N-Type Alternator Wiring¶

Power and field plug wired for an N-type alternator, terminals labelled Battery +, Ground and Field: the bridge spans terminals 2 and 4, and the field wire lands in terminal 3

Quick reference¶

Aspect	Specification
Wire	12 AWG tinned stranded on GND; 14 or 16 AWG acceptable on BAT+ and field
Regulator Power Wire (BAT+)	A + bus bar or distribution point downstream of the bank's main fuse, not the battery post; on the shunt's load side when the shunt is in the positive lead
Regulator Ground Wire	Battery negative post or a bus bar at the same potential; on the shunt's load side when the shunt is in the negative lead; shortest run
Wire termination	Bare stranded under screw, 5 mm strip maximum
Jumper	EBP 3-5 with middle blade removed
Screw torque	0.5 to 0.6 N·m
Field fuse	10 A
BAT+ fuse	10 A
Field supply fuse	10 A, only if the field is fed by an external wire
Cat6 tap fuses	1 A each, on the conductors that tap boat power
Fuse voltage rating	32 V DC on 12 and 24 V, 80 V DC on 36 and 48 V
Fuse holder	12 AWG: IHWOM12HD on 12/24 V, LPR-02B-12R on 36/48 V
Tap fuse holder	18 AWG: IHWO18 on 12/24 V, LPR-02B-18R on 36/48 V

Terminal assignments (left to right)¶

Terminal	Connects to
1, BAT+	A + bus bar or distribution point downstream of the bank's main fuse (the shunt's load side when the shunt is in the positive lead), through a 10 A fuse
2, GND	The battery negative post or a bus bar at the same potential (the shunt's load side when the shunt is in the negative lead), and jumper
3, FIELD_FOR_N_TYPE	Regulator Field wire to the alternator, through the field fuse
4, FIELD_FOR_P_TYPE	Jumper blade only, bridged to terminal 2

Where to land the regulator's battery wires

Shunt in the positive lead

Power (red): the load side of the shunt, downstream of the bank’s main fuse.

Ground (black): the battery negative post, or a bus bar at the same potential. This wire must be 12 gauge and as short as possible.

Voltage sense, Cable 2 pin 11: the battery positive post, on the battery side of the shunt.

Shunt sense, Cable 2 pins 9 and 10: across the shunt.

Field supply wire, where the alternator brings one out: the load side of the shunt, like any other load.

Before wiring pins 9 and 10 to a shunt in this lead, read what it exposes them to, below.

No battery voltage correction is needed.

Shunt in the negative lead

Power (red): the + bus bar, or another distribution point downstream of the bank’s main fuse.

Ground (black): the load side of the shunt. This wire must be 12 gauge and as short as possible.

Voltage sense, Cable 2 pin 11: the battery positive post.

Shunt sense, Cable 2 pins 9 and 10: across the shunt. The battery voltage correction needs them.

Field supply wire, where the alternator brings one out: its B+ or ignition source, on the positive side.

The regulator corrects its battery voltage reading for the shunt’s drop by itself, once Shunt Location is set to Negative lead and Cable 2 pins 9 and 10 run to this shunt.

If your shunt is in the battery negative lead and its current reaches the regulator only over NMEA 2000 or VE.Direct, the regulator’s own battery voltage reading runs high while charging, by charging current × shunt resistance (10 mV per 100 A on a 500 A / 50 mV shunt). Wiring Cable 2 pins 9 and 10 to the shunt removes it.

With no shunt, the Regulator Power Wire lands on a + bus bar or distribution point downstream of the bank’s main fuse, the Regulator Ground Wire on the battery negative post or a bus bar at the same potential, the voltage sense wire on the battery positive post, and Cable 2 pins 9 and 10 are not used.

At the same potential. The Regulator Power Wire is not part of the battery voltage reading, so it does not need the post: it lands on a bus bar or distribution point downstream of the bank’s main fuse, on the correct side of the shunt (the fuse rating appendix below explains why). The Regulator Ground Wire and the voltage sense wire are the two ends of the battery voltage reading, so for them it means bolted to the post, or joined to it by a short heavy link with no fuse, switch, or shunt in it. Every milliohm between the post and the landing, times the battery current flowing through it, adds to the reading: 0.5 mΩ of switch, fuse, and cable is 50 mV at 100 A, five times the shunt’s own drop in the graph below.

