ABYC Standard E-11, as amended July 2023:
11.10.1.1.1 Overcurrent Protection Device Location - Ungrounded conductors shall be provided with overcurrent
protection device(s) within a distance of seven inches (178 mm) of the point at which the conductor is connected to the
source of power measured along the conductor (see FIGURE 8).
EXCEPTIONS:
1. Cranking motor conductors.
2. If the conductor is connected directly to the battery terminal and is contained throughout its entire distance
in a sheath or enclosure such as a conduit, junction box, control box , or enclosed panel, the overcurrent
protection shall be placed as close as practicable to the battery, but not to exceed 72 in (183 cm).
3. If the conductor is connected to a source of power other than a battery terminal and is contained throughout its entire distance in a sheath or enclosure such as a conduit, junction box, control box, or enclosed panel, the overcurrent protection shall be placed as close as practicable to the point of connection to the source of power, but not to exceed 40 in (102 cm).
4.Overcurrent protection is not required in conductors from self-limiting alternators with integral regulators if the conductor is less than 40 in (102 cm), is connected to a source of power other than the battery, and is contained throughout its entire distance in a sheath or enclosure.
5. Overcurrent protection is not required at an alternator if the ampacity of the conductor is equal to or greater than the rated output of the alternator.
6.Pigtails less than seven inches (178mm) are exempt from overcurrent protection requirements.
NOTES:
1.Multiple main overcurrent protection devices may be connected to a common busbar connected directly to the source of power.
2.If the DC electrical distribution system is not connected as a grounded system per E-11.5.2.3, then both the positive and the negative DC conductors are ungrounded conductors.
11.10.1.1.2 In addition to the provisions of E.11.10.1.1.1 the ungrounded conductors to a battery charger, alternator, or another charging source shall be provided with overcurrent protection within the charging source, or within seven inches (178 mm) of the charging source, based on the maximum output of the device.
EXCEPTION: Self-limiting devices.
I have questions based on statements made above:
Why should a solar panel or solar controller be considered a self-limiting device? A battery charger is not. Why one and not the other?
Two points I'd like to offer:
1. ABYC excludes alternators from the OCP requirement IF the cable is larger than the rated output. Why is this not acceptable for a battery charger?
2. Assume a 30A MPPT controller. The output is wired to the DC bus with 10AWG and within the distance limits for 3% voltage drop. With the panels providing maximum output, no OCP on the controller output, and a dead short into the wire between the controller and positive busbar, something's going to smoke. smolder, or burst into flame. Could be the wire. Could be the controller. Why take the risk?
My standard practice is to fuse the output of a power source. Convince me it's unnecessary.