National Electrical Code Tips: Article 690 -- Solar Photovoltaic Systems,
Only about 15% to 20% of the work of installing a Solar Photovoltaic (PV)
System is electrical. But that electrical portion can easily result in disaster
if not done correctly. Thus, Article 690 provides requirements for that portion.
Something many people don't realize is that as the battery systems of PV
systems get larger, they begin to resemble the battery systems in data centers.
People in the battery industry are very aware of this, as are the relevant NEC
CMP (Code Making Panel) members and their counterparts on the IEEE battery
committee. Consequently, the battery requirements for PV systems draw from a
rich depth of experience, practical knowledge, and empirical data.
We continue here with the battery requirements coverage that began in
- If the battery installation has more than 24 2V cells connected in series
(48V nominal), you must provide a disconnecting means accessible only to
qualified persons. This must disconnect the grounded circuit conductors
to permit maintenance [690.71(E)]. If, by some really strange set of conditions,
these batteries are not subject to field maintenance, then you don't need to
provide this disconnect.
- Pertaining to point 1 above, you must also have a disconnect for the
ungrounded circuit conductors [690.71(F)]. It can't be the same
disconnect as the one above.
- A battery system that consists of more than 24 2V cells (operates above 48V)
can operate with ungrounded conductors [690.71(G)] . But only if four
conditions are met. Those are spelled out in [690.71(G)].
- New with the 2014 NEC is [690.71(H)]. This provides five requirements you
must meet if the energy storage device input and output terminals are more than
5 ft from connected equipment. This is a very likely scenario.
- The five requirements of [690.71(H)] also apply if the circuits from input
or output terminals pass through a wall or a partition.
- Charge control is another major issue with batteries. Getting it right is
tricky, and it gets trickier as the battery grows in size. For example, a
four-tier battery rack in a data center presents thermal complexity that simply
does not exist in a single-tier rack. The NEC provides an exemption for
providing charge control if you meet certain conditions [690.72(A).]
- If the PV has a diversion charge controller as its sole means of regulating
the charging rate, it must also be equipped with a means to prevent overcharging
- The NEC provides specific requirements to meet if your regulator is of the
buck/boost type [690.72(C).]
- You can use flexible cables (as identified in Article 400) in sizes 2/0 and
larger within the battery enclosure to connect from the battery terminals to a
nearby junction box [690.74]. In that box, they must connect to an approved
- Flexible cables can be only those listed for hard service. If you use
flexible cables that are fine-stranded (and most of them are fine-stranded), you
can terminate them only with terminals, lugs, devices, or connectors per Article
110 requirements [690.74].
This concludes our coverage of Article 690 requirements for batteries. The
NEC presents those requirements in Part VIII.
The next and final Part of Article 690 addresses specific requirements for
systems over 1000V. Since those requirements are minimal and plainly expressed,
we won't cover them. Thus, this Part 11 in this series also concludes our
coverage of Article 690/