Author Topic: Mains cable size  (Read 5716 times)

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Offline ricko_ukTopic starter

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Mains cable size
« on: August 04, 2020, 03:05:30 pm »
Hi,
I just had someone supposedly expert insist that when someone says "1.5mm mains cable" it refers to the copper diameter because it says mm not mm^2.

That does not make any sense for two reasons: first and foremost it is the area that matters when carrying current and secondly you cannot measure the diameter of a multi stranded wire accurately because it varies depending on how much you twist the strands

But he is adamant he is right and his colleague supports his point too.

Can someone confirm that is not correct and despite the fact that in normal parlance it is say 1.5mm it is supposed to be 1.5mm^2 (i.e. square)?

Thank you
 

Offline Benta

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Re: Mains cable size
« Reply #1 on: August 04, 2020, 04:18:59 pm »
Both of you are right (and wrong). In the EU, power cables are specified using the copper cross-sectional area. But in that case it should have the unit mm^2, sometimes you also just see a square symbol (like a box). This is true for both stranded and solid wires.
The diameter specification is used mainly in electronics for lead thickness, varnish isolated wires for coils etc. and of course has the dimension mm.

« Last Edit: August 04, 2020, 04:22:53 pm by Benta »
 
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Offline themadhippy

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Re: Mains cable size
« Reply #2 on: August 04, 2020, 05:35:16 pm »
Ask the "expert " to give you a bit of 2.5mm or 6mm and youll measure the results,dont accept 1.5mm as the diameter and area are pretty close
 
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Online Zero999

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Re: Mains cable size
« Reply #3 on: August 04, 2020, 05:41:56 pm »
In the UK, mains cables are specified in mm2 but many electricians don't bother mentioning the square bit. I once asked for some 1.5mm square heat resistant cable, in an electrical shop and they said they don't have any square cable, but only round. I laughed to myself and siad "That will do, thanks." :-DD I didn't have the time to get into a discussion. I just wanted some cable for my parent's 3kW emersion heater, as the gas boiler had stopped working and the pillock who rewired the airing cupboard had taken the socket out, so I had to run a cable to the nearest outlet.

My advice is, point them to the correct information. If they still won't accept it, move on. Choose your battles.

An explaination of cable sizes and crossectional area.
https://www.diydoctor.org.uk/projects/cablesizes.htm

Note how mains cables in RS and similar UK suppliers, are specified in mm2
https://uk.rs-online.com/web/c/cables-wires/electrical-power-industrial-cable/lighting-electrical-cable/

In the UK most electrical cables are specified in sizes listed by IEC 60228.
https://en.wikipedia.org/wiki/IEC_60228

Although we also use 1.25mm2 for flexible cables on 13A plugs. Presumably this is because it's rated to 13A and cheaper than 1.5mm2, which has a 15A rating and is overkill for mains appliances with a 13A plug.
https://www.diynot.com/pages/el/el004.php
« Last Edit: August 05, 2020, 01:56:15 pm by Zero999 »
 
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Offline TimFox

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Re: Mains cable size
« Reply #4 on: August 04, 2020, 06:22:37 pm »
In another thread, I mentioned my confusion on temporary duty in UK where the local guy said "mils", meaning "millimeters", when he really meant "mm2".  I knew he didn't mean "mils", as in the American usage of 0.001 inch for diameter, and luckily the cable did not overheat (there is a noticeable difference between 6 mm diameter and 6 mm2 area).  I have been accused of being a stickler for language, but proper usage is important in technical applications.
 
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Offline ricko_ukTopic starter

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Re: Mains cable size
« Reply #5 on: August 04, 2020, 06:41:43 pm »
Thank you all :)

And all funny stories!!  :-DD :-DD
 

Offline Benta

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Re: Mains cable size
« Reply #6 on: August 04, 2020, 06:52:35 pm »
In another thread, I mentioned my confusion on temporary duty in UK where the local guy said "mils", meaning "millimeters", when he really meant "mm2".  I knew he didn't mean "mils", as in the American usage of 0.001 inch for diameter, and luckily the cable did not overheat (there is a noticeable difference between 6 mm diameter and 6 mm2 area).  I have been accused of being a stickler for language, but proper usage is important in technical applications.

