Why is daisychaining multiple extension cords considered unsafe, even if only done to the length of a standard cable?

Submitted ⁨⁨2⁩ ⁨weeks⁩ ago⁩ by ⁨Baku@aussie.zone⁩ to ⁨[deleted]⁩

“never plug extension cords into extension cords” is probably the most common piece of electrical related advice I’ve ever heard. But if you have, say, 2 x 2m long extension cords, and you plug one into the other, why is that considered a lot more unsafe than just using a single 4 or 5 meter cord?

Does it just boil down to that extra connection creating another opportunity for the prongs to slip out and cause a spark or short circuit? Or is there something else happening there?

For that matter - why aren’t super long extension cords (50 or more meters) considered unsafe? Does that also just come down to a matter of only having 2 connections versus 4 or more on a daisy chained cord?

Followup stupid question: is whatever causes piggybacked extension cords to be considered unsafe actually that dangerous, or is it the sort of thing that gets parroted around and misconstrued/blown out of proportion? On a scale from “smoking 20 packs of cigarettes a day” to “stubbing your toe on a really heavy piece of furniture”, how dangerous would you subjectively rate daisy chaining extension cords, assuming it was only 1 hop (2 extension cords, no more), and was kept under 5 or 10 metres?

I’m sure there’s probably somebody bashing their head against a wall at these questions, but I’m not trying to be ignorant, I’m just curious. Thank you for tolerating my stupid questions

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Kolanaki@yiffit.net ⁨2⁩ ⁨weeks⁩ ago
It increases the risk of electrical overload and overheating as it adds more resistance to the circuit.

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- Baku@aussie.zone ⁨2⁩ ⁨weeks⁩ ago
  Thanks for the response! Would you mind going a bit more in depth about that please? I could understand increasing the risk of overload if you were to daisychain power boards, as they add more power points to the circuit than it was designed for. But extension cords (at least in my experience) only have 2 ends - one with a single plug receptacle, and the other that plugs into a power point
  
  Is it the actual connection between the two that adds more resistance to it? If it were the wiring, then wouldn’t that also pose a problem for longer extension cords?
  
  In either case, what sort of resistance add are we talking about (feel free to pick random lengths of examples make it easier to explain)?
  
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  - FourPacketsOfPeanuts@lemmy.world ⁨2⁩ ⁨weeks⁩ ago
    I don’t think what they said is actually a problem, it’s just a back-justification for the original trope. Daisy chaining them and strictly sticking to only the few appliances that would fit in one extension strip is fine. But that’s complicated to explain, it’s better to just tell people not to do it rather than expect them to understand what’s going on
    
    A couple things that can happen…
    
    plugging in too many appliances over several daisy chained power strips trips the circuit breaker because too much current is being drawn
    
    if the country you live in has lax electrical safety standards then, yes, perhaps you can overload the daisy chain without tripping the main circuit which would lead to overheating
    
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- Zacryon@feddit.org ⁨1⁩ ⁨week⁩ ago
  Isn’t the added cable resistance small enough to not cause issues so soon? In case you just chain a few ( < 10 ) together.
  
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  - Cort@lemmy.world ⁨1⁩ ⁨week⁩ ago
    It’s not the cable resistance but the added resistance at each connection point. Since the plugs aren’t the same piece of metal, just touching.
    
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BillibusMaximus@sh.itjust.works ⁨2⁩ ⁨weeks⁩ ago
The longer the distance, the larger the diameter of the wire you need, due to resistance/heat.

Typically, extension cords are going to be manufactured with the thinnest wire they can get away with based on the safety requirements, in order to save on materials cost.

So plugging 2 short cords together might cover the same distance as 1 longer cord, but the longer cord will use thicker wire to maintain the proper margin of safety.

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- scarabic@lemmy.world ⁨1⁩ ⁨week⁩ ago
  It’s not just the minimum materials in order to be cheap, period. They are given the minimum copper and shielding they need for the length they are made.
  
  As soon as you plug two together, you’re operating at greater resistance than either one was made for, and relying on the margin of error.
  
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  - Lanthanae@lemmy.blahaj.zone ⁨1⁩ ⁨week⁩ ago
    I’ve run a full DJ setup with speakers, a mixer, soundboard, laptop, etc. off a single line of 6-8 daisy-chained extension cords more times than I can count.
    
