Why do charging cables not spark when held close to the intended device?


close as in almost touching but not inserted.

In: Engineering

There is not enough current running through the cable to make the jump through the air and complete the circuit. If there were, this would be extremely dangerous and you for example, could not plug in a charger and leave the cable sitting on a metal table or near anything metal, lest it start arcing.

The voltage on a USB charger is only 4.2 volts and a max of 2.1 amps. This is extremely low lower and unless released quickly with a capacitor will not really spark.

Small electronics, by design, operate on a tiny bit of power, most of it going to the screen. The batteries can get very hot and burn even but to get a spark your need quite a bit more voltage.

The charging cable doesn’t have enough voltage to jump the air gap to create an arc. This makes low voltage electronics pretty safe to use.

USB for instance is 5 volts, while outlet power is 120 volts (or 220v depending where you are)

Some of it may have to do with the fact that it is using DC. Air gaps block DC, which is part of how capacitors work. AC generates magnetic fields and can flow across air gaps, which is how transformers work.

Something not mentioned yet is that most high power chargers only supply 500mA until a device that supports more power is detected, it then ramps up the amperage to 2 or 3 amps (3000mA).

There’s not enough voltage (potential difference) to jump a gap or create a visible spark.

Higher voltages can jump further – lightning is many millions of volts. Your USB cable is 5v.

To put some numbers on the good answers already posted: the breakdown voltage of air is about 3000 volts per millimeter. Even a 120-volt wall outlet can only throw a spark across an air gap about the thickness of a sheet of paper.