The shunt inputs with a positive-lead shunt. A shunt in the positive lead puts the regulator’s two shunt inputs, Cable 2 pins 9 and 10, at battery voltage. They are rated to 85 V and have no surge clamp of their own, unlike the voltage sense input on pin 11. A voltage spike on the battery wiring, such as a BMS opening the battery while the alternator is charging, reaches them, and the chip they connect to is the one that measures the battery voltage the regulator charges to. On 12 and 24 V systems a spike that size is unlikely, and it would harm most of the other electronics on board too. On 36 and 48 V systems, 85 V is much closer to normal operating voltage: a 48 V bank absorbs near 58 V. Put the shunt in the negative lead on any system where you have the choice. On 36 and 48 V systems with the shunt in the positive lead, bring its current in over VE.Direct or NMEA 2000 instead of wiring pins 9 and 10 to it.

Wire and Connectors¶

Wire. The GND terminal requires 12 AWG marine-grade stranded tinned copper, Type II or Type III stranding per ABYC E-11. The BAT+ and field terminals take the same wire, and in a retrofit they also accept existing 14 or 16 AWG boat wiring. 12 AWG is a tight fit in the 5.08 mm plug, and it fits, including at the terminal that shares its hole with the jumper blade.

Wire termination. Plain stranded wire under the screw, no ferrule required. Strip back no more than 5 mm (0.2 in) from the insulation. See Short hazard below.

Jumper. The supplied Phoenix Contact EBP 3-5 (p/n 1733172) with the middle blade snapped out (already done by X Engineering) gives a 2-position bridge with 10.16 mm prong spacing, matching the regulator's terminal layout.

To install:

Insert the jumper blade flat into the wire entry hole, gray plastic angled down and away (towards the wall or bulkhead) to make the most space for wires.
Push the harness wire fully into the same hole, on top of the blade.
Torque the screw to 0.5 to 0.6 N·m.
Tug-test the wire firmly. If it pulls free, something is wrong, so re-seat and repeat.

Effect of Regulator Ground Wire gauge and length on Battery Voltage Measurement Accuracy¶

Regulator Ground Wire length is to be minimized! In XREG-010, the battery voltage sense chip shares a ground with the field itself, and wires that are excessively long or small gauge can lead to intolerable errors. In those cases, set Battery voltage for charge stage changes to an external reading: NMEA 2000, including a BMS that publishes battery status, or Victron VE.Direct. That moves the bulk, absorption, float, and rebulk decisions onto the external reading. The voltage control loop and the protections still use the onboard sensor, so the voltage the regulator holds keeps the error shown below. The choice is offered during commissioning.

12 V system24 V system48 V systembench measured*

* battery voltages during test were typical nominal levels, i.e. 13.7 V for a 12 V system.

Short hazard at the bridged-over terminal¶

Uncontrolled full-field hazard — inspect carefully during installation

Bare copper of an excessively stripped wire can accidentally touch the jumper's broken-off middle blade stub. In N-type wiring this is the Regulator Field wire, and the bridge carries GND. Contact shorts the Regulator Field wire straight to the bridge, bypassing the regulator's field switch entirely. The field locks on at full drive, the regulator cannot shut it off, and the field fuse will not blow (full-field current is normal current). The alternator runs unregulated and drives the system into overvoltage. This is obviously extremely dangerous, and at that point only a BMS can save the battery and possibly the boat.

EBP 3-5 bridge with middle blade snapped out: bright conductive metal remains exposed at the break point in the center notch — The bridge after snapping out the middle blade. The bright metal in the center notch is the remnant of the blade, still live whenever the bridge is.

Bridge installed on the plug. The bridged-over wire entry hole is still empty, with the conductive stub directly under it — The bridge installed in the P-type position, no wire in the bridged-over hole yet. The stub is directly under that hole, 2nd from left here; in the N-type position it is 3rd from left, under the Regulator Field wire.

Left hand black (and red) wire in the bridged-over hole stripped too far, with bare strands outside the housing, near the stub — The black wire (left) is stripped too far, with exposed strands at risk of touching the stub. Fail.

Correct installation: the wire in the bridged-over hole is fully seated with no bare copper visible near the stub — A good installation: the black wire in the bridged-over hole fully seated, no copper showing at the stub. The red wire is still bad here, but the risk is lower since it's not near the stub.

