Author Topic: 0.75mm² AC cable question  (Read 906 times)

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Offline Halcyon

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0.75mm² AC cable question
« on: July 29, 2019, 04:55:01 am »
We recently purchased some new equipment and like many cheap products, they came bundled with cheap cables. Straight away the thickness of the IEC leads looked too thin to me. Inside are 3x 0.75mm² stranded cores. According to the markings on the cable, it's rated at 250V, 10A. Is this acceptable?

I'm not sure if it's copper-clad aluminium or proper copper (I don't really want to do the "flame test" in the office).

At home I tend to use old power leads of reputable quality which I've kept in a box for many years.
 

Offline Black Phoenix

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Re: 0.75mm² AC cable question
« Reply #1 on: July 29, 2019, 05:57:47 am »
What I've done for years is that, I get reliable cable what I know is stranded cooper and add proper plugs.

I have around 4x 2meter 1.5mmx3 extensions to power up any equipment that I need with this c15 plugs in the end:

[attachimg=1]

I love this suckers, they are normally used in server environment where you can simply stick a strap on them to unplug in hard to reach places in case of need.

Then on the other end normally have a good quality schuko plug or in my opinion the best constructed plug, the Type G English Plug with Fuse.

The way as they wire the house were every outlet have a switch and every plug have a fuse is in my opinion the best solution (I hope not opening a can of worms because of my opinion). And when in a multi plug strip all cables exit the same place, not as sometimes with the schuko plut type multi plug strip where if you have a wall wart some have to exit from the left and other from the right and sometimes even block the adjacent plug.

Normally in datacenters, I can get a lot of good high quality cooper cables, since most of the servers and switches come with the C15-C14 plug for the PDUs and some even bring a lot of different cables ended in the Type G plug, the Type F and Even some with Type I. I simply cut the plugs I don't want and reuse the high quality cable.
« Last Edit: July 29, 2019, 06:08:37 am by Black Phoenix »
 

Offline soldar

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Re: 0.75mm² AC cable question
« Reply #2 on: July 29, 2019, 09:42:11 am »
According to the markings on the cable, it's rated at 250V, 10A. Is this acceptable?

What current does the equipment use? Because if it's 10 A I would say it is kinda tight but if it is 1 or 2 A I would say it is fine.

And if you have any doubt why not just replace them?
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Offline SteveyG

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Re: 0.75mm² AC cable question
« Reply #3 on: July 29, 2019, 10:04:57 am »
3x 0.75mm² is common for IEC cables. You tend to see 3x 1.0mm² on the higher quality cables though.

The 10A rating is more than likely the rating of the connectors though. It would not be normal to print a current rating on flex as there are too many variables to give it a current rating.
 
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Offline Zero999

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Re: 0.75mm² AC cable question
« Reply #4 on: July 29, 2019, 11:03:39 am »
I believe 5A is the maximum current rating for standard PVC insulated flexible cable, operating in open air at room temperature.
 

Offline Brutte

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Re: 0.75mm² AC cable question
« Reply #5 on: July 29, 2019, 11:44:33 am »
Inside are 3x 0.75mm² stranded cores.
a) "there are 3x0.75mm2 stranded cores because there is a 3x0.75mm2 marking on cable" or
b) "there are 3x0.75mm2 stranded cores because I took a micrometer and measured all three cores" or
c) "there are 3x0.75mm2 stranded cores because these look like 3x 0.75mm2 to me"

?

Quote
I'm not sure if it's copper-clad aluminium or proper copper
.
Then why are you concerned about the cross seciton?
 

Online wraper

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Re: 0.75mm² AC cable question
« Reply #6 on: July 29, 2019, 11:58:08 am »
0.75 mm2 is standart for IEC cables. More than 95% of IEC cables are like this. Occasionally you can find 1 mm2 cables though. 0.75 mm2 is completely enough for 10A IEC connector is rated for. Although cable will get warm when continuously operated at such current. What's more important is if this cross section is genuine. I've stumbled on some counterfeit cables with very thin conductors. They can come with cheap Chinese crap equipment or when bought separately. Can be easily checked though, if you have a half decent multimeter with at least 0.01 Ohm resolution. They have much higher resistance than genuine cables.
« Last Edit: July 29, 2019, 11:59:42 am by wraper »
 

Offline Zero999

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Re: 0.75mm² AC cable question
« Reply #7 on: July 29, 2019, 01:44:21 pm »
10A is too high for an ordinary 0.75mm2 flexible cable, with PVC insulation. I think you're confusing a single conductor in free air, which would be fin up to 10A. I did a Google which led me to a table saying 6A. I know said 5A, but that was because it's the nearest common plug top fuse, available in the UK.

