this post was submitted on 26 Dec 2024
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No Stupid Questions

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176
Why is daisychaining multiple extension cords considered unsafe, even if only done to the length of a standard cable? (aussie.zone)
submitted 21 hours ago by Baku@aussie.zone to c/nostupidquestions@lemmy.world
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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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[–] uis@lemm.ee 6 points 6 hours ago* (last edited 6 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 insulation temperature until it melts and spontaneously combusts. This applies to extension cords in general.

[–] tacosplease@lemmy.world 1 points 3 hours 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.

[–] JordanZ@lemmy.world 23 points 11 hours ago* (last edited 11 hours ago) (6 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.

[–] MonkderVierte@lemmy.ml 1 points 3 hours ago* (last edited 3 hours ago) (3 children)

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

[–] Mongostein@lemmy.ca 9 points 3 hours ago (1 children)

This is also known as a router

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

Oohkay.

[–] Mongostein@lemmy.ca 1 points 2 hours ago

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

[–] Battle_Masker@lemmy.world 3 points 3 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

[–] lime@feddit.nu 19 points 10 hours ago (3 children)

lol "gauge"

americans will use anything except the metric system

[–] Thavron@lemmy.ca 5 points 5 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 3 points 1 hour ago (1 children)

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

[–] PM_Your_Nudes_Please@lemmy.world 2 points 1 hour 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 11 points 8 hours ago* (last edited 8 hours ago) (1 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.

[–] Wolf314159@startrek.website 3 points 8 hours ago (1 children)

Both are measurements of cross-sectional AREA and are defined in terms of square millimeters (mm^2), not mm.

[–] Successful_Try543@feddit.org 3 points 7 hours ago* (last edited 7 hours ago)

That's exactly what I wrote mm^2 should be rendered to square millimeters (mm^2 ) by the browser / app.
In my understanding, 'cross section' always referrs to an area. The other property would be the diameter which is measured in units of length.

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[–] Free_Opinions@feddit.uk 18 points 14 hours ago* (last edited 12 hours 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 12 points 12 hours 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.

[–] uis@lemm.ee 3 points 7 hours ago

Inductance is not the reason here

[–] brown567@sh.itjust.works 2 points 7 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 1 points 7 hours ago

Yes! There is a video about this. Heat in spool of cord is trapped.

[–] Kolanaki@yiffit.net 120 points 21 hours ago (21 children)

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

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[–] BillibusMaximus@sh.itjust.works 60 points 21 hours ago (7 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.

[–] scarabic@lemmy.world 7 points 15 hours ago* (last edited 15 hours ago) (5 children)

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.

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[–] uis@lemm.ee -4 points 7 hours ago (1 children)

The longer the wire, the more heat it can dissipate, so no, you don't need wire to be thicker.

[–] gazter@aussie.zone 1 points 3 hours 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 41 points 21 hours ago (8 children)

Meanwhile landlords: "one 50 year old outlet should be enough for two bedrooms right?*

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