Choosing the right wire gauge for IEC inlets - Page 1
Forum section: electronics / beginners

author: pope
author_rank: Frequent Contributor
timestamp: February 01, 2025, 09:50:10 am
content: Hi there,I'm building a linear power supply with a 60VA transformer (2x30V) and I wonder what wire should I use for the interconnections (IEC inlet/ fuse holder, power switch, Transformer). Everything before the secondaries actually.What should I be looking for?FWIW, The transformer has 20AWG for both the primaries and the secondaries.Should I go with 20AWG or with something thicker like 18AWG?Also, for the PE I have some 16AWG, which hopefully is sufficient?Thank you all!

author: pope
author_rank: Frequent Contributor
timestamp: February 01, 2025, 06:59:06 pm
content: No one?

author: Benta
author_rank: Super Contributor
timestamp: February 01, 2025, 07:19:10 pm
content: 0.75 mm2with Faston spade connectors.

author: floobydust
author_rank: Super Contributor
timestamp: February 01, 2025, 07:48:20 pm
content: In North America, the wire must have the voltage rating (>300V) and be thick enough to clear the supplying fuse/breaker without melting.60VA is not much, maybe a 315mA fuse, I would say you can use skinny wire only downstream of the IEC inlet fuse.But the PE wire must be thick enough to trip the branch circuit which is typically 15A here. It's usually 18ga or 1mm.What a certification agency will do is apply 15A through the ground and observe temperature to see if it's decent.I'm not sure how Europe can have a "6A" IEC cord with skinny wire, yet a 16A branch circuit breaker supplying it. I guess it does not burn when overloaded.

author: Benta
author_rank: Super Contributor
timestamp: February 01, 2025, 09:03:28 pm
content: Quote from: floobydust on February 01, 2025, 07:48:20 pmWhere on earth did you see that? Highly illegal. The IEC cord should have a 16 A "Schuko" plug or equivalent.The 6 A type you refer to would normally have a shaver-style 2-pole female connector.And 0.75 mm2is minimum in all cases.

author: Xena E
author_rank: Frequent Contributor
timestamp: February 02, 2025, 09:31:53 am
content: A lot of commercial equipment has poorly specified cable and seem to choose based on the short runs involved. For instance a metre of 0.75mm* won't "burn" but it should not be considered in coordination with (say) a 16/10 Amp chassis plug for long runs as volt drop along its length will be significant.At full load*Just looking at several manufactured IEC molded line sockets will show this as correct.If this is a product for sale:Use 1.5mm CSA #16 AWG throughout and you're fine. (Extra points if its double insulated singles in equipment).rate for the connector,notthe fuse, or internal load. You are not then responsible for end users who replace the fuse with something unsuitable.X

author: pope
author_rank: Frequent Contributor
timestamp: February 02, 2025, 11:20:06 am
content: I'm a bit confused.Are you guys saying that all these 3A/ 6A/ 10A IEC cords available are illegal? Something like this10A, 3 x 0.75 mm²for example?https://www.schurter.com/en/datasheet/typ_6004.0114.pdf

author: pope
author_rank: Frequent Contributor
timestamp: February 02, 2025, 11:25:18 am
content: Quote from: pope on February 02, 2025, 11:20:06 amAlso, if the transformer has 0.5mm² (20 AWG) wires for both the primaries and the secondaries, is there any benefit in using thicker wire for the inlet/ power switch/ transformer connections?

author: mariush
author_rank: Super Contributor
timestamp: February 02, 2025, 11:43:30 am
content: It's a 60 VA transformer ... if you're gonna power it with 230v AC (as you are in Poland) then the input AC current is going to be under 60 VA / 230V = 0.26 AIt would probably be fine to use a 0.5A slow blow / time delay fuse on your primary as protection.So if you consider that you're gonna have less than 1A of current on the input, you'll be fine with AWG20 or even thinner primary wires.It's all about the insulation, and how much the wires heat up and potentially heat up the insulation when current flows the wires. Get some wire with insulation rated for 300v or more for the primary side. Because you're gonna have such short length of cable from transformer to your mains plugs and all that, it's not even worth calculating the losses in the cables. For example, awg18 wires have 0.021 ohm per meter ... so assuming you're going to have 50 cm of wire from transformer to plug (so 1m in total) and you have 230v in , 0.25A ... you'll have maybe V=IxR = 0.021 x 0.25A = 0.005 v drop or 50mV drop? and the wire will dissipate p = i^2xr = 0.25 x 0.25 x 0.021 = 0.0013 watts?on the secondary side, you don't need insulation that can handle 300v, something that's good for 100v or higher is fine.... 100v is far enough from 60v.Same story with the thickness, though you have 2 30v windings, so you have 30VA on each winding or around 1A , not 0.25A as you have on primary -- if you want as small losses and heat in the wire, it would make sense to go with a bit thicker wire, like AWG16 or AWG18 ... but again, we're not talking about tens of amps here, we're talking 1-2A of current...

author: pope
author_rank: Frequent Contributor
timestamp: February 02, 2025, 12:00:16 pm
content: That's also my understanding.I was thinking of using 0.75mm2 (18AWG) for the Live and Neutral and 16AWG for the PE. However, this might end up being a commercial product (very low scale) so I'd like to get it right from the beginning.But I got confused about the IEC cord rating comments. I'm using plenty of 3A/6A/10A "Schuko" type cords at home. Especially the 10A ones seem to be the most popular and most common.

