Though there are many green buildings being designed and built from the start with significant considerations for the environmental effect or footprint, many renovation projects include alternative or renewable-energy sources, such as solar power. Depending on the scale and integration of the project with utility power, these projects can require significant attention to manufacturer’s installation instructions, code-compliance requirements and the power quality impacts, which may not all be in sync with each other.
In addition, as I heard recently during a meeting with several National Joint Apprenticeship and Training Committee (NJATC) personnel, some people undertaking such projects are falsely considering it to be a low-voltage direct current (DC) system that doesn’t require licensed contractors or compliance with the National Electrical Code (NEC). Some systems have output voltages of more than 500 volts alternating current (V AC) and power levels in the megawatt range, which make it a necessity to take proper precautions with these and all electrical installations to prevent injury, loss of life and damage to property. This issue is at the core of the reason the National Fire Protection Association (NFPA) first established and continues to evolve NFPA 70, the NEC.
For renovation work, areas of the building that are not affected by the work may be exempt from compliance with the 2008 revision of the NEC, since the document is generally not considered retroactive to existing installations.
“The extent to which it will be applied to an existing condition is left to the enforcing jurisdiction,” writes Frederic P. Hartwell in “Inspecting Electrical Renovations,” IAEI Magazine, March 2003. “There may be a threshold, such as a percentage of the building involved or a change of use category as covered in the applicable building code, beyond which the work is considered new construction. If this is the case, all wiring must meet the current NEC requirements that would apply in the same jurisdiction to new buildings.”
If the project calls for a new renewable-power source installation that will interconnect to the existing electrical infrastructure, it would be prudent to get the system up to Code and improve the overall power quality prior to the introduction of a new set of potential issues.
It would be difficult to imagine any renovation project that is adding a renewable power source that has to deal with the provisions of the Code relating to “separately derived systems,” except if the renewable-power source is an isolated system that is the sole source of power for the new construction. Separately derived systems involve grounding and bonding requirements and components, such as the bonding jumper, the grounding-electrode conductor, the grounding electrode, the grounded conductor, and the equipment-bonding jumper, which are also key factors in maintaining that equipotential grounding system that is important for optimal power quality.
While Code-Making Panel 5 (CMP 5) continually strives to improve that portion of the Code, new technologies, such as renewable-power sources, make a working understanding of sections 250.20 and 250.30 of the NEC even more important for safe and reliable operation of the facility.
One of the aforementioned renewable-power sources are the photovoltaic (PV) arrays found on roofs of commercial, industrial and residential structures as well as free-standing installations of PV arrays in fields.
One of the biggest problems with PV and driving it to utility scale is the sudden change in output due to the movement of clouds and weather conditions. In fact, the name for this output change is “cloud transients.” In the power quality realm, we tend to consider transients as sub-quarter-cycle events or events lasting less than 4 milliseconds. Cloud transients are obviously not of the same time frame, but they are a power quality consideration, nonetheless, as they can result in modulation of the power output. In addition, PV systems with inverters create harmonic currents, just like with uninterruptible power supply systems, also a power quality issue.
However, the more important consideration to the power delivery from PV should first be given to the proper installation of the arrays. This column does not cover Code-review per se, but an overview of those articles related to PV as well as those potentially affecting the power quality is important as the basis for such a discussion.
Revisions to Article 690, Solar Photovoltaic Systems, go on every three years, and the 2005 and 2008 revisions have made significant changes that relate to PV. I will discuss requirements, including 2008 revisions of the Code, ranging from where and how to use finely strained wire, listing of components, and marking of panels and connectors in Article 690, in next month’s article.
Other relevant articles in the NEC applicable to PV systems include Article 110, Requirements for Electrical Installations; Article 250, Grounding; Article 300, Wiring Methods; Article 310, Conductors for General Wiring; and Article 480, Storage Batteries, since the output of the PV arrays are used in hybrid systems to charge batteries for use in the nonsunny periods. There also is much information on this matter on the Web.
BINGHAM, a contributing editor for power quality, can be reached at 732.287.3680