He's in the Netherlands.
On the secondary, tie the '0'V to the adjacent '240'V wire, to create the center tap and GROUND point. These are the middle two taps on the secondary.
Then put the 240V across the primary, and also..tie the shield to the ground, or what is now the centertap on the secondary. The two endpoints on your secondary are now 120VAC each, for a split rail balanced AC configuration. Grounding the centertap to the shield kills some of the isolation effect, but helps prevent some serious disasters from occuring in your house.
Remember to derate the transformer KVA rating by about 40%. Most certainly, no less than that, meaning If it was rated at 5 KVA as a standard AC isolation transformer, don't try to run it at 4.0KVA. That's too much. Since part of the original rating is thermal, you don't have to de-rate it by the full 50%. But don't stray too far from the 40% point. As a matter of fact, that's pushing it. Play it safe.
If it is, lets say, rated at 5kVA, then don't try to draw over 2.5KVA continuously,as the amp will sonically 'tube' out on you, ie, dynamics, or transient current draw will be limited at upper and lower frequencies, for an over smooth effect, but too rounded. When attempting to shove such a transformer into balanced AC use, this is the only way to keep the sonics decent. Please understress the transformer.
I'm running at about 500WPC, but with overall draw rarely exceeding 50w.
I'm using a reconfigured isolation transformer, at 550lbs and 50KVA rating, with a 1 minute 100KVA rating. Mine is wired the exact way I reccomended.
