what is the reduced neutral size for a 200 amp residential service in the new code book?
is it table #17 #6 awg.
Your question is rather vague at best.
Table 17 refers to the "Minimum Size of Grounding Conductor". And yes, a #6 is the correct size for a grounding conductor with 200 amp service conductors.
It, Table 17, does not directly have anything to do with the size of the service neutral conductor.
Minimum requirements for the system neutral conductor are detailed in 4-022. In no case may it be smaller then a #10 copper or a #8 aluminum or smaller then the system ground conductor as determined by Table 17.
As well the service neutral conductor must be sized so it can handle the unbalanced load from the system. The size of the "unbalanced load" is based on the demand calculations of section 8.
If you are going to down size a service neutral you had better have the calculations ready to present to the inspector. I'll bet you will be asked for them, I would ask for them.
You might also want to ensure that the CEC 20th edition has been adopted by the AHJ in your region.
Rick Kelly...