Dear all,

I have veen following anxiously the issue of electrical regulations,
XVII ed. (part P?) or similar (seems like citing some obscure Criminal
Law Act though...).

Now the problem: in 2000 I had my electrical system partially rewired
and 'updated' to the current regulations of the times (Scotland).
A CU with no RCD for light and power in the house, plus another CU
with RCD (there were no split units at the time).

A 49Amp MAX armoured cable (should be 2.5mm^2, not certain but I'm
certain it's 49 Amp MAX) which is some 40 metres long goes from the
RCD-protected CU straight into the summer house to provide power.

I originally asked some supposed sparkies and the majority seemed to
conclude that I could manage the work myself as it were a 'shed-like
outhouse' but I', mot this very much convinced of that. If that's not
the case I would still do the job myself according to current
regulations and than waste a bit of money on the usual (un)qualified
guy to let him fill a certificate of compliance/whatever.

Now...

1) I read somewhere (now well buried in one of the posts) that I'd
better link the armoured cable, at the house to the non-RCD CU and
then provide a split unit at the summer house end rather than keeping
the current setup.

2) Anything else to comply with these apparently frightening
regulations? (I would create ring circuits inside the summer house,
have a RCD-protected and a non-RCD protected split unit if possible,
etc). Note that I would use the summer house for woodworking involving
a range of professional power tools

Thanks

E.

"Woland" wrote in message
...
Dear all,

I have veen following anxiously the issue of electrical regulations,
XVII ed. (part P?) or similar (seems like citing some obscure Criminal
Law Act though...).

Now the problem: in 2000 I had my electrical system partially rewired
and 'updated' to the current regulations of the times (Scotland).
A CU with no RCD for light and power in the house, plus another CU
with RCD (there were no split units at the time).

A 49Amp MAX armoured cable (should be 2.5mm^2, not certain but I'm
certain it's 49 Amp MAX) which is some 40 metres long goes from the
RCD-protected CU straight into the summer house to provide power.

I originally asked some supposed sparkies and the majority seemed to
conclude that I could manage the work myself as it were a 'shed-like
outhouse' but I', mot this very much convinced of that. If that's not
the case I would still do the job myself according to current
regulations and than waste a bit of money on the usual (un)qualified
guy to let him fill a certificate of compliance/whatever.

Now...

1) I read somewhere (now well buried in one of the posts) that I'd
better link the armoured cable, at the house to the non-RCD CU and
then provide a split unit at the summer house end rather than keeping
the current setup.

2) Anything else to comply with these apparently frightening
regulations? (I would create ring circuits inside the summer house,
have a RCD-protected and a non-RCD protected split unit if possible,
etc). Note that I would use the summer house for woodworking involving
a range of professional power tools

Thanks

E.


Hi
I would put a radial circuit in. That way you only have to isolate that
circuit, if you have to work on it. Also if it does go down your whole house
does not.

Ring rinals are on their way out.
I know this because I am at Leeds College of Technology, I am studying for
Level 3. We covered this very subject today.
I am about to rewire my home and am putting in radial circuits in every
room.


Kind Regards.


Micky Savage.

P.S. Testing is also a lot quicker on Radial circuits, so you won't have to
pay the sparky as much for your testing.

On Sep 18, 5:54*pm, "Micky Savage" wrote:
"Woland" wrote in message

...



Dear all,

I have veen following anxiously the issue of electrical regulations,
XVII ed. (part P?) or similar (seems like citing some obscure Criminal
Law Act though...).

Now the problem: in 2000 I had my electrical system partially rewired
and 'updated' to the current regulations of the times (Scotland).
A CU with no RCD for light and power in the house, plus another CU
with RCD (there were no split units at the time).

A 49Amp MAX armoured cable (should be 2.5mm^2, not certain but I'm
certain it's 49 Amp MAX) which is some 40 metres long goes from the
RCD-protected CU straight into the summer house to provide power.

I originally asked some supposed sparkies and the majority seemed to
conclude that I could manage the work myself as it were a 'shed-like
outhouse' but I', mot this very much convinced of that. If that's not
the case I would still do the job myself according to current
regulations and than waste a bit of money on the usual (un)qualified
guy to let him fill a certificate of compliance/whatever.

Now...

1) I read somewhere (now well buried in one of the posts) that I'd
better link the armoured cable, at the house to the non-RCD CU and
then provide a split unit at the summer house end rather than keeping
the current setup.

