Hi,

I was reading somewhere about wiring those outdoor 150W (or 500W!)
halogen PIR lights. Different web sites and forums have given
different opinions and I am wondering what is right/best?

Since the light is mounted on a bracket away from the wall, it was
suggested that T&E should not be used because it is not flexible (OTOH
once positioned, will the lamp ever be moved again?). I also rad that
T&E is not UV stable.

Another suggestion was to put the T&E in conduit but another web site
said that only black conduit is UV stable. Is that true? if white
conduit were used would it eventually go brittle, and would it also
allow UV through, because if so, that would defeat the object of using
it in the first place.

Another forum said the correct cable to use was arctic cable because
being outdoors, the temperature can get very cold in winter but I've
only ever seen arctic in bright yellow or bright blue. I'm looking for
something prettier than black conduit or bright arctic cable!

I know I ought to drill through the wall and run the cable under the
floorboards, then I wouldn't need to worry about anything along the
outside of the house, but that means making sure I drill at the right
height into the floor void and not through the wallpaper of the room
above or below! It also means having to move furniture and carpets to
lift boards etc, which is a bit of a hassle.

TLC sell hituf, which claims to be UV resistant but is there anything
special in it to make it so, or is all black PVC UV resistant by
design? After all, aren't coax and external telephone cables black
too? Would any old black flex do?

TIA

Fred wrote:
Hi,

I was reading somewhere about wiring those outdoor 150W (or 500W!)
halogen PIR lights. Different web sites and forums have given
different opinions and I am wondering what is right/best?

OK

Since the light is mounted on a bracket away from the wall, it was
suggested that T&E should not be used because it is not flexible (OTOH
once positioned, will the lamp ever be moved again?).

If lamp will not be moved, then it's not a problem. If the lamp is
hanging by the cable, then the cable needs to be a flexible cord.

I also rad that T&E is not UV stable.

It's not, but again, it's generally not a problem if the T&E is undisturbed.


Another suggestion was to put the T&E in conduit but another web site
said that only black conduit is UV stable.

Correct. As a general rule, black cable, conduit (or indeed cable ties
and cable clips) is/are UV resistant (stable is probably not the correct
word) and if they're white or grey or "natural" then they're not UV
resistant.

Is that true? if white
conduit were used would it eventually go brittle, and would it also
allow UV through, because if so, that would defeat the object of using
it in the first place.

I doubt very much that white conduit would let a significant amount of
UV through.


Another forum said the correct cable to use was arctic cable because
being outdoors, the temperature can get very cold in winter but I've
only ever seen arctic in bright yellow or bright blue.

Arctic cable is just a special grade of PVC which stays flexible at low
temperatures. But you don't need flexibility and Arctic grade PVC is not
UV resistant (unless it's black of course).

I'm looking for
something prettier than black conduit or bright arctic cable!

Just use T&E and be done with it.


I know I ought to drill through the wall and run the cable under the
floorboards, then I wouldn't need to worry about anything along the
outside of the house, but that means making sure I drill at the right
height into the floor void and not through the wallpaper of the room
above or below! It also means having to move furniture and carpets to
lift boards etc, which is a bit of a hassle.

If you can (and you usually can), you should drill from the inside out,
so you don't have to dead-reckon the height. However, if you are too
gung-ho, you can break off a chunk of brick when you burst through. This
is ugly, so if you do drill from inside out, use an SDS drill and be
careful.


TLC sell hituf, which claims to be UV resistant but is there anything
special in it to make it so, or is all black PVC UV resistant by
design?

It is the "black" that makes PVC and Nylon (and possibly other plastics,
but PVC and Nylon for sure) UV Resistant.

After all, aren't coax and external telephone cables black
too? Would any old black flex do?

You could use black flexible cord and black cable clips, yes.

HTH
DaveyOz

Arctic cable does not have BASEC approval and some "knock-offs" are
very rough with the insulated cores clearly visible through the
insulation. It is likely Arctic cable will be depreciated in favour of
H07RNF in the future, the N = Neoprene which is tough, rot proof,
waterproof & UV stable.

Generally black things have carbon black loading, which makes them UV
resistant. White or cream on the other hand depends on UV additives
which unless BASF-quality in the right quantity tend to be rather
poor.

TLC do offer black rubber cable, but do not indicate what the cable
actually is. H05RRF has R = Rubber sheath, but that has a finite life.
H07RNF has N = Neoprene sheath, which has a much longer life. H =
Harmonised, 05 = 300/500V insulation, 07 = 500/700V, R = Rubber, N =
Neoprene, F = Fine strand. You can see why 05 is sold becuase UK 1ph
domestic is 240/330V (RMS/Peak) and so does not require the noticeably
thicker insulation of 07 rated cable. However, that misses the point
about the sheath being Rubber v Neoprene.

