It depends on whose definition you use but in the US its easier to follow NEC standards. Using those stanards if you take an incoming supply voltage with a neutral...ie 120vac from a 240vac split phase panel then its DEFINITELY a neutral and is not fused but may be switched.
If there is a "fault" between neutral and the 120vac I would hope the breaker tripped or fuse blew...this is not a ground fault. This is a shorted circuit. This would also apply to the circuit if both wires were 120vac...ie 240vac circuit. If the 2 phases connect then its a "short".
Ground is or should be at ZERO potential so any voltage "sensed" on ground should trip a ground fault or GFCI. It may not trip a breaker or blow a fuse...just depends. Thats one reason GFCI's are required in certain situations.
Fuses (and/or circuit breakers) are there to protect the integrity of the system. If an overload condition occurs then heat is generated which can cause a fire or other damage, the idea is for the fuse etc to go before damage may occur.
Fuses nor circuit breakers alone can protect against a ground fault nor single phasing. In the case of a ground fault an overcurrent condition may not apply.
In the case where a separate transformer is used and one leg is grounded then that leg is called a "neutral" but by NEC standards it is a grounded conductor. Following NEC standards the grounded conductor should not be fused but again may be switched.
I have the vocabulary (and hopefully some knowledge) but not the words to properly state the information.
As for the original question:
I am curious as to how many of you fuse L1 and L2 before a motor starter to a single phase 120VAC motor. We have some people here that have said that it is required, but I don't see why you could not just fuse L1.
If the supply voltage is 120vac and has a neutral or grounded conductor then just one leg is fused.
We had a similar discussion on something similar here:
http://www.patchn.com/forum1/viewtopic.php?t=476