So what is it about hot things like irons, heaters, air conditioners being the exception, and hair dryers that cause the fuse to go out?
for example, if I plug in a dryer while my heater is on the same circuit, 90% of the time, the fuse will blow out.
Why does the hot appliance translate to hot power cord?
Can’t they design it so it doesn’t do that?
How much Wattage is your heater + your dryer? I’d be willing to be that it’s more than the fuse is rated for.
Power cords get warm because the manufacturer uses the smallest cord that will pass safety regulations. Bigger cords have more copper, cost more, and are much stiffer.
You’re getting confused - you just have old, overloaded wiring and many “heating” type appliances pull a lot of power. That is the fuse burns out when you are pulling too much juice, not because any particular appliance is doing something weird. Heaters, AC, Hair Dryers, etc just happen to pull a lot of power.
To fix the problem you need to upgrade your electrical system.
To add a bit more info, most appliances that generate heat do so by using resistive heating. That is, they run a big current through a resistor and the resistor gets hot. (Look at a working toaster and you’ll be able to see the elements glowing red hot.)
The key here is that the more current you run through the resistor, the hotter your appliance gets. So that means that things like hair dryers and clothes dryers take up a lot of current. Only so much current can flow through a circuit in the house before a fuse blows. So if you hook up two appliances that take a lot of current, you’re likely going to blow a fuse unless the circuit is rated for a lot of amps.
a heating appliance can use 700 to 1500 Watts of electricity. that is nearly half to the total amount that a fuse might handle. numbers and amounts are just approximate.
It’s not just hot things, it’s power-hungry things in general. It’s just that the average consumer is more familiar with heating appliances than with appliances that do mechanical work, such as shop-vacs, air compressors, and table saws. Plug those last three items into the same circuit, and you can expect to blow a fuse or pop a circuit breaker pretty quick, despite the fact that they don’t generate a huge amount of heat.
Power tools can sometimes be made more efficient - that is, for a given amount of mechanical work output they can be made to produce less waste heat, and therefore use less electrical power. Not so with a heating appliance: they already turn 100% of their electrical power into heat, so no improvement can be had.
Sorry: if you want your hair dryer or iron “this hot,” it needs this much power. No way around it.
All of the items you mention draw a lot of electrical current. That’s why your fuses are blowing.
While they can design some devices to draw less current (such as the compressor in a portable air conditioning unit, which is why newer models are more efficient than older ones), there’s not much you can do do a simple device like an iron or a hair dryer. As other posters have indicated, these devices work by directly converting electrical power into heat using resistors. More heat equals more electrical current being drawn.
Your fuses are blowing because they are trying to prevent you from putting too much of an electrical load on your house wiring. The alternative is the risk of overloading your house wiring and burning your house down.
You either need to reduce the electrical load on your wiring (by not plugging in a hair dryer on the same circuit as a portable air conditioner, for example), or upgrade your wiring.
All the other posts are correct about your overloading the circuit.
Other considerations are that the given circuit could be improperly fused. Perhaps a dedicated circuit should be set up for that outlet. And there are rare occasions where a circuit breaker or a very old fuse will trigger prematurely.
You must first assume the overload. Stop plugging too many big draws in at the same time.
20 amps is 2400 watts, 15 amps is 1800 amps. If your is near and exceeds those numbers the breaker should trip.
Ok so my house is 100AMP. My friend said old houses usually had 60AMP.
So a simple iron or hair dryer uses more current to produce heat.
So I shouldn’t plug in a hair dryer and heater into the same circuit which goes back to the fuse which is rated 25, 20 or 15amp.
I definitely wouldn’t have thought a simple iron that generates heat would require so much power.
Thanks for all the responses.
But each circuit is fused at 20AMP typically. If you plugged in your heating devices in different circuits, you can use more at the same time than if you plugged them in the same circuit. And 100AMPs for a house nowadays isn’t all that much.
It requires so much power *because *it’s simple.
…1800 watts. And that at the standard North American wall voltage of 120 V.
I was looking through the specs for an inexpensive electric stove, and each element when set to max would draw something like 2400 W. The stove and especially the broiler would draw 4800 W. All together, with everything on, the stove could draw over 10 000 W! This is why electric stoves are connected to special high-power outlets… 240 V, not 120, so they draw half the number of amps for a given power, but the outlets are still rated for thirty or forty or fifty amps. (12 000 W / 240 V = 50 A)
Similarly, other heaters like electric dryers and watrer heaters and baseboard heaters get special plugs and outlets or get wired in permanently.
older houses with fuses with 60A or 100A service would likely have 15A appliance circuits wired with 14AWG wire.
on an appliance there is likely a label indicating the amount of power that it uses in Watts, divide that value by 120 (volts typical value for a convenience receptacle [outlet]) which gives the current (Amps) used by the device. you add together all the values for electrical current on a fused circuit. that total value (for the appliances that are turned on) has to be less than the value for that fuse or it will blow the fuse.
heating devices are big users of electrical current.
This is why I can’t run the dishwasher and the washing machine at the same time - they run off the same 13A socket and the combined draw is enough to blow the fuse.
I guess appliance manufacturers could conceivably create irons that didn’t draw as much instantaneous power from the wall socket. It would have to be more “complicated” in that it would draw a trickle charge to a large rechargeable battery. Once the battery had enough juice, the ready light on the iron would finally turn on.
It solves the issue of blown fuses but I have a feeling consumers wouldn’t care to wait several hours for the iron to turn “on” or dedicate the floor space to a huge cumbersome battery.
Well, maybe an iron or a toaster would be a good candidate for a heat pump? 
Note that the one “exception” listed by the OP, an air conditioner, is probably the most common household device that actually does mechanical work. Roughly speaking, AC units compress their coolant, then let it expand. When the coolant expands, it cools off, drawing heat from the air. That first step, the compression, requires mechanical work.
ETA: that and the fridge, of course. But the fridge more often has its own dedicated circuit than a window AC unit does.