    …uh…how have I never learned of this.
    
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- kevincox@lemmy.ml ⁨1⁩ ⁨week⁩ ago
  But unless coiled up on the ground the longer cable also has more area to dissipate heat, so the longer cable doesn’t change anything here. The heat output will be consistent for any section of the cable no matter how much more cable there is on easier side of it.
  
  The only think that the different resistance would affect is the voltage drop to the end device. But voltage drop varies wildly so you are unlikely to have a meaningful difference caused by a few extension cords (unless maybe you are already a bad case like an apartment building to start).
  
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  - Xtallll@lemmy.blahaj.zone ⁨1⁩ ⁨week⁩ ago
    Resistance of a cable is (resistivity x Length)/(πr^2) so the residence increases with length, which is why longer extension cords are designed thicker to reduce resistance. Power grids are voltage stabilized so the voltage drop will be negligible but it will take more power to get down the daisy chain, producing more heat.
    
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  - HeckGazer@programming.dev ⁨1⁩ ⁨week⁩ ago
    The longer wire (being also thicker) has less resistance and is therefore wasting less power as heat, that’s where the Voltage drop is going.
    
    Sure, most of the time it’s fine if you know what you’re doing, but that’s why it’s general wisdom and not a hard rule, like “don’t put metal in the microwave”, it’s said to protect those that have no idea what they’re doing/why the saying exists
    
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- fine_sandy_bottom@lemmy.federate.cc ⁨1⁩ ⁨week⁩ ago
  I have no idea whether this really is the answer but it seems like the most plausible answer.
  
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- douglasg14b@lemmy.world ⁨1⁩ ⁨week⁩ ago
  Distance by itself would be no different than a single cord of the same length.
  
  However, connection points are areas of localized resistance where connectors meet. This can introduce dangerous areas.
  
  The practical, human, problem here is important. Connectors come loose, which makes them dangerous. The majority of this thread is treating this question like a paper test problem, when in reality there are other factors that outweigh the “under ideal circumstances” problem.
  
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- uis@lemm.ee ⁨1⁩ ⁨week⁩ ago
  The longer the wire, the more heat it can dissipate, so no, you don’t need wire to be thicker.
  
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  - gazter@aussie.zone ⁨1⁩ ⁨week⁩ ago
    Not sure if you’ve ever used fuse wire before. It’s what was used before capsule fuses and breakers. Essentially, if too much current goes through it, it will melt, breaking the circuit as protection. The thicker the fuse wire, the more current it can pass through without melting. The length of the wire doesn’t come into it. 1cm of 10 amp fuse wire will melt at the same current as 1 meter of 10 amp fuse wire.
    
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tiefling@lemmy.blahaj.zone ⁨2⁩ ⁨weeks⁩ ago
Meanwhile landlords: "one 50 year old outlet should be enough for two bedrooms right?*

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- EleventhHour@lemmy.world ⁨2⁩ ⁨weeks⁩ ago
  50 years old? Most of the landlords I’ve dealt with in my life consider 100 year old outlets to be perfectly sufficient, along with their carrying capacity and number in each room.
  
  “ it was enough to power a lightbulb in 1925, so it should be perfectly sufficient for your needs with all of your TVs and computers and such.”
  
  With one landlord, I actually had to call the city inspector into the building in order to verify that the power supply for each apartment fell beneath city requirements. He spent the next three years doing everything in his power to get me out. It cost him 50 grand.
  
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- Baku@aussie.zone ⁨2⁩ ⁨weeks⁩ ago
  This, along with hotels that hide their only PowerPoint behind the bed but have 50 bloody phone jacks, are my pet peeves. But it kinda makes sense when you consider they were mostly built before the days of having a ton of devices in the bedroom. A lamp and alarm clock, maybe a TV if you’re well off, would’ve been perfectly fine for a lot of people
  
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  - glimse@lemmy.world ⁨2⁩ ⁨weeks⁩ ago
    The absolute worst is when the Word Documents are stashed away in some random drawer. Or when you find an Excel spreadsheet under the mattress!
    
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  - litchralee@sh.itjust.works ⁨2⁩ ⁨weeks⁩ ago
    I once read a theory on an electricians forum about how the USA electrical code’s mandated maximum distance between adjacent outlets on a wall, coupled with the typical bedroom layout, as well as home builders trying to be as cheap as possible, led to only a single outlet being placed directly in the middle of the longest wall. This is also the most logical position for a bed, so the theory is that the bed pressing against the outlet over time was a contributing factor to electrical-related house fires.
    
