Vitaliy, In the US the ground wire is bonded to at least one copper rod that=20 is driven into the ground on the outside of the house. Two or more rods=20 may be required depending on soil conditions. This wire is bonded to the=20 ground bus in the main circuit panel. The wire must not be cut nor=20 spiced. It has to be one continuous run connecting all of the rods and=20 going to the box. The neutral and ground buses are bonded together in the main panel.=20 >From this point forward the ground and neutral buses are not bonded in=20 any additional panels. I.E. In a house the neutral and ground buses are=20 bonded at one point and only one point. The white neutral wire is the=20 return to complete all 120 volt circuits. The green or bare copper wire=20 is a safety wire. It is there so that if the hot wire comes loose or a=20 short develops between the hot side of the circuit and the device the=20 circuit breaker will blow. This is the way that it is supposed to be=20 done. I can not speak to commercial or industrial installations. I also=20 can not speak to other countries. Now as to is the ground side of the DC output of a power supply=20 connected to the AC ground. Ninety plus percent of the power supplies=20 that I seen that have a three wire connection the negative side of the=20 DC output has been connected to the green ground wire that goes back to=20 the main electrical panel. I have not seen any DC output grounds=20 connected to the neutral side of the AC supply that only have a two wire=20 power connection. When I build a power supply that has a three wire AC connection I=20 hook the DC output ground side to the green AC ground. If I only used a=20 two wire AC connection I do not connect the DC ground connection to=20 anything. You can reference the NEC of the US and there should be electrical=20 codes for the country that you live in. I also believe that there is a=20 European Union electrical code that actually superceeds the codes of the=20 countries in the European Union. Please check the codes of your country=20 to find out exactly how to do this. I only know the code as it applies=20 to US homes. thanks, rich! On 7/11/2014 2:16 PM, Vitaliy M wrote: > On Jul 11, 2014, at 10:26, Justin Richards wr= ote: >> Earth and Neutral are connected >> together in the meter box where the power enters the house. > AFAIK this is not true in most cases, at least in North America. Earth is= a separate conductor, connected to an earthing rod. > > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .