I was asked this question on a recent blog about GFCI protection. Because this does come up on inspections fairly often, I thought I would clarify it with a post. Ground Fault Circuit Interrupter (GFCI) is the proper and full name. The name comes from the fact that the device is monitoring the current in the circuit. If too much current is leaving the device and not coming back, it must be going to ‘ground’ – a ground fault. When it detects the ‘ground fault’ it interrupts (turns off) the voltage/current to the circuit.
I believe the only reason the the acronym GFI is used instead of GFCI often times is that it is much easier to say. Not much of a reason, but I do it myself sometimes. I think the fact that it is one letter shorter and still conveys the meaning makes sense. After all you are already reducing it to first letters only, you might as well reduce it a little more.
Thanks to Charles Perkins for asking this question and suggesting to make it a post!