2) Anything else to comply with these apparently frightening
regulations? (I would create ring circuits inside the summer house,
have a RCD-protected and a non-RCD protected split unit if possible,
etc). Note that I would use the summer house for woodworking involving
a range of professional power tools

Thanks

E.

Hi
I would put a radial circuit in. That way you only have to isolate that
circuit, if you have to work on it. Also if it does go down your whole house

It is already radial in the sense that there is one armoured cable
from the 40A electronic fuse in the home CU to the summer house, so
the total load should not exceed 40A x 240V.

It's just inside the summer house that I would place another CU on
the receiving end of the armoured cable and create a local ring, the
idea being that either the summer house CU electronic fuses deal with
overloads/spikes/ whatever or in the worst case the 40A fuse in the
house Cu deals with it.

W.

On Sep 18, 5:54*pm, "Micky Savage" wrote:
"Woland" wrote in message

...



Dear all,

I have veen following anxiously the issue of electrical regulations,
XVII ed. (part P?) or similar (seems like citing some obscure Criminal
Law Act though...).

Now the problem: in 2000 I had my electrical system partially rewired
and 'updated' to the current regulations of the times (Scotland).
A CU with no RCD for light and power in the house, plus another CU
with RCD (there were no split units at the time).

A 49Amp MAX armoured cable (should be 2.5mm^2, not certain but I'm
certain it's 49 Amp MAX) which is some 40 metres long goes from the
RCD-protected CU straight into the summer house to provide power.

I originally asked some supposed sparkies and the majority seemed to
conclude that I could manage the work myself as it were a 'shed-like
outhouse' but I', mot this very much convinced of that. If that's not
the case I would still do the job myself according to current
regulations and than waste a bit of money on the usual (un)qualified
guy to let him fill a certificate of compliance/whatever.

Now...

1) I read somewhere (now well buried in one of the posts) that I'd
better link the armoured cable, at the house to the non-RCD CU and
then provide a split unit at the summer house end rather than keeping
the current setup.

2) Anything else to comply with these apparently frightening
regulations? (I would create ring circuits inside the summer house,
have a RCD-protected and a non-RCD protected split unit if possible,
etc). Note that I would use the summer house for woodworking involving
a range of professional power tools

Thanks

E.

Hi
I would put a radial circuit in. That way you only have to isolate that
circuit, if you have to work on it. Also if it does go down your whole house
does not.

Ring rinals are on their way out.
I know this because I am at Leeds College of Technology, I am studying for
Level 3. We covered this very subject today.
I am about to rewire my home and am putting in radial circuits in every
room.

Kind Regards.

Micky Savage.

P.S. Testing is also a lot quicker on Radial circuits, so you won't have to
pay the sparky as much for your testing.

Funny, considering the ring circuit has such safety advantages
http://www.wiki.diyfaq.org.uk/index....e=Ring_circuit


NT

wrote in message
...
On Sep 18, 5:54 pm, "Micky Savage" wrote:
"Woland" wrote in message

...



Dear all,

I have veen following anxiously the issue of electrical regulations,
XVII ed. (part P?) or similar (seems like citing some obscure Criminal
Law Act though...).

Now the problem: in 2000 I had my electrical system partially rewired
and 'updated' to the current regulations of the times (Scotland).
A CU with no RCD for light and power in the house, plus another CU
with RCD (there were no split units at the time).

A 49Amp MAX armoured cable (should be 2.5mm^2, not certain but I'm
certain it's 49 Amp MAX) which is some 40 metres long goes from the
RCD-protected CU straight into the summer house to provide power.

I originally asked some supposed sparkies and the majority seemed to
conclude that I could manage the work myself as it were a 'shed-like
outhouse' but I', mot this very much convinced of that. If that's not
the case I would still do the job myself according to current
regulations and than waste a bit of money on the usual (un)qualified
guy to let him fill a certificate of compliance/whatever.

Now...

1) I read somewhere (now well buried in one of the posts) that I'd
better link the armoured cable, at the house to the non-RCD CU and
then provide a split unit at the summer house end rather than keeping
the current setup.

2) Anything else to comply with these apparently frightening
regulations? (I would create ring circuits inside the summer house,
have a RCD-protected and a non-RCD protected split unit if possible,
etc). Note that I would use the summer house for woodworking involving
a range of professional power tools

Thanks

E.

Hi
I would put a radial circuit in. That way you only have to isolate that
circuit, if you have to work on it. Also if it does go down your whole
house
does not.

Ring rinals are on their way out.
I know this because I am at Leeds College of Technology, I am studying for
Level 3. We covered this very subject today.
I am about to rewire my home and am putting in radial circuits in every
room.

