Earth, Ground and Neutral

Earth and ground are the same .Neutral is the junction of 3phases connected in star.A fuse is used to protect circuits against overload which reflects as a excess current.Many types of fuses were in Vogue like the ordinary wire fuse in Porcelain housing used in houses to HRC fuses.With the advent of MCB's and mccb's less and less of fuse is used.In certain cases HRC fuses are used as back up against mainly short circuit.Fuse once it blows needs a replacement .Relay is a vast subject.It monitors different parameters which it is designed to. With advent of electronic relays many functions can be combined in a single relay.It operates and protects the circuits/ devices and can be reset.For a detailed reading you can refer to a good hand book on Electrical Engineering.

< earth,= MOTHER EARTH

ground,= BODY of anything--TV,Computer,Motor---

neutral.= the reference potential-which is mostly Earth connected

i want to know diff between

fuse= something melting and thus conductive path discontinued--thus protecting others down the current path

and relay= Senses overload( overvoltage/undervoltage---------) and causes disconnection and so protecting other loads down the line.

What I understand from your question that you are asking about the difference among earthing, grounding & neutra. If I my guess is right then difference is as follows :

Earthing - Non current carrying metallic part of an electrical equipment is conncted to ground potential through copper / GI conductor for safety to operating personnel. This is called earthing.

Grounding - The neutral point of a star connected electrical equipment (solidly grouded or through NGR) or artificial neutral of delta connected equipments (through zig zag transformer) are connected to the ground potential for earth fault protection & to divert the unbalnce circulating current to the ground. This is called grounding.

The other points are nicely covered by other members.