Faac C721 trips mains when connecting transformer

[Gatehelp]

Hi, I have installed a faac c721 with 4 Photocells and everything we connect the transformer it trips the power in the house. We have tested and we get 250v but cannot understand why it keeps shorting the circuit. The c721 is just sat on driveway can't get around it. Has anyone noticed problems with this before - the transformer could just be a smoke screen it's brand new only a couple of weeks old. Faac have said send it back for testing but that's a nightmare with all the blockwork settled back in. I have the nylon racking off also. Any help would be grateful.