Resistance increases over longer distance cable, and increased load from appliances. (Especially don't with american electrics, they aren't fused so the wire can overheat and set fire to the surroundings.)
this post was submitted on 26 Dec 2024
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To clarify a bit, the benefit of the UK system isn't the end device having a fuse, but the cable itself having a fuse.
In the US the setup would be something like
- Wall has 20A wiring.
- Electrical panel has 20A fuse to avoid the wire in the wall from overheating.
- Extension cord is designed for 10A
- You plug in 2 10A devices to the extension cord.
- The wall wiring is fine, it can take 20A.
- The circuit breaker doesn't trip as it is also 20A.
- The extension cord overheats and starts a fire.
In the UK the 10A extension cord will have its own 10A fuse in the plug. So when you turn on the two 10A devices the fuse in the extension cord will blow and prevent the extension cord from overheating.
Bold of you to assume that the wall outlet would have a 20a breaker. Most don’t, unless they’re in a kitchen.
But you’re right about the resistance. Also, most extension cords are undersized for the loads they pull, they’re commonly made with 16 or even 18awg wire, further increasing resistance (which translates to heat).
Source: am electrician in US
The circuit power doesn't matter for the example. I was just picking easy numbers. You can have the same problem as long as the rating of the extension cord is less than the circuit breaker. (And as you pointed that out this is a very common case due to the frequently low rating of extension cords.)
I think it is partly a US specific problem as the quality of the extension cords really suck. Meanwhile in Eurpoe (or at least in Germany) the extension cords actually use the same wire grade as your in wall wires, so there is a basically no difference in using daisy chained extension cords versus different wall outlets (as long as the outlets are in the same curcuit)
Yep, came here to write the same. We have 240V and not 120V like the US. To power the same appliance in the US you have double the Ampere and therefore higher risk of fire (correct me if I'm wrong)
I strongly disagree... We just have higher standards regarding power wires. Since we have more voltage running through the wires we need tougher ones, but that is what regulation is for
So the higher Ampere doesn't require thicker cables? Genuinely asking. The higher standards and regulations are absolutely part of why you don't hear this rule here.
Yes, as US uses an voltage of 120 V, the current drawn by a load P is approximately double the current drawn by the same load P in EU with 230 V. Thus, the wires used in Europe only need approximately half the cross section compared to US. However, the insulation of the wires needs to be of higher standard.
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I always thought it was to stop people from plugging too many appliances into all the outlets.
I think that would be more relevant to power boards than extension cords. Unless nomenclature is different elsewhere, extension cords here generally only have a single plug. Although there are usually warnings to not run things like clothes dryers or portable stovetops through an extension cord because it can apparently melt the cable. Truthfully, I don't entirely get that either, as I would've assumed they'd be built to the same standard as internal wiring
Oh sorry I didn't know the distinction, am not a native English speaker
Ah, no worries! I'm not sure if it's even universally agreed upon across native English speakers. Where I'm from though, a powerboard (or power strip in other parts of the world) has one plug that then leads on to usually 4 or more additional power points/sockets. An extension cord on the other hand usually only allows a single device be connected to it (whether that's another extension cord or something else)
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I would also like to hear an expert opinion on this. Never really made sense to me either, but it also doesn't sound unreasonable.
The longer the cable, the thicker it needs to be to carry the same amount of current without getting hot. This is due to resistance (Wikipedia does a good job with the details). Basically:
20' cable be long and thick.
10' cable be short and thin.
10' + 10' cables be long and thin.
Long and thin = heat then fire.
That being said, put an LED light bulb at the end, no problem. Put a gaming PC on the end, problem.
I don't think you're right about heat. Two cables in series have double the resistance and therefore double the total heat generation, but that heat energy is split between the two cables so each one does not get hotter than if it was the only cable.
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I have an RV with 2x 10 gauge, 50' extensions running power to it. I have a built-to-purpose coverat the connection point. Its fine and safe enough. Just keep slack at the connection. It cant be under pull stress.
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