Kind Regards.

Micky Savage.

P.S. Testing is also a lot quicker on Radial circuits, so you won't have
to
pay the sparky as much for your testing.

Funny, considering the ring circuit has such safety advantages
http://www.wiki.diyfaq.org.uk/index....e=Ring_circuit


NT


No not funny it's going to be fact.

Micky.

Micky Savage coughed up some electrons that declared:


wrote in message
...
On Sep 18, 5:54 pm, "Micky Savage" wrote:
"Woland" wrote in message

...



Dear all,

I have veen following anxiously the issue of electrical regulations,
XVII ed. (part P?) or similar (seems like citing some obscure Criminal
Law Act though...).

Now the problem: in 2000 I had my electrical system partially rewired
and 'updated' to the current regulations of the times (Scotland).
A CU with no RCD for light and power in the house, plus another CU
with RCD (there were no split units at the time).

A 49Amp MAX armoured cable (should be 2.5mm^2, not certain but I'm
certain it's 49 Amp MAX) which is some 40 metres long goes from the
RCD-protected CU straight into the summer house to provide power.

I originally asked some supposed sparkies and the majority seemed to
conclude that I could manage the work myself as it were a 'shed-like
outhouse' but I', mot this very much convinced of that. If that's not
the case I would still do the job myself according to current
regulations and than waste a bit of money on the usual (un)qualified
guy to let him fill a certificate of compliance/whatever.

Now...

1) I read somewhere (now well buried in one of the posts) that I'd
better link the armoured cable, at the house to the non-RCD CU and
then provide a split unit at the summer house end rather than keeping
the current setup.

2) Anything else to comply with these apparently frightening
regulations? (I would create ring circuits inside the summer house,
have a RCD-protected and a non-RCD protected split unit if possible,
etc). Note that I would use the summer house for woodworking involving
a range of professional power tools

Thanks

E.

Hi
I would put a radial circuit in. That way you only have to isolate that
circuit, if you have to work on it. Also if it does go down your whole
house
does not.

Ring rinals are on their way out.
I know this because I am at Leeds College of Technology, I am studying
for Level 3. We covered this very subject today.
I am about to rewire my home and am putting in radial circuits in every
room.

Kind Regards.

Micky Savage.

P.S. Testing is also a lot quicker on Radial circuits, so you won't have
to
pay the sparky as much for your testing.

Funny, considering the ring circuit has such safety advantages
http://www.wiki.diyfaq.org.uk/index....e=Ring_circuit


NT


No not funny it's going to be fact.

Micky.

Lecturers sometimes have their own slant on things and it may or may not
align with reality :-

OK - rather than just state what I think, lets have some fun instead...

I would like to postulate that 32A final socket circuits are good for many
applications because they doesn't keel over when you plug two 3kW
appliances in. If you disagree, the debate is dead, if agree, please go to
next step:

Next step: Can you construct a 32A radial circuit using 13A sockets?

Cheers

Tim

Tim S wrote:

Lecturers sometimes have their own slant on things and it may or may not
align with reality :-

Quite. AFAIK there's no intention whatever to abandon the faithful ring
circuit, but there is something of a campaign going on to educate
electricians about the radial alternatives. Hence Appendix 15 in the
New Red Book.

Next step: Can you construct a 32A radial circuit using 13A sockets?

Yes, of course - it's one of the standard circuits: 4 mm^2 cable for the
main circuit, spurs in 2.5 subject to the same rules as for rings,
max. floor area served 75 m^2.

--
Andy

Woland wrote:

I have veen following anxiously the issue of electrical regulations,
XVII ed. (part P?)

The 17th edition and Part P are quire separate things. The latter
doesn't apply in Scotland.

Now the problem: in 2000 [...] (there were no split units at the time).

Oh yes there were.

A 49Amp MAX armoured cable (should be 2.5mm^2, not certain but I'm
certain it's 49 Amp MAX) which is some 40 metres long goes from the
RCD-protected CU straight into the summer house to provide power.

With that length of run the effective current rating of your submain
will be limited by voltage drop and not by the current rating of the cable.

You might find
http://wiki.diyfaq.org.uk/index.php?...ricity_outside
useful.

--
Andy

Now the problem: in 2000 [...] *(there were no split units at the time).

Oh yes there were.

Was just a hypothesis

A 49Amp MAX armoured cable (should be 2.5mm^2, not certain but I'm
certain it's 49 Amp MAX) which is some 40 metres long goes from the
RCD-protected CU straight into the summer house to provide power.

