On Tue, 26 Jul 2005 00:01:18 +0100, "Doctor Drivel"
wrote:


"Andy Hall" wrote in message
.. .
On Mon, 25 Jul 2005 22:05:43 +0100, "Doctor Drivel"
wrote:


"Andrew Gabriel" wrote in message
. ..
In article ws.net,
"Doctor Drivel" writes:

And the MCBs also prevent a large load on the supply cable.

But not a fault in the cable or CU.

That is normal and the average domestic installation. What protects the
cable from the meter to the CU is the main fuse.

In the case of the main house CU, yes.

In the case of a garage one some metres away additional protection at
an appropriate and lower current rating is required.

Can you cite this please. The breakers on the garage CU woud protect it.


Go and buy a copy of BS7671 and refer to sections 431 to 436 (among
others).





No misinformation whatsoever. Conduit is also used. SWA looks naff,
conduit looks neat.

Which one looks neater is a matter of opinion. SWA is almost always
used between detached buildings.


--

..andy

To email, substitute .nospam with .gl

"John Rumm" wrote in message
...
Doctor Drivel wrote:

And the MCBs also prevent a large load on the supply cable.

You seem to have a fundamental misconception of the purpose of the
overcurrent devices (MCBs). They are for protection of the downstream
circuits *only*, explicitly *not* the upstream supply. It is the
function of a protective device at the *origin* of the supply to be
responsible for the protection of this sub main.

It also protects the supply cable too. If the downstream supply exceed the
MCBs rating then the supply cable is protect, if the cable is higher rated
than the total of the garage CU MCBs. That is abundantly obvious.

Hence overcurrent devices at the substation protect the cable runs to
the houses. The main fuse protects the cable runs to the CU and guards
against faults in the CUs themselves (unless they are more than two
meters from the fuse in which case an additional switchfuse should be
inserted). The MCBs in the CUs protects the cables in the house wiring,
and also performs the function of disconnection in the case of certain
fault conditions.

So in the same way that your 100A main supply fuse can not protect the
main cable (which will be supplying several properties), your MCBs can
not protect the meter tails since the maximum potential load of all
circuits combined will exceed the main fuse capacity. Also you may have
more than one CU.

In the garage situation, if the supply cable is rated higher than the total
of the MCBs in the garage, it is protected, whether upstream or downstream.
It is just simply protected. It cannot be loaded up above its rating.

If the garage CU has a 30A ring and A lighting circuit, then the supply
cable should be rated more than 35A. Then the MCBs protect the supply
cable.
Get it? Think about it. Nah, don't think, it is fatal.

You are missing the point. Consider these situations:

Detached garage with two circuits: 6A lighting, and 32A sockets.
Sub main cable to garage CU rated for 40A nominal capacity.
Cable fed directly from a junction box that splits the tails from the
meter.
Supply rated for 100A, TN-C earthing.

Your garage catches fire. It melts the garage CU and results in a L-N
short on the sub main cable. What happens?

The what hapens if the house burns down. What you are saying is that every
CU should have a protective breaker between the meter and the CU.

Since there is no suitably sized protection for the sub main cable at
its origin, the cable may burst into flames. What was a fire in your
garage is now a fire in the house as well.

You are digging in the garden and manage to stick a spade into the
cable. You cause a phase earth short. Lets say that the cable does not
burst into flames this time, but the main electricity companies fuse
blows taking out all circuits in the entire property and technically
requiring the assistance of the electricity company to come and fix the
fuse - which won't do because your knackered cable and spade are still
wired in, and there is no isolation for them.

--
Cheers,

John.

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

On Tue, 26 Jul 2005 09:48:29 +0100, "Doctor Drivel"
wrote:


"John Rumm" wrote in message
...
Doctor Drivel wrote:

And the MCBs also prevent a large load on the supply cable.

You seem to have a fundamental misconception of the purpose of the
overcurrent devices (MCBs). They are for protection of the downstream
circuits *only*, explicitly *not* the upstream supply. It is the
function of a protective device at the *origin* of the supply to be
responsible for the protection of this sub main.

It also protects the supply cable too. If the downstream supply exceed the
MCBs rating then the supply cable is protect, if the cable is higher rated
than the total of the garage CU MCBs. That is abundantly obvious.

That is not the purpose and not how electrical systems are designed.
THe circuit protection is installed at the supply end of the cable.