    I cannot find where I read that originally, and certainly the granularity of nationally-reported fire data is not sufficient to prove that theory. And while the electrical code’s distance requirements haven’t changed, more homes will now put enough outlets so the only one isn’t behind the bed.
    
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- Boozilla@sh.itjust.works ⁨2⁩ ⁨weeks⁩ ago
  Years ago, I used to play live music. We played in a lot of shitty dive bars. Thinking back on all the ancient decrepit plugs we used to power our instruments, amplifiers, and stage lights with…it’s a miracle we never started a fire. Nightmare fuel now that I’m older and a little bit wiser.
  
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JordanZ@lemmy.world ⁨1⁩ ⁨week⁩ ago
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- lime@feddit.nu ⁨1⁩ ⁨week⁩ ago
  lol “gauge”
  
  americans will use anything except the metric system
  
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  - Successful_Try543@feddit.org ⁨1⁩ ⁨week⁩ ago
    16 AWG – 1.3 mm^2
    14 AWG – 2 mm^2 12 AWG – 3.3 mm^2 10 AWG – 5 mm^2
    
    For us from the civilised part of the world ;-)
    
    However, as in Europe we have 230 V system, approximately half the cross section, stated in the table above, is sufficient.
    
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  - Thavron@lemmy.ca ⁨1⁩ ⁨week⁩ ago
    I’ve always found gauge to be especially odd, because the number gets smaller as you go bigger, so at one point you can’t go any further even though you can go fatter.
    
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  - Kaput@lemmy.world ⁨1⁩ ⁨week⁩ ago
    What is the metric unit for cables?
    
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  - GrammarPolice@lemmy.world ⁨1⁩ ⁨week⁩ ago
    !anythingbutmetric@discuss.tchncs.de
    
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- douglasg14b@lemmy.world ⁨1⁩ ⁨week⁩ ago
  Is it just me or is anyone else perturbed that the cable sizes in this infographic are all the same gauge?
  
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  - rekabis@lemmy.ca ⁨1⁩ ⁨week⁩ ago
    
    the cable sizes in this infographic are all the same gauge?
    
    They’re not. They are clearly marked as different gauges, except the left most two which have different plug types… one is two prong, the other is three prong.
    
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  - Mesophar@lemm.ee ⁨1⁩ ⁨week⁩ ago
    Do you just mean the art showing them as the same size? Because that’s common in a lot of infovraphics to not be to scale if they are clearly labeled
    
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- rekabis@lemmy.ca ⁨1⁩ ⁨week⁩ ago
  
  a 50ft 12 gauge extension cord is about $40
  
  $40USD would be $58CAD.
  
  A 50-ft 12-gauge extension cord costs $112+ CAD anywhere in Canada. A 100-ft is $200+ CAD. Like… fffffuuuuuck.
  
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- MonkderVierte@lemmy.ml ⁨1⁩ ⁨week⁩ ago
  Space heaters are “medium duty” while a router is “heavy duty”?
  
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  - Mongostein@lemmy.ca ⁨1⁩ ⁨week⁩ ago
    This is also known as a router
    
    Image
    
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  - Battle_Masker@lemmy.world ⁨1⁩ ⁨week⁩ ago
    router as in ‘tool for finer details in woodworking.’ most router motors can spin at 10000rpm at their lowest and anything with a motor, by definition, uses more power than something without a motor
    
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- uis@lemm.ee ⁨1⁩ ⁨week⁩ ago
  It doesn’t make sense. Temperature difference does not depends on length.
  
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  - lightnsfw@reddthat.com ⁨1⁩ ⁨week⁩ ago
    Adding length creates more resistance which creates more heat. Thinner conductors can’t handle it as well.
    
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Dark_Arc@social.packetloss.gg ⁨2⁩ ⁨weeks⁩ ago
There are two things going on here.

The first is that yes, more connections causes more opportunities for the plugs to slip. So you can get short circuits or even arcing that can start a fire.