With that length of run the effective current rating of your submain
will be limited by voltage drop and not by the current rating of the cable.

You might findhttp://wiki.diyfaq.org.uk/index.php?title=Taking_electricity_outside
useful.

I had read that and I was expecting a serious voltage drop (no load
reading doesn't count, obviously).
So I set up the usual easy measurement with a 2 KW load (circular saw
+ lights + other resistive loads) and... strange but true no drop!

Experiment repeated several time... same result. I am actually curious
to find out why I'm not withnessing any voltage drop... maybe the load
is too small?

W.
--
Andy

"Woland" wrote in message
...
Now the problem: in 2000 [...] (there were no split units at the time).

Oh yes there were.

Was just a hypothesis

A 49Amp MAX armoured cable (should be 2.5mm^2, not certain but I'm
certain it's 49 Amp MAX) which is some 40 metres long goes from the
RCD-protected CU straight into the summer house to provide power.

With that length of run the effective current rating of your submain
will be limited by voltage drop and not by the current rating of the
cable.

You might
findhttp://wiki.diyfaq.org.uk/index.php?title=Taking_electricity_outside
useful.

I had read that and I was expecting a serious voltage drop (no load
reading doesn't count, obviously).
So I set up the usual easy measurement with a 2 KW load (circular saw
+ lights + other resistive loads) and... strange but true no drop!

Experiment repeated several time... same result. I am actually curious
to find out why I'm not withnessing any voltage drop... maybe the load
is too small?

You're obviously using special zero-ohm oxygen-free speaker cable.
Supplier/price?

Woland wrote:

I had read that and I was expecting a serious voltage drop (no load
reading doesn't count, obviously).
So I set up the usual easy measurement with a 2 KW load (circular saw
+ lights + other resistive loads) and... strange but true no drop!

A saw's not much good as a test load because the current drawn will vary
wildly with the mechanical load. Use a 3 kW fan heater or similar.

Experiment repeated several time... same result. I am actually curious
to find out why I'm not withnessing any voltage drop... maybe the load
is too small?

How are you measuring? Is the cable perhaps bigger than you think?

The resistance of a 40 m run of 2.5 2-core will be about 0.6 ohm. If
you were to allocate the whole 3% permitted drop (for lighting) to the
submain on the assumption that there'll be little more in the short
wiring in the summerhouse, the max load will be 6.9 V / 0.6 ohm which is
only 11.5 amps.

What equipment do you propose to use in the summerhouse? For a 32 A
supply you really need a 10 mm^2 cable, or 6 mm^2 (4 at a pinch) for a
16 A feed.

--
Andy

Andy Wade coughed up some electrons that declared:

Tim S wrote:

Lecturers sometimes have their own slant on things and it may or may not
align with reality :-

Quite. AFAIK there's no intention whatever to abandon the faithful ring
circuit, but there is something of a campaign going on to educate
electricians about the radial alternatives. Hence Appendix 15 in the
New Red Book.

Next step: Can you construct a 32A radial circuit using 13A sockets?

Yes, of course - it's one of the standard circuits: 4 mm^2 cable for the
main circuit, spurs in 2.5 subject to the same rules as for rings,
max. floor area served 75 m^2.


Thanks Andy - it was really for Mickey. Anyway, I'll follow through on the
thought I was hoping to provoke:

Assuming I'm reading Table 4D2A (IEE regs, 17th) correctly, 4mm2 cable
derates to 25A capacity in thermal insulation and 30A in conduit in wall,
so quickly becomes unsuitable for a 32A radial circuit.

A BS1363 socket has a stated terminal capacity of 3 x 2.5mm2, or 2 x 4mm2
conductors per terminal, with occasionally a manufacturer allowing 1 x
6mm2.

So, my argument to Mickey and his lecturer:

Suppporting a 32A radial circuit in practise is difficult.
A 20A radial is easy enough, but personally, I find them conceptually less
useful for general purpose use, where loading is unpredictable and the
possibility of wanting a load 20A on a particular circuit is quite
likely.

Ergo, I don't think radials are the way to go, except in limited cases where
20A is known to be adequate.

Cheers

Tim

Micky Savage wrote:

P.S. Testing is also a lot quicker on Radial circuits, so you won't have
to
pay the sparky as much for your testing.

Funny, considering the ring circuit has such safety advantages
http://www.wiki.diyfaq.org.uk/index....e=Ring_circuit


NT


No not funny it's going to be fact.

Well leaving aside any issues of why you would be paying anyone else to
test your circuits for you, one needs to consider the circumstance.

