Why do some electrical devices have a ground and others don't?

Question

I noticed in my kitchen that the toast oven and the range hood had a ground fault, first by using a voltage detector pen, when getting near it the pen would activate from a distance (around 5cm without touching the case). Both of these didn't have a ground wire so I replaced the entire AC wires to put one with a ground wire that I tied to the metal chassis of both devices

The faults are "fixed", or at least gone to ground, however, I still wonder: When these devices when designed they knew both were going to be near water sources, why weren't they designed with a ground wire plug cable in the first place?

What defines when the case of a device should or should not be grounded?

What happens when a device has a fault and it's fixed like this to the ground wire in the home? Will the ground voltage go up? I'm currently sitting around 2v last time I checked (measuring neutral and GND with AC mode in a multimeter that doesn't have RMS values).

Answer 1

The IEC suggests 5 protection classes that are followed by the electrical appliance manufacturing industry.

According to IEC 61140, equipments does not require a safety connection to earth because the exposed parts are single insulated Class “0”, and double insulated class “II” (NOT class 2).

Class 0 appliances can be sold to dry areas only, but in some countries sales or imports prohibited at all. Class II mark is like this (two squares)

EDIT

The simplest earthing design and install solution against insulation faults for mobile, semi-fixed and portable loads is this:

You can see the companies transformer (Y), common and earth. Does not require coninues monitoring. Just a periodic check on the RCD, which is the device that protects the persons. Each insulation fault results an interruption in the supply of power.

The bellow connection it is not adviced for souch loads.

Answer 2

The voltage detector pen may not be indicating a ground fault, it senses electric field, which is quite normally present around conductors, even if you can't touch them. See this instructable for some more details.

If you have RCD protection on the circuit feeding the appliances, then the ground wires you added would cause it to trip if there is a fault which leaks more than the trip current to the part you have grounded (usually 30mA).

Double insulated (Class II) appliances do not need a ground connection as the exposed metal has at least two types or layers of insulation between it and any dangerous voltages. However, the exposed metal does not all have to be connected together (because it's never expected to be dangerous and need earthed), so if you did have a fault and only grounded one point there could still be a dangerous voltage on other points on the metalwork.

It would be worth getting an electrician to check if there is an earth fault on your appliances, it sounds like there isn't, but if there is your fix might have made it more dangerous in the long term. The voltage on a piece of metal isn't as important as the current that will flow when you touch it, so measuring 2V with a multimeter isn't in itself a cause for concern.

The ISO 61140 standard (viewable online as the South African COMESA 301 ) defines the threshold of perception at 0.5mA for a 'standard' 2000 ohm human body model, but some product standards for installed equipment limit leakage for Class II appliances to 0.75mA (0.5mA for portable appliances), so it is possible, though fairly unusual, for a 'safe' item to produce a 'tingle' when touched. Some people are more sensitive to the perception than others, and other effects (wet skin, for example) can reduce the body impedance to increase the current.