Blue Sea Fuse Block correct wire gauge

[Rangeric79]

Will be installing a Blue Sea fuse block 12 circuit w/ground bus this weekend.

1. What is the correct wire gauge size from the battery to the fuse block? (there will be a 30 amp breaker in this run.)

2. What is the correct wire gauge size from the fuse block to the various accessories. (4 Lowrance HDS units for starters)

Thanks in advance.

[Ann-Marie]

It depends on the distance the fuse block is from the battery.
3 feet 10 gauge
10 feet 8 gauge
20 feet 6 gauge

[ifishinxs]

10 gauge is ideal but It really depends on your current draw from the fuse panel. It your just running a few graphs 12 gauge will be fine. Larger gauge will give you less current drop.

[Jonestrollingmotor]

10 gauge is ideal but It really depends on your current draw from the fuse panel. It your just running a few graphs 12 gauge will be fine. Larger gauge will give you less current drop.

If he's going to use a 30A breaker, 12 gauge is not "fine". Depending on how far from the battery will depend on carrying capacity for the 10ga. He stated a 12 circuit fuse block and initially his graphs. The OP needs to plan for what else may be fused off this block. I would suggest 8ga so he can go with a 40A breaker later down the road if needed.
John

[bqtoot]

Getting ready to do the exact same thing on my boat with the same Blue Sea fuse block. Here's an excerpt from the ABYC Handbook:

How to Choose Marine Wire Size:

There are three factors when choosing the right wire gauge:

1. Current draw of the device – measured in Amps
2. Total length of the run – measured in feet as a “round trip”
3. Allowable voltage drop – measured in % loss of voltage

ABYC says that non-critical loads like a livewell, or courtesy lights should have no more than a 10% voltage drop, while critical loads like a bilge pump or navigation lights should have no more than a 3% voltage drop.
Remember, length of the run is a “round trip”… so from the battery, out to the load and back. Example calculations are below the table.
Example 1:
Your livewell pulls 6A. There is 10 feet from the battery to the switch panel, then 5 more feet from the switch panel to the console livewell.
Length of run is 10 + 5 + 5 + 10 = 30ft (from battery to load, and back again)
On a livewell a 10% voltage drop is acceptable, so we use the top table. We’ll round up the 6A, to 10A, and use 14AWG wire.
Example 2:
Your LED navigation lights pull 3A. There is 10ft from the battery to the switch panel, then 14ft of wire from the switch panel to the lights.
Length of run is 10 + 14 + 14 + 10 = 48ft (from the battery to load, and back again)
Navigation lights are critical, so only 3% voltage drop is allowed, so we use the bottom table. We’ll round the 3A up to 5A, and 48ft up to 50ft, and use 10 AWG wire.

[Lou r Pitcher]

I agree and use the wire selection method presented above by bgtoot and ABYC that is considering the 'Allowable Voltage Drop. I prefer to use for the value of 'Total Current', the actual manufacturer's (Blue Sea Systems) carrying capacity of the fuse panel even if at time of the installation the panel'capacity is not going to be used fully. As the panel may be used to power electronics, the max total voltage dropped is 3% (not 10%) for the full circuit path. (I prefer for the fuse panel's battery side of the circuit to have only a 1 to 1 & 1/2% max drop.

For me, the suggested use of 'carrying capacity' of a given wire size is never a good method to use for selecting boat wiring as doing so permits far too high of a voltage drop. Excessive voltage drops can cause sensitive electronics to reset or shut down such as when an engine is cranked or a tilt motor's stall limit is reached.