You should ask PEA directly, because every office seems to work from their own policies, not very different from any other public government office in Thailand. But from my experience, they are very rigid about their own system and property. PEA needs access to their equipment and adding private locks, just think about the key system they would need for monthly checks, so it would be a universal key for avery meter in that case. And if someone really wants to cut your electric, a simple lock will not stop them anyway. They can still cut the supply before it even reaches the cabinet, so to me it can easily become false security. A small solar system or battery backup will give you more control, and also live status of your system. Then you can see when the power goes off, when the system switches to backup, and when the battery gets low, which will send messages/alarm to your app.