If you have just installed a new ring final circuit, then it is no more
difficult or time consuming to test than a radial. The time that a ring
circuit becomes more difficult to test is when you are attempting to
discover and reverse engineer its topology after a period alterations etc.

IME the general fault tolerance in real world situations is better with
rings than radials since the most typical faults have a lesser impact:

http://www.wiki.diyfaq.org.uk/index...._circuit_types



--
Cheers,

John.

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

On Sep 19, 12:11*am, Woland wrote:
Now the problem: in 2000 [...] *(there were no split units at the time).

Oh yes there were.

Was just a hypothesis

A 49Amp MAX armoured cable (should be 2.5mm^2, not certain but I'm
certain it's 49 Amp MAX) which is some 40 metres long goes from the
RCD-protected CU straight into the summer house to provide power.

With that length of run the effective current rating of your submain
will be limited by voltage drop and not by the current rating of the cable.

You might findhttp://wiki.diyfaq.org.uk/index.php?title=Taking_electricity_outside
useful.

*I had read that and I was expecting a serious voltage drop (no load
reading doesn't count, obviously).
So I set up the usual easy measurement with a 2 KW load (circular saw
+ lights + other resistive loads) and... strange but true no drop!

Experiment repeated several time... same result. I am actually curious
to find out why I'm not withnessing any voltage drop... maybe the load
is too small?

W.

Begs the question of how you're measuring it. Basic physics tells us
there will be a v drop.


NT

Begs the question of how you're measuring it. Basic physics tells us
there will be a v drop.

No it doesn't. The OP is not indulging in petitio principii. It might
raise the question, but it doesn't beg it.

And to sound off on ring circuits vis-a-vis radials: weren't rings in
part devised to cope with post-WW2 copper shortages - wouldn't it be
'greener' to continue using rings as radial usage would increase
copper usage.

And another thing...with all the campaigning to minimise the use of
'standby' rather than physically 'off' switches, and encourage people
to unplug mobile phone chargers and the suchlike when not in use,
won't the requirements for RCDs significantly increase base-load power
consumption? All the RCDs I've come across dissipate a few watts.
Replacing all the rewireable fuses in my consumer unit with RCBOs; or
indeed replacing sockets with ones that have RCD protection build in
will increase consumption.

Regards,

Sid

wrote:

And to sound off on ring circuits vis-a-vis radials: weren't rings in
part devised to cope with post-WW2 copper shortages - wouldn't it be

They were... although

'greener' to continue using rings as radial usage would increase
copper usage.

Prolly better to use whichever is most appropriate for the particular
circumstances. Depending on layout a ring might use more copper than a
4mm^2 radial anyway.

And another thing...with all the campaigning to minimise the use of
'standby' rather than physically 'off' switches, and encourage people
to unplug mobile phone chargers and the suchlike when not in use,
won't the requirements for RCDs significantly increase base-load power
consumption? All the RCDs I've come across dissipate a few watts.
Replacing all the rewireable fuses in my consumer unit with RCBOs; or
indeed replacing sockets with ones that have RCD protection build in
will increase consumption.

Can't say I have ever noticed a RCD getting warm, but then again I have
never measured their power consumption. Either way, you can't expect
joined up thinking from the government can you?

--
Cheers,

John.

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

On Fri, 19 Sep 2008 19:38:48 +0100, John Rumm wrote:

won't the requirements for RCDs significantly increase base-load power
consumption? All the RCDs I've come across dissipate a few watts.

Can't say I have ever noticed a RCD getting warm, but then again I have
never measured their power consumption.

There is a difference between "dissipate" and "consume". The key is does
and RCD get warm when it is not passing any load? I don't think they do so
they don't "consume" any power in their own right. They simply "dissipate"
a bit when carrying a load, just like the cables do as well. No increase
in base load.

--
Cheers
Dave.

On 19 Sep, 22:04, "Dave Liquorice"
wrote:
On Fri, 19 Sep 2008 19:38:48 +0100, John Rumm wrote:
won't the requirements for RCDs significantly increase base-load power
consumption? All the RCDs I've come across dissipate a few watts.

Can't say I have ever noticed a RCD getting warm, but then again I have
never measured their power consumption.

There is a difference between "dissipate" and "consume". The key is does
and RCD get warm when it is not passing any load? I don't think they do so
they don't "consume" any power in their own right. They simply "dissipate"
a bit when carrying a load, just like the cables do as well. No increase
in base load.

--
Cheers
Dave.

