I have a 240volt single phase panel and I need to hook up a 3phase 208 volt sub panel to it for a festival this weekend,can I do it? I know I will only be able to use 2phases of the 3 phase panel.I don't need 3phase anyway

What is your position at this festival? Are you an electrician?

Yes,but I've been away from the trade for awhile. Im helping someone out on this and they want to use the material they have if its safe and if it
Will work.

It'll work. You just have to avoid the dead leg.
Also make sure any openings are closed.

Have had a problem with the local supply (overhead in the cotswolds) Just recently suffered power cuts of short duration but in quick succession and voltdrop down to 216v in the low demand time. Engineers from the local supplier have agreed that the loss of an American style fridge/freezer and food was their fault. My problem is how to protect the new fridge freezer from future supply voltdrop problems. Any ideas? Used to be Tech Electrician-now retired. C/unit is to the 17th.

Locate a UPS unit of sufficient size in KW/KVA to provide uninterruptible power to the fridge during short duration power outages.