Google has not been my friend lately. Seems simple but I can't
locate some electrical data.

Where on Google can I find a simple table showing the typical
resistence per metre of mains flex with copper conductors and
different cross-sectional areas (0.5 mm^2, 0.75 mm^2, etc)?
Measured at room temperature. Would *tinned* copper conductors
make a a noticeable difference to the resistivity?

I am in ther UK. If I measure the resistence of 10 metres of
mains flex with my DC ohm-meter then will my resistence reading be
noticeably different to the resistence when I actually make use of
the 10 metre flex to light a 500W floodlight powered from the AC
mains at 230 volts/50 Hz?

Thank you.


--



Hope the cross-posting is seen as being made to relevant groups.
Don't flame me! :-)

In article ,
JS wrote:
I am in ther UK. If I measure the resistence of 10 metres of
mains flex with my DC ohm-meter then will my resistence reading be
noticeably different to the resistence when I actually make use of
the 10 metre flex to light a 500W floodlight powered from the AC
mains at 230 volts/50 Hz?

You might find this more useful in practice.

http://www.tlc-direct.co.uk/Technica...ltageDrop.html

--
*Time is what keeps everything from happening at once.

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

JS said the following on 07/12/2005 14:08:
Google has not been my friend lately. Seems simple but I can't
locate some electrical data.

Where on Google can I find a simple table showing the typical
resistence per metre of mains flex with copper conductors and
different cross-sectional areas (0.5 mm^2, 0.75 mm^2, etc)?
Measured at room temperature.

he http://www.batt.co.uk/images/pics/31874H3A.pdf

Would *tinned* copper conductors
make a a noticeable difference to the resistivity?

Tinned copper will not materially affect the resistance (not resistivity
- wrong word in this context).


I am in ther UK. If I measure the resistence of 10 metres of
mains flex with my DC ohm-meter then will my resistence reading be
noticeably different to the resistence when I actually make use of
the 10 metre flex to light a 500W floodlight powered from the AC
mains at 230 volts/50 Hz?

No.


Table 4H3B gives the volt drop of the cable in mV/A/m. You should allow
for a maximum of 2% drop in voltage at the far end of your flex.

I'm not sure *why* you would want to know the resistance per se, but you
can work out the resistance from these figures.

So,

Assume your voltage is 240V A.C. 2% volt drop is 0.02 * 240 = 4.8V

The current through your halogen lamp is I=P/V = 500/240 = 2.08A

If you used 1mm sq flex, the volt drop would be 46mV/A/m

So the volt drop in this example would be 46mV * 2.08 * 10 = 0.95V which
is well under 4.8V. :-)

HTH

On Wed, 07 Dec 2005 14:08:08 GMT, JS
wrote:

Google has not been my friend lately. Seems simple but I can't
locate some electrical data.

Where on Google can I find a simple table showing the typical
resistence per metre of mains flex with copper conductors and
different cross-sectional areas (0.5 mm^2, 0.75 mm^2, etc)?

There should be hundreds of tables of copper wire resistance
on the web. You can download a very nice and FREE calculator
at www.wiretron.com. Get their Wire Info Software.

Measured at room temperature. Would *tinned* copper conductors
make a a noticeable difference to the resistivity?

No.

I am in ther UK.

The resistivety of copper is the same in countries :-) It
may be one of the few things that have not been changed by
our various governments.

If I measure the resistence of 10 metres of
mains flex with my DC ohm-meter then will my resistence reading be
noticeably different to the resistence when I actually make use of
the 10 metre flex to light a 500W floodlight powered from the AC
mains at 230 volts/50 Hz?

If the wire does not get very warm, the answer is no. At
frequencies considerably higher than 50 Hz the "skin effect"
will set in and the resistance will go up.

Thank you.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

Dave Plowman (News) said the following on 07/12/2005 15:06:



You might find this more useful in practice.

http://www.tlc-direct.co.uk/Technica...ltageDrop.html


Doh! Good call.

