The short answer. Lay a boat DC panel out in the order the current flows. Battery positive, main fuse, battery switch, then a positive busbar. Each cable leaving the busbar gets its own fuse. One feed goes to a fuse block with a fuse per circuit. Every negative comes home to a negative busbar, then one cable goes back to the battery.
You’ll need
- A main fuse sized for your battery and main cable
- A battery switch (the Egis switch is in the Boat lithium upgrade kit)
- Two busbars, one positive and one negative: Victron Busbar 250A 4-point with cover
- A fused feed: Egis ANL fuse block, up to 4/0, 35-750A
- A branch fuse block: Egis RT 12-position fuse block with ground
- Optional low-voltage cutoff: Victron Smart BatteryProtect 100A
- Tinned cable sized with the Wire gauge calculator, fuses picked with the Fuse size calculator
- Lugs that match each stud, a crimper, heat shrink, a torque wrench, labels
Most messy DC panels grew one wire at a time. A good one gives every wire one home and every cable a fuse that protects it, so you can find a fault fast with a flashlight.
You can lay this out yourself. Plan it on paper first, then on the board, then in copper. Here’s the layout, then the steps.
What does a boat DC panel layout look like?
Red is positive, black is negative. Yellow is a fuse. Not to scale. If you run a shunt monitor, it sits between the battery negative and the negative busbar.
Read it left to right. Current leaves the battery, gets one main fuse, one switch, then spreads out at the positive busbar. Every branch off that busbar is fused. The negatives come back the same way in reverse: many wires into one busbar, one cable back to the battery.
How do I lay out a boat DC panel? Step by step
- List every load. Bilge pumps, nav lights, electronics, fridge, inverter, windlass. Write the current each one draws from its manual. That list decides everything else.
- Split big from small. Small circuits (lights, pumps, electronics) go on the fuse block. Big loads (inverter, windlass, thruster) each get their own fused feed straight off the positive busbar.
- Switch off and isolate. Switch everything off and disconnect the battery negative. Reconnect it last, after step 10, once the wiring is done and the covers are on.
- Mount the main fuse right at the battery. It goes on the positive cable as close to the terminal as it fits, before the switch. Fusing a lithium bank: Lynx, MRBF and class T covers which type to use.
- Put the switch after the fuse. Then run one cable to the positive busbar. The Egis battery switch lives in the Boat lithium upgrade kit.
- Fit the positive busbar. Victron’s 250A busbar has four 5/16 inch (8 mm) studs and a 70 VDC limit. Torque each nut to 110 lbf-inch (13 N-m).
- Fuse every cable that leaves the busbar. The fuse goes at the busbar end, sized to protect that cable. An Egis ANL fuse block, up to 4/0, 35-750A holds one ANL fuse for a feed.
- Feed the fuse block. Run the fused feed to the Egis RT 12-position fuse block with ground. Then land each circuit on its own fuse.
- Bring every negative home. Small negatives go to the fuse block’s ground block. That ground block, the big loads and the chargers all go to the negative busbar. One cable runs from there to the battery negative (or to the shunt, if you have one).
- Label, cover, check. Label every circuit at both ends. Put the covers on. Check the torque again after the first trip.
Don’t overthink it. If you can draw it with a pencil, you can build it.
What’s the difference between a busbar and a fuse block?
A busbar is a bare copper strip with studs. It joins wires. It doesn’t protect anything. Victron’s 250A busbar is tin-plated copper on a black base, rated 250A and 70 VDC.
A fuse block also joins wires, but each output goes through its own fuse. The Egis 8026 has 12 positions for ATO, ATC or ATF blade fuses, up to 30A per circuit, on 0-36V DC systems. Each circuit has a blown-fuse LED, so a dead light shows you which fuse to pull.
The ANL block is the big brother: one fuse, big cable. The Egis 3903 takes ANL fuses from 35 to 750A and cables up to 4/0. It’s rated 80 Vdc max and sealed to IP66, IP67 and IP6K9K. The cables land on their own studs, not on the fuse tab, so swapping a fuse doesn’t mean fighting a heavy lug.
Short version: busbars gather, fuse blocks protect.
Does every wire off a busbar need a fuse?
Every positive one, yes. Victron’s Wiring Unlimited is plain about it: each consumer that connects to the battery gets its own fuse in the positive cable, no matter how small. The layout is one main fuse at the battery, then a fuse on each branch.
Negatives don’t get fuses. They go to the negative busbar.
Size each fuse to the cable it protects, not to the load. The Fuse size calculator and Wire gauge calculator do the math together.
How many busbars do I need?
Two at minimum: one positive, one negative. With four studs each, count your connections before you buy.
On the positive busbar, one stud takes the cable from the switch. The rest take fused feeds and charger outputs. On the negative busbar, one stud goes back to the battery or shunt, and the rest take negatives: fuse block ground, inverter, chargers, engine ground.
Running out of studs? Add a second busbar of the same type and link them with a short, heavy cable. Don’t stack four lugs on one stud.
What about a fused busbar?
A fused busbar puts the busbar and the fuses in one unit. Victron’s Lynx Distributor is one example: a positive and a negative busbar, with four fuse-protected connections on the positive side. It does the same job as a busbar plus separate fuse holders, just in one box. It’s a good fit on bigger systems. Fusing a lithium bank: Lynx, MRBF and class T compares it with separate parts.
