“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
Nailed it in far fewer words than me.
Another bit of explanation I just thought of –
Think of an incandescent light bulb. It has a filament. You run electricity through the filament and it heats up enough to glow, producing light to see by. It does that because the thin filament has high resistance; it resists allowing current to flow through it.
Any piece of conductive material will do the same thing if you put enough current through it. Even an extension cord. It will heat up enough to glow. Being an extension cord, it will then melt the insulation and dramatically increase the likelihood of setting something on fire.
This is primarily a concern because extension cords aren’t fused, and there’s no control over how they are routed.
Most wiring in your walls come after a circuit breaker and are designed to allow for a certain amount of heating. The electrician follows a code that guarantees that the circuit breaker will trip before there’s any possibility of too much heat. This table indicates a higher ampacity rating for higher temperature ratings.
Now most extension cords are made cheaper by using lower gauge than the wiring in your walls. The general assumption is that they’re spread out, so the heat has no way to build up, and you won’t be plugging them permanently into something drawing the peak 15A allowed by the circuit breaker.
If you were to pile up a 100 foot extension cable and plug in a hairdryer, you’d probably start a fire. If it was all spread out, likely your hair dryer would just receive less than the 120V it’s expecting, and it wouldn’t get very hot.
Ironically, dinky christmas lights make very safe extension cords because they’re fused inside the plug.
And because the wire gauge is less than the wiring in the wall the breaker won’t trip before it reaches the point where it’s overloaded either.
Other way around. Low resistance - high power.