The second is that the wire in the cord has a certain rating on it. Many of those cords do not use 12 (20 amp) or 14 (15 amp) gauge wire; so, they’re not rated for the full capacity of the wire in the wall. The breakers are sized to protect the wires in the wall, they don’t know anything about the things plugged into them. So what can happen is you plug too much into the extension cord (particularly if it’s a power strip) and the load on the extension cord is not enough to trip the breaker (because the walls are fine) but it’s enough to overload the extension cord wire. In other words, the extension cord can start getting so hot it melts and possibly arcs up as the insulation fails.

You can have a fire from overloading a single power strip in just the same way. However, the more you chain together, the more likely you are to overload the power strip.

Ideally, you just think about what you’re doing… But historically the easy answer is just to tell people not to chain things.

In short it’s not about the distance, it’s about the insulation and quality of the wire itself along with the number of connections.

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- Baku@aussie.zone ⁨2⁩ ⁨weeks⁩ ago
  Awesome answer - thank you!!
  
  Although I guess a more general question - why aren’t all power boards and extension cords mandatorily fitted with their own circuit breakers/overload protection circuits? I guess it’s cheaper to just tell people never to daisy chain, but at the same time, when you factor in overall costs incurred by anybody (or insurance companies, etc) from people unintentionally overloading them and causing them to melt and burn down houses, wouldn’t it be in everybody’s best interests to raise the price a few dollars and include a resettable overload protection system?
  
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  - Catoblepas@lemmy.blahaj.zone ⁨1⁩ ⁨week⁩ ago
    Technology Connections made a 25 minute video about American extension cords and why they’re dangerous, if you want to watch a long form answer.
    
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  - DaPorkchop_@lemmy.ml ⁨2⁩ ⁨weeks⁩ ago
    iirc British plugs do have a fuse built in to every plug, but they are also the only ones who do that
    
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  - Dark_Arc@social.packetloss.gg ⁨2⁩ ⁨weeks⁩ ago
    Some power systems do actually put a fuse in the extension cord… I think it’s the UK that does this. Basically every power system other than the US uses different (safer) plug designs that solve the arcing problem.
    
    In practice daisy chaining rarely causes a serious problem and it makes things more expensive so it never really became a thing that was legislated or common within the US. Similar to how the plug designs themselves rarely cause a problem so it hasn’t made sense to actually change them.
    
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Free_Opinions@feddit.uk ⁨1⁩ ⁨week⁩ ago
Related thing about extension cable reels that many don’t know is that even if you need like 3 meters of cable you should still unspool the entire thing as otherwise it’s acting as a coil and creating resistance. Most cable reels have different ratings marked on them for when they are spooled / unspooled.

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- modeler@lemmy.world ⁨1⁩ ⁨week⁩ ago
  Many years ago, my mother used the electric lawn mower without unspooling all the wire. When it finally shorted, all the plastic wire insulation was in the process of turning into a melty plastic soup. A Lesson Was Learned.
  
  The reason isn’t resistance - it’s that the coiled wire makes an electromagnet that stores energy in the magnetic field. The alternating current in the mains switches 50 or 60 times a second. In each cycle the magnetic field is created, destroyed then recreated in the opposite direction, then destroyed. This dumps a lot of energy (and therefore heat) into the coil.
  
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  - brown567@sh.itjust.works ⁨1⁩ ⁨week⁩ ago
    The coil wouldn’t make a significant magnetic field because the cable has two wires with opposite current flow in close proximity
    
    But when the cable is coiled, its ability to dissipate heat is less, so normal resistive heating can create higher temperatures
    
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  - uis@lemm.ee ⁨1⁩ ⁨week⁩ ago
    Inductance is not the reason here
    
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- uis@lemm.ee ⁨1⁩ ⁨week⁩ ago
  Yes! There is a video about this. Heat in spool of cord is trapped.
  
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SolOrion@sh.itjust.works ⁨2⁩ ⁨weeks⁩ ago
First, I’m not an electrician, or anything even vaguely approaching one.

I’ve never heard that advice with extension cords, only power strips.

You could theoretically link enough extension cords together to cause problems, but it would need to be some extremely shit extension cords or a LOT of them. Resistance increases over distance, which in power cables manifests as them getting hotter. That isn’t a problem until all the sudden it is a problem.

