Couple of wiki articles for your delectation and comments:

This one came out of discussions we have had in the past about wiring
failures on rings and radials, and how each of them cope with the
faults. I have added stuff on detecting, repair and test as well:

http://wiki.diyfaq.org.uk/index.php?...Circuit_faults

At some point in that article, I found need to talk about crimping
cables. So thought that probably deserved a section on its own. So I did
a pictorial tutorial:

http://wiki.diyfaq.org.uk/index.php?...Cable_crimping

Comments here on on the wiki discussion page as you prefer.


--
Cheers,

John.

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

On Thu, 17 May 2007 01:11:35 +0100, John Rumm
wrote:


Couple of wiki articles for your delectation and comments:

This one came out of discussions we have had in the past about wiring
failures on rings and radials, and how each of them cope with the
faults. I have added stuff on detecting, repair and test as well:

http://wiki.diyfaq.org.uk/index.php?...Circuit_faults

At some point in that article, I found need to talk about crimping
cables. So thought that probably deserved a section on its own. So I did
a pictorial tutorial:

http://wiki.diyfaq.org.uk/index.php?...Cable_crimping

Comments here on on the wiki discussion page as you prefer.

An excellent piece of work. Thanks.

One comment would be a slight expansion about soldering, mentioned
only in passing, but of interest.

John Rumm wrote:
So I did
a pictorial tutorial:

http://wiki.diyfaq.org.uk/index.php?...Cable_crimping

I see your illustrative talents are not restricted to Sketchup! Great
stuff.

David

Lobster wrote:

I see your illustrative talents are not restricted to Sketchup! Great
stuff.

Yup I too can push a button! ;-)

(although it would have helped to have three hands at times - next time
I will take the tripod)

--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"John Rumm" wrote


Couple of wiki articles for your delectation and comments:


Excellent stuff John - thanks for your efforts.
One minor comment which may or may not be covered in the reference info is
the fact that your "shorted plug" will knock out all ciruits protected by a
common RCD.
Or maybe it's taken as read that all ciruits will be isolated not just the
subject one.

Phil

TheScullster wrote:
"John Rumm" wrote

Couple of wiki articles for your delectation and comments:


Excellent stuff John - thanks for your efforts.
One minor comment which may or may not be covered in the reference info is
the fact that your "shorted plug" will knock out all ciruits protected by a
common RCD.

That is a good point. I was trying to find a more "consumer friendly"
way of testing that did not involve opening the CU and disconnecting
wires there, and so came up with the plug based solution. Originally I
linked just L to N, but later when writing the bit on finding CPC
related faults the link to Earth came in handy. However that does
connect N to E indirectly.

Or maybe it's taken as read that all ciruits will be isolated not just the
subject one.

I shall spell that out a little more.

--
Cheers,

John.

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In article ,
John Rumm writes:

http://wiki.diyfaq.org.uk/index.php?...Cable_crimping

Comments here on on the wiki discussion page as you prefer.

Looks good. A few minor points/thoughts...

I would put a picture of the right tool somewhere near
the beginning or the article, not just the wrong tool,
and perhaps a pile of different size crimps.
(You could add pliers, mole wrench, and hammers to the
picture of wrong tools.)

"[screwed terminal] method is only acceptable where the joint
will remain accessible for future inspection and maintenance,
since screwed terminal connections can become loose over time."
Please provide a citation for such a justification.
(I don't believe that accurately describes the reason, and
Wiki's need to be accurate when giving facts like this, or
make it clear this is speculation of the author.)

In the sample damage you've shown, I would probably not have
cut and rejoined an undamaged conductor.

A blue crimp is the wrong size for the earth conductor. You
could use one if you folded the conductor double, or the
crimp has no central barrier such that you can push the
conductors through to overlap and crimp both conductors
together. Whilst in practice a blue crimp probably would
work OK as you have done, an article explaining how to
crimp probably should get this right.

It's probably worth explaining crimp sizes and colour
codes. Otherwise someone unfamiliar with them could well
think they need a red one on the live, a blue one on the
neutral and a yellow one on the earth ;-0

This is getting to the really minor nit level, but when I
join T&E, I usually stagger the joins even more than you did,
such that none of the crimps overlap at all. Then the cable
thickness doesn't increase as much at the join, and it can
if necessary be pulled through any holes with the cable intact.
This is something which might happen many years later without
gaining access the repair site (or even knowing about it).