Victor Roberts wrote...
If I measure the resistence of 10 metres of
mains flex with my DC ohm-meter then will my resistence reading be
noticeably different to the resistence when I actually make use of
the 10 metre flex to light a 500W floodlight powered from the AC
mains at 230 volts/50 Hz?

If the wire does not get very warm, the answer is no. At
frequencies considerably higher than 50 Hz the "skin effect"
will set in and the resistance will go up.

But you must never use the cable whilst tightly coiled up (unless you have
deliberately overspecified its capacity). A coiled cable has a much higher
AC impedance due to induction and can overheat alarmingly. I have seen a
coiled 13A extension cable melt with a 3kW load! Typically a 9m extension
rated 13A unwound is derated to only 8A when fully wound.

David

On Wed, 7 Dec 2005 17:02:52 -0000, "David Lee"
wrote:

Victor Roberts wrote...
If I measure the resistence of 10 metres of
mains flex with my DC ohm-meter then will my resistence reading be
noticeably different to the resistence when I actually make use of
the 10 metre flex to light a 500W floodlight powered from the AC
mains at 230 volts/50 Hz?

If the wire does not get very warm, the answer is no. At
frequencies considerably higher than 50 Hz the "skin effect"
will set in and the resistance will go up.

But you must never use the cable whilst tightly coiled up (unless you have
deliberately overspecified its capacity). A coiled cable has a much higher
AC impedance due to induction and can overheat alarmingly.

I have seen a
coiled 13A extension cable melt with a 3kW load! Typically a 9m extension
rated 13A unwound is derated to only 8A when fully wound.

A coiled cable does not have enough inductance to matter at
50 Hz. In addition, inductance does not generate heat, only
resistive loss can do that. High frequency coils will have
higher skin effect losses than straight wires operated at
the same high frequency, and this can generate extra heat
since the skin effect will decrease the effective area of a
conductor and therefore increase its resistance. However,
there is little to no skin effect at 50 Hz.

Coiled cords get hotter than equivalent straight cords
simply because the heat generated by the resistive losses
cannot escape as easily.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

David Lee brought next idea :
But you must never use the cable whilst tightly coiled up (unless you have
deliberately overspecified its capacity). A coiled cable has a much higher
AC impedance due to induction and can overheat alarmingly. I have seen a
coiled 13A extension cable melt with a 3kW load! Typically a 9m extension
rated 13A unwound is derated to only 8A when fully wound.

The inductive heating is tiny compared to its heating as a result of
resistive heating. Basically the fact that it is coiled means that it
cannot dissipate much heat to the surrounding air and it then
overheats.



--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On Wed 07 Dec 2005 18:24:48, Victor Roberts
wrote:

But you must never use the cable whilst tightly coiled up
(unless you have deliberately overspecified its capacity). A
coiled cable has a much higher AC impedance due to induction and
can overheat alarmingly.

I have seen a
coiled 13A extension cable melt with a 3kW load! Typically a 9m
extension rated 13A unwound is derated to only 8A when fully
wound.

A coiled cable does not have enough inductance to matter at
50 Hz. In addition, inductance does not generate heat, only
resistive loss can do that. High frequency coils will have
higher skin effect losses than straight wires operated at
the same high frequency, and this can generate extra heat
since the skin effect will decrease the effective area of a
conductor and therefore increase its resistance. However,
there is little to no skin effect at 50 Hz.

Coiled cords get hotter than equivalent straight cords
simply because the heat generated by the resistive losses
cannot escape as easily.

I have often wondered about how much of an effect my very neat
coils of mains flexes for my PC was having! And I really do seem
to have a lot of devices which plug into the mains.

What about the magentic or ERF effects of a tightly coiled main
flex? Say, 12 neat-ish turns with a diameter of 5 or 6 inches
..... How much of a nuisance might such a thing be to electronic
equipment like my PC?

JS wrote:

[snip]

I have often wondered about how much of an effect my very neat
coils of mains flexes for my PC was having! And I really do seem
to have a lot of devices which plug into the mains.

What about the magentic or ERF effects of a tightly coiled main
flex? Say, 12 neat-ish turns with a diameter of 5 or 6 inches
.... How much of a nuisance might such a thing be to electronic
equipment like my PC?