For power strips, the main danger is that you’re potentially introducing more outlets than any of them are rated for. If you’re just using 2 3ft power bars to functionally make a 6ft cable that you’re only plugging a single thing into… you’re fine. Or at least I was, idk I did it for like a whole year. If you’re plugging 16 things into a single wall outlet via power strips you can trip the circuit breaker, or potentially much worse stuff can happen like things getting melty and starting a fire.

If you know enough of what you’re doing to math out the power draw+what your outlet/power strips are rated for you can pretty (afaik) safely daisy chain them if you wanna.

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- kevincox@lemmy.ml ⁨1⁩ ⁨week⁩ ago
  Yeah, there are two components here
  
  Adding extra length.
  
  Adding more outlets.
  
  2 is the main problem, but you need a little of 1 to have it fail in an unsafe way (ie. not just tripping the circuit breaker).
  
  If you just add a lot of extra outlets and plug lots of stuff in then you will simply trip the circuit breaker. (Assuming that everything is properly set up according to code.) In order to create a problem you need some extra wiring that is rated for less load than the wall wiring. (Now in practice every splitter has some amount of wiring, so these can be the same device, but most power bars are rated to be “fully used” or have a fuse internally). So the problem looks something like this:
  
  Have a 20A wall circuit.
  
  Plug a 10A extension cord into it.
  
  Plug a power bar or other splitter into the extension cord.
  
  Put enough devices into the splitter to generate 15A of current.
  
  Now you are overloading the extension cord and risking fire.
  
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uis@lemm.ee ⁨1⁩ ⁨week⁩ ago

On a scale from “smoking 20 packs of cigarettes a day” to “stubbing your toe on a really heavy piece of furniture”, how dangerous would you subjectively rate daisy chaining extension cords

As dangerous as one extension cord of their combined length. Don’t forget to verify that every cord is below load rating.

AND NEVER COIL OR THERMALY INSULATE! Cords rely on convection for heat dissipation, and spooling and insulating reduces it, thus increasing insulation temperature until it melts and spontaneously combusts. This applies to extension cords in general.

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- tacosplease@lemmy.world ⁨1⁩ ⁨week⁩ ago
  Because this is the Internet, I’ll be pedantic and say the interface where each cord plugs into the next probably adds some resistance as well.
  
  So, 50 cords 1 ft each plugged into each other would have a higher resistance than the same wire at a single 50ft length.
  
  I doubt it really matters in the practical terms of your answer and the question being asked though.
  
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  - uis@lemm.ee ⁨1⁩ ⁨week⁩ ago
    *insert technically correct*
    
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douglasg14b@lemmy.world ⁨1⁩ ⁨week⁩ ago
Connectors come loose, which makes them dangerous.

They are uninsulated points that allow water and material ingress, and can partially or fully pull apart, causing arching. Which can cause combustion.

This is the main reason these are dangerous, which the majority of this entire thread misses. The added length or connector resistance is somewhat negligible here unless you’re daisy chaining long conductors, which often isn’t the case for in-home extensions.

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litchralee@sh.itjust.works ⁨2⁩ ⁨weeks⁩ ago

I’m not trying to be ignorant, I’m just curious.

I think you’re in the right community! Don’t let anyone tell you to shy away from asking curious questions. (well, unless the question is also bigoted, illegal, baiting, sealioning, or otherwise disingenuous)

I’m not an electrician in any jurisdiction, but one answer for why two 2-meter (~6 ft) extension cords in series is inadvisable compared to a single 4 meter cord is that it’s not an apples-to-apples comparison. Longer cords necessarily have to be built differently than shorter cords, not only because of electrical codes (eg the NEC in USA) or product safety specs (eg UL, CSA) but also being well-designed for their expected use. There’s also the human aspect, which all good designs must account for as well.

Here in the USA, common extension cord lengths are ~2 m (6 ft), ~7.5 m (25 ft), ~15 m (50 ft), and ~30 m (100 ft). Of those cords, the common wire gauge used might be 18 AWG (~1 mm^2), 14 AWG (~2 mm^2), 16 AWG (~1.5 mm^2), and 12 AWG (~3.5 mm^2). I’ve intentionally rounded the metric units so they’re more analogous to common wire gauges outside the USA. Finally, the insulation used can be anything from “thin, indoor only” to “heavy, abrasion and sunlight resistant”. And while the USA technically has a boat-load of AC connectors, the grand majority will use the standard 2-pin or 3-pin 120v connector, formally known as NEMA 1-15 and NEMA 5-15 respectively. What this means is that chaining extension cords is both possible and somewhat common. The problem is one of mismatched designs.