This, like pipesoldering demos, is the bench demo. In real
life (TM) you'll be doing it in some corner where you can't
both feel and see what you're at the same time, you can't
swing the crimp tool into the right position and get any grip
on the handles, and there's only 2mm of conductor exposed
from a 3' thick bomb shelter wall ;-)

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Oh and one other thing, practice on some cable off-cuts first,
and try pulling your practice joins apart.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Andrew Gabriel wrote:

Looks good. A few minor points/thoughts...

I would put a picture of the right tool somewhere near
the beginning or the article, not just the wrong tool,

I did (sort of) by linking to the TLC site. But yup, a piccie can be
arranged.

and perhaps a pile of different size crimps.
(You could add pliers, mole wrench, and hammers to the
picture of wrong tools.)

Hacksaw ;-)

"[screwed terminal] method is only acceptable where the joint
will remain accessible for future inspection and maintenance,
since screwed terminal connections can become loose over time."
Please provide a citation for such a justification.
(I don't believe that accurately describes the reason, and
Wiki's need to be accurate when giving facts like this, or
make it clear this is speculation of the author.)

Which bit are you querying: that they come loose in the first place, or
that being the reason they need to remain accessible?

In the sample damage you've shown, I would probably not have
cut and rejoined an undamaged conductor.

I may lose the "before" picture since it adds nothing to the story I am
trying to tell really.

A blue crimp is the wrong size for the earth conductor. You
could use one if you folded the conductor double, or the
crimp has no central barrier such that you can push the
conductors through to overlap and crimp both conductors
together. Whilst in practice a blue crimp probably would
work OK as you have done, an article explaining how to
crimp probably should get this right.

I did think about this for a while, given that red is a better size
match as you say. However if you look at the spec I listed for blue, it
does show the minimum wire CSA as 1.04mm^2 which is acceptable on the
1.5mm^2 CPC in the 2.5mm^2 T&E I was illustrating.

It's probably worth explaining crimp sizes and colour
codes. Otherwise someone unfamiliar with them could well
think they need a red one on the live, a blue one on the
neutral and a yellow one on the earth ;-0

Good idea sir, I shall nick that!

I think a table etc is a very good idea. (might swipe some piccies to go
with it)

This is getting to the really minor nit level, but when I
join T&E, I usually stagger the joins even more than you did,
such that none of the crimps overlap at all. Then the cable
thickness doesn't increase as much at the join, and it can

;-) Yup so do I normally!

Only having cut them a tad short and already taken a few photo's I CBA
to start over.

This, like pipesoldering demos, is the bench demo. In real
life (TM) you'll be doing it in some corner where you can't
both feel and see what you're at the same time, you can't
swing the crimp tool into the right position and get any grip
on the handles, and there's only 2mm of conductor exposed
from a 3' thick bomb shelter wall ;-)

BTSTGTTS.

--
Cheers,

John.

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|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

At some point in that article, I found need to talk about crimping
cables. So thought that probably deserved a section on its own. So I
did a pictorial tutorial:

http://wiki.diyfaq.org.uk/index.php?...Cable_crimping

As someone who has not yet tried crimping for mains wiring I found this
very helpful. It left me with two small questions:

(i) wd it be helpful/possible to give a steer as to what size heatshrink
is suitable for common applications (eg 1.0mm and 2.5 twin & earth)? I
ask as TLC list 6mm etc heatshrink which left me scratching around to
find out if this is diameter or radius or what; and then off to work out
the circumference of "flat" cable. I think I got there in the end (eg
6242Y 2.5mm is approximately 9.5 x 5.25 so circumference rounds up to
30mm; heat shrink appears to be quoted by diameter so 12mm starts off at
38mm which should slide on and shrink nicely). But (a) I could be wrong
and (b) even if I am right in principle, in practice........?

(ii) when doing a few bits of heatshrinking for car and other low
voltage electrics over the years I found (in the days when I smoked) a
cheap, disposable cigarette lighter a handy tool. Would one of them be
ineffective (or otherwise unacceptable)?

Sorry if I am looking to be spoon-fed too much.
--
Robin

In article ,
Robin wrote:
(ii) when doing a few bits of heatshrinking for car and other low
voltage electrics over the years I found (in the days when I smoked) a
cheap, disposable cigarette lighter a handy tool. Would one of them be
ineffective (or otherwise unacceptable)?

I'd rather not use a naked flame for H&S reasons, although it can work ok.

Sorry if I am looking to be spoon-fed too much.

I actually have the correct hot air gun designed for heat shrink but never
use it as it's too slow. They are also pretty expensive. My preferred
device is a cheap dual heat hot air paint stripper gun bought from a shed
used on the low setting. It included a wrap round nozzle shield designed
to get the hot air to the back of a pipe etc so ideal for awkward cables.
I reserve this tool purely for this job and have another for general work.

