40A fuse blew on first engine start

[Mark Albery]

I ran my CC340 engine for the first time at the weekend and all seemed OK until after shut down the main bus was dead.

It seems that the 40A fuse between master solenoid and main bus had blown. The battery was in a lower state of charge due to panel and EFIS testing earlier, so I expect the alternator was putting out its full rated output on start-up.
The 50A breaker between alternator and main bus was still in, so I presume there was enough surplus current from the alternator to blow the fuse.

Has anyone else come across this issue?
Would it be better to use a 50A fuse in the receptacle?

[Pete D]

I would check very closely that things are wired correctly and that there is no possibility that that wire between the bus and solenoid doesn't have a screw into it or something. The purpose of that fuse is to protect that wire, if the drawing says 40 amp I would not replace it with anything bigger.

I have never seen a nuisance blow of that fuse, suspect that there is a short some where.

[Mark Albery]

I replaced the fuse and everything powered up as normal. A short to ground between the fuse and bus bar would show up when the master was switched on.

My best guess is that as their was very little current draw from the bus so nearly all the alternator output went through the fuse to recharge the low battery. Maybe the fuse was below spec or the alternator outputting more than 40A.

I'm mostly interested to know if anyone else has experienced that.