From ordering cable form TLC in the past, I think their rubber cable
is H07RNF - perhaps they pick up the post.

The ideal would be H07RNF in 1.0mm (10A rating), a few sparks use
1.5mm but that is a bit too large in diameter. You can fix via nail
clips or because it is flex it may be better to drill / plug / screw
with black nylon P-clips available on Ebay which work rather
attractively. FP200 cable in white attracts some, but unless it is
Prysmian FP200GOLD it will have silicone insulation which is
vulnerable to "nicks" during termination.

At the light fitting, use a drip loop (dip the cable before entering
the light) and sleeve the wall penetration. Ebay lists black nylon
16mm o.d. (outer diameter) flexible conduit at about £3 for 3m, that
will take most domestic cables with ease and allows you to use a 16mm
masonry drill which is not difficult to use (drill 8mm 12mm 16mm if
you have a simple percussion non-SDSI drill).

js.b1 wrote:

snip
TLC do offer black rubber cable, but do not indicate what the cable
actually is. H05RRF has R = Rubber sheath, but that has a finite life.
H07RNF has N = Neoprene sheath, which has a much longer life. H =
Harmonised, 05 = 300/500V insulation, 07 = 500/700V,

pedant mode = on

Close: 05 = 300/500V, 07 = 450/750V

R = Rubber, N =
Neoprene, F = Fine strand. You can see why 05 is sold becuase UK 1ph
domestic is 240/330V (RMS/Peak)

Close: 240/340V (i.e. 240 x sqrt2 = 339.4), but I'm sure you knew that ;-)

pedant mode =off


and so does not require the noticeably
thicker insulation of 07 rated cable.

True, but the 300/500V rating is not 300V rms/500V peak. The 300V
represents the rms potential difference conductor-to-earth and the 500V
represents the max. rms potential difference conductor-to-conductor[1],
so your reference to the peak voltage is a red-herring ;-(.


However, that misses the point
about the sheath being Rubber v Neoprene.

From ordering cable form TLC in the past, I think their rubber cable
is H07RNF - perhaps they pick up the post.

The ideal would be H07RNF in 1.0mm (10A rating), a few sparks use
1.5mm but that is a bit too large in diameter.

You could also use cable advertised as suitable for ponds, sometimes
referred to as UK type 3183P. This is equivalent to (or the same as) HAR
H05RN-F


;-)
DaveyOz



[1] 300/500V is expressed in the form Uo/U, whe

Uo is the voltage between conductor and earth or conductor and earthed
metallic cover (concentric conductor screen, armouring or metal sheath).
U is the voltage between phase conductors.

As there is no concentric conductor screen, armouring or metal sheath on
a H05/H07 cable, the Uo value is effectively the voltage between the
phase conductor and earth conductor.

So, for a single phase supply, Uo (phase to earth) is nominally 230V and
U (phase - neutral) is nominally 230V.

For a three phase supply wired in star, Uo (phase to earth) is nominally
230V and U (phase-phase) is nominally 400V.

So, you can use H05 for a 3-phase supply, but suppliers generally don't
offer H05 in high-current four or five wire versions.

On Aug 31, 1:24*pm, Dave Osborne wrote:
You could also use cable advertised as suitable for ponds, sometimes
referred to as UK type 3183P. This is equivalent to (or the same as) HAR
H05RN-F

Ah yes, 3183P is easier to search for.
Ebay item 20570576754 is 3x 0.75mm H05RN-F 10m, lots of online places
do it from a Google.

For H07RNF (such as extension leads) the marquee suppliers do it
65-76p/metre, www.10outof10.com for example (no connection, just used
them).

js.b1 wrote:
On Aug 31, 1:24 pm, Dave Osborne wrote:
You could also use cable advertised as suitable for ponds, sometimes
referred to as UK type 3183P. This is equivalent to (or the same as) HAR
H05RN-F

Ah yes, 3183P is easier to search for.
Ebay item 20570576754 is 3x 0.75mm H05RN-F 10m, lots of online places
do it from a Google.

For H07RNF (such as extension leads) the marquee suppliers do it
65-76p/metre, www.10outof10.com for example (no connection, just used
them).

Yes, I'll give 10outof10 ten out of ten as well. :-)

Fred wrote:
Hi,

I was reading somewhere about wiring those outdoor 150W (or 500W!)
halogen PIR lights. Different web sites and forums have given
different opinions and I am wondering what is right/best?

