Fuse? Identification

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Diep

Member
Joined
Dec 4, 2021
Messages
19
Location
PNW
Vessel Make
Grand Banks 42-970
New to us GB 42 with largely intact original wiring layout. Saw something I didn't understand and ran out of time to trace it out. I am assuming I am looking at a pair of fuses here.



I was initially concerned by the smaller conductors in contact with the fusible links which seems like a bad idea. It looks like I could break them out of the loom and easily re-route them.
Now that I am looking at the photo I am thinking more about the smaller conductors. This fuse certainly would not be protective of that wiring so I don't know if that is a bad idea to be feeding them off this fuse block.

I'm not at the boat but have the original wiring schematics. I thought this was DC but 3 and 4 look like the AC plug circuits. This element is not depicted in the schematic. Those circuits are already breaker protected. Blue/Black is original AC wiring scheme but red for AC + is unusual. It is strange that the blue/black wire color changes across the fuse. Obviously I need to keep digging to confirm what this is.

Main questions:
* Is this a fuse? What type? (I didn't see it in Calder)
* Should wires be moved out of contact
* Should this be updated to a newer style fuse and/or covered? (No, put it on a list, yes you're about to die)

Other thoughts?

IMG_4532.JPG
 
Thank you 3OE!

Now that I know what I am looking at I can see these appears to be shunts on the P and S main engine alternators, feeding the ammeters at the helms.
 
If I am not mistaken, those feeds to the ammeters should be fused! There is higher current there available than those small wires can support.
 
Interesting point. I can trace them and see if there is a fuse in the runs to the meters. I am guessing not as it isn't indicated on the schematic. Unless the meter itself provides protection a short on the sensing wires could see the full output of the alternator. If a fuse is added I wonder if it would spoil the meter calibration.
 
Interesting point. I can trace them and see if there is a fuse in the runs to the meters. I am guessing not as it isn't indicated on the schematic. Unless the meter itself provides protection a short on the sensing wires could see the full output of the alternator. If a fuse is added I wonder if it would spoil the meter calibration.
1 the protection (fuse) should always be at the start of the thinner wire (because the wire is only protected downstream of the fuse). That is, there should be fuses immediately next the shunts in the thin wires going to the meter. There are "inline" fuses available. Personally I like the style in the link below.

Note: assuming the shunt is in the positive ("hot") line then fuses are needed in both wires.

2 the presence of fuses will have no effect whatsoever on the meter reading (the current going to the meter is very low).

 
Great, we will look to add some fuses to the lines. While at it I suppose it would also be recommended to provide a shield of some sort to prevent accidental contact with the terminals or shunts.
 
If I am not mistaken, those feeds to the ammeters should be fused! There is higher current there available than those small wires can support.
Not really. Your concept is spot on but the “higher current/wire size” comment is not. The sense wires carry milli or micro amps. They only sense voltage but they absolutely require fusing.1A inline glass fuses would be sufficient.
 
Not really. Your concept is spot on but the “higher current/wire size” comment is not. The sense wires carry milli or micro amps. They only sense voltage but they absolutely require fusing.1A inline glass fuses would be sufficient.
Charlie, I probably wrote that poorly. My comment was to suggest that there is high current available from the Alternator wires at the shunt so the smaller wires need protection. As you mentioned current to the meters is very small but if a fault were to occur current would most likely be higher than the meter wires could handle.
 
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