In a 200 amp residential application can I put 3 conductors of 4/0 and 1 conductor of # 6 into a 2 inch EMT. I am using RW90/X link Aluminum.

Why the #6 ? it this the lateral between the Meter Socket/base and the main disconnect for the Service Panel ??

Yes, it's a five run with an LB and 4 weather tight connectors between the meter socket & the disconnect switch. I am thinking the # 6 may be a requirement of the CEC although the ground rods should be connected to the disconnect switch I think.

I should add the bare # 6 is to ensure the meter base remains at ground potential even if the LB and related exterior fittings loosen over time. In the meter cabinet there is a ground lug and I am using a ground bushing on the EMT inside the building. BTW, I am using a ground plate, not rods as previously posted.

The conduit fill is fine but the #6 is not required and will be of little value in a fault. the service pipe gets a bond bushing and the neutral is bonded in the meter base and again at the main switch so adding a #6 only parallels the neutral and the service raceway. I would only add a bond wire if I used PVC as the service raceway even though the neutral meets the minimum code for bonding the meter and mast to the panel. Many inspectors would insist on a bond wire if PVC was used between the meter and panel but it is not required as the grounded service conductor serves both purposes until the neutral bus in the main panel.

mikesh, I appreciate your answer, I always agreed with everyone that the number 6 is NOT a code requirement. My only question was IF it was requested by the local AHJ would I need to upsize the 2 inch conduit as I could not find an actual code reference. The thought of having to change out the conduit (maybe) did not sit well with me. There is a little more to this story but it is no longer relevant as you have answered my question. THANKS to you and dougwells for the feedback. Case closed.

10-814(f) i think says that your EMT will be your bond

and also, if you had to add the number 6 to your conduit, than you would have to follw the steps from Tables 8, 9 and 10 in order to find your conduit size