Hence overcurrent devices at the substation protect the cable runs to
the houses. The main fuse protects the cable runs to the CU and guards
against faults in the CUs themselves (unless they are more than two
meters from the fuse in which case an additional switchfuse should be
inserted). The MCBs in the CUs protects the cables in the house wiring,
and also performs the function of disconnection in the case of certain
fault conditions.

So in the same way that your 100A main supply fuse can not protect the
main cable (which will be supplying several properties), your MCBs can
not protect the meter tails since the maximum potential load of all
circuits combined will exceed the main fuse capacity. Also you may have
more than one CU.

In the garage situation, if the supply cable is rated higher than the total
of the MCBs in the garage, it is protected, whether upstream or downstream.
It is just simply protected. It cannot be loaded up above its rating.


That is not correct design. Refer to BS7671 and publications derived
from it.




You are missing the point. Consider these situations:

Detached garage with two circuits: 6A lighting, and 32A sockets.
Sub main cable to garage CU rated for 40A nominal capacity.
Cable fed directly from a junction box that splits the tails from the
meter.
Supply rated for 100A, TN-C earthing.

Your garage catches fire. It melts the garage CU and results in a L-N
short on the sub main cable. What happens?

The what hapens if the house burns down. What you are saying is that every
CU should have a protective breaker between the meter and the CU.

No he isn't. The protection for the meter tails and CU itself is the
supplier main fuse.




--

..andy

To email, substitute .nospam with .gl

Doctor Drivel wrote:

It also protects the supply cable too. If the downstream supply exceed the

It *may* protect the supply cable under *some* fault conditions. However
since it is not able to give adequate protection in *all* fault
conditions is it not relied on.

The correct design approach is to protect at the origin only. Any side
benefit you get from a downstream protective device is just that, a side
benefit not something you rely on.

MCBs rating then the supply cable is protect, if the cable is higher rated
than the total of the garage CU MCBs. That is abundantly obvious.

Obvious yes, but dangerously neieve.


You are missing the point. Consider these situations:

Detached garage with two circuits: 6A lighting, and 32A sockets.
Sub main cable to garage CU rated for 40A nominal capacity.
Cable fed directly from a junction box that splits the tails from the
meter.
Supply rated for 100A, TN-C earthing.

Your garage catches fire. It melts the garage CU and results in a L-N
short on the sub main cable. What happens?


The what hapens if the house burns down.

There are issues here you are failing to grasp. Firstly meter tails are
sized such that their capacity exceeds the main fuse rating. In a fault
condition the main fuse will operate before there is risk of these
causing a fire.

A sub main feed to an outbuilding is unlikely to be sufficently large
for this to be the case. Hence it must have its own dedicated
overcurrent and earth fault portection at its source. You can ignore
anything on its destination end since you can't rely on the fault
occuring after the destination - you have to considde fault conditions
that affect the cable itself, or the CU it terminates in.

What you are saying is that every
CU should have a protective breaker between the meter and the CU.

No, that is what the main fuse is for. You only need additional
overcurrent protection and isolation between the main fuse and the CU if
the CU is more than a couple of meters from it.

--
Cheers,

John.

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

In article ,
Andy Hall wrote:
No misinformation whatsoever. Conduit is also used. SWA looks naff,
conduit looks neat.

Which one looks neater is a matter of opinion. SWA is almost always
used between detached buildings.


Conduit can never look as neat as SWA on the average run to a garage since
it will inevitably have bends or elbows.

Plastic conduit - the only sort Evil is likely to use given his poor
skills - will look even worse, and not give anything like the same
protection to mechanical damage as SWA. Then there's the problem of
pulling through TW&E, and the fact that the ECC in all probability won't
be adequate. And the combination costs more as well as being more labour
intensive. A lose lose lose situation. So typical Drivel.

--
*I wished the buck stopped here, as I could use a few.

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

In article ws.net,
Doctor Drivel wrote:
You seem to have a fundamental misconception of the purpose of the
overcurrent devices (MCBs). They are for protection of the downstream
circuits *only*, explicitly *not* the upstream supply. It is the
function of a protective device at the *origin* of the supply to be
responsible for the protection of this sub main.

It also protects the supply cable too.

[snip dangerous advice from Drivel]

--
*A fine is a tax for doing wrong. A tax is a fine for doing well.

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

In article ,
Andy Hall wrote:
It also protects the supply cable too. If the downstream supply exceed
the MCBs rating then the supply cable is protect, if the cable is
higher rated than the total of the garage CU MCBs. That is abundantly
obvious.