Not that much. Most of the flux linkages caused by the load current in
one conductor will be canceled by the current returning in the adjacent
conductor in the same cable assembly. There will be a small coupling
between separate turns of the cable, but nothing like the effect you'd
get by constructing a single conductor coil of similar dimensions.

--
Paul Hovnanian
------------------------------------------------------------------
The large print giveth and the small print taketh away.
-- Tom Waits

On Thu, 08 Dec 2005 02:22:25 GMT, JS
put finger to keyboard and composed:

On Wed 07 Dec 2005 18:24:48, Victor Roberts
wrote:

But you must never use the cable whilst tightly coiled up
(unless you have deliberately overspecified its capacity). A
coiled cable has a much higher AC impedance due to induction and
can overheat alarmingly.

I have seen a
coiled 13A extension cable melt with a 3kW load! Typically a 9m
extension rated 13A unwound is derated to only 8A when fully
wound.

A coiled cable does not have enough inductance to matter at
50 Hz. In addition, inductance does not generate heat, only
resistive loss can do that. High frequency coils will have
higher skin effect losses than straight wires operated at
the same high frequency, and this can generate extra heat
since the skin effect will decrease the effective area of a
conductor and therefore increase its resistance. However,
there is little to no skin effect at 50 Hz.

Coiled cords get hotter than equivalent straight cords
simply because the heat generated by the resistive losses
cannot escape as easily.

I have often wondered about how much of an effect my very neat
coils of mains flexes for my PC was having! And I really do seem
to have a lot of devices which plug into the mains.

What about the magentic or ERF effects of a tightly coiled main
flex? Say, 12 neat-ish turns with a diameter of 5 or 6 inches
.... How much of a nuisance might such a thing be to electronic
equipment like my PC?

The magnetic field produced by any number of turns of mains flex is
zero. Think about it.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

In article ,
JS wrote:
Coiled cords get hotter than equivalent straight cords
simply because the heat generated by the resistive losses
cannot escape as easily.

I have often wondered about how much of an effect my very neat
coils of mains flexes for my PC was having! And I really do seem
to have a lot of devices which plug into the mains.

Nothing on a PC takes much current. The IEC leads used are all way over
specified for this use.

--
*The statement above is false

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

On Thu, 08 Dec 2005 02:22:25 GMT, JS
wrote:

On Wed 07 Dec 2005 18:24:48, Victor Roberts
wrote:

But you must never use the cable whilst tightly coiled up
(unless you have deliberately overspecified its capacity). A
coiled cable has a much higher AC impedance due to induction and
can overheat alarmingly.

I have seen a
coiled 13A extension cable melt with a 3kW load! Typically a 9m
extension rated 13A unwound is derated to only 8A when fully
wound.

A coiled cable does not have enough inductance to matter at
50 Hz. In addition, inductance does not generate heat, only
resistive loss can do that. High frequency coils will have
higher skin effect losses than straight wires operated at
the same high frequency, and this can generate extra heat
since the skin effect will decrease the effective area of a
conductor and therefore increase its resistance. However,
there is little to no skin effect at 50 Hz.

Coiled cords get hotter than equivalent straight cords
simply because the heat generated by the resistive losses
cannot escape as easily.

I have often wondered about how much of an effect my very neat
coils of mains flexes for my PC was having! And I really do seem
to have a lot of devices which plug into the mains.

What about the magentic or ERF effects of a tightly coiled main
flex? Say, 12 neat-ish turns with a diameter of 5 or 6 inches
.... How much of a nuisance might such a thing be to electronic
equipment like my PC?

As has been said, the net magnetic flux far from the coil is
zero since you have two identical currents flowing in
opposite directions. The local effects are also just about
zero since the frequency is only 50 Hz. If this were 50 MHz,
then there would be turn-to-turn coupling and additional
heating.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

Table 4H3B gives the volt drop of the cable in mV/A/m. You
should allow for a maximum of 2% drop in voltage at the far end
of your flex.

I'm not sure *why* you would want to know the resistance per se,
but you can work out the resistance from these figures.

