The Mk3 astra is prone for wiper motor failures, I suspect that one of your motors may have a fault. If the fuse blows when you go to operate the wipers then I would suggest you try individually disconnecting each wiper motor in turn to isolate the problem.
P.S they aren't cheap to replace via Vauxhall. Last time I enquired I was told £115, plus VAT. So I left the shop before they took my shirt. ;o)
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