Bow and stern thruster wiring: cable size and fuse, in AWG

The short answer

Start from the maker's current draw

Everything below starts from one figure: the current the thruster draws. Get it from the maker, in the installation manual or on the spec sheet, for your model at your voltage. Do not calculate it.

The tempting shortcut is to divide the motor's kW rating by the system voltage. It is wrong in the dangerous direction. A motor rating is the power the motor delivers. The circuit has to carry the current the motor draws. A thruster working hard, near the point where the propeller would stall, draws far more than its rating suggests.

The table sets that shortcut against Sleipner's own published figures, from the same page of the same manual:

What gauge you need

With the draw and the run length in hand, the rest is arithmetic. Resistance is copper's own figure times the length, divided by the area of the cable. The voltage lost is that resistance times the current.

The gauge you want passes two tests. It keeps the loss inside the limit you have chosen, and ABYCThe American Boat and Yacht Council, the body that writes the standards US boats are built and wired to. A surveyor or an insurer who asks whether wiring is to standard means ABYC’s.'s ampacityThe most current a cable can carry all day without overheating, as the standards table it. It depends on the size of the copper and how hot the space it runs through is. table rates it for the draw. E-11 takes the larger of the two sizes.

The first table below does that for the published draws above, at ABYC's 10 percent. The columns are how far the battery sits from the thruster, one way. The second table does the same at the tighter drop limit.

Here is the same thing at the tighter limit. ABYC's 3 percent applies to circuits "where voltage drop must be kept to a minimum". ABYC gives example circuits for each limit, and a thruster is on neither list. Choosing the tighter limit would cost this much copper:

Nobody wires a thruster to the second table. The makers' own tables target the looser limit. At 3 percent, a 12 volt thruster stops being a wiring job and becomes a civil engineering one. The table also shows what 12 volts costs you, and the 24 volt section takes that up.

Is your model or distance missing from these tables? The wiring calculator runs the same arithmetic on your own draw and distance, at both limits. It also runs it the other way, giving the volts a cable already fitted loses before the current reaches the motor.

ABYC's second limit: how much current a cable can carry

Voltage drop is one limit. Ampacity is the other, and a maker's cable table does not address it. ABYC publishes an allowable amperage for every conductor size.

That limit is about the cable not overheating, whatever voltage arrives at the far end. On a thruster circuit the two limits give very different answers.

The largest size that table carries is 4/0, at 445 amps clear of the engine compartment (378.3 through it). Four of the eight published draws above are higher than that:

• SEP60/185S at 24 V, 170 A. Covered by a single 2, rated 210 amps clear of the engine compartment.
• SE80/185T at 24 V, 280 A. Covered by a single 1/0, rated 285 amps clear of the engine compartment.
• SE100/185T at 24 V, 340 A. Covered by a single 3/0, rated 385 amps clear of the engine compartment.
• SEP60/185S at 12 V, 370 A. Covered by a single 3/0, rated 385 amps clear of the engine compartment.
• SE210/250TC at 24 V, 500 A. No single conductor up to 4/0 is rated to carry it. Paired conductors per leg, which is what the maker specifies at length anyway.
• SE80/185T at 12 V, 530 A. No single conductor up to 4/0 is rated to carry it. Paired conductors per leg, which is what the maker specifies at length anyway.
• SE170/250TC at 24 V, 550 A. No single conductor up to 4/0 is rated to carry it. Paired conductors per leg, which is what the maker specifies at length anyway.
• SE100/185T at 12 V, 740 A. No single conductor up to 4/0 is rated to carry it. Paired conductors per leg, which is what the maker specifies at length anyway.

The makers' own tables name single conductors well below these figures. The largest gap in Sleipner's published set is the SE100/185T at 12 volts. Its stated draw is 740 A, on the 3/0 AWG their table names for its 7 meter band.

That is 192% of what ABYC allows that size to carry clear of the engine compartment.

The two documents answer different questions. A maker's cable table is a voltage drop table. It tells you the least copper that still gets usable voltage to the motor.

ABYC's is a heating table, written as a continuous rating. A thruster runs for seconds at a time, and most makers publish a duty cycleHow long a motor may run before it must rest, as the maker rates it. "2 to 3 minutes" means that long at full power, then a pause to cool down. limit of a few minutes.

