this post was submitted on 26 Dec 2024
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"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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[–] douglasg14b@lemmy.world 7 points 13 hours 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.

[–] JordanZ@lemmy.world 35 points 1 day ago* (last edited 1 day ago) (9 children)

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.

[–] rekabis@lemmy.ca 4 points 12 hours 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.

[–] douglasg14b@lemmy.world 4 points 13 hours ago (1 children)

Is it just me or is anyone else perturbed that the cable sizes in this infographic are all the same gauge?

[–] rekabis@lemmy.ca 2 points 11 hours 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.

[–] lime@feddit.nu 23 points 1 day ago (4 children)

lol "gauge"

americans will use anything except the metric system

[–] Kaput@lemmy.world 3 points 14 hours ago (1 children)

What is the metric unit for cables?

[–] lime@feddit.nu 3 points 14 hours ago

for cross-sectional area? mm^2^.

[–] Thavron@lemmy.ca 11 points 21 hours ago (1 children)

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.

[–] spizzat2@lemm.ee 9 points 18 hours ago (2 children)

Oh, you can get bigger! Just keep adding 0s. It's fine.

[–] Thavron@lemmy.ca 6 points 15 hours ago

Oh ffs I should've known.

[–] PM_Your_Nudes_Please@lemmy.world 8 points 17 hours ago

Yup, I work with 4/0 (0000) cable pretty regularly, for things like generators or powering large systems. We have a few trunks full of cable, and it takes a crew of 2 or 3 to actually lay it because it’s so heavy. Usually one person pushing the trunk along, one focuses on uncoiling it from the trunk, and one focuses on actually laying the cable. We use five conductors at a time (one neutral, three 120v hots leads, and a ground,) so it’s a big bundle. Each cable weighs a little over a pound per foot, and there are five bundled together. So a 150’ coil can easily weigh 750-800 pounds.

[–] Successful_Try543@feddit.org 14 points 1 day ago* (last edited 2 hours ago) (7 children)

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:
Screenshot_20241227-221529_Eternity_1

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[–] MonkderVierte@lemmy.ml 2 points 19 hours ago* (last edited 19 hours ago) (3 children)

Space heater is "medium duty" while a router is "heavy duty"?

[–] Mongostein@lemmy.ca 15 points 19 hours ago (1 children)

This is also known as a router

[–] MonkderVierte@lemmy.ml 2 points 19 hours ago (1 children)
[–] Mongostein@lemmy.ca 3 points 18 hours ago (1 children)

It’s for putting holes in things. Creating routes? I dunno.

[–] Maiq@lemy.lol 2 points 14 hours ago

Exactly, can be used to round off corners and all manor of nifty woodworking. Keep hands away from the spinny bit.

[–] Battle_Masker@lemmy.world 6 points 19 hours 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 11 points 23 hours ago* (last edited 13 hours ago) (1 children)

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.

[–] tacosplease@lemmy.world 9 points 19 hours ago (1 children)

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.

[–] uis@lemm.ee 1 points 13 hours ago

*insert technically correct*

[–] Kolanaki@yiffit.net 133 points 1 day ago (22 children)

It increases the risk of electrical overload and overheating as it adds more resistance to the circuit.

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[–] Free_Opinions@feddit.uk 21 points 1 day ago* (last edited 1 day ago) (2 children)

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~~ heat. Most cable reels have different ratings marked on them for when they are spooled / unspooled. This is especially true when the device you're powering takes >1000 watts

[–] modeler@lemmy.world 11 points 1 day ago (2 children)

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.

[–] brown567@sh.itjust.works 7 points 23 hours 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

[–] uis@lemm.ee 6 points 23 hours ago

Inductance is not the reason here

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[–] BillibusMaximus@sh.itjust.works 64 points 1 day ago (17 children)

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.

[–] douglasg14b@lemmy.world 1 points 13 hours ago* (last edited 13 hours 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.

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.

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