That is not the purpose and not how electrical systems are designed. THe
circuit protection is installed at the supply end of the cable.

Something this obvious a child would have no problem understanding.

--
*The fact that no one understands you doesn't mean you're an artist

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

John Rumm wrote:

You are digging in the garden and manage to stick a spade into the
cable.

Wishful thinking!

--

Matt wrote:

You are digging in the garden and manage to stick a spade into the
cable.


Wishful thinking!

Yup, that is what SWMBO is for! ;-)


--
Cheers,

John.

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

"Andy Hall" wrote in message
...

I am not suggesting anything other than what I just said. That is making
a
point with a man who doesn't know very much at all.

If you don't know very much at all about something, as has been
pointed out (so glad you realise the error of your ways),

No error in my suggestion to the OPs problem.

why do you persist in peddling
incorrect and dangerous information?

IT is clear you don't know much about this.

"Andy Hall" wrote in message
...
On Tue, 26 Jul 2005 00:01:18 +0100, "Doctor Drivel"
wrote:


"Andy Hall" wrote in message
.. .
On Mon, 25 Jul 2005 22:05:43 +0100, "Doctor Drivel"
wrote:


"Andrew Gabriel" wrote in message
. ..
In article
ws.net,
"Doctor Drivel" writes:

And the MCBs also prevent a large load on the supply cable.

But not a fault in the cable or CU.

That is normal and the average domestic installation. What protects
the
cable from the meter to the CU is the main fuse.

In the case of the main house CU, yes.

In the case of a garage one some metres away additional protection at
an appropriate and lower current rating is required.

Can you cite this please. The breakers on the garage CU woud protect it.


Go and buy a copy of BS7671 and refer to sections 431 to 436 (among
others).

No misinformation whatsoever. Conduit is also used. SWA looks naff,
conduit looks neat.

Which one looks neater is a matter of opinion. SWA is almost always
used between detached buildings.

Not for aesthetics.

"Andy Hall" wrote in message
...
On Tue, 26 Jul 2005 09:48:29 +0100, "Doctor Drivel"
wrote:


"John Rumm" wrote in message
...
Doctor Drivel wrote:

And the MCBs also prevent a large load on the supply cable.

You seem to have a fundamental misconception of the purpose of the
overcurrent devices (MCBs). They are for protection of the downstream
circuits *only*, explicitly *not* the upstream supply. It is the
function of a protective device at the *origin* of the supply to be
responsible for the protection of this sub main.

It also protects the supply cable too. If the downstream supply exceed
the
MCBs rating then the supply cable is protect, if the cable is higher
rated
than the total of the garage CU MCBs. That is abundantly obvious.

That is not the purpose and not how electrical systems are designed.
THe circuit protection is installed at the supply end of the cable.

Are you saying it would not be protected?

Hence overcurrent devices at the substation protect the cable runs to
the houses. The main fuse protects the cable runs to the CU and guards
against faults in the CUs themselves (unless they are more than two
meters from the fuse in which case an additional switchfuse should be
inserted). The MCBs in the CUs protects the cables in the house wiring,
and also performs the function of disconnection in the case of certain
fault conditions.

So in the same way that your 100A main supply fuse can not protect the
main cable (which will be supplying several properties), your MCBs can
not protect the meter tails since the maximum potential load of all
circuits combined will exceed the main fuse capacity. Also you may have
more than one CU.

In the garage situation, if the supply cable is rated higher than the
total
of the MCBs in the garage, it is protected, whether upstream or
downstream.
It is just simply protected. It cannot be loaded up above its rating.


That is not correct design. Refer to BS7671 and publications derived
from it.




You are missing the point. Consider these situations:

Detached garage with two circuits: 6A lighting, and 32A sockets.
Sub main cable to garage CU rated for 40A nominal capacity.
Cable fed directly from a junction box that splits the tails from the
meter.
Supply rated for 100A, TN-C earthing.

Your garage catches fire. It melts the garage CU and results in a L-N
short on the sub main cable. What happens?

The what hapens if the house burns down. What you are saying is that
every
CU should have a protective breaker between the meter and the CU.

No he isn't. The protection for the meter tails and CU itself is the
supplier main fuse.

As per the garage too.

"John Rumm" wrote in message
...
Doctor Drivel wrote:

It also protects the supply cable too. If the downstream supply exceed
the

It *may* protect the supply cable under *some* fault conditions. However
since it is not able to give adequate protection in *all* fault
conditions is it not relied on.

