“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
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.
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.
It’s obvious you know more or less all there is to know about this topic. So much so that I suspect you have trouble explaining it to laypersons like me because it’s difficult for you to determine which parts of your knowledge are obvious common knowledge and which parts are specialist knowledge.
This is junior highschool level stuff. Not a vector or phasor in sight.
Your school taught anything at all about electricity? Mine sure didn’t.
My high school had a lot of vocational courses. I took auto shop, construction, welding, and small engine mechanics. Several of those covered electricity.
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lol “gauge”
americans will use anything except the metric system
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.
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.
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 themselves can also have a bit of extra resistance.
Two pieces of advice that will make the biggest difference:
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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.
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Buy extension cords with higher wire gauges (higher wire thicknesses). A 12 gauge cable (4mm2) will provide notably less resistance than a 14 (2.5mm2) or 16 gauge cable (1.5mm2). 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 as a whole. I have seen some very, very thick extension cords with absolute trash wires inside.
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