD etc.
don't have any earth wiring, so surely they wouldn't cause this short?

In article ,
Richard writes:

Is it unwise or prohibited to run heavy loads such as immersion heater
and oven via an RCD?

It's unnecessary and slightly unwise. It's not that they're heavy
loads, it's that they are stationary or fixed appliances which
don't represent any significant electrocution risk, and both these
particular appliances are known to occasionally trip RCDs which
will be inconventient in that it will stop them working when they
would otherwise have done so fine, and knock out other things.

This is how things were installed in my place when we bought it. NB the
previous owners did no DIY! FWIW

It has been quite common to RCD protect a whole installation,
even though it is not correct to do so.
I suspect this is because a 30mA RCD was often used to substitute
an older Voltage Operated earth leakage circuit breaker. These
do different things, and whilst it was correct to protect a
whole installation with a single Voltage Operated earth leakage
circuit breaker, it is not correct to do this with a single 30mA
RCD.

--
Andrew Gabriel

wrote:

On top of this, there wasn't any earth at all until I put one in. The
mains supply is labelled as being PME but there was no connection for
earth. At the moment I've earthed the CU via the cold water inlet,
which is cast iron and the gas inlet (which I have just had replaced)
which is now copper. Presumably then, my system is acting as a TT
system? The regs say a 30mA RCD though and don't mention a time delay
for a TT system.....?

A TT system requires all circuits to be protected by a RCD. Typically a
100mA trip one is used for this. There is a also a requirement for
sockets likely to feed portable appliances used outside to be further
protected by a 30mA trip RCD.

This creates a potential discrimination problem, in that with a typical
split load CU (with the 100mA RCD as the incomer) the 30mA RCD is
downstream of the first RCD. Should you get a fault occur on a socket
circuit you can't predict which RCD will trip and may end up killing the
lights as well as the socket power.

The solution to this is either to use a 100mA RCD with a built in time
delay on the incomer. That ensures that in a fault situation on a socket
circuit, the main RCD will not trip instead of, or as well as, the
socket circuit one. Alternatively, use two separate CUs in parallel with
a 100mA RCD in one and the 30mA one in the other.

Sounds like you need to get the supply company to come and instate the
PME earth connection PDQ however.

--
Cheers,

John.

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

Quote:

"Sounds like you need to get the supply company to come and instate the

PME earth connection PDQ however."

Yep, and that is my intention. get it installed, get it certified, and
then get the supply to connect a decent earth. What I have now is ALL
new, as opposed to the bakelite and spur earthless nightmare that was
in before.......

wrote in message
oups.com...
wrote:

On top of this, with the mains on and some lamps switched on or even
off, when I press the "T" button to test the RCD, nothing happens.
Shouldn't it trip itself? I'm thinking (hopefully) that I haven't
done
anything stupid, and that the RCD is in fact faulty out of the box.
Can

thats right.


But I would also rewire the new CU differently next time. Running a
whole house off an RCD is just asking for ongoing trouble.

If you can spring another £100 or so, your best bet is to:
1. use a split CU
2. put each power socket circuit on its own RCBO,
3. have the lights with no RCD anywhere
4. Use type C mcb for lights, not type b.

And if you have the opportunity, put the fridge freezer and boiler on a
circuit with no RCD.

I'm assuming you dont have TT system, if you do you'd need to add a
100mA time delay RCD in front of that CU configuration.

If you cant afford another penny, at least use a split CU with RCD only
covering things that need the RCD. Lights should not be on RCD, nor
immersion heater and cooker.

It must be a split CU as the RCD is 63 amp

Regards Jeff

wrote:
Hmm..... Does that mean that I could have a good RCD and just a bad
connection somewhere?

no, that was mistaken advice. If your RCD doesnt trip when the test
button is pressed, its dead.


NT

wrote:
Thanks for the information. I had a feeling I was right about the RCD
being faulty. I'm going to split the circuits for now then and run
the
upstairs and downstairs sockets on a new RCD and run the kitchen
(boiler, fridge, freezer; I don't have an electric cooker or an
immersion heater) and lights without.

ok, just one thing, you need to ensure that a socket likely to be used
by outdoor equipemnt is on an RCD to pass inspection.


