I asked that question this morning - the answer was there is no limit set in law, it's at the discretion of the immigration officer dealing with the person on arrival.
I just called 1111, which is apparently the immigration department hotline, and was told that the 14-day period for Cambodians cannot be extended within Thailand.
No it's more complicated than that. Wife and kids are also here on tourist visa, I'll be going away for one day alone and want to keep the visas aligned
Hi Josh, used to be the case that you could get them for up to 3 years back to back. But there's been a lot of abuse of this visa type lately so the authorities are tightening up and the goalposts can be moved at any time.