How to use the wiring tool

This guide shows how to use the NBCE wiring tool, step by step. It is about the tool itself, not about 12V theory. For the why behind the sizes, see our guides: how to size a 12V system, cable sizing and voltage drop, fusing a 12V system, MPPT vs PWM controllers and Anderson plugs.

The tool is new and still in its infancy. Read the box it opens with, and check every size in its plan against the maker's instructions before you order. We double-check every order that comes from it before it ships.

Before you start

The first time you open the tool it asks you to read a short disclaimer. Read the full disclaimer opens the whole text inside the box. Press I understand and agree to go on; your browser remembers it.

The opening question: Plan a new system, I already have some of my parts, Work out cables, fuses and connectors — The three ways in. Pick the one that fits where you are.

Then it asks what you would like to do:

Plan a new system: a few questions about what you run and how you camp, then the tool sizes the battery, charging and solar and lists the parts. Start here if you are starting from nothing.
I already have some of my parts or parts in mind: pick the parts you have chosen or already own, one screen each, and the tool draws the system around them.
Work out cables, fuses and connectors: for a system you have planned or already have. Type your run lengths and get cable sizes, fuses, lugs and connectors.

At the top of the page, Quick plan shows the main parts only and Full plan adds every cable, fuse and connector. Switch between them any time; nothing you have entered is lost. Start again clears everything.

1. Plan a new system

Question 1: what is it for? Caravan, camper trailer, 4WD canopy or ute, boat, shed — Question 1 sets typical cable run lengths. You can change them later.

What is it for? Pick the closest: a caravan, a camper trailer, a 4WD canopy or ute, a boat or a shed. This only sets typical run lengths, which you can change later in the Full plan.

Question 2: what do you run, and for how long? A table of appliances with draw and hours a day — Tick what you run. The draw and the hours a day are typical figures; change them to suit you.

What do you run, and for how long? Tick the appliances you run, 12V ones and 240V ones through an inverter. Each row has a typical draw in watts and hours a day; type your own if you know them. A fridge's hours are its compressor's running time over a day, not the hours it is switched on. + Add something else adds a row of your own. The line under the table adds it up: your daily use in watt-hours and amp-hours, and the inverter size the largest 240V appliance needs.

How long between charges? One day, a weekend, a long weekend or most of a week, and the battery type. The tool works out the bank size from your daily use and the days, and says so in plain figures under the choices.

Question 4: how do you charge? Driving, solar on the roof, folding panel or blanket, mains at powered sites — Tick every way you charge. The lines underneath say what each adds to the plan.

How do you charge? Tick each one that applies: Driving (a DC-DC charger from the alternator), Solar on the roof (sized from your daily use, then capped by your roof space), a Folding panel or blanket (with its own controller) and Mains at powered sites. If you ticked roof solar, the next question asks about how much roof you have. In the Full plan there is then one short screen per cable run with a typical length filled in, or Use the defaults.

Your plan is ready: the battery, charging, solar and inverter sizes, with Pick the parts and See my plan — The plan in figures, before any product is chosen.

Your plan is ready shows the sizes: the battery bank, the DC-DC charger, the solar and its controller, the inverter. Pick the parts goes on to choose a product for each (the next section). See my plan skips that and shows the drawing and the parts list with the cheapest product that fits each part. Full plan: add cables & fuses goes straight on to the run lengths and the full table.

2. I already have some of my parts

Pick your parts, 1 of 6: Battery bank. A list of store batteries that fit, cheapest first, with Customer supplied at the top — One screen per part. Click a product, or skip to keep the cheapest that fits.

This route, and Pick the parts from a new plan, go through your parts one screen at a time: the battery bank, the DC-DC charger, the solar panels and their controller, the inverter, the battery monitor. Each screen lists the store products that fit the size, cheapest first, with a search box to narrow it. Click one to choose it, or Skip this part to keep the cheapest. Customer supplied is for a part you already own: it stays in the sizing and comes out of the parts list. Skip to the full form leaves the screens and shows everything at once.

3. Work out cables, fuses and connectors

The form: system voltage, the battery bank, the DC-DC charger and solar, each with a product picker — The form behind every route. Each part has a picker; the sizes come from what you pick.

The form holds the whole system: the system voltage (12, 24 or 48V), the battery bank, the DC-DC charger, solar on the roof, a blanket, the inverter, the battery monitor and the loads. Each part has a Choose… button that opens its picker; a part you pick sets the sizes below it. The green switches turn a part on or off.

The Cables and fuses table: run, current, length, cable, volt drop, protection, connectors and notes for each run — One row per cable run. Type your lengths under Cable run lengths, or click a cable on the drawing; everything else follows.

In the Full plan the Cables & fuses table has one row for every run in the system. For each run it shows the current, the length (one-way: you type it under Cable run lengths on the form, or in the box a cable on the drawing opens), the cable (size and rating), the volt drop in percent and volts, the protection (the fuse or breaker and its rating) and the connectors at each end. Auto is the tool's choice of connector; the drop-down offers the other lugs and plugs that fit. change… under a cable or a fuse lets you override it; the tool then shows what it would have suggested, so you can see the difference.

4. The drawing

The wiring diagram: engine charging, solar roof, the busbars, the battery, the DC loads and the AC system — Red is positive, black negative, yellow solar. A small hop is a wire crossing a busbar it does not join.

The drawing updates as you type. Red is positive, black negative, yellow the solar PV side, and the thin faded red line the battery monitor's sense lead. Each cable carries its size and length; each fuse its rating. Click a part on the drawing to open its picker there. Click a cable label to open a box with that run's length and its cable sizes, each with its rating and the volt drop it would give; pick one to change the cable.

The drawing on a phone: the Battery zone, with tabs for Overview, Engine, Solar, Battery, Loads and AC — On a phone, one zone at a time.

On a phone the drawing shows one zone at a time from a row of tabs: Overview, Engine, Solar, Battery, Loads and AC.

5. The parts list and the cart

The parts list: Main components open, with each part's product, quantity and price, and Add to cart buttons — Grouped by what it is, each group with its subtotal and its own Add to cart.

The parts list is the store products the plan needs, one line per product: the same cable in several runs is one line, with every run it covers listed under it. The groups (Main components, Distribution, Fuses, breakers & holders, Cable & heatshrink, Lugs & connectors) open and close with a click, and each has a subtotal and its own Add … to cart. The green tick includes a line in the total; untick it to leave it out. The number box is the quantity, and × drops a product so the line goes back to the tool's own choice.

A product picker open from the parts list: a search box, Customer supplied, then the store products that fit — Click a product in the list to swap it for another that fits.

Click any product in the list to open its picker: the store products that fit that part, cheapest first, with a search box. view opens the product's own page in a new tab.

Add all to cart adds every included line to the store's cart at today's prices. If a product is sold out, the tool names it and adds the rest. Check the cart before you check out: quantities and lengths are a starting point, and we double-check every order from the tool before it ships.

The parts list on a phone: each line as a card with its product, quantity and price — On a phone each line is a card.

6. Save, share and start again

The tool saves your plan in your browser as you go. Next time you open it, the opening question offers Continue where I left off. Change what I'm doing, in the Start card, switches between the three ways in without losing your figures, and Start again clears everything.

The tool's figures are a guide, not a certified design. Read the full disclaimer under the heading, follow each maker's instructions, and have 240V work done by a licensed electrician. Questions about a plan? Contact us and we will go through it with you.

Written for the wiring tool as it was on 8 October 2026 (v61). The pictures were taken from the tool itself and are refreshed when it changes.