Fusing¶

Regulator BAT+ wire, at the end it taps: a + bus bar or distribution point downstream of the bank's main fuse rather than the battery post (the fuse rating appendix below explains why). 10 A.
Regulator Field wire, at the alternator end. 10 A. In N-type the field is fed from inside the alternator, so that end is the source and the fuse belongs there.
Field supply wire, if the alternator has one, at the end it taps. 10 A, the same part as the field fuse. Most N-type machines take the field's positive from an internal tap, so there is nothing to fuse. On the ones that bring it out to a terminal instead and feed it from B+ or the ignition circuit, that wire carries full field current and needs its own fuse, unless what feeds it is already fused. The excite or lamp terminal of a stock internally-regulated alternator is a different thing and carries well under an amp.
Every Cat6 conductor that taps a source of power outside the regulator, at the end it taps. 1 A each, the same fuse in every case: Cable 2 pin 11 (battery), Cable 1 pin 4 (stator), Cable 3 pin 6 (ignition), and Cable 2 pin 16 (BMS output) where one is fitted. Fuse, holder, and termination: Data Cables & Pinout. Nothing else on the four cables is fused: the rest are grounded, fed from the regulator's own current-limited rails, or land on a device output with no source behind them.

On N-type the BAT+ fuse is not a field kill switch

The field is fed from the alternator's own B+, so clearing the Regulator BAT+ fuse leaves it excited. With the battery leads reversed, the crowbar diode clears that fuse and the board goes unpowered, but the winding stays energized through the return diode for as long as the BAT+ terminal has a path to the battery. Do not run the engine until the wiring is corrected. A TVS that fails short above 71 V clears the same fuse with the same result. On a P-type installation the bridge feeds the field from downstream of that fuse, so blowing it removes field power. Where you have the choice, P-type is the safer configuration for that reason, and any alternator can be converted by rewiring the brushes.

Which fuse to buy, by system voltage¶

All three fuses are ATO blade fuses, and which one you buy depends on the system voltage. A standard automotive blade fuse is rated 32 V DC and the marine "high voltage" ones stop at 58 V; above its rating a fuse can hold an arc instead of clearing the fault, and a 48 V bank absorbs near 58 V. So 12 and 24 V systems take the 32 V part, and 36 and 48 V systems take an 80 V DC rated one.

The power and field fuses are 10 A, on 12 AWG holders:

System voltage	Fuse, 10 A	In-line holder, 12 AWG
12 V and 24 V	Sherco USATC10, 32 V DC	Sherco IHWOM12HD, waterproof
36 V and 48 V	OptiFuse ANR80-UL-10A, 80 V DC	OptiFuse LPR-02B-12R, 125 V DC, IP67

The Cat6 tap fuses are 1 A, on 18 AWG holders. NEC Table 725.144 rates a 24 AWG conductor in a single 4-pair data cable at 2.0 A, and less than that where cables share a bundle, so the fuse has to be small. These wires carry milliamps, which leaves the whole margin available to the conductor. 18 AWG is the finest lead these holders come on, and it splices to a 24 AWG Cat6 conductor in one step-down crimp:

System voltage	Fuse, 1 A	In-line holder, 18 AWG
12 V and 24 V	Sherco ATO1A, 32 V DC	Sherco IHWO18, waterproof
36 V and 48 V	OptiFuse ANR80-UL-1A, 80 V DC	OptiFuse LPR-02B-18R, 125 V DC and IP67 by its maker

Field resistance¶

There is no meter step during wiring: the regulator measures the field resistance itself during setup, in the field resistance test right after the Prerequisites screen. On a 24 V and up boat with no battery shunt on Cable 2 pins 9 and 10, that test needs a DC clamp meter or a multimeter with a 10 A range. A 12 V boat with no shunt can skip it.

Next step¶

Continue to Data Cables & Pinout for the four data-cable pinouts, then install the sensors: Current Sensor and Temperature Sensors.

Appendix: conduction paths

Output on. Battery positive → alternator B+ stud → internal tap → field winding → Regulator Field wire → FIELD_FOR_N_TYPE → Q3 → jumper → board ground → battery negative.

The full field current leaves the regulator through the Regulator Ground Wire every time the switch is on.

Output off. The field's freewheel current circulates through the Regulator BAT+ wire and the alternator's output cable, not through the Regulator Ground Wire: field winding → Regulator Field wire → return diode → BAT+ terminal → Regulator BAT+ wire → alternator output cable → alternator B+ stud → internal tap → field winding. On an alternator with an external field supply wire, the loop closes through that wire instead of the internal tap.

What the shunt measures. The battery supplies field current only during the on part of each switching cycle. During the off part the field winding keeps its own current circling through the loop above, and the battery supplies none of it. Every other load on the boat lands on the shunt's load side. Whichever regulator wire shares the shunt's lead, power or ground, lands there too, as the drawings above show, and that keeps the loop out of the shunt. The shunt then reads exactly what the battery supplies: the field current while the switch is on, plus the board's own draw. Land the Regulator BAT+ wire on the battery post with the shunt in the positive lead and the freewheel current crosses the shunt as well, and state of charge, tail current, and the battery-current limit would all count it as battery current.