Hi Rumble

I was hoping to measure the resistence across the live/neutral pins
of the mains plug and then deduct the resistence of the main lead
(which is approx 10m of 1.0 mm^2).

From the result I was looking to know what the cold bulb resistence
is and from that infer the wattage.

The idea is to save opening up the housing and taking the bulb out to
measure the resistence.

Your table is useful and I have kept it but it does not directly
address my problem unless I do your calculations below each time.

Can I find a simple table which gives me resistence per metre of 1.0
mm^2 wire (or whatever cable I am using)?


So, Assume your voltage is 240V A.C.
2% volt drop is 0.02 * 240 = 4.8V

The current through your halogen lamp is I=P/V = 500/240 = 2.08A
If you used 1mm sq flex, the volt drop would be 46mV/A/m

So the volt drop in this example would be 46mV * 2.08 * 10 =
0.95V which is well under 4.8V. :-)


--

On Thu 08 Dec 2005 06:00:12, Franc Zabkar
wrote:

The magnetic field produced by any number of turns of mains flex is
zero. Think about it.

Hmmm. Yes. :-)

I was hoping to use a compass deflection as a way of telling how much
heat/power was being lost in neatly wrapped coiled of mains flex.

Surely there is a loss of something due to the neatness - or perhaps
not?

On Thu, 08 Dec 2005 14:43:11 GMT, JS
wrote:

On Thu 08 Dec 2005 06:00:12, Franc Zabkar
wrote:

The magnetic field produced by any number of turns of mains flex is
zero. Think about it.

Hmmm. Yes. :-)

I was hoping to use a compass deflection as a way of telling how much
heat/power was being lost in neatly wrapped coiled of mains flex.

Even if you had a net magnetic field, it would be an AC
field, and your compass would not respond to that. Also,
there is no direct correlation between the strength of the
magnetic field and the power loss. You need to include a
number of other factors.

Surely there is a loss of something due to the neatness - or perhaps
not?

Why should neatness lead to loss? In the days before all
electronic devices used printed circuits, with systems were
connected with point-to-point wiring, high frequency
electronic systems had much neater wiring than low frequency
equipment, since it lead to shorter lengths of wire and
lower capacitance between wires.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

On Thu, 08 Dec 2005 14:39:17 GMT, JS
wrote:

Table 4H3B gives the volt drop of the cable in mV/A/m. You
should allow for a maximum of 2% drop in voltage at the far end
of your flex.

I'm not sure *why* you would want to know the resistance per se,
but you can work out the resistance from these figures.

Hi Rumble

I was hoping to measure the resistence across the live/neutral pins
of the mains plug and then deduct the resistence of the main lead
(which is approx 10m of 1.0 mm^2).

From the result I was looking to know what the cold bulb resistence
is and from that infer the wattage.

The idea is to save opening up the housing and taking the bulb out to
measure the resistence.

Your table is useful and I have kept it but it does not directly
address my problem unless I do your calculations below each time.

Can I find a simple table which gives me resistence per metre of 1.0
mm^2 wire (or whatever cable I am using)?

See the answer I gave you yesterday. You can find a
resistance calculator for copper wire at www.wiretron.com

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

In article ,
JS wrote:

Hmmm. Yes. :-)

I was hoping to use a compass deflection as a way of telling how much
heat/power was being lost in neatly wrapped coiled of mains flex.

Surely there is a loss of something due to the neatness - or perhaps
not?

Lower probability of managing to "accidentally" trip an unwanted
in-law over the mounds of loose cable lying around on the floor? Some
would call that a significant loss :-)

Semi-seriously, though - I believe that the actual power loss in the
wire, and thus the total amount of heat generated, is as close to
identical in the two cases as makes no difference.

The reason for not coiling up high-amperage mains cable is probably
one of heat dissipation, rather than heat generation. If the cable is
lying out in a straight line, or just piled up loosely, it can shed
the waste heat effectively via radiation, conduction to the ground,
and convection into the air. If you coil it up on a spindle of some
sort, the heat generated in the inner turns of the coil will have no
easy means of escape... it can only get out via conduction through the
outer turns of the coil, which are rubber- or plastic-insulated and
thus have a high thermal resistance.

