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.
- Connectors used in PV circuits must comply with 690.33. For the installer,
this simply means you must use connectors listed for use with PV systems. The
manufacturers of these connectors are the ones who must ensure the connectors
comply with 690.33 so they can be listed for use in PV circuits.
- Be careful where and how you locate boxes. You can put junction, pull, and
outlet boxes behind PV modules, but if you locate them there then you must make
it so the wiring inside the box is directly accessible by dint of easily moving
the PV module out of the way [690.34]. From an engineering and maintainability
standpoint, you want to avoid this situation. But sometimes it may not be
practical to due space considerations or other limitations.
- A PV system can have an ungrounded PV source and ungrounded output circuits.
But only if you meet the conditions outlined in 690.35 (A) - (G). Note that
"ungrounded" does not mean "metallic objects are not bonded." Systems not
meeting the conditions of 690.35 (A) - (G) must be grounded and meet the
requirements of Article 690, Part V (690.41 - 690.50) [690.41].
- Exposed non current-carrying equipment must be bonded, not "grounded" as
stated in 690.43(A). See the Article 100 definitions of "bonding" and
"grounding", Article 250 Part V, and the IEEE Green Book.
- You must install an equipment "grounding" (bonding) conductor between a PV
array and other equipment [690.43(B)].
- Under specified conditions, you can use the structure as an equipment
bonding conductor [690.43(C)].
- You have to run the equipment "grounding" (bonding) conductors in the same
raceway (or cabling) where you run those conductors to a point outside the
vicinity of the PV array [690.43(F)]. For example, if this is a supplemental
power source for the building then you will need to bond the PV system's
equipment "grounding" (bonding) system to the equipment "grounding" (bonding)
system of the utility power or other bonding system. Do not drive a ground rod
as a means of doing this; it does not electrically accomplish this purpose. Only
the main equipment bonding jumper should connect to the grounding system;
otherwise, you get ground loops that defeat the equipment bonding system.
- Size the equipment "grounding" (bonding) jumpers no smaller than what's
specified in 690.45. You can size them larger, if you choose. But don't make the
mistake of jamming oversized wires into the bonding lugs and assume that creates
a better system. It actually creates differences in potential due to the poor
connection. So don't oversize bonding conductors relative to the 690.45
requirements unless you can also upsize the connectors.
- Be careful when applying 690.47, "Grounding Electrode System." Remember, you
cannot use the earth as a bonding jumper; attempts to do so create dangerous
differences of potential. Grounding is mainly for lightning protection. All
grounding electrodes (e.g., driven rods) must be bonded together. You cannot
have "separate" grounding systems, because the "ground" (earth) is not at
infinite resistance (permitting separation). Nor is it low resistance,
permitting it to act as if it's a #4 copper wire.
- After misusing the term "grounding" in reference to bonding conductors,
Article 690 finally uses the correct (per Article 100 and other references)
terminology in 690.50. Don't let this confuse you into thinking there are
equipment bonding jumpers to install in addition to equipment "grounding"
conductors. What's happening here is the NEC is slowly correcting misuse of the
word "grounding" with each revision. So you get these anomalies in terminology.
To avoid confusion, always refer to the Article 100 definitions. And remember:
You BOND equipment. You NEVER ground it. Even if grounding is a condition of
warranty, don't do it. Such a requirement, because it violates the NEC, basic
electrical engineering principles, and several authoritative references, is
Just be sure to send the mfr a letter to this effect before there's a warranty
claim. It will be helpful to draw out the circuit and show that, per the Law of
Parallel Circuits, electricity takes all paths before it in inverse proportion
to the impedance of each path to the total path impedance. It does not take "the
path of least resistance," a myth that defies all we know about circuit design.
Don't let the ignorance and incompetence of a manufacturer intimidate you into
installing equipment in a manner that is certain to cause interruption in
operations or even get people killed. Most manufacturers don't have this
problem, but some do. It is ethically imperative that you install a safe