yes it is .I would size up to 250mcm acwu for the voltage drop,as the 4/0 al in the canadain code book table4 is rated for 185amp for a service conductor. The electrical panels that I use for a 200 amp service will take a 250mcm conductor,the problem is when you use a 4/0 on a 100 amp panel.

No it isn't. 4/0 is only approved for 185 amps and Jack's statement is not true except for a residential service or feeder and you did not specify it is a residential service. What is the calculated load? Is it continous or non? Did you also do a VD check? Now if your continuous load is 185 amps you are good with 4/0 because table 13 allows you to use a 200 amp breaker. Your service is not a 200 but a 185 amp service in this case. Do A VD calc and the 4/0 might not be big enough to meet that rule. MJ2000 if you can fill in a couple of the missing bits we can offer a better answer. You did not mention 3 or 4 wire which gives differnt answers too.

It is residential service 3 wire. How to calculate VD when I don't know what is the load? Do we calculate VD with calculated load or with 200A? What is allowed VD from transformer to meter base? Existing service is 100A and customer wants upgrade to 200A.

See Appendix B Section 4 and use the tables in Appendix D. It's a good question about the load for voltage drop. Perhaps use the intended service size and calculate as a non-continuous load. Or, just use 250 MCM ACWU. If more than 3 meters is above ground, you need to use the above-ground ampacity, anyway (I think). The above ground calculations are here: http://www.codemath.com/cgi-bin/Run.pl?script=CecAwgRw Use 200A, 240V, 1P, Aluminum, 90 degree insulation, non-continuous load.

Acording to the table D-13B from diagram B4-3 detail 1 for %80 rated equipment you are good for 210 amps. I should have looked at these diagrams but I believed they only applied for 2 or more raceways or cables. So for ampacity the 4/0 is good. What do you used for VD calcs? Great question but I can think of 2 answers. Do your standard house calculation and use the amps you get as the minimum ampacity for the service without spare capacity Use that number to get your wire size. So lets say you get 135 amps for the load. You can do the VD for 135 amps but the cable you get can only be fused at 150 amps from table 13. To get the full service capacity you need to use 200 amps for the VD and the wire size is the answer. Use the appendix B solution as THW has astutely pointed out and you will even get some bonus ampacity for just 1 cable over table 4. My VD calculator gives 4/0 for a 3% drop or 300 kcm for a %2 drop. Total VD is at %5 from meter to load. Recomended drop is %2 for feeder and %3 for branch. I was surprised you need 300 and not 250 for just the %1 improvement. I think I would accept the 4/0 but check with your inspector just in case he is stricter. Now if We were talking continuous loads I too would have required the 300 KCM but a house is generally never loaded to the service nameplate