The correct design approach is to protect at the origin only. Any side
benefit you get from a downstream protective device is just that, a side
benefit not something you rely on.

MCBs rating then the supply cable is protect, if the cable is higher
rated
than the total of the garage CU MCBs. That is abundantly obvious.

Obvious yes, but dangerously neieve.

But protected. That is obvious

You are missing the point. Consider these situations:

Detached garage with two circuits: 6A lighting, and 32A sockets.
Sub main cable to garage CU rated for 40A nominal capacity.
Cable fed directly from a junction box that splits the tails from the
meter.
Supply rated for 100A, TN-C earthing.

Your garage catches fire. It melts the garage CU and results in a L-N
short on the sub main cable. What happens?


The what hapens if the house burns down.

There are issues here you are failing to grasp. Firstly meter tails are
sized such that their capacity exceeds the main fuse rating. In a fault
condition the main fuse will operate before there is risk of these
causing a fire.

Yep.

A sub main feed to an outbuilding is unlikely to be sufficently large
for this to be the case.

You size to suit. I have said that all along. In this case the supply is
high level conduit.

Hence it must have its own dedicated
overcurrent and earth fault portection at its source. You can ignore
anything on its destination end since you can't rely on the fault
occuring after the destination - you have to considde fault conditions
that affect the cable itself, or the CU it terminates in.

What you are saying is that every
CU should have a protective breaker between the meter and the CU.

No, that is what the main fuse is for. You only need additional
overcurrent protection and isolation between the main fuse and the CU if
the CU is more than a couple of meters from it.

"Dave Plowman (News)" wrote in message
...
In article ,
Andy Hall wrote:
No misinformation whatsoever. Conduit is also used. SWA looks naff,
conduit looks neat.

Which one looks neater is a matter of opinion. SWA is almost always
used between detached buildings.

Conduit can never look as neat as SWA on the average run to a garage since
it will inevitably have bends or elbows.

Bends and elbows? You don't say.....

"Dave Plowman (News)" wrote in message
...
In article ws.net,
Doctor Drivel wrote:
You seem to have a fundamental misconception of the purpose of the
overcurrent devices (MCBs). They are for protection of the downstream
circuits *only*, explicitly *not* the upstream supply. It is the
function of a protective device at the *origin* of the supply to be
responsible for the protection of this sub main.

It also protects the
supply cable too.

snip idiotic drivel

"Dave Plowman (News)" wrote in message
...
In article ,
Andy Hall wrote:
It also protects the supply cable too. If the downstream supply exceed
the MCBs rating then the supply cable is protect, if the cable is
higher rated than the total of the garage CU MCBs. That is abundantly
obvious.

That is not the purpose and not how electrical systems are designed. THe
circuit protection is installed at the supply end of the cable.

Something

More lunacy snipped.

In article ws.net,
Doctor Drivel wrote:
If you don't know very much at all about something, as has been
pointed out (so glad you realise the error of your ways),

No error in my suggestion to the OPs problem.

So many to be positively dangerous. Luckily, most here know you for the
charlatan you are, and ignore your 'advice'.

why do you persist in peddling
incorrect and dangerous information?

IT is clear you don't know much about this.

It's clear you know nothing about electrics. And by default, little about
anything else.

--
*Why do we say something is out of whack? What is a whack? *

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

On Tue, 26 Jul 2005 22:03:42 +0100, "Doctor Drivel"
wrote:


"Andy Hall" wrote in message
.. .

I am not suggesting anything other than what I just said. That is making
a
point with a man who doesn't know very much at all.

If you don't know very much at all about something, as has been
pointed out (so glad you realise the error of your ways),

No error in my suggestion to the OPs problem.

You've made about 6 different ones, all of which have either had
unsuitable or dangerous information or both.




--

..andy

To email, substitute .nospam with .gl

On Tue, 26 Jul 2005 22:04:46 +0100, "Doctor Drivel"
wrote:


"Andy Hall" wrote in message


Which one looks neater is a matter of opinion. SWA is almost always
used between detached buildings.

Not for aesthetics.

It's a lot less conspicuous than conduit.



--

..andy

To email, substitute .nospam with .gl

In article ws.net,
Doctor Drivel wrote:
A sub main feed to an outbuilding is unlikely to be sufficently large
for this to be the case.

You size to suit. I have said that all along. In this case the supply is
high level conduit.

This man is deranged.