I don't have any spare cash at
the moment as I'm doing up a house that time forgot.

OK. If you want you can do it in a way that costs you nothing extra
now, but leaves room to upgrade the RCD aspect later if you ever need
to. The way to do this is just to have a fewe spare ways on the CU so
that MCBs can be replaced with the double wide RCBOs later. You may
never need to do this upgrade, but a significant number of single RCD
protected installs do have ongoing problems.

If youve got time, running a separate wire in for fridge etc would also
enable you to put that on a separate non RCD conection as well. if not
thermally insulated, a 2.5mm radial needs 20A breaker, or 4mm can be
one a 32A breaker.

Just in case theres any unclarity, radial means one wire rather than a
ring.

If youre replastering over the wire runs, now is a good time to put
some low v cable in as well. Cat5e is ideal, but even 4p/metre bell
wire can be quite useful later, for phones, internet, etc. If OTOH
youre running wiring thru floor cavities, including string makes it
possible to pull more wiring through any time later.



Before I put the
new wiring in, I had one spur circuit for lights and one spur circuit
for sockets.

I guess you mean radials, with each item spurred off the previous. Even
round pin sockets shouldnt be wired like that.


There was one surface mouted socket in each room, and a
few round pin type bakelite sockets too, to go with the bakelite
light
switches.

ohhh.


Nasty. Once it's all in I'm going to get it certified.
On top of this, there wasn't any earth at all until I put one in. The
mains supply is labelled as being PME but there was no connection for
earth.

The neutral feed will be the PME earth. PME is a method of using the
neutral as earth as well.


At the moment I've earthed the CU via the cold water inlet,
which is cast iron and the gas inlet (which I have just had replaced)
which is now copper.

ok, that should work ok, but will not pass inspection. You need a pukka
earth rod with inspection pit, and earthy things need to be connected
up with the right size wire.

Bathroom equipotential bonding is also required for a pass.


Presumably then, my system is acting as a TT
system?

yep. Running it as PME would be better really, and cheaper as theres
then no need for a whole house 100mA time delayed RCD.


The regs say a 30mA RCD though and don't mention a time delay
for a TT system.....?

it is required regs wise - and it matters, as TT earths are often
inadequate to blow the MCBs. With a TT earth and less than complete RCd
cover, you could have a fault running to earth and the entire earthed
system sit there live, waiting to bite everyone, and gobbling power.


Thanks for the advice. Much appreciated.

Hope you dont get prosecuted for dramatically improving the safety of
you and your family


NT

Andrew Gabriel wrote:

In article ,
Richard writes:

Is it unwise or prohibited to run heavy loads such as immersion heater
and oven via an RCD?


It's unnecessary and slightly unwise. It's not that they're heavy
loads, it's that they are stationary or fixed appliances which
don't represent any significant electrocution risk, and both these
particular appliances are known to occasionally trip RCDs which
will be inconventient in that it will stop them working when they
would otherwise have done so fine, and knock out other things.


This is how things were installed in my place when we bought it. NB the
previous owners did no DIY! FWIW


It has been quite common to RCD protect a whole installation,
even though it is not correct to do so.
I suspect this is because a 30mA RCD was often used to substitute
an older Voltage Operated earth leakage circuit breaker. These
do different things, and whilst it was correct to protect a
whole installation with a single Voltage Operated earth leakage
circuit breaker, it is not correct to do this with a single 30mA
RCD.



Thanks Andrew,

When we moved in (genuinely 5 years ago) the entire installation apart
from the freezer spur was fed from an RCD.

I fitted two CUs - one fed from the RCD and the other (lighting, garage
- with own RCD/CU - and freezer) not fed from the RCD.

In doing so I found that the upstairs ring had not been opened and
expanded to include the attic - as I presumed because there were only
two rings shown in the CU - rather a loop had been taken from the
upstairs ring into the attic and back to the same point on the upstairs
ring. But the return was not connected - just a live end tucked into
the floor void!!!!! And this was done by a building firm when they did
the attic conversion.

Maybe this sort of thing is what Part P will stop?

