Of course it's a violation of the electrical code to wire up a 120V outlet to 240V, and if there is a fire incident or appliance injury anyone or any insurance agent who finds out about this will try to blame it on this even if it didn't cause the incident. If you are legally subject to the electrical code, then it is also a violation of the law.

But being LEGAL is often not the same as being SAFE.

It's actually very unlikely that plugging a 120VAC device in to a 240VAC outlet would cause personal injury. Most things will either blow fuses or smoke and burn out. This is what happens anyway when these devices fail due to wearing out or due to defects. The biggest risk is probably some someone plugging in some kind of transformer or motor that will appear to work fine but will take several minutes to over heat and potentially catch fire (which it would also do at 120VAC if it had a shorted winding). For that to even happen it would have to lack proper thermal fusing or be some non UL listed imported device. Surge protectors, especially ones from the 90s, can also catch fire. They're a hazard waiting to happen even at 120VAC. The line to earth shock hazard at 240VAC is still 120VAC due to the split phase wiring system.

Due to the typical duty cycle of welders, the NEC allows dedicated outlets for welders (which are standard and don't prevent other appliances from plugging in) to be fused at twice the normal current carrying capacity of the wiring. Normally this would cause a lot of harsh opposition on a forum like this, much like using 6-15 in place of 5-15, but because the NEC allows it, there is little to no opposition.

I checked out a situation where the neutral line feeding a rental house had snapped. The 120V circuits were surging high enough to partially melt the plastic and let black smoke out of a surge protector. That could have caused a fire. Do you spend several hundred dollars on buying an official 240VAC EV charger, or do you spend it getting rid of dangerous surge protectors and improving the ground rod for the building? Doing one of those things will make you NEC compliant, and the other will actually make you safer.

I once shared my intention to put a thermostat on a car engine to kill the ignition if it overheated, to save the engine. Some people thought this was a terrible dangerous idea. In the real world, the danger of an engine stalling in a properly driven vehicle is very small. What can happen is that the car will be destroyed, the owner will instead ride their motorcycle to work where they will be over 10 times a as likely to die in an accident per mile traveled.

The conclusion is that safety is in your own hands. You can choose to be legal and code compliant, but being safe costs money too, and it often gives you less safety to spend money on struct code compliance than other often forgotten safety issues.

Of course it's a violation of the electrical code to wire up a 120V outlet to 240V, and if there is a fire incident or appliance injury anyone or any insurance agent who finds out about this will try to blame it on this even if it didn't cause the incident. If you are legally subject to the electrical code, then it is also a violation of the law.

But being LEGAL is often not the same as being SAFE.

It's actually very unlikely that plugging a 120VAC device in to a 240VAC outlet would cause personal injury. Most things will either blow fuses or smoke and burn out. This is what happens anyway when these devices fail due to wearing out or due to defects. The biggest risk is probably some someone plugging in some kind of transformer or motor that will appear to work fine but will take several minutes to over heat and potentially catch fire (which it would also do at 120VAC if it had a shorted winding). For that to even happen it would have to lack proper thermal fusing or be some non UL listed imported device. Surge protectors, especially ones from the 90s, can also catch fire. They're a hazard waiting to happen even at 120VAC. The line to earth shock hazard at 240VAC is still 120VAC due to the split phase wiring system.

Due to the typical duty cycle of welders, the NEC allows dedicated outlets for welders (which are standard and don't prevent other appliances from plugging in) to be fused at twice the normal current carrying capacity of the wiring. Normally this would cause a lot of harsh opposition on a forum like this, much like using 5-15 in place of 6-15, but because the NEC allows it, there is little to no opposition.

I checked out a situation where the neutral line feeding a rental house had snapped. The 120V circuits were surging high enough to partially melt the plastic and let black smoke out of a surge protector. That could have caused a fire. Do you spend several hundred dollars on buying an official 240VAC EV charger, or do you spend it getting rid of dangerous surge protectors and improving the ground rod for the building? Doing one of those things will make you NEC compliant, and the other will actually make you safer.

I once shared my intention to put a thermostat on a car engine to kill the ignition if it overheated, to save the engine. Some people thought this was a terrible dangerous idea. In the real world, the danger of an engine stalling in a properly driven vehicle is very small. What can happen is that the car will be destroyed, the owner will instead ride their motorcycle to work where they will be over 10 times a as likely to die in an accident per mile traveled.

The conclusion is that safety is in your own hands. You can choose to be legal and code compliant, but being safe costs money too, and it often gives you less safety to spend money on struct code compliance than other often forgotten safety issues.