The ground wire that comes from the meter to the main breaker is too short for the new box I want to install. Can I butt splice the ground to make it longer. This is the 4.0 ground and is about 18" short

I would use a "Bug".
This:
Split Bolt Connectors - Wire Connectors - Electrical - Grainger Industrial Supply (http://www.grainger.com/Grainger/split-bolt-connectors/wire-connectors/electrical/ecatalog/N-8i3?op=search)
Hope you mean a #4 ground , not a 4/0 ground.

I would use a "Bug".
This:
Split Bolt Connectors - Wire Connectors - Electrical - Grainger Industrial Supply (http://www.grainger.com/Grainger/split-bolt-connectors/wire-connectors/electrical/ecatalog/N-8i3?op=search)
Hope you mean a #4 ground , not a 4/0 ground.

It is the ground wire that goes from the 200 amp main outside to the 200 amp main inside I believe it is what they call4/0

4/0 is 0000 AWG and about 0.460 in diameter which is a little less than 1/2 inch.

4/0 is 0000 AWG and about 0.460 in diameter which is a little less than 1/2 inch.

That's the one it is the same wire coming from the overhead to the meter socket. I have butt splicer that size and I was told that I could use it to splice the ground but I want to make sure

4/0 is a much larger wire than #4,
You also mention the Ground wire that goes to the Breaker? Are you sure you don't mean the supply wire?

Probalby is referring to the bare neutral of a 3 wire SE cable.

This is the grounded conductor, not the "ground".

The splt bolt method Strat mentioned is fine for this conductor.

If you have a butt splice for #4/0, you must have the special crimping tool and die?

A true grounding electrode conductor must be continuous or use a irreversible connection, such as CadWeld, or a compression connector.

4/0 is a much larger wire than #4,
You also mention the Ground wire that goes to the Breaker? Are you sure you don't mean the supply wire?

The wire is the ground wire and it 4/0 aluminum I have a butt splicer that size it has burndy ams4/0 on the side of it

Are u steel having problem with your ground wire they sala a permanet conector for it and you won't have any problems

Are u steel having problem with your ground wire they sala a permanet conector for it and you won't have any problems