A bilge pump that stays ready
Keep the automatic bilge circuit powered when you switch off the rest of the boat.
Follow the circuit
01
Split before the switch
The battery feeds the 24-hour half of the fuse block directly. The other half receives power through the house switch, so switching off the lights leaves the pump available.
02
The float controls the pump
The float is shown closed, as if water were high. In the editor, turn the house switch off, then open the float to see the two circuits behave independently.
03
Protect the smaller branch
The battery fuse protects the main feed. The pump's smaller fuse protects its branch; match that fuse to the actual pump manual before replacing the generic pump.
The source and this example
Blue Sea's ST Blade Split Bus drawing separates 24-hour circuits from switched house circuits.
We feed both halves of the 5032 from one AGM battery, instead of the source's two batteries, and add a generic float-controlled pump. Pump current and cable lengths are example choices.
- Blue Sea: split bus application drawing ↗
Page 2: switched and 24-hour circuit example.
- Blue Sea: 24-hour circuit guidance ↗
Before you build
- Test automatic operation with the house switch off.
- Keep pump connections above expected bilge water.
- Replace the example lengths with measured cable runs.
This is a planning example. Cable sizing uses Crimp’s ABYC-based method; the drawing does not certify an installation.
Cable sizes and connections · 10 conductors
Lengths are one way. Sizes and currents come from the same Crimp model as the drawing. Each drop value covers one drawn conductor; the full circuit includes its supply and return. AWG values are approximate counterparts to the metric areas.
| Connection | Length | Wire | Design current | Fuse | Drop |
|---|---|---|---|---|---|
| C1 · House battery + → Supply split | 20 cm | 4 mm²AWG 11 | 4 A | — | 0.03% |
| C2 · Supply split → Blue Sea 5032 ST Blade Split Bus Fuse Block 24H + | 30 cm | 1.5 mm²AWG 16 | 3.5 A | — | 0.10% |
| C3 · Blue Sea 5032 ST Blade Split Bus Fuse Block 24H 1 + → Float switch A | 30 cm | 1.5 mm²AWG 16 | 3.5 A | 7.5 A | 0.10% |
| C4 · Float switch B → Automatic bilge pump + | 2 m | 1.5 mm²AWG 16 | 3.5 A | — | 0.68% |
| C5 · Automatic bilge pump − → Blue Sea 5032 ST Blade Split Bus Fuse Block − 1 | 2.3 m | 1.5 mm²AWG 16 | 3.5 A | — | 0.78% |
| C6 · Supply split → House switch A | 30 cm | 1.5 mm²AWG 16 | 0.5 A | — | 0.01% |
| C7 · House switch B → Blue Sea 5032 ST Blade Split Bus Fuse Block SW + | 40 cm | 1.5 mm²AWG 16 | 0.5 A | — | 0.02% |
| C8 · Blue Sea 5032 ST Blade Split Bus Fuse Block SW 4 + → Navigation lights + | 3 m | 1.5 mm²AWG 16 | 0.5 A | 3 A | 0.15% |
| C9 · Navigation lights − → Blue Sea 5032 ST Blade Split Bus Fuse Block − 7 | 3 m | 1.5 mm²AWG 16 | 0.5 A | — | 0.15% |
| C10 · Blue Sea 5032 ST Blade Split Bus Fuse Block NEG − → House battery − | 50 cm | 1.5 mm²AWG 16 | 4 A | — | 0.19% |
A dash means no fuse is assigned to that conductor; upstream protection may apply. Recheck the exact device, holder and placement after edits.
Equipment · 7 components
- House battery
12 V · 110 Ah
12 V, 110 Ah AGM Deep Cycle (BAT412101084), rated at C20. Victron prefers charging at 0.2C (22 A); this is a recommendation, not an absolute maximum. Flat terminals have 8 mm through-holes.
- Supply split
A wire splice — any number of cables can meet here. Born from a cable dropped into empty space; promotes to a real junction once a second cable lands on it.
- Blue Sea 5032 ST Blade Split Bus Fuse Block
Two isolated groups of six ATC/ATO fused circuits share a common negative bus. Use one group for switched loads and the other for 24-hour circuits. Rated 30 A per circuit, 80 A per group and 100 A total at up to 32 V DC.
- Float switch
Generic two-wire float switch, shown closed (water high). Set it off to represent a dry bilge. Select a real switch rated for the pump.
- Automatic bilge pump
3.5 A load allowance
Auto float-switch bilge pump, ~3.5A while running.
- House switch
Single-circuit ON/OFF battery switch. 300 A continuous, 500 A intermittent (5 min), 900 A cranking (30 s); 3/8-inch-16 tin-plated copper studs. Ignition protected.
- Navigation lights
0.5 A load allowance · 6 W
Modern LED navigation lights — port, starboard, stern and masthead. Low draw, suitable for night passages.
Crimp checks · 2 findings to review
These are the current engine findings for the saved example. They remain visible when you open it in Crimp.
- warning: Check fuse suitability: House battery
- warning: No charging source
More boat examples
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Follow a solar panel through its controller to a house battery, chartplotter and navigation lights.
A separate trolling motor battery
Give the trolling motor its own battery and keep the chartplotter on a separate supply.
Charge two batteries at the dock
Use separate charger outputs to replenish two batteries without joining their positive terminals.
Choose either house battery
See how a 1–2–Both switch feeds the same boat circuits from either battery.
Crimp for AI agents · public beta
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