question: Why do charging cables not spark when held close to the intended device?
comment: 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.
passages: Since these currents are larger than in the original standard, the extra voltage drop in the cable reduces noise margins, causing problems with High Speed signaling. Battery Charging Specification 1.1 specifies that charging devices must dynamically limit bus power current draw during High Speed signaling; 1.2 specifies that charging devices and ports must be designed to tolerate the higher ground voltage difference in High Speed signaling.
   BULLET::::- More expensive – Inductive charging also requires drive electronics and coils in both device and charger, increasing the complexity and cost of manufacturing.
  
  BULLET::::- Inconvenience – When a mobile device is connected to a cable, it can be moved around (albeit in a limited range) and operated while charging. In most implementations of inductive charging, the mobile device must be left on a pad to charge, and thus can't be moved around or easily operated while charging. With some standards, charging can be maintained at a distance, but only with nothing present in between the transmitter and receiver.
   Section::::Properties.:Safety.
  
  The J1772 standard includes several levels of shock protection, ensuring the safety of charging even in wet conditions. Physically, the connection pins are isolated on the interior of the connector when mated, ensuring no physical access to those pins. When not mated, J1772 connectors have no power voltages at the pins, and charging power does not flow until commanded by the vehicle.
   However, if direct current is used, the cable capacitance is charged only when the cable is first energized or if the voltage level changes; there is no additional current required. For a sufficiently long AC cable, the entire current-carrying ability of the conductor would be needed to supply the charging current alone. This cable capacitance issue limits the length and power-carrying ability of AC power cables. DC powered cables are limited only by their temperature rise and Ohm's Law. Although some leakage current flows "through" the dielectric insulator, this is small compared to the cable's rated current.
   BULLET::::- Control pilot: Communication line used to signal charging level between the car and the EVSE, can be manipulated by vehicle to initiate charging as well as other information.
  
  A 1 kHz square wave at ±12 volts generated by the EVSE on the control pilot line to detect the presence of the vehicle, communicate the maximum allowable charging current, and control charging begin/end.
  
  The connector is designed to withstand 10,000 mating cycles (a connection and a disconnection) and exposure to the elements. With 1 mating cycle per day, the connector's lifespan should exceed 27 years.
  
  Section::::Properties.:Charging.
   The input impedance of the circuit is almost zero because of the Miller effect. Hence all the stray capacitances (the cable capacitance, the amplifier input capacitance, etc.) are virtually grounded and they have no influence on the output signal.
  
  Section::::Design.:Ideal circuit.
  
  An "ideal circuit" for analysing charge amplifier operation is shown below:
   The strength of the joint comes from the strength of the pins and the L slots, and the spring. To disengage unintentionally, the pins must break, the sleeve into which the connector slides must be distorted or torn enough to free the pins, or the spring must fail and allow the connector to be pushed down and rotate - for example due to vibration.
  
  It is possible to push down the connector and rotate it, but not far enough to engage and lock; it will stay in place temporarily, but accidental disconnection is very likely.
   Where electrical safety is an issue, sheathed plugs and sockets are used. These plugs have fixed or sliding sheaths or other devices to protect the user from accidental contact with live conductors, but are still largely compatible with the original design. When inserted, the sheaths of the plug and socket overlap fully, ensuring that no live metal is exposed. A typical design is now required (IEC 61010) on multimeter test leads and several other measurement and laboratory equipment. In this design, the metal banana plug is entirely sheathed in a plastic tube and inserts into a deeply recessed jack in the multimeter. Alternatively, the equipment may use a deeply recessed male banana plug, while the test lead uses a sheathed banana jack. Additionally, the test lead wire must be made with insulation rated for higher voltages.
   BULLET::::- Loudspeaker outputs, especially on low-end equipment. On professional loudspeakers, Speakon connectors carry higher current, mate with greater contact area, lock in place and do not short out the amplifier upon insertion or disconnection. However, some professional loudspeakers carry both Speakon and TRS connectors for compatibility. Heavy-duty  in loudspeaker jacks are rated at 15 A maximum which limits them to applications involving less than 1,800 watts.  in loudspeaker jacks commonly are not rigged to lock the plug in place and will short out the amplifier's output circuitry if connected or disconnected when the amplifier is live.
  
  BULLET::::- Line outputs.
   BULLET::::- charge continues as determined by PEV
  
  BULLET::::- charge may be interrupted by disconnecting the plug from the vehicle
  
  The technical specification was described first in the 2001 version of SAE J1772 and subsequently the IEC 61851-1 and IEC TS 62763:2013. The charging station puts 12 V on the Control Pilot (CP) and the Proximity Pilot (AKA Plug Present: PP) measuring the voltage differences. This protocol does not require integrated circuits, which would be required for other charging protocols, making the SAE J1772 robust and operable through a temperature range of −40 °C to +85 °C.
  
  Section::::Signaling.:Control Pilot.
   Section::::Protection.
  
