There are various single-phase power socket standards in use. Some countries use plugs that can be plugged in the socket only in a specific orientation (for example, the United Kingdom) while other sockets accept the plug in either orientation (for example, Germany).

British plug:

British plug

German plug:

German plug

Do engineers have to account for this fact when designing electrical devices? Could certain designs be simplified if line and neutral always were clearly defined?

  • \$\begingroup\$ Thanks for adding pictures. I understand the German connector much better now. I like the design because it is reversible and still grounded. \$\endgroup\$ – HL-SDK Jan 10 '14 at 18:23
  • \$\begingroup\$ @HL-SDK: The only times I've felt that might be advantageous are with adjacent oversized wall-warts. Even then, I'm not sure it would have helped. \$\endgroup\$ – RedGrittyBrick Jan 10 '14 at 20:28

No, there really isn't any significant simplification possible. When you interface to the power line, you have to make your design as robust and fail-safe as possible, in order to avoid product liability issues.

Even if the design of the wall socket permits only one physical orientation, there are enough mis-wired wall sockets out there that you really need to treat both Line and Neutral as "hot" inside your product.

  • \$\begingroup\$ What if a specific orientation was the global standard and miswired sockets would indeed be considered miswired? (I mean in the way current products don't consider the case where the protective earth is wired to line or something, because that's just wrong.) Would there be any technical benefits? \$\endgroup\$ – ntoskrnl Jan 10 '14 at 21:11
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    \$\begingroup\$ Even if you do not consider mis-wired sockets, or even if you consider fix wired equipments only, you have to treat Neutral as "hot" in most grounding systems because the systems are not designed to ensure that the Neutral may never reach lethal voltages. \$\endgroup\$ – Laszlo Valko Jan 11 '14 at 4:18

In all of the mains connected projects/products I've worked with, I specify a 3 prong connector where possible. This only works in one orientation and provides a dedicated ground (unless circumvented by the building wiring or an adapter I'll link to below)

Three-prong to 2-prong

Line and neutral should always be defined, but for some applications it does not matter. Think small holiday lights or some power tools.

When consumers are involved, it can come down to case grounding. If the product is designed inside a conductive metal case, the case can be left floating or ideally grounded. Without knowing which conductor is neutral or ground, the case could potentially be at the hot potential.

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    \$\begingroup\$ Even the adapter you pictured provides a ground connection (through the center screw) if it's installed correctly. Of course the number of cases where it's installed correctly is vanishingly small. \$\endgroup\$ – The Photon Jan 10 '14 at 17:34
  • \$\begingroup\$ Holiday lights in the US have for years required polarized connectors because they include a fuse in the plug which must necessarily be on the "hot" side. \$\endgroup\$ – supercat Jan 10 '14 at 17:43
  • \$\begingroup\$ The German connector is grounded but symmetric. \$\endgroup\$ – ntoskrnl Jan 10 '14 at 17:53

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