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A lot of European countries use type F outlets that are not polarized, i.e. you can plug in both orientations. This means that there is a big risk (50%) to invert live and neutral. Is that not a major safety hazard?

To my understanding circuit breakers cut only the live wire, meaning that they are not effective 50% of the time, if 50% of appliances are connected in reverse.

I read some info about some circuit breaker cutting both live and neutral, but that was for addressing issues with incorrect grounding, not reversed polarity.

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    \$\begingroup\$ See Schuko. \$\endgroup\$ Jul 23, 2023 at 12:53
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    \$\begingroup\$ What issues you might mean? Or what safety hazards? What difference would it make for a device in which way it is plugged in? And circuit breakers cut the live before they enter the device so anyway the live to device is cut. I am simply trying to gather info what kind of explanation you want after the "no it's not an issue". \$\endgroup\$
    – Justme
    Jul 23, 2023 at 13:18
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    \$\begingroup\$ Re, "circuit breakers..." Presumably you mean, a circuit breaker that is built-in to the appliance itself. (See Justme's comment about breakers in the building wiring.) If the plug can be plugged in the wrong way, then I guess it must not have a safety ground, and so I guess the appliance must be double-insulated. The only purpose for a built-in circuit breaker in a double-insulated appliance would be to protect against an over-current fault. Interrupting the neutral conductor is just as effective as interrupting the hot conductor in that scenario. \$\endgroup\$ Jul 23, 2023 at 14:21
  • \$\begingroup\$ You do understand that type F doesn't define which of the two pins is L and N? And different sockets, in the same room, can be wired in opposite ways. Which means it's essentially undefined in the appliance. There's no "risk" of this happening; it's explicit that it's part of the normal operating parameters. \$\endgroup\$
    – jonathanjo
    Jul 23, 2023 at 15:35
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    \$\begingroup\$ Devices designed for Europe must be designed as if both wires are live. Switches switch both wires, and maybe that is why switches are not as common as in Australia. \$\endgroup\$
    – user253751
    Jul 24, 2023 at 10:52

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To my understanding circuit breakers cut only the live wire, meaning that they are not effective 50% of the time, if 50% of appliances are connected in reverse.

If a circuit breaker cuts the connection to the live wire, then the appliance cannot be at the live wire's potential, regardless of which orientation the plug for the appliance has been connected.

Is it an issue that type F outlets are not polarized?

In the US, we have screw type light fixtures. If a light bulb is partially screwed in, it is possible to touch the threads of the bulb which are in contact with the threads of the fixture. If the threads of the fixture are connected to the live wire, this would pose a shock hazard. As a result, in the US, the plugs for portable lamps must be polarized to ensure that the threads of the light fixture are connected to neutral. Wherever such lamps are in use, non-polarized plugs should not be used. However, if such lamps, and appliances with similar safety issues, are not available in a country, then non-polarized plugs should not be an issue in that country. I.e. if you make your appliances safe to use with non-polarized plugs, then non-polarized plugs will be safe.

Edit: @Janka informs me that in continental Europe, screw type light bulbs are used, as well as unpolarized plugs. Individuals are warned not to change light bulbs with lamp plugged in. Relying upon warnings and the intelligence of end users is sometimes effective. For example, I think it would be quite rare for someone to be foolish enough to attempt electrical work on a microwave oven which is energized. However, having unpolarized plugs on lamps with screw type light bulbs does pose a potentially lethal hazard, even if the public is educated and wise enough to steer clear of that hazard.

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    \$\begingroup\$ We have Edison sockets in Continental Europe, too. And non-polarized plugs. And light switches at the appliance that only cut one wire. It's not a problem because they tell people only to switch bulbs when the lamp is not plugged in. \$\endgroup\$
    – Janka
    Jul 23, 2023 at 13:09
  • \$\begingroup\$ @Janka do some people ignore the warning and change bulbs that are plugged in and get electrocuted? Or has the warning been effective? \$\endgroup\$ Jul 23, 2023 at 13:13
  • \$\begingroup\$ I don't think it's a huge issue otherwise there had been a huge campaign against it already. \$\endgroup\$
    – Janka
    Jul 23, 2023 at 13:16
  • \$\begingroup\$ @Janka I did a quick google search and found the link below. It does happen, but it is news, suggesting it isn't so common that it gets ignored by news outlets. belfasttelegraph.co.uk/news/northern-ireland/… \$\endgroup\$ Jul 23, 2023 at 13:18
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    \$\begingroup\$ It proves my point as that's from Derry, which is in Ireland, and they use polarized plugs and bayonet type lamp sockets where the housing is grounded. Some people manage to overcome all safety obstacles. \$\endgroup\$
    – Janka
    Jul 23, 2023 at 13:19
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A lot of European countries use type F outlets that are not polarized, i.e. you can plug in both orientations. This means that there is a big risk (50%) to invert live and neutral. Is that not a major safety hazard?

