AC cord to use for DC application - Page 1
Forum section: electronics / beginners

author: Greorge
author_rank: Regular Contributor
timestamp: April 01, 2014, 09:29:51 am
content: Hope you don't mind my question.I have 3 cores wire (ex-extension cord) that I want to use for 12V arrangement.I can connect brown core to (+) and Blue to (-) and not worry about the earth wire.But since it is there I thought I’ll connect it too.Have bit of dilemma to couple it with (+) or (-)I thought to connect it to (-) since in real life electrons travel from (-) to (+)How bad is this logic?Does it matter how I connect it?

author: David_AVD
author_rank: Super Contributor
timestamp: April 01, 2014, 09:32:43 am
content: I usually connect a spare (odd) wire to the -ve, mainly to reduce the voltage drop. This can make a difference when you want the "0V" at each end to be as close to each other as possible.Overall there is no advantage either way. Both will reduce losses in the doubled up line.

author: Greorge
author_rank: Regular Contributor
timestamp: April 01, 2014, 09:55:17 am
content: Thanks for help.If I'll get my hands on another ex-2 or 3 core cable,I might use one just for (+) side and the other one for (-)This way I might even put them few centimetres from each other to improve protection against shorting and heat dissipation but with few amps at 12V this should not happen.

author: Psi
author_rank: Super Contributor
timestamp: April 01, 2014, 10:22:20 am
content: +1 for doubling up on ground wire.

author: Zero999
author_rank: Super Contributor
timestamp: April 01, 2014, 07:28:20 pm
content: I agree with the above.What current are you drawing? Don't forget to use a fuse and to respect the current rating of the cable you're using.

author: chipwitch
author_rank: Frequent Contributor
timestamp: April 02, 2014, 02:09:37 am
content: Is there really enough benefit in paralleling only one of the current carrying conductors to make a reasonable argument? I realize there are theoretical benefits, but would a hobbyist, such as myself even be able to discern the difference?

author: David_AVD
author_rank: Super Contributor
timestamp: April 02, 2014, 02:13:31 am
content: There most certainly is benefit; less voltage drop in the cable is almost always a good thing.When other signals are involved (as well as pure DC supply), decreasing the resistance of the common return can also minimise interaction of current surges and signal integrity.

author: chipwitch
author_rank: Frequent Contributor
timestamp: April 02, 2014, 02:23:06 am
content: What I'm asking is could I see a measurable difference as a beginner? It isn't like I have a $4000 bench meter. I realize there is a voltage drop, but on short runs how noticeable would it be? For the sake of argument, since the OP didn't specify, I'm assuming we aren't talking about a huge load here. It would help if I knew what kind of circuit this was. I'm thinking about pretty basic circuits.

author: David_AVD
author_rank: Super Contributor
timestamp: April 02, 2014, 03:34:57 am
content: Quote from: chipwitch on April 02, 2014, 02:23:06 amBut can you assume that the OP is not talking about a huge load?He asked if connecting the spare wire to either + or - would make a difference so I replied in a general way.You asked if there was a discernible difference - that will depend on the load, but in many cases it will be plainly visible using a $10 DMM.

author: VK5RC
author_rank: Unknown
timestamp: April 02, 2014, 09:43:11 am
content: I would go with connecting the spare along with the negative, keeping your grounds (usually the negative) as close to 0v is helpful in stopping odd ground currents if more than one device gets connected later on. You may as well use it if it is sitting there.

author: Greorge
author_rank: Regular Contributor
timestamp: April 02, 2014, 09:33:19 pm
content: Right now it doesn't go above 3A at 12 - 14V DCDistance is about 10 metres

author: Greorge
author_rank: Regular Contributor
timestamp: April 02, 2014, 09:54:37 pm
content: EDIT : JUST CABLE TO BE USED FOR 12V APPLICATION WITHOUT PLUGSHave one topic on AC cable used for DC application, but not sure if better to continue there or start a new one.Other topic was what to do with 3-rd core.Question I have now is how to work out equivalent core cable?If 3 core 1mm AC heavy duty 25m extension cord is used for DC application.Can I safely say that it is equivalent to 3mm DC cable?From what I read there are 4mm and 6mm DC cables for DC applications, but when I look at the prices, I’ll spend less money using 2 AC extension cords than 2 DC cables 4mm onesAlso it will be cheaper to use 4 AC 25m extension cords 1mm 3 core instead of 2 DC cables 6mm onesIs my equivalence assumption correct?DC cables are single wire, AC extension cords are not. Does it make them less suitable?AC cables are for 10A thou.Topics merged.

