Seek resistance table for main flex

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.

Reply to
JS
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You might find this more useful in practice.

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Reply to
Dave Plowman (News)

There should be hundreds of tables of copper wire resistance on the web. You can download a very nice and FREE calculator at

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Get their Wire Info Software.

No.

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 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.

Reply to
Victor Roberts

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

Reply to
David Lee

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.

Reply to
Victor Roberts

David Lee brought next idea :

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.

Reply to
Harry Bloomfield

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?

Reply to
JS

[snip]

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.

Reply to
Paul Hovnanian P.E.

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

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.

Reply to
Franc Zabkar

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

Reply to
Dave Plowman (News)

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.

Reply to
Victor Roberts

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)?

Reply to
JS

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?

Reply to
JS

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.

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.

Reply to
Victor Roberts

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

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Reply to
Victor Roberts

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.

Reply to
Dave Platt

Dave Platt...

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

Reply to
David Lee

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

Reply to
Ian Stirling

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?

Reply to
Ian Stirling

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