Amen!

Precise language in engineering is vital, otherwise someone will get killed at some point.

"Mils" is ridiculous.

I have nothing against abbreviations if they're unambiguous, they're part of daily work life.
For instance, in Germany it is usual to refer to 1.5 mm^2 cable as "1.5 quadrat" (quadrat means square), which can't be misunderstood in any way (at least not between electricians).
 
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Offline TimFox

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Re: Mains cable size
« Reply #7 on: August 04, 2020, 07:32:04 pm »
The "mil" = 0.001 inch in American usage is unambiguous, and gives rise to a standard unit of area the "circular mil" which is the area of a circle one mil in diameter.  Transformer design guides often quote recommended wire size using a "amps per circular mil" value.  The circular mil is easier to calculate than the true square mil.  Where things start getting archaic is the largest wires used in mains wiring, such as 250 MCM, which is more appropriately written as "250 kcmil"; Its true diameter is easily calculated as 0.50 inch = 500 mils, without using a calculator.   The "M" is a holdover from accountants' use of Roman numeral M = 1000.  Approximately, 2 MCM = 1 mm2 (in true area).
 
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Online langwadt

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Re: Mains cable size
« Reply #8 on: August 04, 2020, 07:35:47 pm »
In another thread, I mentioned my confusion on temporary duty in UK where the local guy said "mils", meaning "millimeters", when he really meant "mm2".  I knew he didn't mean "mils", as in the American usage of 0.001 inch for diameter, and luckily the cable did not overheat (there is a noticeable difference between 6 mm diameter and 6 mm2 area).  I have been accused of being a stickler for language, but proper usage is important in technical applications.

Amen!

Precise language in engineering is vital, otherwise someone will get killed at some point.

"Mils" is ridiculous.

I have nothing against abbreviations if they're unambiguous, they're part of daily work life.
For instance, in Germany it is usual to refer to 1.5 mm^2 cable as "1.5 quadrat" (quadrat means square), which can't be misunderstood in any way (at least not between electricians).

yep same here
 
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Online Zero999

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Re: Mains cable size
« Reply #9 on: August 04, 2020, 10:07:03 pm »
The "mil" = 0.001 inch in American usage is unambiguous,
Only in the US. In the UK and no doubt other countries, mil is regularly used as an abbreviation for millimetres. Someone will ask for a 1 mil thick sheet of steel, when they mean 1mm. If you want 0.001 inches, then you should ask for 1 thou. If you ask any electrician in the UK for some 1 mil cable, they'll get you 1mm2 cable. The only people who'll know about the US usage are those who've dealt with US companies or used US CAD software.

Quote
a standard unit of area the "circular mil" which is the area of a circle one mil in diameter.
We generally don't use imperial units much in engineering over here, certainly not in technical documents. I've never heard of circular mil, until now.

Whenever working in a country, it's very important to familiarise themself with the slang and customs used there. In an international setting, stick to SI units, whenever possible. Avoid customary/imperial units such as circular mil, pints, pounds etc. like the plague.
 

Offline TimFox

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Re: Mains cable size
« Reply #10 on: August 04, 2020, 10:17:34 pm »
I was careful to start my post with "in American usage".  Yes, we still use "conventional units" in engineering in the United States, even though the country is legally metric.  "Imperial units" is a British term.
However, if a European or British engineer were  working in my lab (before I retired), I would not expect him to use "mils" in the American sense, but would show him what sizes of wire are commercially available here.
I still oppose the use of "mil" or "mm" to mean "mm2".
It can take a long time to learn all the slang terms used in a foreign country.
By the way, on that multi-week business trip to UK, I ran up a 2240 GBP hotel bill (including meals), which I reported back to my company in the US as a "ton of money", which is approximately a "tonne of money".  In the US, we call that a "long ton", while 2000 lb av is a "short ton" or just "ton".  I still don't understand the British definition of a cwt = hundredweight as 8 stones, which is less than 100 lb.
« Last Edit: August 04, 2020, 10:27:15 pm by TimFox »
 

Offline tooki

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Re: Mains cable size
« Reply #11 on: August 05, 2020, 10:26:10 am »
Hi,
I just had someone supposedly expert insist that when someone says "1.5mm mains cable" it refers to the copper diameter because it says mm not mm^2.

