Mike Dolt Enterprises
Mike Dolt Enterprises
User: jdlovins, Location: Mission Viejo, CA
Asked on: Wednesday, April 27, 2011 at 2:17 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:41 am EDT
Question: I am the installation manager for a renewable energy company that specializes in photovoltaic systems. I have a technical question about a condition that may arise in some of our projects. I have not been able to get a clear answer on this topic from wire manufacturers, internet searches, electrical engineers, or a member of an NEC code making panel. Article 310.13 of the 2008 NEC, or Article 310.104 from 2011, has a fine print note that references a condition called electroendosmosis. I understand that FPNs are not enforcable parts of the Code but we do not want to do an installation that may result in wire failure. From my understanding, this condition may occur when DC conductors with thermoplastic insulation are installed in wet locations. From the research that we have done by looking at other systems, it seems that THWN-2 rated wire is used in outdoor installations in conduit for photovoltaic systems. This rating gives a 90 degree rating in a wet location. Again, this seems to be an industry standard but it opens up the possibility for electroendosmosis to occur and damage the insulation of the wire. The solution would be to install XHHW-2 but this increases costs as this wire is more expensive. So, my question is if this condition ever occurs in the real world or if this is just a situation that can be created in a laboratory setting. Two leading wire manufacturers have told us that it is not an issue and most of the other methods that we have explored have never even heard of this. Online searches do not reveal too much useful information either. Thank you for taking the time to read this and I look forward to any feedback.David
Definition of Electroendosmosis
Electroendosmosis is a phenomenon where moisture migrates through the insulation of a DC conductor due to the presence of an electric field. This can lead to the accumulation of ions and the degradation of the insulation over time.
Occurrence in Real-World Photovoltaic Installations
While electroendosmosis is a potential concern, it is not considered a common occurrence in real-world photovoltaic installations. Here's why:
редко используется : THWN-2 wire, which is commonly used in PV installations, is a thermoplastic insulation rated for use in wet locations. While it is possible for electroendosmosis to occur with thermoplastic insulation, it is less likely in properly installed systems. Тщательная герметизация : Photovoltaic systems are typically installed in conduits or other forms of raceways that provide protection from moisture ingress. This helps prevent the accumulation of water in the vicinity of the conductors.* Короткое расстояние : DC conductors in photovoltaic systems are usually relatively short, reducing the potential for moisture migration through the insulation.
Solution with XHHW-2
While electroendosmosis is unlikely to occur in most PV installations, XHHW-2 wire can be used as a more robust solution if desired. XHHW-2 is a cross-linked polyethylene insulation that is more resistant to moisture and electroendosmosis. However, as you mentioned, this option is more expensive.
Conclusion:
Based on current industry practices and research, electroendosmosis is not a significant concern in properly installed photovoltaic systems using THWN-2 wire. However, if you have specific project conditions that raise concerns about moisture exposure, it may be advisable to consider using XHHW-2 wire as a precautionary measure. It is always recommended to consult with a qualified electrical engineer for guidance on specific project requirements. Flag for review