  A resistor in series with the line can be used to limit the current charging input capacitors. However, this approach is not very efficient, especially in high-power devices, since the resistor will have a voltage drop and dissipate some power.
   BULLET::::- Bow-tie trees: Bow-tie trees are trees which start to grow from within the dielectric insulation and grow symmetrically outwards toward the electrodes. As the trees start within the insulation, they have no free supply of air which will enable continuous support of partial discharges. Thus, these trees have discontinuous growth, which is why the bow-tie trees usually do not grow long enough to fully bridge the entire insulation between the electrodes, therefore causing no failure in the insulation.
   Per the base specification, any device attached to a "standard downstream port" (SDP) must initially be a low-power device, with high-power mode contingent on later USB configuration by the host. Charging ports, however, can immediately supply between 0.5 and 1.5 A of current. The charging port must not apply current limiting below 0.5 A, and must not shut down below 1.5 A or before the voltage drops to 2 V.
   The effects of a bent pin on system operation may or may not be immediately obvious, but they are potentially catastrophic. There are several possible failure modes. If a pin that normally carries a signal or power has bent, the electrical path is now broken. If the bent pin does not touch a neighboring pin or a grounded shell, then there are no shorts to other paths. Figure 2 shows how pin spacing and diameter in one common military-type connector are such that a bent pin can fall between two others without making contact. If the bent pin touches the grounded shell, then the pin’s signal is now shorted to chassis ground. If the bent pin is touching another contact (or two other contacts), then there is an electrical short between two (or three) paths (Figure 3). In some very commonly used miniature D connectors, it is possible that a bent pin can touch two neighboring contacts plus a grounded connector shell, thus shorting chassis ground to three electrical paths. The connector in Figure 3 is an example: its mating plug connector (not shown) fits inside the Figure 3 receptacle shell, and the plug's shell is therefore closer to the pins than the receptacle shell. This means that the bent pin in the figure can touch a shell.
   The charging resistors, Rc, need to be properly sized for both charging and discharging. They are sometimes replaced with inductors for improved efficiency and faster charging. In many generators the resistors are made from plastic or glass tubing filled with dilute copper sulfate solution. These liquid resistors overcome many of the problems experienced by more-conventional solid resistive materials, which have a tendency to lower their resistance over time under high voltage conditions.
  
  Section::::Short pulses.
   The points allow the coil magnetic field to build. When the points open by a cam arrangement, the magnetic field collapses inducing an EMF in the primary that is much larger than the battery voltage and the transformer action produces a large output voltage (20 kV or greater) from the secondary.
   The Control Pilot line circuitry examples in SAE J1772:2001 show that the current loop CP-PE is connected permanently on the vehicle side via a 2.74 kΩ resistor, making for a voltage drop from +12 V to +9 V when a cable is hooked up to the charging station, which activates the wave generator. The charging is activated by the vehicle by adding parallel 1.3 kΩ resistor resulting in a voltage drop to +6 V or by adding a parallel 270 Ω resistor for a required ventilation resulting in a voltage drop to +3 V. Hence the charging station can react by only checking the voltage range present on the CP-PE loop. Note that the diode will only make for a voltage drop in the positive range; any negative voltage on the CP-PE loop will shut off the current as being considered a fatal error (like touching the pins).
   Some non-compliant cables with a USB-C connector on one end and a legacy USB-A plug or Micro-B receptacle on the other end incorrectly terminate the Configuration Channel (CC) with a 10kΩ pullup to V instead of the specification mandated 56 kΩ pullup, causing a device connected to the cable to incorrectly determine the amount of power it is permitted to draw from the cable. Cables with this issue may not work properly with certain products, including Apple and Google products, and may even damage power sources such as chargers, hubs, or PC USB ports.
  
  Section::::Hardware support.:Compatibility issues.
   Any current-carrying conductor, including a cable, radiates an electromagnetic field. Likewise, any conductor or cable will pick up energy from any existing electromagnetic field around it. These effects are often undesirable, in the first case amounting to unwanted transmission of energy which may adversely affect nearby equipment or other parts of the same piece of equipment; and in the second case, unwanted pickup of noise which may mask the desired signal being carried by the cable, or, if the cable is carrying power supply or control voltages, pollute them to such an extent as to cause equipment malfunction.
   Proximity Pilot: The Proximity pin, PP (also known as "plug present"), as shown in the SAE J1772 example pinout, describes the switch, S3, as being mechanically linked to the connector latch release actuator. During charging, the EVSE side connects the PP-PE loop via S3 and a 150 Ω R6; when opening the release actuator a 330 Ω R7 is added in the PP-PE loop on the EVSE side which gives a voltage shift on the line to allow the electric vehicle to initiate a controlled shut off prior to actual disconnection of the charge power pins. However many low power adapter cables do not offer that locking actuator state detection on the PP pin.
   In Europe and elsewhere where the normal domestic voltage is around 230 V there may be less risk of causing fire through overheating of cables for any given power due to the lower current. However most European extension reel cables now include an automatic current cut-out to avoid misuse of the cable. This requires manual resetting if excess current is drawn through the cable. (American multi-plug cords also include such a device, but single- or triple-outlet cords do not.)
  
  Section::::Hazards.
   BULLET::::4. Shielding cables – A shielded cable can be thought of as a Faraday cage for wiring and can protect the wires from unwanted noise in a sensitive circuit. The shield must be grounded to be effective. Grounding the shield at only one end can avoid a ground loop on the shield.
   For short cable runs of less than about with only a few devices, it is sometimes possible to operate without termination. At short distances, cables with higher capacitance and different characteristic impedance such as microphone cable can be used. As the cable length or number of devices increases, following the specification for termination and correct cable impedance becomes more important.
   MC Multilam Technology claims that constant spring pressure provides reliable low resistance contacts. However, it is very important to never connect or disconnect them under load, even on low-voltage (12-48 V) systems. An electric arc may form which can melt and seriously damage contact materials, resulting in high resistance and subsequent overheating. This is partly because direct current (DC) continues to arc, whereas commonly used alternating current (AC) more readily self-extinguishes at the zero-crossing voltage point.
   The operation of the HC in the electron collection mode is called the plasma contacting (or ignited) operating mode. The “ignited mode” is so termed because it indicates that multi-ampere current levels can be achieved by using the voltage drop at the plasma contactor. This accelerates space plasma electrons which ionize neutral expellant flow from the contactor. If electron collection currents are high and/or ambient electron densities are low, the sheath at which electron current collection is sustained simply expands or shrinks until the required current is collected.
  