GFIs work by measuring the current going to a load on the phase conductor and the current returning from the load on the neutral. They should total zero. If not, they trip. GFIs don't use a ground lead. Any departure from that zero total is current going elsewhere, potentially through a person. The typical destination of these stray currents is to ground (the power system reference). Hence the term ground fault detector. In Europe it is called a residual current detector, perhaps a little more accurate. The only way a shock could escape the detection of a GFI or RCD is if the person were connected across both wires leading from the GFI, for example sticking your finger in a lamp socket. This is pretty unlikely since it it generally involves two insulation faults.
Ray_Russell wrote: > I'm curious if anyone knows why Europe or other countries have not > required GFI protection. US National Electrical Code requires GFIs in bathrooms, kitchens, pools, boathouses, marinas, mobile homes, outdoor receptacles, garages, construction sites, health care facilities, and a few other areas. They (or immersion detectors) are also now required as integral parts of hair dryers and curling irons since they are often used in bathrooms (since older homes will not have built in GFIs). The required locations are expanding as GFIs become cheaper. They have been considered the primary reason for the dramatic drop in electrocutions in the US in recent years. Patrick Lawler wrote: > ... > Having said that, I think a three-leaded version of a GFI could > protect against line-neutral current imbalance, as well as high > leakage current. > Does anyone sell them? I don't understand how a three wire GFI would work unless you are talking about three phase. GFIs are reactive to leakage current. Currents not returning on the phase and neutral such as through filter caps will trip GFIs if sufficiently high.