Since the light is mounted on a bracket away from the wall, it was
suggested that T&E should not be used because it is not flexible (OTOH
once positioned, will the lamp ever be moved again?). I also rad that
T&E is not UV stable.

Another suggestion was to put the T&E in conduit but another web site
said that only black conduit is UV stable. Is that true? if white
conduit were used would it eventually go brittle, and would it also
allow UV through, because if so, that would defeat the object of using
it in the first place.

Another forum said the correct cable to use was arctic cable because
being outdoors, the temperature can get very cold in winter but I've
only ever seen arctic in bright yellow or bright blue. I'm looking for
something prettier than black conduit or bright arctic cable!

I know I ought to drill through the wall and run the cable under the
floorboards, then I wouldn't need to worry about anything along the
outside of the house, but that means making sure I drill at the right
height into the floor void and not through the wallpaper of the room
above or below! It also means having to move furniture and carpets to
lift boards etc, which is a bit of a hassle.

TLC sell hituf, which claims to be UV resistant but is there anything
special in it to make it so, or is all black PVC UV resistant by
design? After all, aren't coax and external telephone cables black
too? Would any old black flex do?

TIA

There is absolutely nothing wrong with good old ordinary grey T&E in my
experience. The back of our house is south facing so gets the sun almost all
day. About 18 years ago, maybe even 20 or 21 years ago, I ran a length of
grey T&E (probably about 6m) to a light and about 3 months ago I needed to
take the cable off the wall for something. It was still flexible and bent
easily, with no cracking or any stiffness whatsoever.

Just use ordinary grey T&E and don't fuss about it :-)

For H07RNF (such as extension leads) the marquee suppliers do it
65-76p/metre, www.10outof10.com for example (no connection, just used
them).

actually 10outof10.co.uk

On Tue, 31 Aug 2010 11:22:13 +0100, Dave Osborne
wrote:


Correct. As a general rule, black cable, conduit (or indeed cable ties
and cable clips) is/are UV resistant (stable is probably not the correct
word) and if they're white or grey or "natural" then they're not UV
resistant.

Thanks. That's exactly what I was wondering: whether all black cable
was intrinsically UV resistant because if so I could buy "any old"
black flex rather than pay for hightuf or some other flex which is
over-spec'd for my purpose.

Just use T&E and be done with it.

I have been reassured by the posts here so I probably will do just
that, thanks.

If you can (and you usually can), you should drill from the inside out,

I hadn't thought of that!

I was thinking drilling from outside allowed you to drill through the
mortar rather than the brick but that's not important unless you
remove the flex later and need to fill the hole.

HTH

It certainly did. Thanks again.

On Tue, 31 Aug 2010 04:05:45 -0700 (PDT), "js.b1"
wrote:

Arctic cable does not have BASEC approval and some "knock-offs" are
very rough with the insulated cores clearly visible through the
insulation.

I didn't know that. I bought some from Screwfix a long time ago. I
hope that's ok, I certainly don't remember seeing any cores through
the outer yellow sheath. I bought it because I was making an extension
lead IIRC. I notice that such leads usually come with orange flex. I
guess that's so you see them and don't trip over them. I couldn't find
anyone selling orange at the time, so bought this simply because of
its bright colour.

Generally black things have carbon black loading, which makes them UV
resistant.

Thanks. Just what I wanted to know.

TLC do offer black rubber cable, but do not indicate what the cable
actually is. H05RRF has R =3D Rubber sheath, but that has a finite life.
H07RNF has N =3D Neoprene sheath, which has a much longer life.

Very interesting, thanks. I see they also sell good old pvc in black
too. Are the rubber and neoprene significantly better uv-wise than
pvc? I see you say rubber has a finite life; how finite?

Are there any other reasons not to use pvc? What is the neoprene like
to use? I thought rubber was a pig to cut? Is neoprene any better in
that regard?

The ideal would be H07RNF in 1.0mm (10A rating), a few sparks use
1.5mm but that is a bit too large in diameter

I'm only using a 150W lamp so it wouldn't be pulling much current.
OTOH I suppose buying a thicker one means any left over will be more
versatile. A 6A flex might have limited uses.

Thanks again.

On Tue, 31 Aug 2010 13:53:46 +0100, John Rumm
wrote:

Depends on the conduit. However if the only purpose of the conduit is UV
shielding then it will be fine. You don't really care if it cracks a bit
on goes brittle so long as it keeps the bulk of the UV off the cable.