ABYC's July 2025 edition of E-11 settles what a thruster's cable has to meet. It holds no allowance for a load that only runs in bursts. It sets two tests for the size, in section 11.15.1.2.7.

So the size the standard points to is the heavier of two figures: the maker's cable for your run, and the E-11 minimum. The wiring calculator prints both side by side on your own numbers. Checking the install against the standard is yours, or your surveyor's.

Two cables per leg: what ABYC asks

Past one 4/0, the answer on this site is two cables per leg, and the makers' own tables do the same. E-11 section 11.15.1.2.8 sets the rules for a pair. The July 2025 edition revised them.

The fuse depends on why the pair is there. There are two cases.

The first is a pair fitted because one cable is not rated for the current. Each cable is then 2 AWG or larger, and one fuse protects the pair at the two cables' ratings added together. The pair is also labeled to say the fuse needs both cables connected.

The second is a pair fitted only to cut the voltage drop. Each cable is rated for the whole current on its own, and the fuse is sized to protect one cable.

In both cases ABYC sets three conditions:

1. Both cables the same type, the same length and the same size.
2. Run together in the same bundle or conduit.
3. Both ends on the same terminal of the fuse.

Keep the positive pair and the negative pair in separate bundles. If all four cables run in one bundle or conduit, ABYC's lower Table 4B ratings apply. A 4/0 there is rated 311.5 A clear of the engine compartment, against 445 A in Table 4A, and every pair on this site is sized to Table 4A.

Why the fuse is rated below the draw

Sleipner's current installation guides print an ANL fuse per model, on their Electrical Reference Guide page. The one exception is its EX pod manual, which names an NH00 fuse, a blade fuse in its own base. The older manuals this section was first read from gave no figure. They said only that the fuse must be a slow type, sized to take the amperage draw for at least five minutes. That instruction is the whole design brief. It is also why the fuse you find looks too small.

Sleipner's own webshop sells three ANL slow blow fuses, each listed with the models it is sold for. The table sets each one beside the figure the model's current guide prints:

The guides and the webshop agree on every row but one. The webshop lists the SE210/250TC at 24 V under the ANL500, and its guide prints ANL 400. Where the two differ, match the figure in your own unit's guide.

A 500 amp fuse on a circuit whose motor draws 740 A reads like an error until you know how an ANL behaves. Blue Sea Systems makes them. It puts the blow point of an ANL between 140 and 266 percent of its nominalThe figure a maker prints as the normal running value, as opposed to a peak at start-up or a minimum. value.

An ordinary fuse blows at roughly 130 percent. Blue Sea also says the usual practice of sizing a fuse at 80 percent of its rating does not work for ANLs. A slow ANL is built to carry a large overload for a long time and open on a short circuit.

Of the five pairings in the table, one draws more than 140 percent of its fuse's rating. The SE100/185T at 12 volts draws 148% of its 500 amp fuse's rating. That is inside the range where an ANL may eventually open. It is why the manual insists the fuse hold the stated draw for five minutes, and why the thruster has a duty cycle in the first place.

VETUS prints a number. Every installation manual's table names a slow blow main fuse with its part number. On the brushed units it sits at 60% to 73% of the stated draw. For example, the BOW7512D draws 550 A and takes a 355 A fuse, ZE355.

Every BOW PRO but one runs the other way. There the main fuse is above the nominal draw, 104% to 222% of it. On the 110 to 250 mm units a smaller thruster fuse sits in the controller under it. The BOWA0651, which draws 237 A at 12 V, takes 300 A and 250 A.

The one exception is the BOWB420. It has a 500 A fuse on a 520 A nominal draw, 96% of it, and no thruster fuse. The full set is in the VETUS table below.

ABYC treats a motor's fuse differently from a light's. For an ordinary load, E-11 keeps the fuse at or below what the cable is rated to carry. Where no fuse is made at that rating, the next standard size up is allowed, to at most 150 percent of it.

A motor has its own rule, and a thruster is a motor. It is protected inside the unit, or by a fuse or breaker suited to motor current. The test is that nothing catches fire if the circuit stays switched on for seven hours under any overload, a jammed propeller included.

That is why a maker's fuse can sit above the rating of the lighter cable its table lists for a short run. A breaker on a thruster is the motor kind, marked OL1 or Full Load and tested at ten times its rating.