author: David_AVD
author_rank: Super Contributor
timestamp: April 02, 2014, 10:29:16 pm
content: George,You just need Ohms law to work out the voltage drop, but I wrote a quickcalculatoron my web site that you might find useful.

author: SL4P
author_rank: Super Contributor
timestamp: April 02, 2014, 11:03:09 pm
content: *** PLEASE *** If you are using mains cable to connect low-voltage projects.DO NOT USE THE MAINS STYLE PLUGS & SOCKETSfor anything other than properly wired mains powered devices.

author: con-f-use
author_rank: Unknown
timestamp: April 02, 2014, 11:10:36 pm
content: Quote from: SL4P on April 02, 2014, 11:03:09 pmAgreed. It will almost certainly be plugged into real mains by some poor fool.

author: David_AVD
author_rank: Super Contributor
timestamp: April 02, 2014, 11:43:35 pm
content: Quote from: SL4P on April 02, 2014, 11:03:09 pmI think the OP has already discarded the plug and socket, but a good reminder in general.Quote

author: Greorge
author_rank: Regular Contributor
timestamp: April 03, 2014, 01:10:01 am
content: No plugs, just 3 core cable

author: homebrew
author_rank: Frequent Contributor
timestamp: April 03, 2014, 06:13:28 am
content: Technically you should never use the PE wire for anything other than PE. At least I stick to that rule and make no exceptions!But anyway, with 3 Amps you should't have to worry at all. Decent extension cords are rated at least 10A.As always, play safe!

author: homebrew
author_rank: Frequent Contributor
timestamp: April 03, 2014, 06:23:23 am
content: Quote from: Greorge on April 02, 2014, 09:54:37 pmNo, you can't! Might sound picky but 1mm is something different as 1mm^2.Assuming you meant 1mm^2:Technically it would be the same. Might even be better, due to the enlarged surface for heat dissipation.However (at least in household mains wiring) it is strictly prohibited to double the cores, if a single core is unable to handle the maximum current safely (which would make the doubling pointless). That is because of the danger that one connection could become loose. In that case one core could get overloaded and get hot. And with rising temperature the conductivity decreases and thus even more power is dissipated in that core ...

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: April 03, 2014, 06:29:21 am
content: Just use "figure 8" type speaker cable, it will do the job but cheaper. (Not audiophool grade).Work out your maximum current, specify your maximum allowable voltage drop and you can size the cable accordingly.

author: David_AVD
author_rank: Super Contributor
timestamp: April 03, 2014, 09:29:33 am
content: Quote from: homebrew on April 03, 2014, 06:13:28 amNo sure what you mean here? Are there regulations in some countries that restrict the usage of 3 core cable to mains use?

author: homebrew
author_rank: Frequent Contributor
timestamp: April 03, 2014, 11:37:01 am
content: Quote from: David_AVD on April 03, 2014, 09:29:33 amNo, of course not. But the original question, as I understood, was if it is ok to use all three wires within an extension cord in a low-voltage DC environment.The only regulation, I am aware of is that the green-yellow PE wire must never be used for anything else than PE.But that is just to protect the color coding and prevent accidents. Like some maniacs use standard three-core wire to connect light switches in house installations and use its PE wire as the switched mains live. Later someone else might then mistakenly assume that this wire is PE ...So in essence it is not the 3-core wire whose use is restricted but the color-coding of the PE wire.

author: Holograph
author_rank: Regular Contributor
timestamp: April 03, 2014, 03:50:13 pm
content: How much current are you looking to carry? a 6mm diameter wire would be about 2 gauge (assuming the jacket isn't included in the diameter given), which is good for over 150 amps in most cases. If you really are looking to carry that amount of current, buy thick wire from welding supply shops. Also keep in mind that the current capacity of a wire is mainly determined by the area, so 3x1mm diameter wires are not the same as 1x3mm wire. This gets a bit more complicated at higher AC frequencies where you start getting the skin effect, but that doesn't matter with DC or low-frequency AC.I usually buy power wire for my car audio installations fromhttps://weldingsupply.com/cgi-bin/browsecatalogs.pl?UNDEF:: though I'm not sure what similar sites Australia might have, or how the pricing would be.You technically can combine a bunch of 16 or 14 or 12 (or whatever) gauge wires in parallel, but it doesn't seem advantageous to me to do that. As mentioned above, if you do this, make sure that you always have either all of the wires or none of the wires plugged in. If you're pulling a lot of current and you somehow yank some but not all of the wires, the rest will melt (and could be a potential fire hazard). As also mentioned, this is not within code in structural wiring. But that doesn't necessarily mean it's never acceptable. Just take every precaution that applies to your situation. I mean, heck, the computer you've probably been using to post here is powered by several connections using 16-18 gauge wire in parallel.