Yes, it's a challenge for the equipment designer, particularly novices. They must design their equipment to sufficiently protect the user expecting either pole to be "live", or use the earthing/grounding pin to ground equipment.

I see all sorts of homebrew electronics designs where they directly electrically connect the neutral AC power to their low voltage stuff, and they're like "it's safe, it's neutral". And then they plug it into a Schuko, and 50/50 chance! (mind you that's not safe anywhere - electronics should usually be fully isolated from AC mains - best to use a listed/approved "wall wart" power supply rather than trying to roll your own).

AC mains power is wired like an "isolated system" with both legs (supply and return) wired individually - nothing is "common". However, to enhance safety, one of the legs is bonded to earth - this is done for a bunch of reasons. That conductor then gets a special name: "Neutral" to reflect that if everything is working properly, neutral's voltage will be near earth. That's a big "if", so neutral wires are still insulated.

This neutral-earth bond is done in exactly one place. If it was done in 2 or more places, the earth wire would become an alternate path for neutral, and that would be bad.

On this warm assumption about neutral's low danger, the neutral wire is not circuit breaker protected and does not go through common switches. Some breakers switch neutral, but there is no overcurrent protection on neutral. You could pull 1000 A on that neutral and the breaker would not know or care.

Why does this (usually) work? Beause of what I said above about AC mains being wired as an isolated system. Current from any live wire should return only on its partner neutral wire. Therefore, the neutral would only be overloaded if the partner live is overloaded, and a circuit breaker protects that. If someone were foolish and used neutral as a "common" for multiple live circuits, all bets are off.*

* Except for MWBCs, which are this right here, or the equivalent in 3-phase (where again the neutral can't draw more than the highest phase wire).

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    \$\begingroup\$ I would not call it a huge barrier, as it has been normal for tens of years and not unique to any other country where unpolarized plugs have existed. So this isn't a problem, and it isn't an European problem. \$\endgroup\$
    – Justme
    Jul 23, 2023 at 18:43
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    \$\begingroup\$ Beginner electronics should always be fully isolated from AC mains. Many designs have reasons not to be, but you have to be careful around them and know what you're doing. \$\endgroup\$
    – user253751
    Jul 24, 2023 at 10:54
  • \$\begingroup\$ @Justme sure, I'll go with that. Edited. \$\endgroup\$ Jul 24, 2023 at 18:13
  • \$\begingroup\$ @user253751 Okay, edited. \$\endgroup\$ Jul 24, 2023 at 18:13
  • \$\begingroup\$ The choice between Double insulation and Earthing is orthogonal to whether neutral is treated is live. Plenty of Class 1 appliances are sold across Europe. \$\endgroup\$ Jul 24, 2023 at 18:45
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Yes it's an issue, but it's a manageable one. Un-polarised sockets aren't going to go away, so if you want to make an appliance that is safe to use worldwide then you must treat the neutral conductor as potentially live.

Frankly treating the neutral conductor as potentially live is good practice anyway. Wires break.

When designing an appliance you should consider the purpose of any switch, fuse or breaker, if it's only for functional switching or protecting from overloads then it may be acceptable for it to be only single pole but if it is needed for protection against earth faults or to isolate parts for maintenance then it needs to be a double pole switch.

An example I came across too long ago was the design of a piece of medical equipment with a touch screen display. They were having trouble with interference to the touch screen during EMC testing. To mitigate this they added a common mode choke to the mains input. The common mode choke however increased the impedance from the earth terminal to the case to a level where they could no longer assume that the building wiring would provide adequate protection against earth faults. The fix was to use a mains inlet with double pole fusing.

Placing fuses in the neutral is anathema to Electricans in the US and UK, since it breaks the assumption that "neutral is safe", but it's perfectly acceptable under appliance design standards. A double pole common trip breaker is an even better idea, but it's difficult to find such a thing in a low current rating and small physical size.

Presumably for historical reasons, lighting seems to get a pass on doing things that in almost any other context would been seen as massively unsafe. A device that allowed access to live parts without forcing the user to isolate them first and without requiring them to use a tool would be considered totally unacceptable in most contexts, but is apparently perfectly acceptable for lamp-holders.

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