From a cursory search on the website of a major USA home improvement store, the smallest wire gauge used for a 100 ft cable is 16 AWG. The largest is 10 AWG (nb: smaller numbers mean bigger wire). That thinner cable is marketed for outdoor use. The thicker cable indicates its use “indoor/outdoor” and for heavy-duty applications. It is also branded with a major power-tool company, which would be appropriate as power tools often draw high current.

Whereas looking at 6 ft extension cords, most are 16 AWG but a few were 18 AWG (thinner than 16) or 14 AWG (thicker). But I could not find any thicker cables than that, certainly nothing that uses 10 AWG (~6 mm^2). The “heavy duty” cables of this length also used only 16 AWG wire.

Because electrical resistance is additive in series, and because Ohm’s Law governs the voltage lost at the end of a cord, the use of insufficiently large conductors can cause voltage issues for high-current appliances. Appliances for USA-spec generally require 120 Volts +/- 10%, with utilities aiming to provide 120 Volts +/- 5% from the outlets. This means a “sufficient” power cord should not have a voltage drop of more than 6 volts, give or take. Of course, a high-current appliance will also cause a larger voltage drop than a low-current device, so we only consider the former case.

For a machine that draws 12 Amps attached to a 100 ft extension cord made of 18 AWG wire, the voltage drop would be 15 volts. This is bad for the machine, which now sees a lower voltage than expected. Had the cord been made of 12 AWG wire, the drop is an acceptable 3 volts.

So if you’re operating construction tools, it would be a terrible idea to use three random 6-ft cables, and you should instead use a single 25-ft cable. Even though it’s longer than you need, the fact is that most 25 ft cables use thicker conductors, which reduces the voltage drop overall.

But there’s also that peaky human factor. Sure, there would also be more connectors which could come loose, but the really pressing issue with daisy chained cords is when people do that indoors, because they only have light-duty 6 ft cables handy. And for that Christmas tree, they need to use attach three cables together to go beneath the hallway rug.

This is essentially the worst-case scenario: using thin conductor cords, with thin insulation, underneath very flammable household surfaces, which are also trodden upon by foot traffic. Every step on that cord weakens the insulation and fatigues the conductors. Over time, the conductor becomes thinner where it’s being fatigued, and this increases the voltage drop. An unfortunate result of a voltage drop is that it generates heat. For a cable which is uniformly thin, this heat is spread over the whole length. But for localized conductor damage, the heat is pin-point… directly under a flammable rug.

In the USA, some 3300 house fires started from an extension cord. Because these cords are not within the walls, they are usually beyond the control of often-strict building/electrical codes, something that’s been critiqued by a prominent YouTuber. The US CPSC even goes so far as to create memes to promote their messaging that space heaters – a common, high-current appliance – should not be used with extension cords or strips.

Of course, from an electrical perspective, even a ten-long chain of dinky extension cords would have no problem powering just a single LED night light. But it’s reasonable to ask: 1) is this just asking to be struck down by fate, 2) are there better alternatives like thicker/longer cords, and 3) why isn’t there an outlet where you need it?

(There’s also a scenario where too long or thin of an extension cord can cause a circuit breaker to fail to trip during a short circuit, but it’s fairly esoteric and this post is quite long now)

In short, the blanket recommendation to avoid daisy-chaining cords is to avoid the nasty and sometimes fatal results when that can go wrong, even with it might not always play out that way. There’s almost always something safer than can be done than daisy chaining.

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- Sir_Premiumhengst@lemmy.world ⁨1⁩ ⁨week⁩ ago
  +1 for technology connections video. Was going to post the same link.
  
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fmstrat@lemmy.nowsci.com ⁨2⁩ ⁨weeks⁩ ago
The longer the cable, the thicker it needs to be to carry the same amount of current without getting hot. This is due to resistance (Wikipedia does a good job with the details). Basically:

20’ cable be long and thick.

10’ cable be short and thin.

10’ + 10’ cables be long and thin.

Long and thin = heat then fire.

That being said, put an LED light bulb at the end, no problem. Put a gaming PC on the end, problem.