author: IanB
author_rank: Super Contributor
timestamp: April 03, 2014, 05:33:56 pm
content: Quote from: Greorge on April 02, 2014, 09:54:37 pmAs noted above in this thread, it's very confusing when you write "1 mm cable" where you probably mean 1 mm2cable. Square millimetres (mm2) is a measure of cross sectional area and this is directly proportional to the current carrying capacity of a wire.Further to the preceding comments you should not guess this, you should design it.Decide how much current you need to carry (how many amps), what voltage drop is acceptable, and how long the cable run needs to be. Then consult a cable calculator like this one:http://www.bulkwire.com/wireresistance.aspUsing such a calculator, figure out the smallest gauge wire that meets your needs and go look for that.(Remember the cable length is twice the distance if you have a two core wire taking current out and back.)The suggestion about figure-8 speaker cable is a good one. This can be obtained on large reels in reasonably thick sizes.

author: Zero999
author_rank: Super Contributor
timestamp: April 03, 2014, 07:25:23 pm
content: Yes that's true. Technically, you shouldn't use the yellow/green wire for anything else but protective earth but that's when it's connected to the mains or as part of an installation, along side other wiring. It it's just being used to power a project and isn't in the same place as other mains cables, there shouldn't be any risk of confusion. If the blue and green/yellow wires are connected together at both ends of the cable, I don't see how this could be an issue and 12V isn't a safety hazard.

author: David_AVD
author_rank: Super Contributor
timestamp: April 03, 2014, 09:19:52 pm
content: Also watch out for how some automotive cable is specified with regard to size. They'll say 4mm (for example), but that's the diameter including the insulation - how nuts is that !

author: David_AVD
author_rank: Super Contributor
timestamp: April 03, 2014, 09:23:00 pm
content: Quote from: homebrew on April 03, 2014, 11:37:01 amWhen used in a mains application, yes. When used for another purpose it's just not relevant.

author: IanB
author_rank: Super Contributor
timestamp: April 04, 2014, 03:16:32 am
content: Quote from: Greorge on April 02, 2014, 09:33:19 pmOK, so it looks like 14 awg or 2 mm2cable should be good for that. With a total conductor length of 20 metres and a current of 3 A the voltage drop would be about 0.5 V. So 14 V at the supply would appear as 13.5 V at the load.

author: Greorge
author_rank: Regular Contributor
timestamp: April 07, 2014, 09:26:44 pm
content: Most appreciate replies and advice.I'll crimp them to make sure that all 3 cores are connected.And will do the same in 2 cores for (-)Might solder them as well.Most exciting is that for $32 AUD I can get 25 metres of two cables 3mm square.That's $1.28 AUD per metre.Will check JayCar for figure 8 speaker cable, but doubt can to better than that.

author: David_AVD
author_rank: Super Contributor
timestamp: April 07, 2014, 09:30:52 pm
content: I would double check the claimed wire sizes by using the number of strands and strand diameter. I made a simpleon-line calculatorfor this a while back.

author: Greorge
author_rank: Regular Contributor
timestamp: April 07, 2014, 09:44:24 pm
content: Quote from: IanB on April 03, 2014, 05:33:56 pmI plugged in some different figures into the calculator and noticed that 400V DC and 1000V DC requires much thinner cables than 12V DC for the same amperage and distance.Got me little bit confused.

author: Zero999
author_rank: Super Contributor
timestamp: April 07, 2014, 10:07:18 pm
content: Quote from: Greorge on April 07, 2014, 09:44:24 pmThat's logical. The calculator selects a cable which gives a volt drop of under 4% of the source voltage and the required current, which will be 16V at 400V and 40V at 1000V.

author: LukeW
author_rank: Frequent Contributor
timestamp: April 07, 2014, 10:44:45 pm
content: I don't think it's ideal practice to use brown and blue standard-coloured mains wires for low-voltage wiring,especiallynot if you have a situation where there is both 240VAC and low-voltage DC within the same apparatus.And if you're actually doing anything with 240VAC wiring, then definitely adhere to the standard colours.But if you're just cutting the plugs off an extension lead and re-wiring the ends to supply low voltage DC to some system, then I guess it's OK as long as there is no other wiring around it could get confused with. And, personally, I'd use the brown for positive and the blue for DC ground.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: April 07, 2014, 11:09:52 pm
content: I think you are allow to use mains cable for non mains purposes but you should really make it clear that it is not mains at both ends.

