Sizing cables, fuses and transformers correctly

A burnt-out cable is annoying because it usually happens somewhere inside a wall and everything behind it goes dark. Three rules prevent it: the right cable, a suitable fuse per network and a transformer between big and small networks.

The three cables#

Cable	carries up to	made from	printed in	flammable
Cable (Straight)	5,000 W	Cable Coil	Autolathe, Electronics Printer	yes, from 140 °C
Heavy Cable (Straight)	100,000 W	Cable Coil (Heavy)	Electronics Printer	practically not
Super-Heavy Cable (Straight)	500,000 W	Cable Coil (Super Heavy)	Electronics Printer (tier 2)	practically not

One cable piece occupies a 0.5 m cell. Normal and heavy cable are 5 cm thick, super-heavy 7.6 cm. How many coils a piece costs depends on its shape:

Shape	Coils
straight, corner	1
junction (3 ends), cross (4 ends)	2
junction with 5 or 6 ends	3
straight 3-piece / 5-piece / 10-piece	3 / 4 / 7

So the 10-piece saves 3 coils compared with ten single pieces. A coil stacks up to 50. Wire cutters remove a cable and give the coils back.

When a cable burns out#

Every tick each network calculates the flow: the smaller of what all generators offer and what all consumers request. This flow is compared with every cable piece and every fuse on the network. If it is above the limit of the weakest part, one part breaks – at most one per tick, fuses first.

Three cases to work through:

• Ten panels deliver 5,500 W, the consumers need 800 W. Flow = 800 W. Nothing happens.
• The same panels charge an empty battery. The battery requests its whole free capacity, flow = 5,500 W. The normal cable burns.
• Battery output straight into battery input: both sides are huge, the flow runs into the millions. Even super-heavy cable burns.

What follows: for the cable it does not matter what the generators can do, but what is offered and requested at the same time. Batteries make both large.

Fuses#

The Kit (Cable Fuses) builds five fuses: 1 kW, 5 kW, 50 kW, 100 kW and 500 kW. A fuse sits on a cable piece and draws no power of its own. When it trips, it destroys the cable piece under it as well. That is intended: you know right away where the fault was, and you replace one piece instead of a whole line.

Important: a fuse compares the flow of the whole network it sits on – not just that of the cable piece next to it. A branch that hangs on the main network without a transformer belongs to the main network.

How to choose:

• Never above the weakest cable in the network. On a network with normal cable that means the Fuse (5kW). It then breaks instead of a cable piece somewhere inside a wall.
• Place it at the junction. If it trips there, it cuts off the branch behind it.
• Small fuses only on networks of their own. A Fuse (1kW) on the main network trips as soon as the whole network carries more than 1,000 W. Behind a small transformer a branch is a network of its own – there it suits a few lights and sensors.
• Fuse (50kW) and larger belong on networks of heavy cable.

A fuse is removed with the screwdriver.

Transformers#

A transformer separates two networks. At its output it offers at most its Setting, and only as much as is offered at its input. The flow behind it therefore stays below Setting, however large the network in front of it.

Transformer	at most	data port	build
Transformer (Small)	5,000 W	on the input	on wall or floor
Transformer (Medium)	25,000 W	on the output	on wall or floor
Transformer (Large)	50,000 W	separate port	free-standing

Every transformer needs 10 W itself. The small and medium ones also come as reversed variants, such as the Transformer Reversed (Small), with input and output on swapped sides.

Important for chips: an IC housing only sees the devices on its own network. On the small transformer the data port is on the input, on the medium one on the output. A chip in the branch behind a small transformer therefore cannot see the transformer – behind a medium one it can.

Sizing in three steps#

1. Add up the branch load, with the devices' working load, not just their base draw.
2. Choose a cable whose limit is above the flow. Lines from generators and solar arrays to batteries carry the full generation.
3. Protect the branch: a transformer in front with Setting below the cable limit, a fuse at the start.

Worked example living quarters: three Wall Heater (1,010 W each while heating), one Air Conditioner (355 W while running) and four lights at 50 W.

• Sum: 3 · 1,010 + 355 + 4 · 50 = 3,585 W.
• Normal cable (5,000 W) is enough.
• A Transformer (Small) with Setting 4,500 in front and a 5 kW fuse behind it protect the branch.
• Add a fourth heater and it is 4,595 W – more than the transformer passes. The cable does not burn, but the whole branch switches off. Then a bigger transformer with heavy cable helps, or load shedding, see Backup power and load shedding: separating networks, priorities, IC10.

IC10: showing a branch's load#

The program sets the medium transformer to a fixed value and shows on the IC housing what percentage of its setting the branch requests. Chip and Cable Analyzer sit in the branch behind the transformer.

# --- Monitor a branch behind a transformer ---
define TRAFO -1065725831       # Transformer Medium (StructureTransformerMedium)
define ANALYZER 1036015121     # Cable Analyzer (StructureCableAnalysizer)
define NTRAFO HASH("Trafo Living")   # transformer in front of the branch
define NBRANCH HASH("Branch Living") # analyzer in the branch
define LIMIT 4500              # W: setting, below the cable's 5000 W
define ENABLED 1               # transformer switched on
define PERCENT 100
alias demand r0
alias load r1

start:
yield
# --- 1. Set the transformer (a new one is at 0) ---
sbn TRAFO NTRAFO Setting LIMIT
sbn TRAFO NTRAFO On ENABLED
# --- 2. Measure the branch demand ---
lbn demand ANALYZER NBRANCH PowerRequired 0
bnan demand start              # no analyzer with this name
# --- 3. Show the load in percent ---
div load demand LIMIT
mul load load PERCENT
round load load
s db Setting load
j start

Above 100 % means: the branch requests more than the transformer passes, and all consumers behind it switch off.

Common mistakes#

• Cable burns between solar array and battery: the battery draws the whole solar output. Lay heavy cable from 5,000 W.
• Fuse keeps tripping: it is below the flow of its whole network. Recalculate the load and separate the branch with a transformer – do not simply enlarge the fuse if the cable no longer carries it.
• Everything is dark behind the transformer: Setting is at 0 or below the demand.
• Chip cannot find the transformer: the data port is on the other side.

Further reading#

• Basics: Power grid basics
• Connecting batteries correctly: Batteries and storage: sizes, charging, discharging, a transformer in between
• Recalculate with cable check: Power calculator
• IC10 academy: multiple grids