That 140 to 266 percent is Blue Sea's published figure for Blue Sea's ANL fuses. We have found no equivalent Sleipner figure for Sleipner's fuse, and Blue Sea's is the best public account of how the part behaves.

Where the fuse goes: within 7 inches of the battery

The fuse belongs at the battery end. This is the requirement most often missed on a thruster install. The cable is long, and the fuse tends to end up wherever the run was convenient.

ABYC E-11 asks for overcurrent protection within 7 inches of the point the conductor connects to its source of power, measured along the conductor. An exception allows up to 72 inches where the cable connects directly to the battery and stays inside a protective sheath for that distance.

A cable fed from a bus barA metal bar with several studs that joins many heavy cables at one point, so each does not have to reach the battery itself. or another point of connection, sheathed the whole way, may have its fuse up to 40 inches away. The rule is section 11.10.1.1.1.1 of the July 2025 edition.

The same care goes into the negative side, the main switch and every termination:

• Use a crimpedSqueezing a metal end onto a cable with a tool made for the size, so the copper and the end become one solid piece. It is how heavy marine cable is terminated, never soldered. and sealed lugThe metal end crimped onto a heavy cable so it can be bolted to a terminal. in place of a soldered one.
• Support it so the cable's own weight does not hang on the stud.
• Torque it to the terminal maker's figure.

A loose connection on a circuit carrying 740 A is a heater. If your thruster already works but works badly, that is a fault to find. The page for a thruster that is not working right covers it.

What 24 volts does to the copper

Everything on this page is downstream of one number, the current draw. That number roughly halves when the system voltage doubles.

Sleipner sells the same thruster at both voltages, so the comparison is exact. The SE100/185T draws 740 A at 12 volts and 340 A at 24 volts. It is the same 6.3 kW motor giving the same thrust.

Put both through the same E-11 arithmetic as the first table above, with the battery 20 feet forward: ABYC's ampacity table and its 10 percent drop allowance, the larger size of the two. The 12 volt version needs 2 x 3/0 AWG per leg. The 24 volt version needs 3/0 AWG.

Only the voltage changed. The difference in copper is most of the difference in what the job costs to wire, and it grows with every foot the battery sits further aft.

That is the wiring half. The rest is about the power source:

• whether to put a dedicated bank in the bow instead of running a long cable from the house bankThe batteries that run the boat’s lights, fridge and electronics, as distinct from the engine’s starting battery. They are built for a slow, steady draw.
• what capacity that bank needs, and what chemistry
• why voltage sagThe drop in a battery’s voltage while a heavy load is drawing from it. The battery recovers when the load stops, but the motor only ever sees the sagged figure. costs you thrust

Sleipner states the physics in the same manual the cable table comes from. The actual voltage at the motor while the thruster runs decides the motor's speed, and so the thrust you actually get. The battery page works that through in the makers' own figures.

Still working out what size thruster the boat needs? Start with how much thrust your hull needs. The thruster finder, our free tool that matches a thruster to your boat, shows which types fit your boat at all.

Pricing the whole job? The cable and the fuse are a small line next to the hull work. What a bow thruster costs installed takes the bill apart.

That is the whole of your job: the run, the draw, the gauge, the fuse and the voltage. The six sections that follow check each maker's own cable table against the same arithmetic, for anyone holding one of their manuals.

What Sleipner's cable table says

Sleipner is unusual in publishing a cable table at all. It is more unusual in printing an AWGAmerican wire gauge, the size scale for electrical cable. The number falls as the cable gets thicker: 2 AWG is thicker than 6, and 1/0, 2/0, 3/0 and 4/0 are thicker still. equivalent beside every metric size.

Its current guides print two sizes for each length of run: a minimum and a recommended one. The table below uses the recommended size, the same one each product page shows. In all 15 bands read here, the AWG size is the nearest match for the metric size beside it.

The drop column is the useful part. It is computed at the top of each band, where the run is longest and the drop is worst. There, Sleipner's recommended cable lands between 3.4% and 7.8%.

Of the 15 bands, none meets ABYC's tighter 3 percent figure, and none exceeds the 10 percent one at the very top of the band.

A run shorter than a band's limit does better, which is why the makers publish bands.