Where does a low-voltage disconnect go?
Between the positive busbar and the group of loads you want to protect. The Victron Smart BatteryProtect 100A cuts those loads before the battery runs too low. It handles 100A continuous and 600A peak for 30 seconds, and works from 6 to 35V.
A few rules from Victron’s manual, kept simple:
- Current flows one way only, IN to OUT. IN goes to the battery side.
- It’s not for charging current running backward through it.
- Never put it on an inverter’s DC input. Use the inverter’s remote on/off port instead.
- Its thin GND wire goes straight to the battery negative, with a small fuse in it (Victron says 300 mA is enough).
- Fuse the cable between the battery side and the unit.
On a 12V system it defaults to cutting the loads at 10.5V and reconnecting at 12V. It waits 90 seconds below the setting before it cuts, so an engine start won’t trip it. You can change the levels in the app to suit your battery.
How do I keep the panel safe and tidy?
- Cover the positives. Busbars are bare metal. Wiring Unlimited says to shield them so a dropped wrench can’t bridge two bars. The Victron busbar and the Egis blocks come with covers.
- One home per wire. Fewer connections means fewer hot spots. Busbars help with that.
- Match lugs to studs. The Victron busbar studs are 5/16 inch. Check every other stud size in its manual before you crimp.
- Seal your crimps. Tinned, adhesive-lined heat-shrink terminals keep salt air out. Pacer heat-shrink ring terminal 8 AWG, 3/8 in stud fits 8 AWG wire on a 3/8 inch stud.
- Torque to the number. 110 lbf-inch on the Victron busbar, 9 Nm on the BatteryProtect’s M8 studs.
- Leave room. Spare studs, spare fuse positions, space for a hand. The Egis RT block has two spare fuse spots per six circuits.
It’s your boat. Take your time on this part.
Does this layout fit your boat?
This applies if: – Your boat runs 12V DC. – You’re building or cleaning up a DC panel with one house bank. – Your small circuits run on blade fuses and your big loads need their own feeds.
This doesn’t apply if: – You run 24V, 48V, or several banks in parallel. Follow the battery maker’s wiring guide. – The job touches shore power, an inverter-charger’s AC side, or any AC panel. That work goes to a licensed marine electrician. AC mistakes can shock someone in the water.
Products used in this guide
| Product | Why it’s in the layout |
|---|---|
| Victron Busbar 250A 4-point with cover | One positive, one negative. 250A, 70 VDC, 5/16 inch studs, cover included. |
| Egis ANL fuse block, up to 4/0, 35-750A | The fused feed for a fuse block or a big load. Sealed to IP67. |
| Egis RT 12-position fuse block with ground | One blade fuse per circuit, blown-fuse LEDs, matching ground block. |
| Victron Smart BatteryProtect 100A | Low-voltage cutoff for a group of loads. |
| Pacer heat-shrink ring terminal 8 AWG, 3/8 in stud | Sealed, tinned ring terminals for 8 AWG runs. |
Prices show live from the store. Shop the full range in Switches, fuses and busbars, or start from the Boat lithium upgrade kit. For where the shunt and charger fit in, see Boat lithium battery wiring diagram: 2 simple setups.
Bundles for this job: Wiring and fusing kit (12-circuit panel)
Quick answers
Should the fuse block connect straight to the battery? No. Feed it from the positive busbar through its own fuse. The main fuse at the battery protects the main cable, and the feed fuse protects the cable to the fuse block.
Can I put two fuse blocks on one busbar? Yes. Give each one its own fused feed from the positive busbar, and run each ground block to the negative busbar.
Does the negative busbar need a fuse? No. Fuses go in the positive cables. The negative busbar collects the returns and sends them back to the battery or shunt in one cable.
What size busbar do I need? Bigger than the most current the main cable will ever carry. Victron’s busbar is rated 250A. If your main fuse is bigger than that, look at a higher-rated busbar or a fused busbar like the Lynx.
Can a Smart BatteryProtect switch my inverter? Not on the inverter’s DC cable. Victron says to use it on the inverter’s remote on/off port instead.
Related guides: Battery switch for a lithium boat
Sources
- Victron Busbar 250A 4P and 6P with cover datasheet: https://www.victronenergy.com/upload/documents/Datasheet-Busbar-250-A-4P-and-6P-with-cover-EN.pdf
- Egis 3903 ANL fuse block: https://www.egismobile.com/shop/3903b-anl-fuse-block-for-up-to-4-0-cables-35-750-a-sealed-bulk-pack-8802
- Egis 8026 RT fuse block: https://www.egismobile.com/shop/8026b-rt-fuse-block-12-circuit-w-ground-bulk-4952
- Victron Smart BatteryProtect datasheet: https://www.victronenergy.com/upload/documents/Datasheet-Smart-Battery-Protect-65-A–100-A–220-A-EN.pdf
- Victron Smart BatteryProtect 12/24V manual: https://www.victronenergy.com/upload/documents/Smart_BatteryProtect_12V_24V/114439-Smart_BatteryProtect-pdf-en.pdf
- Victron Wiring Unlimited: https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf
- Victron Lynx Distributor manual: https://www.victronenergy.com/upload/documents/Lynx_Distributor/24531-Lynx_Distributor_Manual-pdf-en.pdf
- Pacer 8 AWG ring terminals: https://www.pacergroup.net/ring-terminals-8-awg-wire/