...."does and [sic] RCD get warm when it is not passing any load?" -
Yes! - At least every single one I have used has done so. They get
even warmer when passing load. My _guess_ is that all the ones I have
come across use a solenoid to keep the contact closed, and some power
is used in the solenoid. It isn't much - somewhere between 0.5 and 5
watts is my estimate when not under load, but multiply that up by the
number of RCDs across the country and it is a lot of power being used.
I have no idea why they warm up under load. I hope its not ohmic
heating across the contacts!

Cheers,

Sid

wrote:
On 19 Sep, 22:04, "Dave Liquorice"
wrote:
On Fri, 19 Sep 2008 19:38:48 +0100, John Rumm wrote:
won't the requirements for RCDs significantly increase base-load power
consumption? All the RCDs I've come across dissipate a few watts.
Can't say I have ever noticed a RCD getting warm, but then again I have
never measured their power consumption.
There is a difference between "dissipate" and "consume". The key is does
and RCD get warm when it is not passing any load? I don't think they do so
they don't "consume" any power in their own right. They simply "dissipate"
a bit when carrying a load, just like the cables do as well. No increase
in base load.

--
Cheers
Dave.

..."does and [sic] RCD get warm when it is not passing any load?" -
Yes! - At least every single one I have used has done so. They get
even warmer when passing load. My _guess_ is that all the ones I have
come across use a solenoid to keep the contact closed, and some power
is used in the solenoid. It isn't much - somewhere between 0.5 and 5
watts is my estimate when not under load, but multiply that up by the
number of RCDs across the country and it is a lot of power being used.
I have no idea why they warm up under load. I hope its not ohmic
heating across the contacts!


NO, they use the solenoid to break the trip.

IIRC they wind live and neutral together round a solenoid, the idea
being the currents cancel..any imbalance causes a net magnetic field and
trips the switch. You need a fair number of turns to get the
sensitivity, so there is an inevitable resistance, especially at high
load currents.


Cheers,

Sid

On Fri, 19 Sep 2008 15:03:22 -0700 (PDT), wrote:

Yes! - At least every single one I have used has done so. They get
even warmer when passing load. My _guess_ is that all the ones I have
come across use a solenoid to keep the contact closed, and some power
is used in the solenoid.

They are magnetic and like TNP said the Live and Neutral are woud around
the same core when there is suffcient current imbalance the resultant
magnetic field pulls the latch set when the device is set to "on" and a
spring causes it to trip off. AFAIK they are not held on by power
otherwise everytime you had a power cut you'd have to reset them...

The only CU RCD here is the same temperature as the MCBs next to it, at
least by touch, ie cold.

I have no idea why they warm up under load. I hope its not ohmic
heating across the contacts!

Quite simply ohmic losses in the coils.

--
Cheers
Dave.

On 20 Sep, 23:30, "Dave Liquorice"
wrote:
On Fri, 19 Sep 2008 15:03:22 -0700 (PDT), wrote:
Yes! - At least every single one I have used has done so. They get
even warmer when passing load. My _guess_ is that all the ones I have
come across use a solenoid to keep the contact closed, and some power
is used in the solenoid.

They are magnetic and like TNP said the Live and Neutral are woud around
the same core when there is suffcient current imbalance the resultant
magnetic field pulls the latch set when the device is set to "on" and a
spring causes it to trip off. AFAIK they are not held on by power
otherwise everytime you had a power cut you'd have to reset them...

The only CU RCD here is the same temperature as the MCBs next to it, at
least by touch, ie cold.

I have no idea why they warm up under load. I hope its not ohmic
heating across the contacts!

Quite simply ohmic losses in the coils.

--
Cheers
Dave.

Ahh - we might be talking about different things. I'll try and
clarify.

All the RCDs I have used are not consumer unit mounted ones, but
either

a) Unit placed between a 13A plug and socket
b) Unit replacing 13A plug

I have found that they can be obtained with a feature of being either

a) latching - if power is restored after a power failure, the RCD will
remake the circuit
b) non-latching - if power is restores after a power failure, the RCD
will NOT remake the circuit

The non-latching variety I have used require a button to be pushed to
make the circuit - it seems to arm a spring loaded mechanism. The
latching variety I have do not have a spring loaded mechanism, but a
pair of microswitches, one to test, and one to make the circuit after
testing or detection of a residual current. This latching variety (of
which I have many examples) gets warm even when passing no load. The
non-latching do indeed have to be reset after a power failure - which
would be a right royal pain if such an RCD were feeding a freezer and
you happened to be away on holiday.