But if the conduit cracked so much it needed replacing, that would be
a pain having to remove and then re-thread the cable.

I doubt I'll use conduit now since it is bigger and therefore more
noticeable (unsightly) than cable on its own.

Arctic is really designed to remain easy to handle (and see) in a wide
range of temperatures. Its not well suited to fixed wiring.

Why? Is it because it is so flexible that it sags?

Measure carefully, and a set of cable rods?

The joists run the wrong way so I would have to lift boards and drill
unfortunately.

Thanks.

On Wed, 01 Sep 2010 23:40:27 +0100, John Rumm
wrote:

They normally use yellow for 110V leads, and blue for 240V on building
sites etc.

Thanks. I wondered why arctic flex was also made in blue. I thought
yellow was for visibility, but now that you have explained that it
makes sense because it matches the colours of the plugs and sockets.

My comments re. orange, non-arctic, flex were based on extension leads
and lawn mower leads at (my) home.

Thanks again.

On Wed, 01 Sep 2010 23:55:14 +0100, John Rumm
wrote:

Partly. Mainly because its a flex and not a cable. Hence the usual
problems of flexes - limted maximum size

Well in this application it is only going to a lamp, so I don't need
it to be very big. I'm sure 0.75mm^2 would be more than enough for me.

Spade bit and a few extensions can cut down the number dramatically. ;-)

That sounds like a good idea! Do those extension pieces really work?
I've only ever heard bad reviews for them.

Thanks again.

On Fri, 03 Sep 2010 03:26:34 +0100, John Rumm
wrote:

I am referring to the long (say 30cm) bars that grip a spade bit in one
end and go in a drill

Yes, I know what you mean, only the reviews I have read have often
complained that the grub screws do not hold the bit/next extension
very securely, or that they protrude enough that bits 13mm cannot be
used (though I realise that 13mm is not that useful for cable
anyway). I suppose that if you are certain there are no pipes or other
cables in the way, they could be a useful way forward. I'll have to
get some and try, failing that reconsider where to put the light
switch and route the cable a different direction. Thanks.

On Tue, 31 Aug 2010 13:24:20 +0100, Dave Osborne
wrote:


True, but the 300/500V rating is not 300V rms/500V peak. The 300V
represents the rms potential difference conductor-to-earth and the 500V
represents the max. rms potential difference conductor-to-conductor[1],
so your reference to the peak voltage is a red-herring ;-(.

Hello again,

I know we've agreed T&E should be ok but this got me looking at web
sites selling cables. I notice that there is 0.75mm^2 flex rated at 6A
and rated for 300V, whilst a more expensive version is still rated at
6A but rated for 500V. This surprised me because I was (naively?)
expecting that if a cable with the same CSA carried more amps, it
woul;d have to do so at a lower voltage. Is the maximum voltage
completely unrelated to CSA? Is only the maximum current dependent on
that?

What is the advantage of 500V rated flex? Is 300V used domestically
and 500V used in 3-phase (450V?) supplies?

One last question, I've also found "heat resistant flex" for sale.
Some of it is intended to be used around boilers, boilers are hot, so
I can understand that but it also says for use on light pendants. I
guess heat rises and 100W light bulb gets hot. But then I also see
other flexes (particularly two core) listed as for use with light
pendants and they are not specifically labeled "heat resistant". So
should a pendant use heat resistant flex or can it be any old flex?
I'm confused!

TIA

On Fri, 03 Sep 2010 15:55:21 +0100, John Rumm
wrote:

If you have bits with flats on the drill end then its not usually a
problem.

I had to think about that. Are you saying that if there is a hex shank
on the bit, the grub screws go further in than on bits with round
shanks?

I was only going from what I had read on the Screwfix review IIRC,
which said the screws either stuck out too far or fell out in use!

The ones on mine don't protrude much, but then again, you
usually want a 16mm hole or bigger to get a couple of cables through
easily - especially if poking through from an adjacent joist.

I thought you could only group light cables through the same hole? If
two ring main cables go through the same hole, don't they have to be
derated? I thought the derating took them below the useful value for a
ring? But I haven't read the OSG to check. I could be wrong

On Aug 31, 9:30*am, Fred wrote:
Hi,

I was reading somewhere about wiring those outdoor 150W (or 500W!)
halogen PIR lights. Different web sites and forums have given
different opinions and I am wondering what is right/best?

Since the light is mounted on a bracket away from the wall, it was
suggested that T&E should not be used because it is not flexible (OTOH
once positioned, will the lamp ever be moved again?). I also rad that
T&E is not UV stable.

