What this sync module does in an S7-400H rack
The Siemens 6ES7960-1AA00-0XA0 is the synchronization module that links the two CPU halves of a SIMATIC S7-400H redundant system. Without it, the paired CPUs cannot mirror process images or execute bumpless switchover on a fault — the redundant architecture simply doesn't function. It draws 210 mA from the 5 V backplane interface and dissipates 1.1 W typ. — modest enough that it won't stress the rack power budget, but the 5 V rail must be sized to accommodate it alongside the CPUs and I/O slices.
Lifecycle reality for the procurement decision
If you are maintaining an existing S7-400H installation, securing the 6ES7960-1AA00-0XA0 now — before the mature stage tips into phase-out — is the prudent call.
Physical and electrical fit
At 60 g and drawing 1.1 W, this module is a lightweight, low-thermal add-on that snaps into a dedicated slot in the S7-400H central rack. It does not consume a general-purpose I/O slot — it occupies the sync slot between the two CPU units. The 210 mA draw from the 5 V interface is the only backplane load — no field-side power supply needed. Confirm that your existing 5 V bus can deliver that additional current without exceeding the power supply's rating.