author: richard.cs
author_rank: Super Contributor
timestamp: April 08, 2014, 08:49:05 am
content: Quote from: LukeW on April 07, 2014, 10:44:45 pmThe standard that defines the blue/brown colour code allows for d.c. power circuits, but technically Brown/Blue is for brown positive and blue earthed, grey/blue for a negative supply, again with blue earthed and brown/grey for a floating d.c. supply.http://electrical.theiet.org/wiring-regulations/cable-colours/harmonised.cfm?type=pdf

author: Holograph
author_rank: Regular Contributor
timestamp: April 08, 2014, 03:47:41 pm
content: Quote from: Greorge on April 07, 2014, 09:44:24 pmFor the same power level, running a higher voltage implies a lower current and a higher impedance circuit, meaning the ratio between the impedance of the circuit and the impedance of the power wires is more favorable with higher voltages (again, keeping load power constant). This means less voltage drop on the wire, which also makes it heat up less, which means you can often use thinner wire.It's best to find a good balance between voltage and current for each specific circuit. You need to consider things like wire gauge / voltage drop / heat, availability of the wire you'd need, the safety of the operator of the equipment (high voltage can present more risk), etc. This obviously matters more and more as the power of the circuit increases.

author: SeanB
author_rank: Super Contributor
timestamp: April 09, 2014, 04:48:57 am
content: I have used IEC connectors for DC power, and sis a simple mod to reduce damage to the equipment if it is accidentally plugged into a mains output ( sometimes people do not read until after the bang). I short live and neutral at the socket inlet, and use the parallel strands as one supply rail, with the earth pin as the common. That way if somebody plugs it into a mains source either the RCD trips or the breaker for the supply trips, with less chance of damage to the device. The shorting wire is normally a 2.5mm stranded conductor pushed through the solder hole in the socket, folded over to the one side again and soldered. It will not blow open before the cable does.Later on I changed to XLR connectors as it is now impossible to confuse power types, though you could have issues with balanced audio though, but there it is less likely to do permanent damage.

author: SL4P
author_rank: Super Contributor
timestamp: April 09, 2014, 05:53:24 am
content: Quote from: SeanB on April 09, 2014, 04:48:57 amRemind me not to come play with your gear !IEC 2/3 way mains connectors for DC is very dangerous.Even 2/3 way Duraplugs (UK/Euro common) for DC is very iffy.

author: David_AVD
author_rank: Super Contributor
timestamp: April 09, 2014, 08:09:55 am
content: Quote from: SeanB on April 09, 2014, 04:48:57 amNow that's just asking for trouble.

author: SeanB
author_rank: Super Contributor
timestamp: April 09, 2014, 06:51:03 pm
content: Like I said, I converted later to use XLR connectors. I used the IEC connectors because I had a shedload, and it was better than taking them and selling to the scrapyard as cable scrap. I did do a lot of them as that though, and even stripped the brass ends off the plugtops to add to the brass pile. Cable $ 1 per kilo and brass $4.

author: N2IXK
author_rank: Frequent Contributor
timestamp: April 09, 2014, 10:21:44 pm
content: Using IEC connectors (or other common mains connectors) for DC is definitely NOT a good idea. At least in the US, it is an electrical code violation, as well.One of my hobbies is model rocketry, and I have seen many rocket clubs which use 50' and 100' cheapo orange extension cords to connect launch pads to the launch control panel. Almost invariably, they leave the standard NEMA 5-15 ends on them because it is easy and cheap. I dread seeing somebody accidentally plugging one of them into the generator running the PA at a launch, while some kid is holding onto a pair of bare alligator clips at the other end.I've mentioned it in passing to a few club safety folks, but most shrug it off as no big deal....Have also seen at least one photographer who used them for flash sync cords on big outdoor shoots.As far as what SHOULD be used, XLRs are good and reasonably rugged. Also available in a 4-pin version if you need another circuit. Neutrik's "speakon" connectors are another good alternative, as are the Anderson powerpoles if the location is dry. There are actually NEMA twistlocks intended and labeled for DC service, but these are seriously obscure, and hard to source.When I put together a small launch system for my local club, I used weatherproof mil-spec PT-series connectors scrounged from surplus. They hold up great, but would cost $$$ to buy new.