--
*Bills travel through the mail at twice the speed of cheques *

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

Robin wrote:

As someone who has not yet tried crimping for mains wiring I found this
very helpful. It left me with two small questions:

(i) wd it be helpful/possible to give a steer as to what size heatshrink
is suitable for common applications (eg 1.0mm and 2.5 twin & earth)?

Yup, that's probably worth adding. (that was 12.7mm/ half inch tube I
was using)

I
ask as TLC list 6mm etc heatshrink which left me scratching around to
find out if this is diameter or radius or what; and then off to work out
the circumference of "flat" cable. I think I got there in the end (eg
6242Y 2.5mm is approximately 9.5 x 5.25 so circumference rounds up to
30mm; heat shrink appears to be quoted by diameter so 12mm starts off at
38mm which should slide on and shrink nicely). But (a) I could be wrong
and (b) even if I am right in principle, in practice........?

That sounds plausible. However each manufacturer may use a different way
of describing it. Diameter does seem to be common though.

(ii) when doing a few bits of heatshrinking for car and other low
voltage electrics over the years I found (in the days when I smoked) a
cheap, disposable cigarette lighter a handy tool. Would one of them be
ineffective (or otherwise unacceptable)?

No, it will work ok. Its a bit harder to direct than the proper hot air
tool, but I usually use a gas flame of some sort (a mini blow torch in
most cases)

Sorry if I am looking to be spoon-fed too much.

Not at all, not much use as a tutorial if it leave important questions
unanswered.

--
Cheers,

John.

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

In article ,
John Rumm wrote:
Comments here on on the wiki discussion page as you prefer.

One comment only - you say to use a purpose made heat gun to shrink the
heat shrink sleeving. These are very expensive and an ordinary hot air
paint stripping type can safely be used - just don't hold it stationary
too close for a long period. A dual heat type on low is the ideal. Hold
about 3 inches from the work and move from end to end until it shrinks.

--
*Parenthetical remarks (however relevant) are (usually) unnecessary *

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

Dave Plowman (News) wrote:
In article ,
John Rumm wrote:
Comments here on on the wiki discussion page as you prefer.

One comment only - you say to use a purpose made heat gun to shrink the
heat shrink sleeving. These are very expensive and an ordinary hot air
paint stripping type can safely be used - just don't hold it stationary
too close for a long period. A dual heat type on low is the ideal. Hold
about 3 inches from the work and move from end to end until it shrinks.

I did describe both (and I use a flame as well usually - or the
catalytic blow head on my micro torch). I thought I ought to include the
"approved" way as the first option, but you are right they are silly money.

--
Cheers,

John.

/================================================== ===============\
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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:

http://wiki.diyfaq.org.uk/index.php?...Circuit_faults

1. Wire resistance table: the figures seem rather high - they appear to
be circuit resistances (i.e. resistance of the phase-neutral loop) at 70
deg. C, as you would use for calculating voltage drop, or fault current
calculations. In the context of resistance measurements made "cold" you
need the figures at 20 deg. C, which are all in Table 9A of the OSG (p.
158). Also note spelling of "metre" :-)

You could refine the table by adding two more columns to give
resistances for a single conductor, for the P-N loop (R1+Rn) and for the
P-E loop (R1+R2) of twin & earth cables.

2. Resistance measurements: the method with a 3-pole shorting plug is
invalid unless you disconnect the relevant neutral at the CU. Remember
that N & E are also shorted at the supply end, in the DNO's cut-out for
PME and further back for TN-S, so there are parallel paths which will
invalidate your resistance calculation. I see you do say "one should
always ensure power is turned off at the main switch" but many will
disregard that, taking it only as a safety warning and not realising the
subtle effect it will have on the measurements.

3. Disconnected CPC, ring circuit "circuit safety mostly unaffected":
that's a rather sweeping statement and there will be cases where a
dangerous situation exists, due to inadequate thermal protection for a
CPC. The worst case is probably a broken CPC at one end of a long ring,
with the old-type 2.5 T&E which only has a 1.0 mm^2 CPC and with a 30 A
BS 3036 (rewireable) fuse. With an earth fault near the broken far end
you might find the CPC protects the fuse and the cable catches fire;
even if it doesn't, the disconnection time is likely to exceed 5 s, let
alone 0.4 s, and the touch voltage other metalwork separately earthed or
bonded to the MET will be over 70% of full mains voltage, so protection
against indirect contact is not achieved.

