First: These are systems that gives you no second chance. Mistake = Dead.
FYI There are several distribution schemes (AC and home setting presumed):
* Three phase delivery where one phase and the neutral is used in outlets.
* Split phase delivery where the two "outer" wires gives the full distribution volt and outer to mid gives half of that.
In the three phase system there's a real neutral. Protective earth is wired to the ground and is _only_ there to protect human life. In some countries it's only wired to ground in the transformer station and is forbidden to ground anywhere else.
There have been cases where the power company has mixed up neutral and phase which of course burns all electrical equipment.
To more practical matters:
You can check the outlet by measure the voltage between outlet protective earth to an earth connection outside your house in the ground (Indoor water piping is not suitable for protective earth in any manner). Then connect a series resistance of 10 ohm and
5W to limit current in series with the multimeter in current mode. There should be a negligible flow. Say less than 1 mA at most. Outlet protective earth connection is not supposed to have any flow to ground at all. But if a phase get in touch with protective earth. Then it should short circuit it all.
Between the two normal holes there should be standard mains voltage. Between any of these holes and protective earth there should be either half for split phase distribution (unsure!) or full mains voltage on one hole and almost none (less than 20V) on the other relative to protective earth in a three phase distribution system (with two power wires to the outlets).
Mains voltage is 110 V in USA, and mostly 230 V in Europe. Japan has both (110/230) depending on south or north location.
To protect:
* Check your outlet wiring by measuring - and don't assume anything
* Have a look for dirt and spider nets inside
* Add
overvoltage protection - that will disconnect instantly on too high volt
* Use
power conditioner that catch current
surges (thunder), crest, capacitive -
inductive imbalance etc
* Install online
UPS * Install main protection for thunder at the central. Only then will per outlet "surge protection" be useful
* Let all conductive wiring (electricity, aerial, water, sewage) enter the house at the same point
* Install
thunder protection ground system so that the house is a
Faraday cage * Install ground Residual-current device breaker (
RCD)
* Use
isolation transformer * Connect the ADSL etc network connection via an
optical Ethernet link. Same for sensitive computers. Voltage difference between the phone line and mains is a common cause in thunder situations for broken equipment.
There is in most cases no standard for which wire is neutral and phase. So you can't rely on that at all. But you can connect equipment to the same outlet (phase) and measure before connecting to avoid preventable mishaps.
* Make use of galvanic isolation transformers for audio etc.
I would say the cheap way to protect is by:
* Check outlet(s) to have protective ground
* Use protection equipment that thwart overvoltage
* Use isolation transformer
* Make use of UPS and isolate with media converters (fiber connection)
* Check if any outlet use a different phase in the same room and label them
Some info on outlets:
wp: Electrical outletIn the end it's all about cost and probabilities.