Another suggestion was to put the T&E in conduit but another web site
said that only black conduit is UV stable. Is that true? if white
conduit were used would it eventually go brittle, and would it also
allow UV through, because if so, that would defeat the object of using
it in the first place.

Another forum said the correct cable to use was arctic cable because
being outdoors, the temperature can get very cold in winter but I've
only ever seen arctic in bright yellow or bright blue. I'm looking for
something prettier than black conduit or bright arctic cable!

I know I ought to drill through the wall and run the cable under the
floorboards, then I wouldn't need to worry about anything along the
outside of the house, but that means making sure I drill at the right
height into the floor void and not through the wallpaper of the room
above or below! It also means having to move furniture and carpets to
lift boards etc, which is a bit of a hassle.

TLC sell hituf, which claims to be UV resistant but is there anything
special in it to make it so, or is all black PVC UV resistant by
design? After all, aren't coax and external telephone cables black
too? Would any old black flex do?

TIA

T&E is ok in sunlight, theres lots of it currently in such use. It
does degrade but only very slightly over decades, not enough to cause
a problem. If youre feeling paranoid, a coat of household gloss can
block uv, and it bonds to the cable well.


NT

On Wed, 08 Sep 2010 01:06:25 +0100, John Rumm
wrote:

Grouping factors usually apply to cables which run together for a
distance - a couple of inches of close proximity is not a problem. Note
also that you don't include grouping for cables in the same circuit. So
a "to" and "from" pair forming part of a ring would be ok anyway.

I never realised that cables in the same circuit could be grouped. I
saw a bit of a recent DIY SOS episode and it looked as though they
were running two cables through one hole, so that would explain how
they could do that. What is the reasoning behind that? I thought it
was all to do with cables getting hot, so why would it matter whether
the wires were on the same circuit or not? If anything, wouldn't being
on the same circuit mean they both get hot at the same time? Thanks.

Fred wrote:
On Tue, 31 Aug 2010 13:24:20 +0100, Dave Osborne
wrote:

True, but the 300/500V rating is not 300V rms/500V peak. The 300V
represents the rms potential difference conductor-to-earth and the 500V
represents the max. rms potential difference conductor-to-conductor[1],
so your reference to the peak voltage is a red-herring ;-(.

Hello again,

I know we've agreed T&E should be ok but this got me looking at web
sites selling cables. I notice that there is 0.75mm^2 flex rated at 6A
and rated for 300V, whilst a more expensive version is still rated at
6A but rated for 500V. This surprised me because I was (naively?)
expecting that if a cable with the same CSA carried more amps, it
woul;d have to do so at a lower voltage. Is the maximum voltage
completely unrelated to CSA? Is only the maximum current dependent on
that?


Voltage rating and current rating for cables are somewhat related.

In simple terms, the current rating of a cable is based on the maximum
current that the cable will pass before it the core temperature of the
copper reaches a certain point. There are a number of standard "points",
the two lowest being 60 deg C and 85 deg C.

Note (as an aside) that the fusing current of the same cable is very
much higher than the maximum continuous current in-service.

A cable may or may not be insulated and may or may not be sheathed (and
indeed armoured and/or screened and over-sheathed).

Basically, the insulation exists to stop current flowing where you don't
want it to flow and the sheath has a number of functions, viz:

1. to bunch together a number of insulated conductors to form a
multi-core cable.
2. to provide additional insulation (from a "belt and braces perspective").
3. to protect the insulation from mechanical abrasion.
4. to protect the insulation from external heat.

Now, the dielectric strength of PVC is about 21kV per mm, so the
insulation rating of a domestic PVC cable has little to do with the
thickness of the insulation per se (which is always going to be
adequate), rather it is a matter of perceived risk or shock if the
insulation is breached by abrasion. That is to say a cable which is
officially rated at 300V is probably good for 10kV as an insulator, but
not good enough for the perceived risk of a 500V shock in terms of its
abrasion resistance.

In summary, the current/voltage rating of a cable is a function of heat
and abrasion resistance and informs the csa of the copper and the type
and thickness of the insulation and the type and thickness of the sheath.



What is the advantage of 500V rated flex?

It can be used on three-phase supplies. On single phase supplies, for
the same current-rating it is physically more robust.


Is 300V used domestically
and 500V used in 3-phase (450V?) supplies?


Essentially, yes, but you may still wish to use 500V rated cable on a
single phase supply for extra physical robustness.