author: richard.cs
author_rank: Super Contributor
timestamp: April 10, 2014, 10:06:30 am
content: Quote from: N2IXK on April 09, 2014, 10:21:44 pmOne way of mitigating this is to reverse everything. The croc clips end in a socket and therefore cannot be made live by any reasonable mistake. The launcher end gets a plug and may thus be damaged by connecting to the generator but that's safer. It could be given a hefty diode in the direction that doesn't conduct firing current, a zener the other way and a fuse. It would then fail safely (by popping the fuse) if accidently connected to a genset.

author: Zero999
author_rank: Super Contributor
timestamp: April 12, 2014, 05:48:35 pm
content: Quote from: richard.cs on April 08, 2014, 08:49:05 amThat makes sense but where can one buy blue and grey or or grey and brown cable from?Most cable is brown and blue so that's what tends to be used for DC, with brown for positive and blue for negative, regardless of which conductor is earthed or whether it's floating or not.

author: richard.cs
author_rank: Super Contributor
timestamp: April 12, 2014, 06:14:12 pm
content: Quote from: Hero999 on April 12, 2014, 05:48:35 pmI would imagine when they wrote the standard they were thinking of singles in conduit. I don't know of any flex is made in those colours* but correct procedure would normally be to add appropriately coloured sleeving. In real life nearly everyone uses either brown/blue or red/black for d.c. power irrespective of voltage to earth, nearly everyone knows that they mean and life is good. I have seen brown/grey on floating 5V d.c. power bricks though so someone somewhere has made an attempt.There are exceptions of course. When DC mains supplies existed in the UK they were often distributed at +/- 200V with an earthed neutral in between and each house got one live and the neutral. But inside the house the red was live and the black neutral irrespective of which was + and -. Germany at one time used red for the earth connection (red because it's important, right?) and that caused some nasty accidents.* I've seen (in current production):Brown + blue (L1, N)Brown + blue + g/y (L1, N, E)Brown + black + grey + blue + g/y (L1, L2, L3, N, E)Brown + black + grey + g/y (L1, L2, L3, E)Brown + black + black + blue + g/y (Same colour for L2 and L3, nice)Black + black + black + blue + g/y (Same colour for all three phases, often numbered every few inches)Black + black + black + black+ g/y (Often numbered, but just getting silly)

author: IanB
author_rank: Super Contributor
timestamp: April 12, 2014, 09:43:11 pm
content: Quote from: richard.cs on April 12, 2014, 06:14:12 pmThis colour standard has puzzled me for a while. Why so many similar, neutral colours? Is it something about allowing the different colours to be apparent to people with various forms of colour blindness?

author: N2IXK
author_rank: Frequent Contributor
timestamp: April 12, 2014, 11:17:56 pm
content: Interesting. The (up to 3-phase) US mains cord color code is:Black--HotRed--Hot phase #2Orange or Blue--Hot phase #3White--NeutralGreen or Green/Yellow--Ground.The US colors can be hard to deal with under some unusual lighting conditions (think Na vapor ).Had an electronics teacher once that was colorblind. He ALWAYS checked resistors with a meter before installing them. Not exactly a bad habit even when normally sighted, as I have caught a few mismarked/hard to read ones over the years.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: April 13, 2014, 03:09:00 am
content: I salvaged an old mains lead from something once probably a light. Two core with an inline switch but an Austalian plug without an earth.It was an manufactured plug not hand done, it bore the brand name Hitachi.So Blue (not light blue) was to Active and was switched.Brown was neutral.Caused me a bit of trouble that one.

author: richard.cs
author_rank: Super Contributor
timestamp: April 13, 2014, 05:45:47 pm
content: Quote from: IanB on April 12, 2014, 09:43:11 pmI greatly prefer the old UK one:Green/yellow stripes (originally just green but stripy is better) for earth.Black for neutral.The three primary colours for phases, Red, Yellow (originally white), Blue, just seems logical if you want to pick three colours to identify something similar but different. Earth and neutral are obviously different from the phase colours and each other, and any bright colour is a phase.The European standard as proposed had all the phase conductors the same, optionally brown or black - Mandating Brown/Black/Grey was a late addition. Brown and black were already used as phase colours in many places only the grey was new. Dark brown, light blue, stripy is fairly colour-blind proof but I don't imagine the three-phase stuff is.

author: IanB
author_rank: Super Contributor
timestamp: April 13, 2014, 05:54:06 pm
content: Quote from: richard.cs on April 13, 2014, 05:45:47 pmWith all phase conductors the same, does that pose a problem for wiring up motors where the phase order matters?

author: richard.cs
author_rank: Super Contributor
timestamp: April 13, 2014, 05:55:56 pm
content: I've been told the thinking was just to use a phase rotation tester, you don't actually care that L1 is connected to the L1 terminal, only that the motor turns the right way.