author: madires
author_rank: Super Contributor
timestamp: February 02, 2025, 12:26:31 pm
content: Yep, 0.5 or 0.75 mm2 H05 should fine. The maximium rating for IEC C13/C14 connectors is 10 A. Standard Schuko is also 10 A for constant load and 16 A for temporary load (IIRC, one or two hours).

author: Xena E
author_rank: Frequent Contributor
timestamp: February 02, 2025, 12:31:17 pm
content: Quote from: pope on February 02, 2025, 11:20:06 amNot necessarily, it's about voltdrop/distance.Installation wiring has normally to take that into account,For instance in the UK, #16 1.5mm CSA is OK for 16 Amp load thats a mandatory thing for installation wiring, and in good condition would never cause any problem in say, a domestic setting.So the engineered choice is to match cabling to the incoming connection, not the outgoing load. If your standard is what's good enough to get the job going and if it's for your own use, use what ever you like:The problems come from fault conditions.For an appliance for sale, you don't have control over what people do, so your choices must not be the cause of any loss or damage.PS... your original post you just specified "IEC inlet" not which one.X

author: pope
author_rank: Frequent Contributor
timestamp: February 02, 2025, 12:39:34 pm
content: Thanks for clarifying.Do you know what are the directives by any chance? It's hard to believe that every manufacturer uses 14/16AWG inside their products.I haven't decided on the IEC inlet yet but I found one that is115/230V 6Aand looks prmising.

author: Xena E
author_rank: Frequent Contributor
timestamp: February 02, 2025, 01:17:45 pm
content: Quote from: pope on February 02, 2025, 12:39:34 pmCheck your local regulations, then don't expect any imported device to meet them! For instance I have seen molded IEC cables that have 0.5mm CSA aluminium cores on a standard british 13A plug... ... that plugged into a device that it wasnt supplied with, the kettle for instance, its going to melt.I visited a factory last year that had a device that caused a fire... the internal cabling had overheated feeding a damaged transformer. The only protective device in circuit was a 10 Amp fuse that was installed as a replacement for a 3.15A one that had failed by the user.If you are using a 10 amp connector your 0.75mm will be adequate over a short run. My confusion was that you just stated "IEC" where there are some that have continuous ratings of 16 Amps C19/20 for instance. I always consider the worst case.https://www.stayonline.com/product-resources/reference-iec320.aspRegardsX

author: Xena E
author_rank: Frequent Contributor
timestamp: February 02, 2025, 01:22:06 pm
content: Quote from: pope on February 02, 2025, 12:39:34 pm3 pole??? Which one?

author: Simmed
author_rank: Frequent Contributor
timestamp: February 02, 2025, 01:23:52 pm
content: there is this chart on the webs about load capability estimationfor the 0.75mm @ 10A, if it is 2 corei think they are stating it at operating temp of 45 50C?so the question would beis the advertizer allowed to bullshit a higher operating temperature ?@ 25C the 10A IEC should be expected to be maybe 19 or 18AWG ?sanity check on digikey, 10A power cords, i see 18AWGeven 6A rated parts are quoted as 18AWGmaybe someone have a better idea about the origin of such a chart

author: pope
author_rank: Frequent Contributor
timestamp: February 02, 2025, 01:31:25 pm
content: Quote from: Xena E on February 02, 2025, 01:22:06 pmhttps://www.qualtekusa.com/product/862-06-007/Why do you find it surprising? There are inlets that are rated all the way down to 1A

author: Xena E
author_rank: Frequent Contributor
timestamp: February 02, 2025, 01:40:39 pm
content: Quote from: pope on February 02, 2025, 01:31:25 pmSelf contained! Never actually used one (not with a combined voltage selector). But looks a good choice and conservatively rated too. For coordination it means that your 0.75 would definitely be OK in a design.X

author: themadhippy
author_rank: Super Contributor
timestamp: February 02, 2025, 01:53:10 pm
content: QuoteBit of a blanket statement,the current rating depends on sevral factors,theirs 1.5mm cable thats rated for 24AAs for what size cable Ib ≤ In ≤ Iz is a good mantra to follow,or that the design current is equal to or less than fuse rating which is less than or equal to the cable rating.Quotewhy the different size? the earth aint gonna be carrying any more current than the other two,infact its often allowable to have the protective conductor half the size of the phase on fixed installations.

author: Xena E
author_rank: Frequent Contributor
timestamp: February 02, 2025, 02:09:18 pm
content: Quote from: Simmed on February 02, 2025, 01:23:52 pmThe chart looks reasonable. I have experience of a load of ≈ 10 A through a 0.75 copper conductor IEC cord being used on equipment not the one supplied by the manufacturer, the connector was ok but after 20 minutes the cable was uncomfortably hot to touch.I think the chart is for reference not recommendation.

author: Xena E
author_rank: Frequent Contributor
timestamp: February 02, 2025, 02:19:43 pm
content: Quote from: themadhippy on February 02, 2025, 01:53:10 pmAbsolutely right.If I had to use thinner singles in equipment then perhaps look at tri-rated,X

author: pope
author_rank: Frequent Contributor
timestamp: February 02, 2025, 04:15:53 pm
content: Quote from: themadhippy on February 02, 2025, 01:53:10 pmThat's a good point.

author: Zucca
author_rank: Unknown
timestamp: February 05, 2025, 07:25:18 pm
content: Quote from: themadhippy on February 02, 2025, 01:53:10 pmI was told that you want the PE to have less resistance than the rest, so the current will for sure "chose" to flow there and trip the GFCI.The bigger the better in a safety point of view.