I now have a separate ring for each floor and one for the kitchen.

Should I relocate the oven and immersion feeds? The wiring is (IMHO)
beutifully dressed into the (RCD) CU.


Cheers

Richard

--
Real email address is RJSavage at BIGFOOT dot COM

The information contained in this post
may not be published in, or used by

http://www.diyprojects.info

Maybe this sort of thing is what Part P will stop?

Richard

I would not bet on it !!

Dave

--
For what we are about to balls up may common sense prevent us doing it
again
in the future!!

In article .com,
writes
Hmm..... Does that mean that I could have a good RCD and just a bad
connection somewhere? The devices I was connecting, like TV, DVD etc.
don't have any earth wiring, so surely they wouldn't cause this short?




As I said it seems very likely that you have a short or low ohms between
the EARTH conductor and the NEUTRAL, any devices like DVD players or
TV's or bedside lights don't even come into this, with respect to earth
wiring.

What is happening is the RCD monitors the current into your house on the
LIVE line, and compares it with what goes OUT on the neutral line and
provided these are the SAME the AMOUNT does not matter (as long as its
within the current capacity of the unit) all will be well.

i.e. as long as 100 milliamps are coming in and 100 going out all is
well, and if say 50 amps are coming in and 50 are going out all is well
to.

But as soon as a fault causes 100 ma in but 70 ma out then this is
tripping time!, as is 50 amps in and 49.970 amps out trip time as well!.

Now suppose you or yours grab hold of a live wire somewhere on the
consumer side of the install, then the current in on the live is
diverted away, to earth, via you or yours!.

There now exists a current unbalance in that less current is now going
out via the neutral conductor in the RCD and provided that this current
is greater than its rated tripping current, usually around 15 to 20 ma
for a 30 ma device, then the trip will disconnect and remove the current
so you don't get a shock!!.

Now conversely if the earth and neutral are shorted !together! somewhere
the same thing in effect happens. Instead of current flowing back
through the neutral conductor of the RCD, it can go directly to earth
and thus is "shunted" away from the RCD neutral current going OUT.

Of course if nothing is switched on then no current will be coming in
the RCD and nothing will be flowing out either so no current UN_BALANCE
can occur.

Now when something is switched on the current that is coming in is
supposed to match the current going out. But because some of this is
going down the earth line and some through the neutral line via the RCD
then with a light load there isn't, as yet, enough current to cause the
trip level to be reached. As the current increases then there will come
a point when this reaches the trip level, and then the trip fires!.

Try to regard this as the live and neutral conductors in your instal
must NOT be connected to earth anywhere on the consumer side of the RCD
they can of course connect together on the supply side as with PME
systems, and it doesn't even matter whatever earthing system you use but
on the CONSUMER side of the RCD, no connections from live or neutral to
Earth FULL STOP!!!.....
--
Tony Sayer

Dave Stanton wrote:




I would not bet on it !!

Dave


Ditto!

But it seems that it will, or attempts to, put paid to competant DIY-ers
who have the time and inclination to do own-use wiring.

Richard

--
Real email address is RJSavage at BIGFOOT dot COM

The information contained in this post
may not be published in, or used by

http://www.diyprojects.info

wrote:
wrote:
On top of this, there wasn't any earth at all until I put one in. The
mains supply is labelled as being PME but there was no connection for
earth.
The neutral feed will be the PME earth. PME is a method of using the
neutral as earth as well.

Except that the separation between Neutral and Earth is carried out
within the service intake and must be kept separate from that point on.
It is not permitted to use a combined earth and neutral conductor on a
customer's wiring.[1]

What I think has happened is the supply network has at some point been
upgraded to PME but the service intake has not. The supply authority
will have to be asked to provide the PME earth terminal.

Owain

[1] Except for privately generated supplies using earthed concentric
wiring, IIRC. Oh, joys.

Good explanation thanks. I have had a good look at my work this
morning, and couldn't find any short. I reinstalled everything, this
time with the bus bar on the CU cut and up- and down- sockets on the
RCD with lights and kitchen not. Everythig works. No trips, and the RCD
tests OK. Bizarre. Thankyou all for your help.