Now, my understanding of RCDs (which is imperfect) is that the sense
coil is wound around the (straight) phase and neutral conductors, and
some RCDs electronically process the output of the sense coil to allow
features like delayed activation, activation when the current is not
sinusoidal, and to prevent activation on normal inrush currents (and
possibly ofr other reasons). Some RCDs use the output of the sense
coil directly to activate a solenoid which triggers a spring loaded
mechanism to disconnect the circuit. The description you have of the
phase and neutral being wound round a core may be a variant of the
latter - possibly used in consumer unit RCDs.(Idle thought - would it
trip if there were an excess of current in the neutral?). AFAIK, they
are only guaranteed to work within specification on sinusoidal
currents.

So, my imperfect knowledge of consumer unit RCDs may be leading me to
make the wrong conclusion. My understanding of consumer unit RCDs is
that they are routinely of the latching variety (i.e. will remake a
circuit on restoration of power after a failure), and that therefore
they will be dissipating power at zero load, as my assumption is that
_all_ latching RCDs disspate power at zero load. Either or both of my
assumptions could be wrong, and I would be grateful if someone with
better knowledge (and hopefully URLs to demonstrate this) could
elucidate. Most of my Google searches end up at Wikipedia, which can
hardly be regarded as authoritative on this matter.

Cheers,

Sid

On Sun, 21 Sep 2008 02:05:32 -0700 (PDT), wrote:

a) latching - if power is restored after a power failure, the RCD will
remake the circuit
b) non-latching - if power is restores after a power failure, the RCD
will NOT remake the circuit

I think you'll find that the latching type stay set, like a CU RCD if the
power fails rather than make/remake the circuit on power/power loss. The
non-latching ones drop out (trip) when the power fails, they may well
consume a little bit of power to hold the latch in. I think that all
plugin type RCDs these days are supposed to be the non-latching type, it's
safer. Means that if are using a portable power tool and the power goes
off it doesn't come back on with the power.

The non-latching variety I have used require a button to be pushed to
make the circuit - it seems to arm a spring loaded mechanism. The
latching variety I have do not have a spring loaded mechanism, but a
pair of microswitches, one to test, and one to make the circuit after
testing or detection of a residual current.

All the ones I have are spring loaded set mechanisiums, one I have looks
like a small microswitch push button with only a small amount of movement
but it still sets a spring loaded latch.

The description you have of the phase and neutral being wound round a
core may be a variant of the latter

A possibly inaccurate a sense coil around the conductors is much more
likely from the enginerring POV, the size of wire required to carry, say
80A, is not conducive to making small compact coils... I've not had dead
RCD to disect. B-)

(Idle thought - would it trip if there were an excess of current in
the neutral?).

They should, any imbalance between the send and return should trip an RCD.

--
Cheers
Dave.

On 21 Sep, 12:45, "Dave Liquorice"
wrote:
On Sun, 21 Sep 2008 02:05:32 -0700 (PDT), wrote:
a) latching - if power is restored after a power failure, the RCD will
remake the circuit
b) non-latching - if power is restores after a power failure, the RCD
will NOT remake the circuit

I think you'll find that the latching type stay set, like a CU RCD if the
power fails rather than make/remake the circuit on power/power loss. The
non-latching ones drop out (trip) when the power fails, they may well
consume a little bit of power to hold the latch in. I think that all
plugin type RCDs these days are supposed to be the non-latching type, it's
safer. Means that if are using a portable power tool and the power goes
off it doesn't come back on with the power.

I have three latching RCDs that interrupt and remake the circuit on
power loss. They are very useful (but not on power tools, obviously).
If all plug-type RCDs are meant to be non-latching these days it
explains why I can't find more of them!

The non-latching variety I have used require a button to be pushed to
make the circuit - it seems to arm a spring loaded mechanism. The
latching variety I have do not have a spring loaded mechanism, but a
pair of microswitches, one to test, and one to make the circuit after
testing or detection of a residual current.

All the ones I have are spring loaded set mechanisiums, one I have looks
like a small microswitch push button with only a small amount of movement
but it still sets a spring loaded latch.

Could be. None of mine have died and I haven't succumbed to the
temptation to take them apart to see how they work.


The description you have of the phase and neutral being wound round a
core may be a variant of the latter

A possibly inaccurate a sense coil around the conductors is much more
likely from the enginerring POV, the size of wire required to carry, say
80A, is not conducive to making small compact coils... I've not had dead
RCD to disect. B-)

That is what I would have thought too, but 'The Natural Philosopher'
thinks otherwise in this thread.