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- ArbitraryValue@sh.itjust.works ⁨2⁩ ⁨weeks⁩ ago
  I don’t think you’re right about heat. Two cables in series have double the resistance and therefore double the total heat generation, but that heat energy is split between the two cables so each one does not get hotter than if it was the only cable.
  
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  - fmstrat@lemmy.nowsci.com ⁨2⁩ ⁨weeks⁩ ago
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    Current and Voltage don’t change, but resistance does (between cable types)?
    
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Boozilla@sh.itjust.works ⁨2⁩ ⁨weeks⁩ ago
The smart answer: it can start a fire, don’t do it.

The honest answer: I’ve done it a zillion times and never started a fire. I buy heavy 12 and 10 gauge cords and only chain them to power things that don’t require a lot of amps, like LED lights.

When in doubt, a plug-in power meter is an option you can use to help monitor the situation. Plugs that draw a lot of amps can get warm, even when not using an extension cord. Also, it’s not uncommon for a device to pull a lot of amps on initial power-up, and then settle down to a lower draw.

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DragonsInARoom@lemmy.world ⁨2⁩ ⁨weeks⁩ ago
Resistance increases over longer distance cable, and increased load from appliances. (Especially don’t with american electrics, they aren’t fused so the wire can overheat and set fire to the surroundings.)

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- kevincox@lemmy.ml ⁨1⁩ ⁨week⁩ ago
  To clarify a bit, the benefit of the UK system isn’t the end device having a fuse, but the cable itself having a fuse.
  
  In the US the setup would be something like
  
  Wall has 20A wiring.
  
  Electrical panel has 20A fuse to avoid the wire in the wall from overheating.
  
  Extension cord is designed for 10A
  
  You plug in 2 10A devices to the extension cord.
  
  The wall wiring is fine, it can take 20A.
  
  The circuit breaker doesn’t trip as it is also 20A.
  
  The extension cord overheats and starts a fire.
  
  In the UK the 10A extension cord will have its own 10A fuse in the plug. So when you turn on the two 10A devices the fuse in the extension cord will blow and prevent the extension cord from overheating.
  
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  - clockwork_octopus@lemmy.world ⁨1⁩ ⁨week⁩ ago
    Bold of you to assume that the wall outlet would have a 20a breaker. Most don’t, unless they’re in a kitchen.
    
    But you’re right about the resistance. Also, most extension cords are undersized for the loads they pull, they’re commonly made with 16 or even 18awg wire, further increasing resistance (which translates to heat).
    
    Source: am electrician in US
    
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sexy_peach@feddit.org ⁨2⁩ ⁨weeks⁩ ago
I always thought it was to stop people from plugging too many appliances into all the outlets.

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- FourPacketsOfPeanuts@lemmy.world ⁨2⁩ ⁨weeks⁩ ago
  This is the correct answer.
  
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- Baku@aussie.zone ⁨2⁩ ⁨weeks⁩ ago
  I think that would be more relevant to power boards than extension cords. Unless nomenclature is different elsewhere, extension cords here generally only have a single plug. Although there are usually warnings to not run things like clothes dryers or portable stovetops through an extension cord because it can apparently melt the cable. Truthfully, I don’t entirely get that either, as I would’ve assumed they’d be built to the same standard as internal wiring
  
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  - sexy_peach@feddit.org ⁨2⁩ ⁨weeks⁩ ago
    Oh sorry I didn’t know the distinction, am not a native English speaker
    
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Rhynoplaz@lemmy.world ⁨2⁩ ⁨weeks⁩ ago
I would also like to hear an expert opinion on this. Never really made sense to me either, but it also doesn’t sound unreasonable.

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BorisBoreUs@lemmy.world ⁨2⁩ ⁨weeks⁩ ago
I have an RV with 2x 10 gauge, 50’ extensions running power to it. I have a built-to-purpose coverat the connection point. Its fine and safe enough. Just keep slack at the connection. It cant be under pull stress.

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- Skyrmir@lemmy.world ⁨2⁩ ⁨weeks⁩ ago
  Check the neutral pin at the pedestal and the connection. After a few months running an AC unit, it’ll be char broiled somewhere along the way.
  
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  - BorisBoreUs@lemmy.world ⁨1⁩ ⁨week⁩ ago
    Had this setup for 4.5yrs. No issues.
    