That does not make any sense for two reasons: first and foremost it is the area that matters when carrying current and secondly you cannot measure the diameter of a multi stranded wire accurately because it varies depending on how much you twist the strands

But he is adamant he is right and his colleague supports his point too.

Can someone confirm that is not correct and despite the fact that in normal parlance it is say 1.5mm it is supposed to be 1.5mm^2 (i.e. square)?

Thank you
What might also confound the issue is that a 1.5mm2 solid wire has a diameter of 1.38mm. So if someone measured it roughly, they might have incorrectly assumed it was 1.5mm diameter. (4/pi, or about 1.27, is where the diameter and area of a circle are the same value.)

But it’s more likely that they’ve simply gone all this time without understanding it correctly, never realizing that there are two systems for measuring wire.

This could be considered a theoretical advantage of the AWG system: since the gauge is an abstract number not directly correlated to the cross section (at least, not in a trivial way), it doesn’t ever lead you down the path of attempting to perform math on the gauge. :P
« Last Edit: August 05, 2020, 10:28:31 am by tooki »
 

Offline vk6zgo

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Re: Mains cable size
« Reply #12 on: August 05, 2020, 12:29:45 pm »
I was careful to start my post with "in American usage".  Yes, we still use "conventional units" in engineering in the United States, even though the country is legally metric.  "Imperial units" is a British term.
However, if a European or British engineer were  working in my lab (before I retired), I would not expect him to use "mils" in the American sense, but would show him what sizes of wire are commercially available here.
I still oppose the use of "mil" or "mm" to mean "mm2".
It can take a long time to learn all the slang terms used in a foreign country.
By the way, on that multi-week business trip to UK, I ran up a 2240 GBP hotel bill (including meals), which I reported back to my company in the US as a "ton of money", which is approximately a "tonne of money".  In the US, we call that a "long ton", while 2000 lb av is a "short ton" or just "ton".  I still don't understand the British definition of a cwt = hundredweight as 8 stones, which is less than 100 lb.

Sorry, no, an Imperial hundredweight is 112 lbs, a stone is 14 lbs, (8x14 =112).
 

Offline JohanH

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Re: Mains cable size
« Reply #13 on: August 05, 2020, 12:48:22 pm »
Over here (EU, Finland) electricians I know always talk about "square" (as in mm2) about cables. I have never observed that this would have been misinterpreted. Cables and labels are always clearly marked. Then again I haven't worked as a real electrician (even though I've done some work in the field).
 

Offline TimFox

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Re: Mains cable size
« Reply #14 on: August 05, 2020, 01:04:20 pm »
Oops about the "cwt"--it can be confusing when the answer is not "100".
With respect to AWG:  the gauge number is logarithmic, and -3 gauges doubles the area to a good approximation.
« Last Edit: August 05, 2020, 01:09:04 pm by TimFox »
 

Offline themadhippy

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Re: Mains cable size
« Reply #15 on: August 05, 2020, 01:42:45 pm »
If you wanna be picky about using the correct terminology would you americans please remember there is the far superior SWG ,so if all you request is 18 gauge dont start screaming the wire the wrong size,maybe we should return to the days of 3/0.29 instead of this confusing 1.5mm2 talk
 

Offline TimFox

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Re: Mains cable size
« Reply #16 on: August 05, 2020, 03:12:40 pm »
SWG is an obsolete British phenomenon, and is not used in the US.  We patriotically named ours "American Wire Gauge", instead of the presumptuous "Standard Wire Gauge".
In fact, all of the gauges for wire (different for copper and steel) and sheet metal were originally proprietary manufacturer's ratings.  AWG originated as the Brown & Sharpe gauge.
 
