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I have some ungrounded receptacles in my house that are GFCI/AFCI protected. I wanted to check if my laptop (power brick) can be safely used on these receptacles. On the power brick I see this information (see screenshot) and the symbol for the appliance class it seems like it is double insulated but there is also a symbol inside that double square and I am not sure what this means (looks like ground?) in combination with the double square? Some online searching did not reveal anything else to me but perhaps on I am searching with the wrong keywords. So my questions are

  1. What does this symbol mean (outlined in the red in the upper right corner)
  2. Can I use this in an ungrounded receptacle?

enter image description here

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  • \$\begingroup\$ 1) Read this: iso.org/obp/ui#iec:grs:60417:6092 2) this adapter has double isolation so you can and may use it without grounding. 3) it still has a functional ground connection. So yes you may use this in an ungrounded wall socket. \$\endgroup\$
    – Bimpelrekkie
    Oct 12, 2021 at 12:21
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    \$\begingroup\$ @Bimpelrekkie but it reads it must be connected to a grounded outlet. Your advice is directly against that. \$\endgroup\$
    – Justme
    Oct 12, 2021 at 12:24
  • \$\begingroup\$ @Justme The symbol by itself doesn't tell us that the grounding is needed. The symbol tells us there is a functional ground connection. I do not see from what you conclude that grounding is needed. Is that in the text maybe? \$\endgroup\$
    – Bimpelrekkie
    Oct 12, 2021 at 12:27
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    \$\begingroup\$ @Bimpelrekkie I simply stated what is written on the device and based on that it must not be connected to an ungrounded outlet. I don't know whether or not the grounding is needed/used, but if the supply has mains input filter with Y caps to ground, that can cause problems if you use a grounded power strip in an ungrounded outlet, so connecting devices with mains inlet filter to the power strip will make strip ground and all the other devices that utilize that ground to float capacitively at half mains voltage. \$\endgroup\$
    – Justme
    Oct 12, 2021 at 12:37
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    \$\begingroup\$ but if the supply has mains input filter with Y caps to ground, that can cause problems I am aware of such issues. There are often questions about "feeling a tingle when touching the ouput of an SMPS". That then relates to the value of these Y type capacitors. For a double insulated device (like this one) the current through these Y caps should be low enough to be harmless. I do agree that earthing the adapter is the better option but if there is no ground available then I would still not worry about it and use the adapter ungrounded. \$\endgroup\$
    – Bimpelrekkie
    Oct 12, 2021 at 12:51

2 Answers 2

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  1. It is a symbol No. 5018 from IEC 60417 standard. It identifies a noiseless ground of an earthing system to avoid causing malfunction of the equipment. It basically means the thing needs grounding to avoid common mode disturbance which can cause poor operation of laptop touchpad for example.

  2. No - basically the text that reads on the power supply forbids connecting it to an ungrounded outlet. That might be just because of regulations needing that wording, but still, you will encounter less problems when using a grounded outlet.

It reads on the device that it must be connected to an earthed/grounded outlet. Simply based on that, it is not intended usage to connect it to an ungrounded/unearthed outlet. Knowing how power supply mains input filters work, connecting to an ungrounded outlet means that it makes the disconnected earth prong to have capacitively coupled voltage of half VAC of the input mains VAC, which is enough to hurt when touched and destroy devices if connected together.

Edit: text and Google translation:

"Apparaten skall anslutas till jordat uttag när den ansluts till ett nätverk." == "The device must be connected to a grounded socket when connected to a network "

"Laite on liitettävä suojamaadoituskoskettimilla varustettuun pistorasiaan." == "The device must be connected to an electrical outlet with protective earth contacts."

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  • \$\begingroup\$ I should have thought to use google lens (translate) on those texts. Brilliant answer thank you. \$\endgroup\$
    – Igor
    Oct 12, 2021 at 14:20
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This symbol is denoted as IEC 60417-5018 and is defined as follows (Taken from IEC 60417):

Title/Meaning/Referent :Functional earthing; functional grounding (US)

Function/description: To identify a functional earthing (grounding) terminal, for example, of a specially designed earthing (grounding) system to avoid causing malfunction of the equipment.

In your case, I would ignore this. If your outlet is GFCI protected, then it is just as safe as a grounded outlet and there is no problem using it. By the way, how many terminals are there on your adapter? If only 2, then it is designed to work with ungrounded outlets. If it has 3 terminals,then it should be connected to a grounded outlet to insure that its safety features will work. FYI, I found this symbol by googling "ground symbol with a semicircle"

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    \$\begingroup\$ The symbol means the ground is needed for the device to operate without malfunction. It is used to minimize common mode disturbance. Chanses are using an ungrounded outlet can negatively affect the operation of a laptop touch screen or touch pad. Which might be the reason why it reads on the power supply that it must be connected to an earthed outlet. \$\endgroup\$
    – Justme
    Oct 12, 2021 at 12:57

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