Mains cable size - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: August 04, 2020, 03:05:30 pm
content: 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 strandsBut 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

author: Benta
author_rank: Super Contributor
timestamp: August 04, 2020, 04:18:59 pm
content: 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.

author: themadhippy
author_rank: Super Contributor
timestamp: August 04, 2020, 05:35:16 pm
content: 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

author: Zero999
author_rank: Super Contributor
timestamp: August 04, 2020, 05:41:56 pm
content: In the UK, mains cables are specified in mm2but 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."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.htmNote how mains cables in RS and similar UK suppliers, are specified in mm2https://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_60228Although we also use 1.25mm2for 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

author: TimFox
author_rank: Super Contributor
timestamp: August 04, 2020, 06:22:37 pm
content: 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 mm2area). I have been accused of being a stickler for language, but proper usage is important in technical applications.

author: ricko_uk
author_rank: Super Contributor
timestamp: August 04, 2020, 06:41:43 pm
content: Thank you allAnd all funny stories!!

author: Benta
author_rank: Super Contributor
timestamp: August 04, 2020, 06:52:35 pm
content: Quote from: TimFox on August 04, 2020, 06:22:37 pmAmen!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).

author: TimFox
author_rank: Super Contributor
timestamp: August 04, 2020, 07:32:04 pm
content: 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).

author: langwadt
author_rank: Super Contributor
timestamp: August 04, 2020, 07:35:47 pm
content: Quote from: Benta on August 04, 2020, 06:52:35 pmyep same here

author: Zero999
author_rank: Super Contributor
timestamp: August 04, 2020, 10:07:03 pm
content: Quote from: TimFox on August 04, 2020, 07:32:04 pmOnly 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 1mm2cable. The only people who'll know about the US usage are those who've dealt with US companies or used US CAD software.QuoteWe 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.

author: TimFox
author_rank: Super Contributor
timestamp: August 04, 2020, 10:17:34 pm
content: 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.

author: tooki
author_rank: Super Contributor
timestamp: August 05, 2020, 10:26:10 am
content: Quote from: ricko_uk on August 04, 2020, 03:05:30 pmWhat might also confound the issue is that a 1.5mm2solid 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.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 05, 2020, 12:29:45 pm
content: Quote from: TimFox on August 04, 2020, 10:17:34 pmSorry, no, an Imperial hundredweight is 112 lbs, a stone is 14 lbs, (8x14 =112).

author: JohanH
author_rank: Frequent Contributor
timestamp: August 05, 2020, 12:48:22 pm
content: 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).

author: TimFox
author_rank: Super Contributor
timestamp: August 05, 2020, 01:04:20 pm
content: 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.

author: themadhippy
author_rank: Super Contributor
timestamp: August 05, 2020, 01:42:45 pm
content: 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 1.5mm2talk

author: TimFox
author_rank: Super Contributor
timestamp: August 05, 2020, 03:12:40 pm
content: 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.

author: Zero999
author_rank: Super Contributor
timestamp: August 05, 2020, 08:51:26 pm
content: 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.

author: Benta
author_rank: Super Contributor
timestamp: August 05, 2020, 09:08:01 pm
content: 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)

author: TimFox
author_rank: Super Contributor
timestamp: August 05, 2020, 09:30:05 pm
content: 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" = 10-4inch, 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".

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 05, 2020, 09:45:44 pm
content: Quote from: TimFox on August 05, 2020, 09:30:05 pmThe 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.

author: langwadt
author_rank: Super Contributor
timestamp: August 05, 2020, 09:45:52 pm
content: Quote from: Benta on August 05, 2020, 09:08:01 pmhere it is "piff"

author: TimFox
author_rank: Super Contributor
timestamp: August 05, 2020, 10:14:56 pm
content: Back in 1960, I heard it called "micky-mikes", for micro-micro-farads.

author: Benta
author_rank: Super Contributor
timestamp: August 05, 2020, 10:15:56 pm
content: @TimFox: you skipped my favorite unit in American machining tolerancing: the RCH

author: TimFox
author_rank: Super Contributor
timestamp: August 05, 2020, 10:18:28 pm
content: 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".

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 05, 2020, 10:28:40 pm
content: Quote from: TimFox on August 05, 2020, 10:18:28 pmWhy would yanks measure in soccer pitches?

author: calzap
author_rank: Frequent Contributor
timestamp: August 06, 2020, 12:20:40 am
content: There's an insane mix of gauges for wire, needles and drill bits in the U.S. SWG (standard wire gauge aka British standard wire gauge) isn't used much ... guitar strings is about it. SWG is not the same as AWG (American wire gauge aka B & S [Browne and Sharpe] gauge), used for electrical wiring. Then there's BWG (Birmingham wire gauge aka Stubs iron wire gauge) used for hypodermic needles and iron (not steel!) wire. There's the crazy number/letter drill gauges. And the W&M (Washburn and Moen) gauge used for steel wire, which is not to be confused with Stubs steel wire gauge. Finally, there is U.S. standard gauge for sheet metal, which is not to be confused with American wire gauge.Help!Mike in California

author: Pawelr98
author_rank: Regular Contributor
timestamp: August 06, 2020, 12:37:07 am
content: I prefer the cross section in mm2 because it allows direct calculation (or looking up the table) of resistance regardless of the shape.In shops very often wiring is only marked as 3x2.5, assuming mm2 as the unit.Only some people use AWG because they deal with US documents.My friend who is a an proffesional RC model racer uses AWG all the time because a lot of documents and guides use AWG.

author: TimFox
author_rank: Super Contributor
timestamp: August 06, 2020, 01:11:13 am
content: The number/letter drill gauges are not crazy. The exponential steps allow one to get within a given fraction of a desired size, just like the standard resistor values. You need a table anyway to specify the tap drill size, even for “non-crazy” screw sizes like M3 or 1/4-20 UNC.

author: langwadt
author_rank: Super Contributor
timestamp: August 06, 2020, 01:28:36 am
content: Quote from: TimFox on August 06, 2020, 01:11:13 amM3 is 0.5mm pitch so the drill size is is 3.0-0.5 = 2.5mm ...

author: TimFox
author_rank: Super Contributor
timestamp: August 06, 2020, 01:52:12 am
content: I would have to look up the pitch on a screw labeled M3. There are also entries in a good tap drill table for “cutting taps” and “forming taps”. For example,https://www.gfii.com/images/Greenfield_Tap_Drill_Recommendations.pdf

author: Clear as mud
author_rank: Regular Contributor
timestamp: August 06, 2020, 02:06:14 am
content: Quote from: vk6zgo on August 05, 2020, 12:29:45 pmOh, I always thought a stone was 20 lbs. I guess whenever I saw a British person give their weight in stones, I thought they were quite a bit heavier than they really were!