Guide to Electrical Equipment for Travelers/Earthing & Grounding
Anyone who travels much is sooner or later likely to find themselves in a situation where no earth is available or the earth that is available won't join with any of their plugs or adaptors. Also, just because sockets have earth contacts doesn't necessarily mean they are actually connected to a properly designed and safe earthing system.
For this reason wherever possible double insulated equipment is the smart choice for the traveller. Where single insulated equipment is all that is available and the sockets have no earths or dubious earths it is best to at least ensure that the earths of all appliances likely to be touched at the same time are connected together (for example by plugging them into the same powerstrip with earth contacts). This way if one of the cases becomes live they all do and therefore there is minimal voltage between them and therefore touching them at the same time won't give a shock (remember current has to flow between two points on a persons body to give a shock). The worst thing to do in this situation is join the earths in groups which are isolated from each other (for example two powerstrips with earth contacts in two unearthed sockets) as this will spread a fault without providing an equipotential zone throughout the equipment.