Sleipner also publishes a minimum battery for each model, in cold cranking ampsCold cranking amps: how much current a battery can deliver in a short, hard burst, which is the rating starter batteries carry. A thruster draws like a starter, so the makers size its battery this way rather than by capacity.. Where the battery should live, what capacity it needs and why sagThe drop in a battery’s voltage while a heavy load is drawing from it. The battery recovers when the load stops, but the motor only ever sees the sagged figure. costs you thrust have their own page: bow thruster batteries.

What Sideshift publishes: a start current and two distances

Sideshift's external unitsA thruster that bolts to the outside of the hull, up near the bow or on the back of the boat. Its propeller hangs in the water below it. Nothing is cut through the hull, so there is no tunnel. carry their own motor controller. The maker publishes three things about the cable to it:

• a start current per series
• one AWGAmerican wire gauge, the size scale for electrical cable. The number falls as the cable gets thicker: 2 AWG is thicker than 6, and 1/0, 2/0, 3/0 and 4/0 are thicker still. size per series
• how far away the battery may sit, printed twice

The installation manual says the total cable run from the battery to the motor controller must not exceed 10 ft. The FAQ says the batteries should be installed not more than 30 feet from the motor controller, with a longer figure for the bigger series.

Both figures are Sideshift's, and they differ. The table computes the drop at each.

Read the two drop columns together. Inside the manual's 10 ft, the maker's own cable holds the drop to 0.6% to 3.6%, even at the start current.

That is inside ABYC's 10 percent allowance on every series. It is under the tighter 3 percent on three of the four.

At the FAQ's distance, with the run counted there and back, the same cable computes to 13.0% to 28.6%. That is over the 10 percent allowance on every series that has a figure.

The start current is a peak that lasts a moment, so the steady figure is lower. The maker does not publish the steady figure.

If your batteries will sit at the FAQ's distance, the last column is the gauge the allowance asks for. If they sit within the manual's 10 ft, the maker's size computes inside the allowance.

The start currents run from 200 A to 550 A across the four series. The battery Sideshift asks for, and why it wants a starting battery rather than a deep-cycle one, is on the battery page. The Sideshift review reads the rest of the manual.

What VETUS publishes: a table per manual, built to half the drop its text allows

Every VETUS installation manual ends with the same table, headed "Battery capacity, battery cables". It gives:

• the smallest and largest battery the unit may have
• the total run of positive plus negative cable, in bands
• the cable size for each band in mm², with an AWGAmerican wire gauge, the size scale for electrical cable. The number falls as the cable gets thicker: 2 AWG is thicker than 6, and 1/0, 2/0, 3/0 and 4/0 are thicker still. size beside it
• the main fuse, with its part number

The text above the table says the drop "must not be more than 10% of the voltage supplied".

The table does not use that figure. Of the 42 rows, 27 come out between 4.3% and 5.1%. Those are every brushed unit but the BOW28548D, every 12 and 48 V BOW PRO but the BOWA0304, and the smallest Boosted unit. The drop is computed at the stated current, at the top of every band, on the metric size printed.

The other 13 Boosted units are built tighter, 0.3% to 3.3% of their 24 or 48 V bank. Two rows follow neither pattern, and the notes below say why.

A run inside a band does better than its top, so VETUS's minimum cable carries more margin than its text asks for. Of Sleipner's 15 bands, 8 compute to more than the five percent rows' highest.

The AWG column needs the same reading as Sleipner's, and it points the other way. Where Sleipner's AWG size is the larger conductor, VETUS's is the smaller. On every size but 150 mm², it names the AWG size below the metric figure by area.

Two manuals are the exception. In the 110 mm and 125 mm BOW PRO manuals the aught sizes (1/0 to 4/0) are written "AWG 0, 00, 000, 0000". Those two give 50 mm² as AWG 0, the nearest size. Every other VETUS manual gives AWG 1.

Buy to VETUS's AWG column and at 25 mm² you have 15% less copper than the metric column asks for. The band tops then compute to as much as 6.0%. That is still inside the manual's 10 percent, because the table started at half of it.

If you want the cable the table was built to, buy the metric size, or go one AWG size up from the one printed.

The table has changed over the years. The December 2019 revision of the BOW55 manual gave each voltage one band. At 12 V it was 70 mm² (printed "AWG 00") to 12 m, 40 ft, which computes to 9.2% at the stated 375 A. At 24 V it was 35 mm² to 23 m, 9.7%. That table was built to the ten percent the text states.