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Online Zero999

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Re: Mains cable size
« Reply #17 on: August 05, 2020, 08:51:26 pm »
I don't think we should allow this thread to turn into a metric vs customary, imperial debate. The point is we need to communicate clearly with one another. Using local conventions, slang and measurements is fine. There's nothing wrong with that, but in technical documentation, designed for an international audience, it's important to stick to international standards, whenever possible. The only issue regarding wire sizes is for under 0.5mm², which isn't standardised, so AWG or SWG are normally used. I hope the IEC standardises the smaller gauges, but as they're not used for mains, it's not a safety issue, so less likely.
 
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Offline Benta

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Re: Mains cable size
« Reply #18 on: August 05, 2020, 09:08:01 pm »
Zero999, I'm with you 100%, couldn't have said it better myself.
Now we just have to teach the marketing people to say "picofarads" instead of "puffs" (No kidding)  :(

 

Offline TimFox

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Re: Mains cable size
« Reply #19 on: August 05, 2020, 09:30:05 pm »
One last thing about American usage, to avoid confusion if the pandemic ever allows us to visit each other again:
"mils" for 0.001 inch is common usage for wire, and is a standard technical term (not slang).  My KiCad (from CERN) has mils as an option for dimensions, as well as US paper sizes.
"thou"  for 0.001 inch is common US slang for sheet metal thickness and machining tolerances, but would never be spelled that way on a blueprint.
From that comes the very confusing US slang of "tenth" = 10-4 inch, when machining tolerance is tighter than 0.001".  Our best instrument maker at my University was asked to achieve a tolerance of 1 micron, which he translated to "half a tenth".
 

Offline Mr. Scram

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Re: Mains cable size
« Reply #20 on: August 05, 2020, 09:45:44 pm »
One last thing about American usage, to avoid confusion if the pandemic ever allows us to visit each other again:
"mils" for 0.001 inch is common usage for wire, and is a standard technical term (not slang).  My KiCad (from CERN) has mils as an option for dimensions, as well as US paper sizes.
"thou"  for 0.001 inch is common US slang for sheet metal thickness and machining tolerances, but would never be spelled that way on a blueprint.
From that comes the very confusing US slang of "tenth" = 10-4 inch, when machining tolerance is tighter than 0.001".  Our best instrument maker at my University was asked to achieve a tolerance of 1 micron, which he translated to "half a tenth".
The problem is that the rest of the world will see "mil" as shorthand for or an abbreviation of millimeter. It's really the most unfortunate choice for a competing term. The whole doing metric within imperial seems odd anyway but I'm not about to start another systems debate.
 

Online langwadt

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Re: Mains cable size
« Reply #21 on: August 05, 2020, 09:45:52 pm »
Zero999, I'm with you 100%, couldn't have said it better myself.
Now we just have to teach the marketing people to say "picofarads" instead of "puffs" (No kidding)  :(

here it is "piff"
 

Offline TimFox

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Re: Mains cable size
« Reply #22 on: August 05, 2020, 10:14:56 pm »
Back in 1960, I heard it called "micky-mikes", for micro-micro-farads.
 

Offline Benta

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Re: Mains cable size
« Reply #23 on: August 05, 2020, 10:15:56 pm »
@TimFox: you skipped my favorite unit in American machining tolerancing: the RCH   :-DD

« Last Edit: August 05, 2020, 10:17:34 pm by Benta »
 

Offline TimFox

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Re: Mains cable size
« Reply #24 on: August 05, 2020, 10:18:28 pm »
I have only heard it quoted as "R", never the other colors.  Some claim that the BCH is finer.  Actually, it is about 4 mils or 0.1 mm, so not good enough tolerance for precision work.  Many blueprints have +/- 0.005" as the default tolerance, unless otherwise specified.  The instrument shop at my university usually shot for +/- 0.001 inch.
Europeans think that Americans only measure distances in "football fields".
« Last Edit: August 05, 2020, 10:31:06 pm by TimFox »
 


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