Thank you all for your useful comments and suggestions. I hadn't realised the question would generate that much response. The two fuses in question were on the transformer secondary, and those fitted were of different sizes and ratings to each other. I have enough info now to get it sorted, thank you. Incidentally, the safety testing wasn't affected by incorrect secondary fuses. The transformer was treated as a Class II appliance and passed all visual checks and dialectric tests. Thanks once again, Evan