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apfelwoiSchoppen@lemmy.world ⁨2⁩ ⁨weeks⁩ ago
Extension cords are rated for certain levels of resistive load based on their length. It typically has to do with the gauge of the wire used in the chord itself. Electrical resistance is typically converted into heat energy. If you daisy chain extension cords and have them plugged into appliances, then the resistive load of the chained cords can be higher than the rating of one or more of the extension cords. This can cause fire.

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givesomefucks@lemmy.world ⁨2⁩ ⁨weeks⁩ ago

“never plug extension cords into extension cords” is probably the most common piece of electrical related advice I’ve ever heard.

Same reason power cables outside are fucking huge and the cord to your TV is tiny.

Electrical loss generates heat, so the longer the cable, the thicker it needs to be before that heat is too much.

Don’t forget a filament in an old school light bulb is just really thin wite. The thinner it is the less energy required to make it glow, which is why there’s like a 200 year old light bulb still going, it’s just a thick filament and very inefficient

So I’d never plug two of those rinky dink indoor extension cords together, it doesn’t take much length before it starts “glowing” like a light bulb filament, which happens at the plug and can burn a house down.

But…

Growing up doing rural construction with heavy gauge extension cords we never thought twice about hooking multiples up as long as it was just something quick for a few minutes at a time. Then never left it plugged into the source when not in use. You’d never do it for like a radio even because eventually it’s gonna heat up back at the aource.

Someone else already mentioned not pulling it right, we’d “doughnut” the connection so that if it did get yanked accidentally it wouldn’t unplug, but obviously it can’t be under constant stress even like that.

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- Eheran@lemmy.world ⁨1⁩ ⁨week⁩ ago
  So many people here talk about the thickness needed of else it heats up. That is simply wrong. The heat is the same per length and is dissipated the same way with twice the length aka the temperature is the same*. The issue is that the short circuit current could drop below the value needed to actually pop the breaker, allowing for a ton of heat to be generated where it shouldn’t be. The same way a light bulb glows bright hot but does not trip the breaker etc., now just imagine the cable to be the glowing part.
  
  *There is another issue if you do not lay them out, that the heat has nowhere to go. Causing coiled wires to have a far lower rating compared to when they are fully extended.
  
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BombOmOm@lemmy.world ⁨2⁩ ⁨weeks⁩ ago
The longer the cord is the more resistance there is; ie the more electrical load on the circuit. As long as you are pulling less than what the circuit and cord is rated for, there isn’t an issue, you will just be wasting a little extra power from the extra resistance. The plugs can also have a bit of extra resistance.

Two pieces of advice that will make the biggest difference:

Keep the total length of all extension cables used as short as is reasonable. Don’t use a 20m cable when a 4m cable will do.

Buy extension cords with higher wire gauges (higher wire thicknesses). A 12 gauge cable (4mm^2^) will provide notably less resistance than a 14 (2.5mm^2^) or 16 gauge cable (1.5mm^2^). The packaging will say what gauge it is. Note, I’m talking about the thickness of the metal itself, not the thickness of the extension cord. I have seen some very, very thick extension cords with absolute trash wires inside.
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- deranger@sh.itjust.works ⁨2⁩ ⁨weeks⁩ ago
  The more resistance there is, the less the electrical load is. Maximum electrical load would be a short circuit; minimum would be a cord or device with infinite resistance.
  
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Lemminnewbie2@lemm.ee ⁨2⁩ ⁨weeks⁩ ago
It’s going to be down to the gauge of the wire and if it’s rated for hard usage. There would be no difference if the 4m cable was the same gauge and insulation type as two 2m cables connected by cord and plug. You couldn’t say how dangerous it is specifically without calculating the load, wire ampacity, ambient temperature, insulation type, distance, and on and on so it’s general advice to prevent fires from overheating wires.

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- adespoton@lemmy.ca ⁨1⁩ ⁨week⁩ ago
  There is a difference, actually. The cords are the same gauge, but with two shorter ones, the wire is broken up in the middle to run through a plug and socket. This whole assembly causes impedance and can heat up.
  
  Not as much of an issue if each plug and socket has a fuse, but if they don’t, those are the heat and arc points.
  
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Emotional@lemmy.blahaj.zone ⁨2⁩ ⁨weeks⁩ ago
I’m not an electrician, but I recall that this video explains it pretty well (along with other interesting things): www.youtube.com/watch?v=K_q-xnYRugQ

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