The May 2026 revision prints 11 bands per voltage at the same 375 A, and the same 70 mm² now reaches only 6.4 m. The older table also printed the 24 V fuse as 125 A beside the part number ZE250, which is the 250 A fuse. The new one prints ZE125.

If your manual came in the box a few years ago, check the current one on vetus.com before you buy cable.

Two more things in the manuals. The BOW PRO tables name two fuses: a main fuse at the battery and a smaller "thruster fuse" inside the motor controller. The manual says this of the thruster fuse: "This fuse protects the controller and motor against short circuit/overloading and it must remain present under all circumstances".

The main fuse figure comes with a condition: "The recommended value of the main fuse applies exclusively to a power supply system in which the bow thruster is the only power consumer." The 110 mm manual also has an odd row. Its BOWA0304 row's feet column is not its meter column converted. There 48.2 m is printed as 140.4 ft, and every band in that row is off by the same share. The drop for that row is computed from the meters.

The larger manuals, read 15 September 2026, add these:

• The 48 V BOW28548D manual prints the 24 V BOW16024D's table line for line: the same 560 A, battery, fuse and bands. At twice the voltage the same cable loses half the share, so its bands compute to 2.5%.
• In the 185 mm Boosted manual the BOWB065 is built to five percent like the brushed range, 4.9%. Its four siblings on the same page sit at 2.3% to 3.3%. The same manual's BOWB130 row prints one band backwards, in both the meter and the feet columns. It reads 13.7 to 19.7 m for 150 mm², then 19.7 to 18.6 m for 2 × 95 mm².
• The 300 and 400 mm Boosted manuals print one fuse, not two, and it sits closer to the draw than the smaller units'. It runs 96% to 116% of the nominal figure, and on the BOWB420 it drops below: 500 A on a 520 A draw. On every smaller BOW PRO the main fuse sits above the draw with a thruster fuse in the controller under it.
• The 125 mm BOW PRO manual prints a larger current for the smaller unit, at both voltages. The BOWA0361 (36 kgf) draws 240 A against the BOWA0421 (42 kgf) at 218 A.
• A Boosted unit's bank is charged from the boat's 12 or 24 V system, and the 185, 300 and 400 mm manuals print a second table for that feed cable. These are looser than the thruster tables: at the charger's printed current the 24 V feed rows compute to 7.4% to 11.1% at their worst band top. The 250 mm manual prints no feed table.
• The 185 mm manual prints one feed table under both a 12 V and a 24 V heading. At the charger's 80 A the 12 V row computes to 18.4%, well over the manual's own 10 percent. That table's feet column is also not its meter column converted (40 m printed as 35.1 ft).
• The RIMDRIVE manual (2017) prints no band table. It gives a cable range per model (RD125: 35 to 50 mm²; RD160: 50 to 70 mm²). It names a 200 A main fuse (ZE200) and a 425 A fuse in the connection unit. It has one rule for the larger size: "Use the largest cable diameter for cable lengths of more than 10 m ( 33 ft) and/or for an expected continuous use of more than 5 minutes."
• The BOW PRO user manual (June 2026) prints one fuse per model. It matches the installation manuals above on every one of the 22 models they share. Where an installation manual gives two fuses, it matches the controller fuse. Where it gives one, it matches the main fuse. The October 2024 revision printed four of them differently: BOWA0304 125 A, now 80; BOWA0651 300 A, now 250; BOWB210 300 A, now 250; BOWB285 355 A, now 425.

The VETUS review reads the rest of these manuals. The battery page has the minimum and maximum battery for each model and what changed between revisions.

What Lewmar publishes: one cable and one run per model, built to about a volt

Lewmar's Gen 2 installation manual has a table headed "Correct cable sizes". It gives each model and voltage three figures: a stated current draw, the smallest cable in mm², and the longest run that size will carry. There is no AWGAmerican wire gauge, the size scale for electrical cable. The number falls as the cable gets thicker: 2 AWG is thicker than 6, and 1/0, 2/0, 3/0 and 4/0 are thicker still. column.

The table carries a note about the run: "Cable length is total from battery to thruster and back."

