690.9(E) Series Overcurrent Protection.

When series string fuse protection is required, it must be installed in each ungrounded conductor. If series string protection is not required, the factory installed dummy fuses can remain in place.
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When series string fuse protection is required, it must be installed in each ungrounded conductor. If series string protection is not required, the factory installed dummy fuses can remain in place.

Code Change Summary: New code language in 690.9(E) now provides rules on overcurrent protection for both grounded and ungrounded PV system modules and conductors.

The previous 2011 text in 690.9(E) only provided rules on overcurrent devices for grounded PV systems. Now, this section covers both grounded and ungrounded PV systems.

Not all PV source circuits require an overcurrent device. Deciding on whether an overcurrent device is required in a PV source circuit depends on if there are any other parallel connected source circuits that can potentially backfeed excess current into the string of modules being protected.

If there are no external current sources such as parallel connected source circuits, batteries, or backfeed from inverters, or if the short-circuit currents from all sources do not exceed the ampacity of the conductors and the maximum overcurrent device size specified on the PV module nameplate, then source circuit overcurrent protection is not required.

When overcurrent protection is in fact required for a grounded PV system, the overcurrent device is only required in one conductor; the ungrounded conductor. This is because the other conductor in a DC circuit is grounded. Generally, throughout the NEC®, grounded conductors are not provided with an overcurrent device except in special circumstances.

When overcurrent protection is in fact required for an ungrounded PV system, an overcurrent device is required in both the positive and negative conductors since both conductors are ungrounded.

Below is a preview of the NEC®.  See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).

2011 Code Language:

690.9(E) Series Overcurrent Protection. In PV source circuits, a single overcurrent protection device shall be permitted to protect the PV modules and the interconnecting conductors.

2014 Code Language:

690.9(E) Series Overcurrent Protection. In grounded PV source circuits, a single overcurrent protection device, where required, shall be permitted to protect the PV modules and the interconnecting conductors. In ungrounded PV source circuits complying with 690.35, an overcurrent protection device, where required, shall be installed in each ungrounded circuit conductor and shall be permitted to protect the PV modules and the interconnecting cables.

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690.9(E) Series Overcurrent Protection.

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

Which of the following is true when it has been determined that series string overcurrent protection is required in a grounded PV system?

A: Overcurrent devices must be placed in both the ungrounded and grounded conductors.
B: Each negative PV source circuit conductor requires an overcurrent device.
C: Each grounded PV source circuit conductor requires an overcurrent device.
D: Each ungrounded PV source circuit conductor requires an overcurrent device.
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