I was looking at an electric heater and it seems to be just some red hot wire and a fan, how can it get so hot without triggering the circuit breaker? Is it a big load? Is it something like the little filament on a lightbulb?
In: Engineering
You’re essentially right, it’s simply a wire that current runs through. How hot it gets is defined by how much current is going through it (more current = hotter, less current = cooler), which itself is a result of both the wire’s resistance and the voltage of the supply. Since the voltage from the supply isn’t going to change, the X-Factor here really is the resistance of the wire – too conductive and the electricity will just zip through and it’ll barely draw any current. Too resistant and it won’t be able to draw any current at all, like plugging a tree into a wall socket. So the amount of current it draws, and thus how hot it gets, is defined by resistance of the wire. If you know the total resistance along the length of the wire, you know the maximum current it can draw from a given wall socket and thus you know it won’t flip the breakers or blow a fuse.
This is why most commercially available heaters top out at about 2200W, as this is 10amps from a 220v AC wall socket – deliverable but below the point it’ll blow a 13A fuse or trip a circuit breaker in most cases, with a little headroom to spare to allow for varying national wall socket power, fluctuations and the possibility of other devices also being turned on.
A *short* circuit is when a connection is made between two parts of a circuit that shouldn’t be connected – maybe a metal filing has fallen onto a circuit board. This is fundamentally a different thing, because this is an example of a circuit not working as intended, where as the fan heater is just a simple circuit that also happens to be short.
It is exactly like the filament on a lightbulb. Technically a light bulb is a heater which not only gets red hot but white hot. And this is why we have switched to better technology which does not include a big heating element.
A heating element, resistor, light bulb, are all the same thing but in different configurations. It is a long thin wire which will have a resistance. By selecting the material of the wire to something more resistive you can get away with a shorter thicker wire which helps the heat transfer and makes the construction cheaper. In general you also want a material with a positive temperature coefficient so that when it gets hotter its resistance will increase and it will use less power. This is a safety measure which prevents the heating element from getting too hot.
No they are essentially resistors and filament lightbulbs are the same – https://en.wikipedia.org/wiki/Resistor
They have appropriate resistance. Plus when wire heats up, its resistance increases. So the wire is selected in such way, that when it reaches its operating temperature it draws designed amount of power.
Yes, and no.
Yes in the sense that a heater can be just a wire that is “shorted” across a voltage.
No, in the sense that the wire has resistance, and as it heats up that resistance increases. The increase in resistance balances out the amount of current that it draws so that it does not draw too much current and trip the breaker (or melt).
The size (thickness), material properties and length of the wire are very important factors in how much current it draws. If you were to shorten the wire (lowering the total resistance) then it would draw too much current and will either melt or trip the circuit breaker.
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