One last question, I've also found "heat resistant flex" for sale.
Some of it is intended to be used around boilers, boilers are hot, so
I can understand that but it also says for use on light pendants. I
guess heat rises and 100W light bulb gets hot. But then I also see
other flexes (particularly two core) listed as for use with light
pendants and they are not specifically labeled "heat resistant". So
should a pendant use heat resistant flex or can it be any old flex?
I'm confused!


A pendant should use heat-resistant flex. Two-core non heat-resistant
flex can be used (e.g.) for double-insulated table lamps, where the bulb
is "cap-down" and the heat rises away from the cap.

On Wed, 08 Sep 2010 01:06:25 +0100, John Rumm
wrote:

But ISTM that if they
grip the shank well well enough, then how far they stick out hardly
matters (with larger spade bits)

Thinking about it, I have used an extension piece in the past and that
was with a bit with flats on the shank and I didn't have any problems.
Perhaps it was just one particular make that attracted bad reviews? I
can see how protruding screws could get in the way with narrow spades
but like you say, how often is a narrow hole useful? 16mm seems a good
size for cabling.

On Wed, 08 Sep 2010 01:16:35 +0100, John Rumm
wrote:

Not sure your observation ties in with the example given (i.e. both
cables rated at 6A).

Oh, I thought we were saying the same thing: that the maximum current
is limited by the CSA and voltage is irrelevant so that's why both
were rated at 6A because they both had the same CSA?

I think the two I found we

http://cpc.farnell.com/pro-power/218...blk/dp/CB11181

http://cpc.farnell.com/pro-power/318...blk/dp/CB11206

The only difference appears to be the rated voltage.

Perhaps that you can use the higher rated one in proximity to other
circuits where there is a phase to phase OD exceeding 300V. Say cables
running in a duct that are connected to different phases.

But in a domestic situation there wouldn't be another phase, so I
guess for the uses I would encounter, the 300V cable would be fine?

Heat resistant is good for boiler and immersion heater connections, or
other appliances that get hot. Using it for lamp flexes might be
overkill unless you have a particularly hot running halogen or something
that is prone to scorching normal flex.

Do people ever change the pendant flex I wonder? I would guess it's
easier to change the whole pendant. So I suppose the conclusion here
is that for lighting there's probably no need to pay the premium for
the heat resistant flex. Around a boiler can see that it is a very
good idea. I thought there was some discussion here though that even
heat resistant pvc wasn't enough for immersion cables and that they
should be rubber?

Thanks.

Fred wrote:
On Tue, 31 Aug 2010 04:05:45 -0700 (PDT), "js.b1"
wrote:

Arctic cable does not have BASEC approval and some "knock-offs" are
very rough with the insulated cores clearly visible through the
insulation.

I didn't know that. I bought some from Screwfix a long time ago. I
hope that's ok, I certainly don't remember seeing any cores through
the outer yellow sheath. I bought it because I was making an extension
lead IIRC. I notice that such leads usually come with orange flex. I
guess that's so you see them and don't trip over them. I couldn't find
anyone selling orange at the time, so bought this simply because of
its bright colour.

Generally black things have carbon black loading, which makes them UV
resistant.

Generally, on building sites Yellow = 55-0-55 (aka 110V) and blue = 240V.

Orange is sometimes, but not always "arctic grade" and is used for
domestic garden machinery flex and for camping/caravanning flex.


Thanks. Just what I wanted to know.

TLC do offer black rubber cable, but do not indicate what the cable
actually is. H05RRF has R =3D Rubber sheath, but that has a finite life.
H07RNF has N =3D Neoprene sheath, which has a much longer life.

Very interesting, thanks. I see they also sell good old pvc in black
too. Are the rubber and neoprene significantly better uv-wise than
pvc? I see you say rubber has a finite life; how finite?

The main problems with PVC are relatively poor abrasion resistance and
relatively high stiffness at low temperatures. If you've tried to use an
old PVC extension outdoors in the winter, you'll know what I mean.

Arctic grade PVC addresses the issue of low-temperature flexibility, but
has no better abrasion resistance.

PVC generally has poor heat resistance, poor chemical resistance, is not
considered to be fully waterproof for long-term fully-submerged use, has
moderately good UV resistance (good UV resistance if black) and under
good conditions, indefinite life.

Natural rubber is better than PVC in every way except rubber has poor UV
resistance, similar abrasion resistance and only moderate life,
(particularly) where exposed to lots of heat.

Synthetic rubber AKA PCP, polychloroprene, Neoprene or "that stuff they
make wetsuits out of" is better than PVC in every way, except perhaps
overall longevity (and the jury's out on that).