We computed each row at the stated current, on that cable, over that run. Every one of the 15 rows loses between 0.83 V and 0.96 V. That is a fixed number of volts, whatever the system voltage:

• 6.9% to 7.8% on the seven 12 V rows
• 3.7% to 4.0% on the six 24 V rows
• 1.8% to 1.9% on the two 48 V rows

So a 12 V Lewmar at its longest allowed run sits inside ABYC's 10 percent and outside its 3 percent. A 24 V one lands within a point above the 3 percent figure. A 48 V one is under it.

The manual's own floor is looser than its table. It says: "The minimum voltage at motor when running should be 10V for 12V and 21V for 24 V units". That allows 2 and 3 volts of loss.

Read the US size column with care on the big units. Of the 15 rows, seven name a metric size with more copper than a single 4/0:

• On five of them, a pair of one size per leg holds it.
• On the other two, the metric size holds more copper than two 4/0 per leg, past any common marine cable. A shorter run is the common-cable answer there.

Industrial cable above 4/0 exists, but it is not common marine stock, and ABYC's table stops at 4/0.

The fuse column runs the way VETUS's brushed units do above. The ladder prints a fuse for every electric model, and every one is below the stated draw, 54% to 95% of it.

Three 24 V 185 mm units share one 130 A fuse: the 3, 4 and 5 kW, drawing 160 A, 235 A and 240 A. On the 5 kW that fuse is 54% of the draw.

The 300 10.8 kW at 24 V has two fuses on the ladder for one current figure: 400 A on the aluminum-gearbox part number and 500 A on the bronze.

Lewmar's whole battery rule is one sentence: "Battery crank capacity should be at least equal to the thruster current."

The battery page puts it beside the other makers'.

Under the table sits a worked example: "a total of 28 m (92 ft) of cable with a model 250 8.0 kW thruster would need 95 mm CSA (000 AWG) cable".

The row above it says 185 mm² to 20 m. At the row's 500 A, the example's cable over the example's run loses 2.54 V. That is 10.6% of 24 V, over ABYC's 10 percent and 2.7 times the row's own figure.

The example belongs to the previous manual. Issue 2 covered the 140TT, 185TT and 250TT. It printed a table of the longest run for each of eight cable sizes, and its 250TT 8.0 kW cell on 95 mm² reads 28 m.

The Gen 2 manual replaced the table and kept the example. Its "000" is the AWG size nearest 95 mm² by area, 3/0. It is the one place the section gives an AWG size at all.

The old table was built to a share of the voltage, and a bigger one:

• the four 12 V rows lose 1.10 V to 1.93 V, 9.2% to 16.1%
• the five 24 V rows lose 1.73 V to 2.60 V, 7.2% to 10.8%

Both straddle ABYC's 10 percent. Every cell of the old table allows more loss than any row of the Gen 2 table.

Its feet table is not the meter table converted. Of the 49 cells that appear in both, 43 are more than a foot away from a conversion, because each table was worked on its own sizes.

For example, the 140TT 2.2kW's 35 mm² cell is 10 m, 32.8 ft, and its AWG 2 cell is 30 ft. If you own a pre-Gen 2 unit and size from its own manual, you are sizing to that older, looser table.

The Lewmar review reads the rest of both manuals: the warranty's one-year exceptions, the run-time rule, and the boat-length bands the maker does not publish.

What Quick publishes: cable by run length and a fuse, and no current

Quick's BTQ installation manual gives every model two things. The first is a fuse, as a CNL DIN rating (a bolt-down fuse standard). The second is a cable cross-section in three bands of total run.

The cable table is footnoted "L = positive cable + negative cable".

The bands are under 5 m, 5.1 to 10 m, and 10.1 to 20 m. Each gives a metric size with an AWGAmerican wire gauge, the size scale for electrical cable. The number falls as the cable gets thicker: 2 AWG is thicker than 6, and 1/0, 2/0, 3/0 and 4/0 are thicker still. size in brackets, and "2 x" where a leg needs two conductors.

Neither of its manuals gives a current draw. Without one, no drop can be computed. The warning in the draw section about working amps from kilowatts applies here as much as anywhere. The table prints what Quick prints and computes only what the table itself can say.

The last column is the table's own shape. At one current, the loss over a run is the run divided by the copper. So meters per mm² at the top of a band measures the loss that band accepts, up to the current the maker leaves out.

