Hello, thank you. I am DYI. Our daughter has home built in the 60s with fused service panel. One fuse has started blowing ; when a new fuse is put in, it will not blow right away, it can go for hours sometimes without blowing. It is a 20- amp fuse/circuit. On the circuit is a microwave and several regular outlets. The microwave has not been in use when the fuse blows. There is nothing excessive on the circuit and just normal use. Nothing out of the ordinary is being used when the fuse blows. I have checked that there are no foreign objects in any of the outlets. I have read that the fuse SOCKET can sometimes be defective, after decades of use. Do u think that is a possibility? The fuse socket contact looks a little pitted to me but I don't know if enough to be a problem. I cleaned it with a toothbrush and electrical cleaner (sparingly) and let it dry well before reinserting fuse. It didn't seem to help, the fuse still blew after a few hours. The fuse blows randomly (no set time or period of time). The panel is dry, I see no evidence of water intrusion. The fuse is Bussman SL 20 amp. I appreciate any help you can give me!