“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
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.
Others have pretty much mentioned it. Too thin of conductors for the total length required which can overload the cable and heat it up. If you’re just charging your phone it’s unlikely to cause a problem but the more amps you pull the riskier it gets.
Here’s a helpful chart…
Edit: Even at harbor freight (cheap hardware store) a 50ft 12 gauge extension cord is about $40 and weighs 7 pounds.
Is it just me or is anyone else perturbed that the cable sizes in this infographic are all the same gauge?
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.
16 AWG – 1.3 mm^2
14 AWG – 2 mm^2
12 AWG – 3.3 mm^2
10 AWG – 5.2 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, as stated in the table above, is sufficient.
Edit: This is how the above text should be displayed:
Both are measurements of cross-sectional AREA and are defined in terms of square millimeters (mm^2), not mm.
It doesn’t make sense. Temperature difference does not depends on length.
Adding length creates more resistance which creates more heat. Thinner conductors can’t handle it as well.
And more surface area for heat dissipation. https://lemm.ee/comment/17115060
They cancel out.
It increases the risk of electrical overload and overheating as it adds more resistance to the circuit.
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)?
The longer the cable, the thicker (heavier gauge) it needs to be to carry the same current without burning up. One extension cord is rated to carry the current it alone is able to carry. Put two of those in series, and both of them together are able to carry less current than either one by itself. This is how fires start.
This is incorrect. I need to increase gauge for voltage drop. Overloading the cable via length can only happen if I have a motor or other magnetic load at the end. A motor will try to draw it’s designed wattage regardless of voltage. A wire of a given ampacity will handle that many amps regardless of the length of the conductor. The relationship is power = voltage x current and voltage = current x resistance for single phase. The fire concern on extension cords tied together indoors is you have 100% strung that shit through a doorway or window, which is a code violation. You are going to pinch it and burn your shit down. all outdoor plugs are gfci these days and on site i can have 4 or 5 extension cords tied together. i only get 109 volts at the end but a heater is a resistive load. Doesnt matter for that application.
I wonder what kind of safety margin is calculated into these…
Admittedly I’ve seen some wildly different shielding or thickness in my time
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…
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plugging in too many appliances over several daisy chained power strips trips the circuit breaker because too much current is being drawn
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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
When the breaker trips then the fundamental issue is unlikely to be present. But to be able to push enough current to cause it to break the connection needs to have a sufficiently low resistance. If that gets too high it will never break, even if you short the cables. And that will result in a fire, because the protection does not work anymore. That is the dangerous part.
Isn’t the added cable resistance small enough to not cause issues so soon? In case you just chain a few ( < 10 ) together.
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 rating is above load rating. I recommend to use at least same rating as circuit breaker or get extension cord with circuit breaker built in and never decrease rating down the line without circuit breaker before it, so even if you somehow overload it, there will be protection from it.
AND NEVER COIL OR THERMALY INSULATE! Cords rely on convection for heat dissipation, and spooling and insulating reduces it, thus increasing electrical insulator temperature until it melts and spontaneously combusts. This applies to extension cords in general.
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.
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.
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.
That said, those aren’t really the problem here:
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.
Said another way: Each cable is given the minimum copper and shielding that cable needs for the length it is 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.
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.
DJ’s really will find any excuse to tell you they’re a DJ
Edit: you wrote and deleted a super unhappy message so just wanted to say sorry, I was just being goofy not trying to rag on you
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).
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.
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
The longer the wire, the more heat it can dissipate, so no, you don’t need wire to be thicker.
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.
Yes, maximum carried current is indeed invariant of length. I explained math behind it in https://lemm.ee/comment/17115060