On the long band it is 1.5 to 2.3 times what it is on the short band. Quick accepts between one and a half and two and a third times the loss at 20 m that it accepts at 5 m. A short run on Quick's minimum cable carries the margin, and a long one does not.

VETUS's tables above work the other way. On 40 of its 42 rows, the bands spread by no more than 1.3 times. The two that spread more, the BOWB385 and BOWB420, are the rows whose table offers two sizes for one run.

Quick's AWG column rounds down like VETUS's. It uses five pairings: 35 mm² as AWG 2, 50 mm² as AWG 1, 70 mm² as AWG 2/0, 95 mm² as AWG 3/0, 120 mm² as AWG 4/0. All of them name the AWG size below the metric one by area. They run from 85% of the metric copper on 50 mm² to 96% on 70 mm².

One cell, the BTQ 3030048's middle band, prints "2 x 70 mm2" beside a bracket of "AWG 2/0" with no "2 x".

The BTQ250 and BTQ300 manual (REV006C) prints one "Section of wire" per model and no run length. Set that against the three-band table's 10.1 to 20 m band for the same model.

It is the same on three models (BTQ 2524024, BTQ 3025024, BTQ 3030048). It is smaller on four (BTQ 2512012, 2 × 95 mm² against 2 × 120 mm²; BTQ 2512024, 120 mm² against 2 × 70 mm²; BTQ 2514024, 120 mm² against 2 × 70 mm²; BTQ 3027024, 2 × 95 mm² against 2 × 120 mm²). On the BTQ 2512012 and BTQ 3027024 it is the three-band table's middle band.

The REV006C fuse column agrees with REV003A on six of the seven models. The BTQ 2524024's fuse cell prints "(2 x AWG 3/0)" where REV003A prints 500 A.

The fuse is the one current-shaped figure Quick prints, and it is not a draw. Two makers above print both. On each of them, every brushed unit's fuse sits below its stated draw: VETUS's at 60% to 73% of it, Lewmar's at 54% to 95%.

Read Quick's 130 A on the BTQ 1102512 as the fuse it is. Get the draw from the installer or the maker before sizing anything from it.

The Quick review reads the rest of both manuals, the run-time rule that lives in the control panel's manual, and the three sets of boat-length bands.

What Max Power publishes: a cable table at two currents, and a fuse sized to the cable

Max Power's CT100/CT125 manual gives each of its two units two current figures, two pages apart. The first is on the performance page, where the data "is measured with an approx. consumption of 680A and 11V for the CT100, or 430A and 22V for the CT125".

The second is in the fuse table, which gives the same units a "Maximum Amperage" of 550 A and 330 A. The cable table is four bands of total run, both legs counted, in mm² with no AWGAmerican wire gauge, the size scale for electrical cable. The number falls as the cable gets thicker: 2 AWG is thicker than 6, and 1/0, 2/0, 3/0 and 4/0 are thicker still. column.

We computed the drop at both currents:

• At the maximum amperage, the CT100's bands hold 4.2% to 5.3% of 12 V, and the CT125's 2.4% to 4.0% of 24 V.
• At the measured consumption, they hold 5.1% to 6.5% and 3.1% to 5.1%.

Every band is inside ABYC's 10 percent at both currents. Only one of the eight, the CT125's shortest, is under the 3 percent figure at the maximum amperage.

The manual says how the fuse is sized: "on the basis of the cable sections in the circuit and NOT the amperage drawn by the appliance".

Both fuses sit below both currents on both units. That is the same direction as every VETUS brushed unit and every Lewmar row above.

Of the eight bands, four name more copper than a single 4/0. A US owner running a CT100 more than 5 m there and back is into a pair of one size per leg.

Past 10 m, the manual's size holds more copper than two 4/0 per leg, past any common marine cable. A shorter run is the common-cable answer there.

The Max Power review reads the rest of the manual. It covers the battery the manual asks for, the one an owner was told to fit, the run-time rule and the selection chart.

What each maker publishes, and what none does

Six makers put figures on this page. Sleipner, VETUS, Lewmar and Max Power published a current and a cable table each, Max Power with two currents. Quick published a cable table and a fuse with no current. Sideshift published a start current, a cable size and a distance.

Here is what this page holds for each brand: