Two 12v supplies on one Seatalk network

[Alex_Blackwood]

Look at this circuit, S1 is on your switch panel & switches on all your navigation electronics, shown here as your Seatalk instruments ST1 to 4 & your radar. The whole circuit is protected by fuse F1 at the switch panel. The Seatalk network has a power connection at A & is protected by its own fuse F2. The radar leg is protected by F3. No problems here.

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Now you add a second supply to the Seatalk network at B like this...

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You get a bad connection at F3. Now the radar's power is coming via the Seatalk network. You send it the command to start transmitting, it overloads fuse F2 which blows, & all your instruments go down. You replace F2, but that doesn't solve the problem.

Angus, Thanks, I get that now. I was basing my thoughts on the original post and assuming the original ST installation connected to the STNG via the convertor. with dedicated supplies. Mind was stuck on that tack! However as you point out any other instrumentation fed from either source could be be "back fed". You wouldn't even need a fault as anything on the output side of either switch would be back fed if that switch is off.