system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are wires generally preferred over ACH when transferring larger amounts of money?

Title. 

Noticed transfers of over $30k+ generally are done over wires and ACH isn't accepted, why so?
gpt
ACH (actually EFTS specifically as wire can be done through an Automated Clearing House too) requires just routing and account number, and in a legal sense is recognized as similar to a personal check.

Wire transfers require two numbers from the bank that aren't easily-accessed public knowledge that you can find on anyone's checkbook, and only a sender can authorize money moving unlike EFTS where the receiver can also make money move like with automatic bill payment. In this sense it's treated more like a cashier's check.

If they use FedWire, that money can be moved in the same business day (or even instantly) also, which is pretty handy. Not sure if FedACH is set up the same way, but FedWire is served by a datacenter with on-site backup, with another "hot" backup a few hundred miles away with *its* own backup of the backup, and a third "warm" backup facility. Even though the process is very quick. This provides a lot of integrity and failsafe to those big amounts of money.