Switch panel fusing

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BabaYaga

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I would be grateful for some advice on fusing:
The wire supplying the distribution panel on my boat has no dedicated fuse. Instead this bit of wiring is protected by a 80A ANL fuse installed close to the domestic battery bank positive take off terminal.
While this fuse is sized for the maximum alternator charging current (70A alt), the aggregated load through the distribution panel is nowhere near as high.
I am now thinking about putting a smaller fuse in the distribution panel wire, probably 30A, but with the option of increasing in the future if needed.
The wiring itself is somewhat oversized – the charging circuit is 35sqmm in order to minimize voltage drop – the wire to the distribution panel is 25sqmm (for reasons I no longer remember).
1. Would such a fuse be a good idea and a benefit to safety? (The distribution panel has both positive and negative feeds, so shorts in this area are not totally unthinkable)
2. What type of fuse would be suitable? I find the ANL type rather bulky, but would prefer to connect to the holder by ring terminals. What do people use for the 30 - 50A range? AMI? Maxi? Midi? Strip link? I find the offerings a bit confusing...
 
The main wire to the distribution panel is already protected by the main fuse as you have stated, each switch from the distribution panel should then be fused for the appropriate appliance or circuit in accordance with the wire used , and amps required
i,e for your lighting circuit , you would have a fuse in place either behind or next to the switch on the distribution panel
has you distribution panel got fuses,?? if so then there is no problems as the main feed wire is more than adequate to take the load and if a short happens the main fuse will blow.
 
moomba said:
has you distribution panel got fuses,?? if so then there is no problems as the main feed wire is more than adequate to take the load and if a short happens the main fuse will blow.
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The panel has fuses for the individual circuits.
My concern is that the fuse protecting the supply to the panel is unnecessarily large, in relation to the total load. But perhaps not worth worrying over, as the wire is large enough (25sqmm) to handle 80A until the fuse blows?
 
I understand what is going on now, no if the wire is heavy enough and the other feeds are fuse protected
then it would be hard to think of a short in the main feed and if there is a short the main fuse will blow.

Interestingly I re wired my boat and have a 200 amp fuse at the battery bank with heavy cable to junction box then feed of from that with 30 amp cable to 2 distribution boards which I fuse at the start of this wire, and then each feed is fused so in essence I have what your asking about , but this is to protect the smaller cable , so in essence I have three fuses protecting the circuit.
 
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I’m slightly confused... But 25mm has a nominal rating of 170A for “battery cable” or 136A tri rated. So you could afford to be slightly conservative with your fuse. A midi or mega fuse will suffice or better still, a circuit breaker which is resettable. Do you have domestic and engine isolators? Also, what boat?
 
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BabaYaga said:
I would be grateful for some advice on fusing:
The wire supplying the distribution panel on my boat has no dedicated fuse. Instead this bit of wiring is protected by a 80A ANL fuse installed close to the domestic battery bank positive take off terminal.
While this fuse is sized for the maximum alternator charging current (70A alt), the aggregated load through the distribution panel is nowhere near as high.
I am now thinking about putting a smaller fuse in the distribution panel wire, probably 30A, but with the option of increasing in the future if needed.
The wiring itself is somewhat oversized – the charging circuit is 35sqmm in order to minimize voltage drop – the wire to the distribution panel is 25sqmm (for reasons I no longer remember).
1. Would such a fuse be a good idea and a benefit to safety? (The distribution panel has both positive and negative feeds, so shorts in this area are not totally unthinkable)
2. What type of fuse would be suitable? I find the ANL type rather bulky, but would prefer to connect to the holder by ring terminals. What do people use for the 30 - 50A range? AMI? Maxi? Midi? Strip link? I find the offerings a bit confusing...
Click to expand...

What you have is correct. The 80a fuse is protecting the cable to the distribution panel, nothing more. It will only blow if you get a short in that cable and it's rated well below your cable, so leave well alone.
 
matthewriches said:
30A distro fuse seems remarkably small unless you only have a few lights, horn, bilge pump, etc...
Click to expand...

Yes, needs are rather frugal, all lights LED, no electric pumps, modest instrumentation etc. But there are some loads that are run from a separate fuse box, e.g. socket for search light.
 
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