https://www.cse-distributors.co.uk/cable/technical-tables-useful-info/table-4f3a/
 

Online wraper

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Re: 0.75mm² AC cable question
« Reply #8 on: July 29, 2019, 01:52:11 pm »
10A is too high for an ordinary 0.75mm2 flexible cable, with PVC insulation. I think you're confusing a single conductor in free air, which would be fin up to 10A. I did a Google which led me to a table saying 6A. I know said 5A, but that was because it's the nearest common plug top fuse, available in the UK.

https://www.cse-distributors.co.uk/cable/technical-tables-useful-info/table-4f3a/
FYI requirements for wiring installations are very different from power cords.
 

Offline Monkeh

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Re: 0.75mm² AC cable question
« Reply #9 on: July 29, 2019, 02:17:20 pm »
10A is too high for an ordinary 0.75mm2 flexible cable, with PVC insulation. I think you're confusing a single conductor in free air, which would be fin up to 10A. I did a Google which led me to a table saying 6A. I know said 5A, but that was because it's the nearest common plug top fuse, available in the UK.

https://www.cse-distributors.co.uk/cable/technical-tables-useful-info/table-4f3a/
FYI requirements for wiring installations are very different from power cords.

So would you care to supply a source indicating that 3182Y or 3183Y are rated at more than 6A for 0.75mm²?
 

Offline Zero999

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Re: 0.75mm² AC cable question
« Reply #10 on: July 29, 2019, 03:10:15 pm »
10A is too high for an ordinary 0.75mm2 flexible cable, with PVC insulation. I think you're confusing a single conductor in free air, which would be fin up to 10A. I did a Google which led me to a table saying 6A. I know said 5A, but that was because it's the nearest common plug top fuse, available in the UK.

https://www.cse-distributors.co.uk/cable/technical-tables-useful-info/table-4f3a/
FYI requirements for wiring installations are very different from power cords.
I know. If anything the current rating is less for flexible cords on potable appliances, than for installations because even if the insulation can withstand higher temperatures, the cable will be too hot to handle.
 

Online Benta

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Re: 0.75mm² AC cable question
« Reply #11 on: July 29, 2019, 09:14:50 pm »
You're overreacting. 2 x 0.75 mm2 or 3 x 0.75 mm2 is absolutely sufficient for 10 A.

In my shed I have a 2 kW heater on 230 V, and the cable doesn't even begin to get warm.

 

Online wraper

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Re: 0.75mm² AC cable question
« Reply #12 on: July 29, 2019, 11:12:05 pm »
I know. If anything the current rating is less for flexible cords on potable appliances, than for installations because even if the insulation can withstand higher temperatures, the cable will be too hot to handle.
It's opposite. Residential installations require higher cross section.
I researched a bit and it seems that 3x0.75 cables are usually rated for 6A, however some occasionally say 10A. Also by the logic that 1.5 mm2 cables are usually rated for 16A, 0.75 mm2 should be good for at least 8A (1.5/2=0.75) instead of 6A  :-//.
 

Offline Zero999

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Re: 0.75mm² AC cable question
« Reply #13 on: July 30, 2019, 07:54:28 am »
You're overreacting. 2 x 0.75 mm2 or 3 x 0.75 mm2 is absolutely sufficient for 10 A.

In my shed I have a 2 kW heater on 230 V, and the cable doesn't even begin to get warm.
Heater cable will have a higher current rating, because the insulation will be rated to a higher temperature. If it doesn't feel warm, it's because the duty cycle is low. My parents have an immersion heater in their house, for when the gas boiler fails. It has a 230V 3kW element and 1.5mm2 cable which does get fairly warm when it's been running for a long time.

I know. If anything the current rating is less for flexible cords on potable appliances, than for installations because even if the insulation can withstand higher temperatures, the cable will be too hot to handle.
It's opposite. Residential installations require higher cross section.
If the cable is buried in a wall, as is often the case in a fixed installation, then yes, it will need a larger cross-sectional area than a free cable.

More often than not the minimum cross-sectional area is determined by the voltage drop, ensuring the breaker trips quickly due to a fault and preventing the voltage on the earth conductor from reaching hazardous levels, due to faults, rather than the cable heating up.

Quote
I researched a bit and it seems that 3x0.75 cables are usually rated for 6A, however some occasionally say 10A.
Yes, that's fairly standard.

Quote
Also by the logic that 1.5 mm2 cables are usually rated for 16A, 0.75 mm2 should be good for at least 8A (1.5/2=0.75) instead of 6A  :-//.
No, because it doesn't scale linearly.
 

