Connecting transformers in parallel is sometimes a risky business,

Some big power distribution transformers are sometimes connecting in
parallel with some external inductance to reduce the imbalance.

Take a separate smallish transformer with a centre tapped low voltage
secondary winding. Connect the centre tap to the load and the two end
of the small transformer to the respective hot terminals on the main
transformers. The primary of the smallish transformer is not
connected, but can contain quite voltages.
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Question : With a load having 2 connections , with the centre tap connected
to 1 connection of the load ,where to connect the other connection of the
load ?

Frank GM0CSZ / KN6WH