Run 20 amps through a heavy-duty extension cord, lose a few volts due to IR
drop, and you can end up with quite a few tens of watts of heat to be
lost. Under prolonged load this might, perhaps, be enough to affect
the integrity of the cord's insulation somewhat, or even cause a
thermal burn.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Dave Platt...
Run 20 amps through a heavy-duty extension cord, lose a few volts due to
IR
drop, and you can end up with quite a few tens of watts of heat to be
lost. Under prolonged load this might, perhaps, be enough to affect
the integrity of the cord's insulation somewhat, or even cause a
thermal burn.

Somewhat more than somewhat! 13A through a typical coiled extension cable
(in a plastic drum) is enough to melt the drum and insulation - I've seen it
happen! My present 9m 13A extension cable is rated 13A fully unwound but
only 8A wound.

Excess extension cable should be neatly but loosely coiled to prevent a trip
hazard whilst maintaining adaquate cooling.

David

JS said the following on 08/12/2005 14:39:
Table 4H3B gives the volt drop of the cable in mV/A/m. You
should allow for a maximum of 2% drop in voltage at the far end
of your flex.

I'm not sure *why* you would want to know the resistance per se,
but you can work out the resistance from these figures.


Hi Rumble

I was hoping to measure the resistence across the live/neutral pins
of the mains plug and then deduct the resistence of the main lead
(which is approx 10m of 1.0 mm^2).

From the result I was looking to know what the cold bulb resistence
is and from that infer the wattage.

The idea is to save opening up the housing and taking the bulb out to
measure the resistence.


I would say it is unlikely that you will be able to reliably infer the
wattage of the lamp from its cold resistance using this method.

The relationship between the cold resistance and the (hot, nominal)
wattage of the lamp may well vary between different manufacturers and
will be dependant upon how old the lamp is (the filament gets thinner as
it ages).

JS wrote:

Can I find a simple table which gives me resistence per metre of 1.0
mm^2 wire (or whatever cable I am using)?

The resistance per metre of a 1 mm^2 copper conductor is 18.1 milliohms
at 20 deg. C and the temperature coefficient is about +0.4% per degree.

--
Andy

In sci.engr.lighting Franc Zabkar wrote:
On Thu, 08 Dec 2005 02:22:25 GMT, JS
put finger to keyboard and composed:

On Wed 07 Dec 2005 18:24:48, Victor Roberts
wrote:

But you must never use the cable whilst tightly coiled up
(unless you have deliberately overspecified its capacity). A
coiled cable has a much higher AC impedance due to induction and
can overheat alarmingly.
snip
I have often wondered about how much of an effect my very neat
coils of mains flexes for my PC was having! And I really do seem
to have a lot of devices which plug into the mains.

What about the magentic or ERF effects of a tightly coiled main
flex? Say, 12 neat-ish turns with a diameter of 5 or 6 inches
.... How much of a nuisance might such a thing be to electronic
equipment like my PC?

The magnetic field produced by any number of turns of mains flex is
zero. Think about it.

For differential mode current only.
For common mode signals, like RFI on all three wires, probably not.

In sci.engr.lighting JS wrote:
Table 4H3B gives the volt drop of the cable in mV/A/m. You
should allow for a maximum of 2% drop in voltage at the far end
of your flex.

I'm not sure *why* you would want to know the resistance per se,
but you can work out the resistance from these figures.

Hi Rumble

I was hoping to measure the resistence across the live/neutral pins
of the mains plug and then deduct the resistence of the main lead
(which is approx 10m of 1.0 mm^2).

From the result I was looking to know what the cold bulb resistence
is and from that infer the wattage.

The idea is to save opening up the housing and taking the bulb out to
measure the resistence.

Unfortunatrely, the cold resistnace of a bulb has very little to do
with its hot resistance.
Design differences may even mean one with lower wattage has a lower
cold resistance.
Does your multimeter happen to have an AC current measurement?