4. Ring continuity tests: the cross-connection method (per OSG, GN3 and
our FAQ) should be mentioned. It's very convenient, having
cross-connected the ends, to go round and measure resistance between L &
N at all sockets. If all is well you should measure the same resistance
value at all points. Ditto for cross-connection of L & E, except that
the resistance will rise slightly toward the point furthest from the
cross-connection, due to the higher resistance of the 1.5 mm^2 CPC.

--
Andy

Andy Wade wrote:

http://wiki.diyfaq.org.uk/index.php?...Circuit_faults

1. Wire resistance table: the figures seem rather high - they appear to
be circuit resistances (i.e. resistance of the phase-neutral loop) at 70
deg. C, as you would use for calculating voltage drop, or fault current
calculations. In the context of resistance measurements made "cold" you
need the figures at 20 deg. C, which are all in Table 9A of the OSG (p.
158). Also note spelling of "metre" :-)

Well spotted that man!

Indeed I did lift them from the wrong table (6E2 in OSG).

Is it just me, or do you spend ages looking for tables in that book that
you know are there, but can never seem to find when you need them?

You could refine the table by adding two more columns to give
resistances for a single conductor, for the P-N loop (R1+Rn) and for the
P-E loop (R1+R2) of twin & earth cables.

Probably worth doing a simplified version of 9A since the original
resistance table I originally only planed to use on L/N round trip,
since it does add other diagnostic options.

2. Resistance measurements: the method with a 3-pole shorting plug is
invalid unless you disconnect the relevant neutral at the CU. Remember
that N & E are also shorted at the supply end, in the DNO's cut-out for
PME and further back for TN-S, so there are parallel paths which will
invalidate your resistance calculation. I see you do say "one should
always ensure power is turned off at the main switch" but many will
disregard that, taking it only as a safety warning and not realising the
subtle effect it will have on the measurements.

Yup, I had already reworded that a bit, but I agree it is still not
clear about all the implications of not switching off.

3. Disconnected CPC, ring circuit "circuit safety mostly unaffected":
that's a rather sweeping statement and there will be cases where a
dangerous situation exists, due to inadequate thermal protection for a
CPC. The worst case is probably a broken CPC at one end of a long ring,
with the old-type 2.5 T&E which only has a 1.0 mm^2 CPC and with a 30 A
BS 3036 (rewireable) fuse. With an earth fault near the broken far end

Yes good point. I did some checks for modern cables and typical circuit
lengths, and it usually hangs together. However older installs are going
to be more vulnerable.

4. Ring continuity tests: the cross-connection method (per OSG, GN3 and
our FAQ) should be mentioned. It's very convenient, having
cross-connected the ends, to go round and measure resistance between L &
N at all sockets. If all is well you should measure the same resistance
value at all points. Ditto for cross-connection of L & E, except that
the resistance will rise slightly toward the point furthest from the
cross-connection, due to the higher resistance of the 1.5 mm^2 CPC.

Yup, personally I favour that method, although for a simple test here it
may get overly complex since we would need a fairly full discussion on
the variations in readings one will get on spurs etc. (There comes a
point where one is just duplicating swathes of the OSG!)


--
Cheers,

John.

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

Andy Wade wrote:

snip lots of good stuff

I have had a hack about. See if you think that strikes a better balance
with respect to safety on CPC faults. Also I have beefed up the
resistance table (and used the right source data this time!)

http://wiki.diyfaq.org.uk/index.php?...Circuit_faults


--
Cheers,

John.

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

John Rumm wrote:

I have had a hack about. See if you think that strikes a better balance
with respect to safety on CPC faults. Also I have beefed up the
resistance table (and used the right source data this time!)

http://wiki.diyfaq.org.uk/index.php?...Circuit_faults

Yes, that's much better. I've just done a few editorial tweaks too.

--
Andy

"John Rumm" wrote in message
...

Couple of wiki articles for your delectation and comments:

This one came out of discussions we have had in the past about wiring
failures on rings and radials, and how each of them cope with the faults.
I have added stuff on detecting, repair and test as well:

http://wiki.diyfaq.org.uk/index.php?...Circuit_faults

At some point in that article, I found need to talk about crimping cables.
So thought that probably deserved a section on its own. So I did a
pictorial tutorial:

http://wiki.diyfaq.org.uk/index.php?...Cable_crimping

Comments here on on the wiki discussion page as you prefer.


--
Cheers,

John.


