The very first thing you do is shut off the breaker to this circuit. Now if you mean in a receptacle or switch box, the incoming cable ground wire, first connects to the box ground screw and then it is twisted with the outgoing ground wire and a wire nut is screwed on the ends of the wire to hold the wires together. In the case of a receptacle the same procedure is applied except there is a short piece of ground wire also twisted to the incoming and outgoing wires. This is called a pigtail and it goes to the green ground screw on the duplex receptacle
On an electrical distribution system there is no allowance for soldering by code. The approved methods are set screw lugs, hypress crimp connections and thermite welds. The reason for no soldering is the low melting point of solder and the high temperature of fault current. On a soldered connection it might work for one fault but if the heat generated melts the solder out of the connection then another fault current on the same system might not have a low enough resistance to carry the fault to trip the breaker. The ground wire is there to create a low resistance low impedance return path back to the distribution panel. A high resistance or open ground connection due to a bad solder connection is prevented by not allowing it in the first place.
Connect the ground wire from the light fixture to the ground wire in the ceiling box.
The green wire on the light fixture is a ground wire. If there is no ground wire in the conduit, the green wire should be attached to the metal box with a screw.
By earth wire I am assuming you mean the bare wire and that a black and white wire are connected to the light. If when you connect the earth wire and breaker trips then there is a short between black and earth. It could be a bad ground connection, an internal short in the light fixture where black wire "hot" is connected to metal on the fixture through a nick in wire.
The fixture box should have a ground screw on the bottom of the box. Sometimes you have to move other wires out of the way to see it. Just reconnect the fixture ground wire to this screw.
If there is a brass colored screw and a silver colored screw, the BLACK wire will connect to the brass screw. If you can't see a difference, connect the black wire to whichever screw connects to the CENTER contact of the light fixture.
Yes, that is the correct connection.
Connect the ground wire to the metal box.
The green wire on the light fixture is a ground wire. If there is no ground wire in the conduit, the green wire should be attached to the metal box with a screw.
If you mean 2 bare copper wires those are the ground wires. Tie them together and then connect the light fixture ground wire which will be green or bare copper to those ground wires.
I always connect the ground wire to the box. However, if there is no real ground wire running back to the panel it really does you no good. The NEC requires that you rewire the circuit with the proper conductors. Remember that the ground is for your protection. Without a proper ground, you run the risk of injury or death if the fixture wiring fails.
If you are referring to a porcelain or plastic ceiling light fixture most do not have a place to connect the ground wire. You cannot ground these type fixtures. Just connect the ground wire to the mounting crossbar and forget about connecting it to the light itself. It is on the ceiling and will never be touched unless you change the bulb and then you will have the switch in the off position. It is perfectly safe.
By earth wire I am assuming you mean the bare wire and that a black and white wire are connected to the light. If when you connect the earth wire and breaker trips then there is a short between black and earth. It could be a bad ground connection, an internal short in the light fixture where black wire "hot" is connected to metal on the fixture through a nick in wire.
The fixture box should have a ground screw on the bottom of the box. Sometimes you have to move other wires out of the way to see it. Just reconnect the fixture ground wire to this screw.
Very often the ground wire in the fixture is ignored, or just connected to the box, if there isn't a conductor to connect to. This, however, is a code violation as any fixture with a ground wire is required to have it properly connected to an equipment grounding conductor back to the panel. This is for YOUR SAFETY. Technically you should rewire the circuit with the proper conductors. It is BAD PRACTICE to connect the ground wire to the neutral or white wire because this could create a hazard of its own.
A ground wire is a typically uninsulated copper wire. The intent is to connect the wire to an electrical appliance or fixture to provide electricity a path to ground in the event of a short, thus preventing electrocution.
If you don't have the wire then you just can't ground it. This should not be too much of a problem. Most light fixtures are not grounded and some don't even have ground wires.
If there is a brass colored screw and a silver colored screw, the BLACK wire will connect to the brass screw. If you can't see a difference, connect the black wire to whichever screw connects to the CENTER contact of the light fixture.
Yes, that is the correct connection.