--
*If PROGRESS is for advancement, what does that make CONGRESS mean?

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

In article ws.net,
Doctor Drivel wrote:
Conduit can never look as neat as SWA on the average run to a garage
since it will inevitably have bends or elbows.

Bends and elbows? You don't say.....

Something else you don't understand.

Please stick to giving unsuitable advice about boilers.

At least there everyone knows to ignore you.

--
*I was once a millionaire but my mom gave away my baseball cards

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

In article ws.net,
Doctor Drivel wrote:
Doctor Drivel wrote:
You seem to have a fundamental misconception of the purpose of the
overcurrent devices (MCBs). They are for protection of the
downstream circuits *only*, explicitly *not* the upstream supply.
It is the function of a protective device at the *origin* of the
supply to be responsible for the protection of this sub main.

It also protects the supply cable too.

[snip dangerous advice from our resident looney]

--
*I have my own little world - but it's OK...they know me here*

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

On Tue, 26 Jul 2005 22:07:32 +0100, "Doctor Drivel"
wrote:



Are you saying it would not be protected?

Cable protection is fitted, by design at the supply end of the cable.
Go and read the standard.



No he isn't. The protection for the meter tails and CU itself is the
supplier main fuse.

As per the garage too.

No. The size of cable that would be used for a connection to the
garage would be too small to carry the current necessary to blow the
main fuse. Hence a lower value circuit breaker is installed *before*
the cable to the garage and *after* the main supplier fuse.

This is the safe combination.



--

..andy

To email, substitute .nospam with .gl

"Andy Hall" wrote in message
...
On Tue, 26 Jul 2005 22:03:42 +0100, "Doctor Drivel"
wrote:


"Andy Hall" wrote in message
.. .

I am not suggesting anything other than what I just said. That is
making
a
point with a man who doesn't know very much at all.

If you don't know very much at all about something, as has been
pointed out (so glad you realise the error of your ways),

No error in my suggestion to the OPs problem.

You've made about 6 different ones,

Nope the original still stands. Take off mcb run single cable cables
through conduit. In fact, my suggestion is just brilliant as usual.

"Andy Hall" wrote in message
news
On Tue, 26 Jul 2005 22:07:32 +0100, "Doctor Drivel"
wrote:

Are you saying it would not be protected?

Cable protection is fitted, by design at the supply end of the cable.
Go and read the standard.

So, it is protected.

On Tue, 26 Jul 2005 23:06:45 +0100, "Doctor Drivel"
wrote:


"Andy Hall" wrote in message
news
On Tue, 26 Jul 2005 22:07:32 +0100, "Doctor Drivel"
wrote:

Are you saying it would not be protected?

Cable protection is fitted, by design at the supply end of the cable.
Go and read the standard.

So, it is protected.

Go and read the standard.



--

..andy

To email, substitute .nospam with .gl

John Rumm wrote:

Matt wrote:

You are digging in the garden and manage to stick a spade into the
cable.


Wishful thinking!

Yup, that is what SWMBO is for! ;-)

But its far better to employ an under utilised plumbing counter
assistant to do the digging .....like Dr Drivel for instance.

No worries Drivel, there will be a 5A MCB in next doors garden shed
that will stop you getting vaporised.


--

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

Matt wrote:

You are digging in the garden and manage to stick a spade into the
cable.


Wishful thinking!

Yup, that is what SWMBO is for! ;-)

But

Some mothers...

snip witless moron

Doctor Drivel wrote:

MCBs rating then the supply cable is protect, if the cable is higher

rated

than the total of the garage CU MCBs. That is abundantly obvious.

Obvious yes, but dangerously neieve.


But protected. That is obvious

As I demonstrated it is *not* adequately protected. This *should* be
obvious.

A sub main feed to an outbuilding is unlikely to be sufficently large
for this to be the case.


You size to suit. I have said that all along.

I explicitly asked if you thus intended use of 35mm sq singles in your
conduit so as to ensure that the cable rating exceeded the main fuse
rating on a 100A supply. You answered "No".

Now you are saying yes?

Would you care to make your mind up please?

In this case the supply is
high level conduit.

The altitude is not relevant.



--
Cheers,

John.

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

Doctor Drivel wrote:
Which one looks neater is a matter of opinion. SWA is almost always
used between detached buildings.
Not for aesthetics.

Just because *you* can't run it neatly.

What's unappealing about the sensuously smooth curves of glossy black
PVC sheath neatly formed and clipped into place?

Owain