Note that pretty much all cables get less flexible as they age. This is
due to a combination of degradation of the polymers and age-hardening of
the copper.



Are there any other reasons not to use pvc? What is the neoprene like
to use? I thought rubber was a pig to cut? Is neoprene any better in
that regard?

Cutting rubber/Neoprene is not a problem at all.

On Wed, 08 Sep 2010 20:42:21 +0100, Dave Osborne
wrote:

Orange is sometimes, but not always "arctic grade" and is used for
domestic garden machinery flex

Yes, that's where I had seen it

The main problems with PVC are relatively poor abrasion resistance and
relatively high stiffness at low temperatures. If you've tried to use an
old PVC extension outdoors in the winter, you'll know what I mean.

Arctic grade PVC addresses the issue of low-temperature flexibility, but
has no better abrasion resistance.

PVC generally has poor heat resistance, poor chemical resistance, is not
considered to be fully waterproof for long-term fully-submerged use, has
moderately good UV resistance (good UV resistance if black) and under
good conditions, indefinite life.

Natural rubber is better than PVC in every way except rubber has poor UV
resistance, similar abrasion resistance and only moderate life,
(particularly) where exposed to lots of heat.

You mentioned moderately good UV resistance, so perhaps that explains
why some people have reported success with T&E outside? I was
surprised to read that rubber has poorer UV resistance, as TLC
suggested I used rubber when I asked which flexes were most UV
resistant. I was also surprised to learn rubber has moderate life when
exposed to heat; all the immersion heater cable I have seen has been
rubber, or perhaps it is a special type of rubber? All very
interesting stuff, thank you very much.

On Thu, 09 Sep 2010 02:18:34 +0100, John Rumm
wrote:

However, some more solid information: grouping factors assume that the
cables in question are carrying close to their maximum load. So two legs
of a ring circuit, ought not be de-rated by the full grouping factor
since even if the circuit were fully loaded, the current per leg would
still be well short of the cables capacity (assuming not other factors
at play here).

Also cables that carry 30% or less of the cables current carrying
capacity can be ignored altogether (so in domestic situations that would
include most lighting circuits).

The impact of these is that grouping rarely comes into play in domestic
situations.

A quick look up on the TLC web site says that 1.5mm^2 T&E is rated for
18A (obviously that's clipped onto the wall and it would be lower if
in conduit, under insulation, etc). Even with 100W light bulbs, that's
a lot of lamps before you reach 18A, so yes, I had heard before that
grouping could be ignored for domestic light circuits.

I hadn't realised the same applied to ring mains because I thought it
would be fairly easy to load these. For example in the winter in a
house with only one ring: a kettle, tumbler drier, and fan heater
could all be getting on for 3kW each. I realise there are holes in
this argument: the kettle only being on temporarily, using CH instead
of fan heaters, etc.

Looking again at TLC, it says 2.5mm^2 T&E is rated at 24A. Since a
ring has a 32A MCB, each leg will carry 16A at full load, which is
24-16=8A below the limit of the cable. 8/24=1/3, or as you said 30%
below the limit. So it would appear that you are right; they can be
grouped together. I never expected that.

Perhaps it is only when the cable has to be derated because it runs in
conduit or insulation that you have to be more careful in a domestic
setting?

ISTR that a radial in 2.5MM^2 is protected by a 20A MCB, in which case
20/24 1/3, so perhaps a radial near full load needs more
consideration? But OTOH a radial only has one cable so there is not
another cable to have to group it with, so perhaps that solves that?

Don't worry, I'm not planning on rewiring the house or anything, just
it is interesting to know these things. If I ever did do any major
work I would rely on something more official than the TLC web site

Thanks again.

On Wed, 08 Sep 2010 20:25:23 +0100, Dave Osborne
wrote:

That is to say a cable which is
officially rated at 300V is probably good for 10kV as an insulator, but
not good enough for the perceived risk of a 500V shock in terms of its
abrasion resistance.

That's interesting, thanks. I would have thought that if a cable got
abraded enough to expose the cores and risk a 300V shock, that would
be just as nasty as a 500V shock! Or is it that 500V is more likely to
arc than 300V?

you may still wish to use 500V rated cable on a
single phase supply for extra physical robustness.

So the difference is the 500V flex is probably a bit thicker.

A pendant should use heat-resistant flex. Two-core non heat-resistant
flex can be used (e.g.) for double-insulated table lamps, where the bulb
is "cap-down" and the heat rises away from the cap.

