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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

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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).

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  • \$\begingroup\$ This 2V is measured with load connected? Did you measured both with load connected and disconnected? Any difference? \$\endgroup\$
    – GR Tech
    Mar 30, 2015 at 20:23

2 Answers 2

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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)

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EDIT

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

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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.

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  • \$\begingroup\$ this is good info to have however that still does not do anything against a fault that the appliances developed even by being insulated, its a hazard for the user and no norm can stop from happening over time \$\endgroup\$
    – GoatZero
    Mar 30, 2015 at 8:05
  • \$\begingroup\$ Depends of the service panel, i.e is neutral and earth connected togeteher? And how long is the additional ground wire? The service panel should be equiped with a residual current device (RCD), to avoide excessive current in case of insulation failure. Ungrounded equipment are the majority of portable, semifixed and mobile divices. \$\endgroup\$
    – GR Tech
    Mar 30, 2015 at 8:33
  • \$\begingroup\$ no they are not connected at the service panel, they are connected at the companys tranformer, in this case there is no RCD just the grounding conductor that goes to earth \$\endgroup\$
    – GoatZero
    Mar 30, 2015 at 17:52
  • \$\begingroup\$ Are you living in USA or Canada? I'm asking this because it is possible to use multiwire branch circuit - 3 wire romex. This split transformer you mean or the local Y (star)? \$\endgroup\$
    – GR Tech
    Mar 30, 2015 at 20:03
  • \$\begingroup\$ US, i meant the local Y star, the electrical system where i live its quite old, so it does not have a multiwire system, it just has a fuse box, and a gorund rod, along its wiring \$\endgroup\$
    – GoatZero
    Mar 30, 2015 at 20:11
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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.

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  • \$\begingroup\$ in the case of the range hood im quite sure its has a fault, you touch it, and you can feel the current through your body, in the case of the oven you can't feel anything, it might be just the electric field due to the high current running trough the heating resistor elements, however what you are suggesting is that i should look exactly whats causing the fault instead of just "hiding" the problem by grounding the chassis of the device? if yes that makes sense however isn't that the purpose of the grounding wire to get rid of leaking currents of faulty appliances? (as a security measure) \$\endgroup\$
    – GoatZero
    Mar 30, 2015 at 17:51
  • \$\begingroup\$ I understand the US product standards (see updated answer for links) for installed equipment (like your range hood) allows up to 0.75mA leakage for Class II, so it is possible for equipment without a fault to have a perceptible 'tingle' when you touch it. However, it is also possible that there is a larger flow, due to a fault, particularly if this is a new problem with the unit, e.g. some grease or debris might be bridging across insulation, allowing water or other conductive material to accumulate, causing increased leakage. \$\endgroup\$
    – rolinger
    Mar 31, 2015 at 8:33

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