John,
a nice article on testing thanks. A few points:

1. Since wiki is available world-wide should you say that you are referring
to UK standards?

2. Are you specifically targetting testing of sockets? If lighting
circuits are involved then there are other issues like switches being on for
testing (all combinations for 2 way switching), bulbs out.

3. Views on other tools? Neon testers (love or hate them?) Electronic
induction things (ditto)?

4. Suggest you add that conductors should be checked before you touch them
(Faulty switch? Wrong switch? Is it up or down for off?).
That you should ensure that others cannot alter switches.
That all circuits are isolated before you disconnect any wiring - even
neutrals (in case of cross connected circuits).

5. Is there a mismatch between the sort of meter you indicate and the sub
ohm values which you refer to in your tables on continuity testing? To
be honest you're probably only looking for an indicated value the same as
shorted leads or for no needle movement at all and I can't think of many
circumstances where that will not be adequate though it will be an issue if
you are completing test reports. Maybe you need to acknowledge that such
testing is on the limits of inexpensive meters?

6. How do you test RCD? Is the test button adequate? A plug with a big
fat resistance of 8K ohm between L and E? Mega expensive test meters which
time the disconnect?

7. How can you test that the earth to the house is okay? Continuity
between N and E?

8. A short glossary? CPC? RCD? MCB? T&E?

thanks again

Phil

Phil B wrote:

a nice article on testing thanks. A few points:

1. Since wiki is available world-wide should you say that you are referring
to UK standards?

I had taken that as kind of implicit since it does start off "Welcome to
the uk.d-i-y wiki!", but having said, that there is no harm in spelling
it out.

2. Are you specifically targetting testing of sockets? If lighting
circuits are involved then there are other issues like switches being on for
testing (all combinations for 2 way switching), bulbs out.

Power circuits were the main focus of the article, but lighting could
certainly be added. (might be worth restricting it to power circuits at
the moment)

3. Views on other tools? Neon testers (love or hate them?) Electronic
induction things (ditto)?

I agree that stuff should be in the wiki someplace, not sure this
particular article needs cluttering with that info though.

4. Suggest you add that conductors should be checked before you touch them
(Faulty switch? Wrong switch? Is it up or down for off?).

I have tried to spell out that the circuit needs to be off at the CU
main switch before getting into any testing.

That you should ensure that others cannot alter switches.

Yes that is worth adding.

That all circuits are isolated before you disconnect any wiring - even
neutrals (in case of cross connected circuits).

5. Is there a mismatch between the sort of meter you indicate and the sub
ohm values which you refer to in your tables on continuity testing? To

Yes there is. The details on resistance checks grew a little beyond the
scope of the basic continuity type tests that I was anticipating at the
start of writing it. Hence the meter I liked to is not appropriate for
some of the tests. (I specifically linked to an analogue type meter to
avoid getting sucked into any problems with false positives you can get
with voltage indications on very high impedance DMMs etc - however those
issues have not really become relevant in the article as it stands)

be honest you're probably only looking for an indicated value the same as
shorted leads or for no needle movement at all and I can't think of many
circumstances where that will not be adequate though it will be an issue if
you are completing test reports. Maybe you need to acknowledge that such
testing is on the limits of inexpensive meters?

I still want to try and keep it at a "useful to the end user" level
rather than let it get too technical, but I think a bit more guidance on
test gear is worth including. Also links to a reasonable DMM might be
appropriate as well as a couple of pointers to real test gear.

In reality the resistance info for anything much beyond 2.5mm^2 circuits
is not that relevant for most circumstances. However a reasonable DMM
will usually give you enough resolution (down to the tenth of an ohm) to
make reasonable use of the tables in more than a go/nogo way.

6. How do you test RCD? Is the test button adequate? A plug with a big
fat resistance of 8K ohm between L and E? Mega expensive test meters which
time the disconnect?

Slightly outside the scope of this article, although I have in mind a
big article on RCD issues in general that would include testing, and
tracking down sources of trips etc since that seems to be a frequent
topic of discussion here.

7. How can you test that the earth to the house is okay? Continuity
between N and E?

The tests using a socket tester would probably highlight a gross failure
of the external earth. However I feel that is getting a bit outside the
scope again. (I want to try and avoid having one article growing and
expanding into a universal document on electrical installations and
becoming so dense that it is impossible to get basic information out of.
I would rather have lots of smaller articles that focus on particular
topics where this is possible).

8. A short glossary? CPC? RCD? MCB? T&E?

Yup certainly, that is already noted in the discussion page as needed.



Thanks for that Phil, good points which I will try and incorporate.

--
Cheers,

John.

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