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| Amperage |
 Title text: Oh, and do you have any tips on how to vacuum up copper that's melted into your carpet? |
Explanation
Cueball explains to Ponytail how he has modified some parts of his house's wiring to avoid having power to his appliances interrupted on account of overcurrent conditions from running too many appliances at once. In many places around the world, there is a main breaker limiting the maximum current available to each property, with common limits for single-unit residences being 60 A, 100 A or 200 A. Individual circuits will then have breakers limiting the maximum current, usually to something between 10 and 50 amperes (the higher end is reserved for major appliances like dryers, vehicle charging stations, or air conditioning systems). 15-20 A is a common breaker size for circuits powering regular outlets in the US, 32 A is common in the UK, while 10-16 A is standard in mainland Europe. However, Cueball has convinced his power company to supply up to 10,000 amps. This size of service is more often used by residential towers with hundreds of units or large business properties, and generally requires the building to run its own transformer to convert from medium voltage to low (one transformer would normally be shared by up to dozens of single-unit residences). This is prohibitively expensive and unnecessary for most individual homeowners.
The purpose this massive upgrade was to allow a similarly oversized electrical panel, with a 500-ampere circuit breaker for each wall socket. Multiple outlets in one room or several nearby rooms usually share a circuit, so this would have required running separate wires to each outlet, and this internal wiring would have had to be much thicker to carry such high currents without overheating and starting a fire (since the house is still standing, Cueball presumably found an electrician willing to do this). North American electrical codes require that the current over a long period be lower (such as 80% of the nominal rating), so 500-amp wires would allow a sustained load of 400 amps under the code.
Both numbers are absurdly high — far more than any consumer appliance could need. This also appears to be where Cueball abandoned the electrical code, as the special wiring has been connected to what appear to be standard 15- or 20-amp US outlets. Cueball admits that regular wires catch fire when used with these outlets, because even if the outlets are tough enough to carry hundreds of amps, regular consumer power cords are not. The title text shows that Cueball has actually tried out his new arrangement and it has melted the copper inside the power cords onto the carpet, and he is now looking for ways to clean it up.
Cueball's reasoning for this is equally absurd: he is frustrated by his circuit breakers. Circuit breakers exist to prevent currents from exceeding a level that would damage the wires or equipment along the path. A tripped breaker is caused by either a short circuit (unlikely here since this could produce currents well over 500 amps) or by the user trying to draw too much power at once (such as by plugging in many large appliances in one room or even into one outlet using power stripes). A tripped circuit breaker caused by coincidental overloads can be reset easily, but constant overloads would require other solutions. Preventing a circuit breaker from tripping, such as by soldering wire into the fusebox in place of the fuses or installing breakers with limits higher than the physical rating of the wires, defeats this safety mechanism, making fires more likely. The usual safe approach to overload issues is to move some devices to different outlets that are on separate circuits. If needed, one can increase the number of circuits in the house, each with its own breaker (as Cureball has done), but it is still important to match the outlet types to the circuit capacities and follow manufacturer's instructions about equipment power limits. Cueball's expensive approach has kept the internal wiring safe while allowing dangerous habits beyond the outlets, such as using power strips to supply multiple large loads from one outlet.
Typical wires for outlets in the US are between 14 and 10 AWG, rated between 15 and 30 amps. In the UK, it would likely be a Twin Core and Earth 2.5 mm² cable rated for 32 A. By drawing anywhere near 500 amps, he will, as he has discovered, most likely melt the wires inside his appliances and start a fire, even if there is no fault. (Pure copper melts at 1085 °C (1984 °F), and the copper in electrical wiring is fairly pure, so Cueball has demonstrably produced temperatures in excess of that. Such temperatures are well above what's necessary to ignite common household items.) Rather than treat this as a sign that his plan was ill-conceived and simply put up with normal levels of power per outlet, though, Cueball is now trying to find more durable cords and wires that can handle the excessive load. If he upgrades all remaining power cords to sizes sufficient for the electricity that they carry, the system might become technically safe. However, electrical inspectors would still flag the mismatched outlets, and any modified power cords would likely fail various other safety standards enforced by governments or insurance companies.
The amount of electrical power you can use in your house depends on both the voltage and the maximum current you're allowed to draw. The latter is usually protected and limited by multiple breakers both in your home and at the local substation. For example, in the US, where the nominal voltage is 120 V, a 15 A breaker would get you a maximum of 1800 watts of power (current multiplied by the voltage). In countries where 230 V is more common, a similarly sized breaker would get you a maximum of around 3500 watts. If you decrease the voltage you can still get the same power by increasing the current drawn. For example, to get 3500 watts in the US on 120 V, you would need to draw around 30A - double the original amount. Higher currents induce higher voltage drops as a function of resistance in lines, which causes heat to generate as the square of current [V=IR; P=IV; therefore P=I×(IR)=I²R], meaning they would need a larger wire to reduce the resistance in the line and allow more surface for heat to dissipate in order to safely draw the power without them overheating and catching fire. Transmission lines solve the problem by transforming the power to a higher voltage (a 400 kV (400,000 volts) line transmitting a maximum of 10 amps can still theoretically give out 4 million watts of power without needing excessively thick cables). Conversely, decreasing the voltage means that you need more current drawn for the same amount of power (for example, to get 3500 watts from a 12 V car battery you need to draw almost 300 amperes, something that would need really thick wires not to overheat, though note that this is a reasonable current draw from a car battery). Assuming Cueball lives in the US with 120 V mains voltage, his 10,000 A will draw 1.2 megawatts of power, equivalent to the usage of a factory or other large facility.
The comic might be a reference to a recent video posted by youtuber styropyro, who connects 400 car batteries and does various experiments, including popping a 6,000 amp fuse. While the voltage on car batteries is only 12 V (or 24 V in some cases), they allow drawing very high amounts of current to provide enough power for the starter engine to turn. Drawing 500 amps and more for a short period of time is not uncommon. While these would only amount to around 6kW of power (12V * 500 A), the higher current requires the cabling to be thick enough to not overheat even in the short amount of time this draw is used (until the starter engine has turned on the main engine — on a modern car in warm weather this should be around a second at most). In the video, styropyro connects 400 of these into 80 parallel 65 V cells, reaching peak currents in excess of 160 kA. His setup requires very thick cables and large pieces of solid metal to handle the extremely high current.
Transcript
- [Cueball and Ponytail are standing near the corner of a room, with Type B outlets on either wall surrounding the corner at about knee height. Cueball has raised one hand slightly to gesture to one of the outlets.]
- Cueball: I got 10,000 amp service and put each outlet on its own 500 amp breaker, so I never have to worry about overloading a circuit again!
- Ponytail: Clever.
- Cueball: Oh, that reminds me- do you know where to buy cords that don't catch fire?
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