Appendix: worst-case battery voltage error by Regulator Ground Wire length

Worst case across the full field current range, 12 AWG.

Ground wire	12 V	24 V	48 V
12 AWG, 2 ft	-0.040 V	-0.022 V	-0.011 V
12 AWG, 3 ft	-0.060 V	-0.033 V	-0.017 V
12 AWG, 6 ft	-0.120 V	-0.066 V	-0.033 V
12 AWG, 10 ft	-0.200 V	-0.110 V	-0.055 V

Appendix: fuse current rating and where to tap BAT+

A fuse carries two current ratings, and they describe different things. The 10 A is the current that melts the element. The interrupting rating is the largest current the fuse can cut off, and it is 1000 A for both 10 A fuses in the fuse table above. OptiFuse publishes 1000 A at 80 V DC for the ANR80. Sherco lists SAE compliance for the USATC10, and SAE blade fuses are rated 1000 A at 32 V DC. A dead short does not draw 10 A, it draws whatever the bank can deliver, and a large bank can deliver thousands of amps. Past the fuse's limit the element vaporizes but an arc keeps burning across the gap, so the fuse goes on conducting instead of clearing the fault, and the body can rupture.

The wire's own resistance limits most of this. 12 AWG runs about 1.6 mΩ per foot, so a 6 ft run out and back is near 19 mΩ, which holds a dead short on a 12 V bank to roughly 700 A, and a longer run limits it further. What the wire does not limit is a short close to the fuse, because the fuse only has to break the current available at its own terminals, and that is set by the bank and the heavy cable feeding it rather than by the 12 AWG downstream.

Feeding the Regulator BAT+ wire from a distribution point downstream of the bank's main fuse rather than straight off the battery post keeps the worst case inside what the fuse is rated for.

Appendix: board input protection, what happens in each fault

The BAT+ input runs through an automotive protection controller (TPS48000-Q1) driving back-to-back MOSFETs, with a TVS diode and a crowbar diode across the input terminals. On N-type wiring the field freewheels through the return diode, which lands on terminal 1 (the BAT+ input) ahead of those MOSFETs, and the loop closes through the Regulator BAT+ wire and the alternator output cable. That loop never passes through the protection stage, so it stays intact whether the stage is conducting or has tripped.

Battery leads reversed. The crowbar diode conducts and clears the BAT+ fuse. The board does not power up and is not damaged. Replace the fuse and correct the wiring before trying again — on an N-type installation the field is fed from the alternator, not from the fuse, so a blown fuse does not stop the field if the engine is run with the leads still reversed.

Bus overvoltage. A load dump, a BMS opening under charge, or a failed external charger trips the controller somewhere between 60 V and 65 V, and it isolates the board in about 5 µs. The field's stored energy decays in the loop through the return diode rather than into the board, so the alternator de-excites while the board is unpowered. Power restores automatically once the bus falls back below about 58 V.

Short circuit on the Regulator BAT+ wire. The external BAT+ fuse clears it. The controller trips on voltage, not on current, so the fuse is the only thing that ends a short on that wire. Fuse rating and holder are in the fusing section above, and the board's own draw is a fraction of an amp, so nothing the regulator does on its own comes near the fuse.

Battery voltage collapses. Below about 5 V at the input the controller shuts down and stays off until the bus recovers, so a flat or disconnected bank leaves the board off rather than browning out.

Regulator Field wire shorted to ground. The field switch is outside the input protection stage entirely, so nothing in this stage detects that fault, and neither fuse does either: full-field current is normal current. This is the failure the short hazard section above is about: strip the wires short and inspect the bridged-over terminal.

Battery connection opened while the alternator is charging. Breaking the charging path under load is a load dump: the alternator's own output has nowhere to go, and the spike reaches everything on the bus. The board's TVS clamps what reaches its input, but the alternator's rectifier is what is usually damaged. Shut down charging before opening a battery switch or a terminal.

Lightning nearby. Induced surges conducted along vessel wiring are clamped by the TVS and cut off by the overvoltage trip. A direct strike is beyond what any of this survives.

Field circuit

Field current does not pass through the input protection stage in either wiring type — see Fusing above. The field fuse is the protection for the field circuit.

For trip levels, timing, and the circuit itself see the Input Protection hardware doc.