(Idle thought - would it trip if there were an excess of current in
the neutral?).

They should, any imbalance between the send and return should trip an RCD.

'Should' is a great word. I may be being simplistic, but an excess of
current on the neutral conductor rather than a deficit will presumably
reverse the direction of the current output of the sense coil, which,
if is being fed into a solenoid, would reverse the direction of the
generated force. This can be accommodated mechanically with suitable
mechanism design, but without tearing a few RCDs apart and testing, I
don't have an easy way of determining what's going on. I would hope
that when people write 'imbalance' that is what they mean, rather than
'excess of phase over neutral', but sloppy thinking and wording are
rife (I'm no exception).

Although we are dealing nominally with AC here, the target disconnect
time of 30ms not much different to one standard mains AC cycle of 20
ms, so 'steady state' assumptions and calculations are not necessarily
valid. The inductance of the sense coil and solenoid, and the effect
of any electronics probably needs to be taken into account, and I'm
definitely not qualified to work out exactly how it all works.

Thank-you very much for taking the time to write your previous
considered reply.

Cheers,

Sid

wrote:

Ahh - we might be talking about different things. I'll try and
clarify.

All the RCDs I have used are not consumer unit mounted ones, but
either

Ah, yup that does make a difference.

Normally when discussing RCD for circuit protection we are talking about
the DIN rail mounting type (last two pictured here):

http://wiki.diyfaq.org.uk/index.php?title=RCD

a) Unit placed between a 13A plug and socket
b) Unit replacing 13A plug

I have found that they can be obtained with a feature of being either

a) latching - if power is restored after a power failure, the RCD will
remake the circuit
b) non-latching - if power is restores after a power failure, the RCD
will NOT remake the circuit

The NVR type often include a solenoid to hold the device "on" once
powered up. I could certainly understand these getting a little warm in
operation - even NVR switches without a RCD function can do this under
load.

The non-latching variety I have used require a button to be pushed to
make the circuit - it seems to arm a spring loaded mechanism. The
latching variety I have do not have a spring loaded mechanism, but a
pair of microswitches, one to test, and one to make the circuit after
testing or detection of a residual current. This latching variety (of
which I have many examples) gets warm even when passing no load. The
non-latching do indeed have to be reset after a power failure - which
would be a right royal pain if such an RCD were feeding a freezer and
you happened to be away on holiday.

Indeed. The standard CU type latch - but the latching is done with a
permanent magnet.

Now, my understanding of RCDs (which is imperfect) is that the sense
coil is wound around the (straight) phase and neutral conductors, and

My understanding also...

some RCDs electronically process the output of the sense coil to allow
features like delayed activation, activation when the current is not
sinusoidal, and to prevent activation on normal inrush currents (and
possibly ofr other reasons). Some RCDs use the output of the sense
coil directly to activate a solenoid which triggers a spring loaded
mechanism to disconnect the circuit. The description you have of the

The solenoid when activated is in effect reducing the mechanical
attraction of the permanent magnet, thus allowing the spring loaded
mechanism that is working against the magnet to pull the contacts open.

phase and neutral being wound round a core may be a variant of the
latter - possibly used in consumer unit RCDs.(Idle thought - would it
trip if there were an excess of current in the neutral?). AFAIK, they

As in greater neutral current than phase? Yes that will trip it.

are only guaranteed to work within specification on sinusoidal
currents.

Depends on the type you specify. MK for example have a number in their
range designed for different conditions like pulsing DC etc:

http://www.tlc-direct.co.uk/Technica...entry/RCDs.pdf

So, my imperfect knowledge of consumer unit RCDs may be leading me to
make the wrong conclusion. My understanding of consumer unit RCDs is
that they are routinely of the latching variety (i.e. will remake a
circuit on restoration of power after a failure), and that therefore

yup...

they will be dissipating power at zero load, as my assumption is that
_all_ latching RCDs disspate power at zero load. Either or both of my

nope, see notes above and also:

http://www.tlc-direct.co.uk/Technica...CD%20Works.htm

(they may dissipate a very small amount due to the electronics in them -
however none of the data sheets I have seen so far give any indication
if this is so, and if so how much).



--
Cheers,

John.

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\================================================= ================/

On 21 Sep, 21:29, John Rumm wrote:
wrote:
Ahh - we might be talking about different things. I'll try and
clarify.

All the RCDs I have used are not consumer unit mounted ones, but
either

Ah, yup that does make a difference.

Thank-you for your reply, John; and the link to the d-i-y wiki.

Sid