That explains it; I had forgotten that not all light fittings are on
the ceiling! What makes the heat-resistant flex different: do they add
something extra to the PVC?

Fred wrote:

ISTR that a radial in 2.5MM^2 is protected by a 20A MCB, in which case
20/24 1/3, so perhaps a radial near full load needs more
consideration? But OTOH a radial only has one cable so there is not
another cable to have to group it with, so perhaps that solves that?

But a radial circuit can branch out into more than one leg. The situation
might arise where the circuit splits at a junction box in an accessible
position but the two cables run alongside each other through a few joists
before diverging in a position where it would have been impracticable to
locate the junction box.

There's also the situation where a single radial cable doubles back on
itself before going to the next accessory.

--
Mike Clarke

John Rumm wrote:
On 10/09/2010 09:52, Fred wrote:

resistant. I was also surprised to learn rubber has moderate life when
exposed to heat; all the immersion heater cable I have seen has been
rubber, or perhaps it is a special type of rubber? All very
interesting stuff, thank you very much.

Immersion cable is probably silicone rather than VIR or TRS...


Immersion Heater cable (3183TQ) is EPR insulated and CSP sheathed.

EPR = Ethylene Propylene Rubber.

CSP = Chlorosulphonated Polyethylene AKA Hypalon (a synthetic rubber
invented by Dupont; similar to Neoprene).

This flex is also called butyl flex or HOFR flex.

The butyl reference is now incorrect as the insulation is EPR, not butyl.

HOFR stands for "Heat Oil and Fat Resistant".

On Fri, 10 Sep 2010 14:47:14 +0100, Mike Clarke
wrote:


But a radial circuit can branch out into more than one leg. The situation
might arise where the circuit splits at a junction box in an accessible
position but the two cables run alongside each other through a few joists
before diverging in a position where it would have been impracticable to
locate the junction box.

There's also the situation where a single radial cable doubles back on
itself before going to the next accessory.

So in these situations I guess you have to be more careful about
grouping?

On Fri, 10 Sep 2010 21:53:09 +0100, Dave Osborne
wrote:

Immersion cable is probably silicone rather than VIR or TRS...


Immersion Heater cable (3183TQ) is EPR insulated and CSP sheathed.

EPR = Ethylene Propylene Rubber.

CSP = Chlorosulphonated Polyethylene AKA Hypalon (a synthetic rubber
invented by Dupont; similar to Neoprene).

This flex is also called butyl flex or HOFR flex.

The butyl reference is now incorrect as the insulation is EPR, not butyl.

Well there's a lot there that I didn't know. Thank you. I was only
going by what I had seen in passing on the tlc web site, which says
PVC and butyl (which I assumed was rubber)
http://www.tlc-direct.co.uk/Main_Ind...tyl/index.html
http://www.tlc-direct.co.uk/Main_Ind...ant/index.html

You said the butyl reference is out of date, perhaps the reference to
pvc is too?

BTW I said in an earlier post that the 300V cable was cheaper than the
500V version.

I see that TLC sell the 500V version by default:
http://www.tlc-direct.co.uk/Products/CA0dot75F3B.html

and I have had a flyer from cpc in which the 500v is cheaper than the
300v, so there's no reason not to "upgrade" to the 500v rated flex. I
think there were some specs on cpc that said the 300v flex had an
overall diameter of 6.1mm and the 500v flex was 6.6mm. I never thought
that half a millimeter would make so much difference!

Fred wrote:
On Fri, 10 Sep 2010 21:53:09 +0100, Dave Osborne
wrote:

Immersion cable is probably silicone rather than VIR or TRS...

Immersion Heater cable (3183TQ) is EPR insulated and CSP sheathed.

EPR = Ethylene Propylene Rubber.

CSP = Chlorosulphonated Polyethylene AKA Hypalon (a synthetic rubber
invented by Dupont; similar to Neoprene).

This flex is also called butyl flex or HOFR flex.

The butyl reference is now incorrect as the insulation is EPR, not butyl.

Well there's a lot there that I didn't know. Thank you. I was only
going by what I had seen in passing on the tlc web site, which says
PVC and butyl (which I assumed was rubber)
http://www.tlc-direct.co.uk/Main_Ind...tyl/index.html
http://www.tlc-direct.co.uk/Main_Ind...ant/index.html

You said the butyl reference is out of date, perhaps the reference to
pvc is too?

Rather the opposite. The butyl reference is out of date (but we know
what you mean when you refer to butyl flex), whereas heat-resistant PVC
(along with silicone) is relatively new to the market and some oldies
would not automatically think of mentioning it.