Online wraper

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Re: 0.75mm² AC cable question
« Reply #14 on: July 30, 2019, 10:23:57 am »
Quote
Also by the logic that 1.5 mm2 cables are usually rated for 16A, 0.75 mm2 should be good for at least 8A (1.5/2=0.75) instead of 6A  :-//.
No, because it doesn't scale linearly.
It doesn't, but in opposite direction that you seem to mean. Increasing cross section has diminishing returns.
 

Offline Zero999

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Re: 0.75mm² AC cable question
« Reply #15 on: July 30, 2019, 11:14:25 am »
Quote
Also by the logic that 1.5 mm2 cables are usually rated for 16A, 0.75 mm2 should be good for at least 8A (1.5/2=0.75) instead of 6A  :-//.
No, because it doesn't scale linearly.
It doesn't, but in opposite direction that you seem to mean. Increasing cross section has diminishing returns.
Oh, I see what you mean now.

Looking at the table I linked to previously.
https://www.cse-distributors.co.uk/cable/technical-tables-useful-info/table-4f3a/

0.5mm2 is suitable for up to 3A, yet doubling the cross-sectional area to 1mm2 increases the ampapacity to 10A, factor of 31/3. Going from 1mm2 to 1.5mm2 only increases the ampacity from 10A to 16A and in order to double the ampacity again, to 32A, a 4mm2 cable, rather than 3mm2 cable, is required.

I think with smaller cables the reverse is true because at the cable insulation and outer sheath starts to occupy most of the cable's volume. A 0.5mm2 cable will have a much grater ratio of insulation material to copper, than a 4mm2 cable, which will artificially restrict its ampacity. The insulation and outer sheath has to be a certain minimum thickness to provide enough mechanical strength, so it can't be reduced, for smaller cables.
 

Offline SteveyG

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Re: 0.75mm² AC cable question
« Reply #16 on: July 30, 2019, 11:35:17 am »
I think with smaller cables the reverse is true because at the cable insulation and outer sheath starts to occupy most of the cable's volume. A 0.5mm2 cable will have a much grater ratio of insulation material to copper, than a 4mm2 cable, which will artificially restrict its ampacity. The insulation and outer sheath has to be a certain minimum thickness to provide enough mechanical strength, so it can't be reduced, for smaller cables.

Indeed, the numbers are effectively derived from temperature rise, so there is an optimal value for any given insulation and sheath thickness/material.

Offline Halcyon

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Re: 0.75mm² AC cable question
« Reply #17 on: July 30, 2019, 08:39:07 pm »
What current does the equipment use? Because if it's 10 A I would say it is kinda tight but if it is 1 or 2 A I would say it is fine.

Very little, but as you know, IEC can be removed and used with just about anything, so there is the potential there for it to be used with high power devices.

And if you have any doubt why not just replace them?

I already have, the question was more curiosity on my part.

b) "there are 3x0.75mm2 stranded cores because I took a micrometer and measured all three cores" or

This one.
 

Offline John B

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Re: 0.75mm² AC cable question
« Reply #18 on: July 30, 2019, 09:16:08 pm »
0.75mm² is what you get on a hairdryer cord, and that will heat up noticeably in free air at less than 10A, after a short period.
 

Online IanB

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Re: 0.75mm² AC cable question
« Reply #19 on: July 30, 2019, 09:55:24 pm »
Now I want to check the conductor size on my electric kettle (240 V, 13 A, 3000 W). It's not a particularly thick or heavy power cord, but maybe it is given a credit for intermittent use (it only takes 3-4 minutes to boil a kettle). It will not be carrying 13 A continuously in that application.
I'm not an EE--what am I doing here?
 

Offline Halcyon

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Re: 0.75mm² AC cable question
« Reply #20 on: July 31, 2019, 02:51:04 am »
I just checked our HP Workstations. They come with 1.00mm² IEC cables as standard.
 

Online IanB

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Re: 0.75mm² AC cable question
« Reply #21 on: July 31, 2019, 02:59:14 am »
Now I want to check the conductor size on my electric kettle (240 V, 13 A, 3000 W).

It's 1.0 mm². It doesn't get warm.
I'm not an EE--what am I doing here?
 

Online amyk

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Re: 0.75mm² AC cable question
« Reply #22 on: July 31, 2019, 03:41:40 am »
The best way to determine the quality is to check the resistance. This will tell you what the voltage drop and dissipation in the cable will be at 10A, and indirectly, how hot it will get.
 


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