PhotoVoltaic Frame Bonding:
ILSCO DB Lugs and Coastal Environments
John Wiles Photovoltaic Power Systems and the 2005 National Electrical Code: Suggested Practices has discussed several methods of bonding the aluminum frames that come with many photovoltaic modules, suggesting that, in the absence of specific manufacturer recommendations, ILSCO Direct Burial lugs would be an acceptable method of frame bonding.
John Wiles works in a semi-arid environment, and a significant part of San Diego is Coastal. Because of the significant cost of the ILSCO lugs and some doubts expressed about their use in a bonding system in a coastal environment, an experiment was proposed to compare their use with alternative bonding methods in common use.
A piece of aluminum angle stock similar to that used in common photovoltaic module frames was prepared with bonding connectors attached;
From left to right, the attachments are:
ILSCO DB lug with #8 AWG bare copper wire
ILSCO DB lug with #6 AWG bare copper wire
ILSCO DB lug with tinned copper braid
Tinned copper braid in direct contact with the angle stock retained by a stainless steel washer
Tinned copper braid separated from the angle stock by a stainless steel washer
Bare copper wire separated from the angle stock by a stainless steel washer
Bare copper wire in direct contact with the angle stock retained by a stainless steel washer
Tinned copper braid in direct contact with the angle stock retained by a brass washer
Tinned copper braid separated from the angle stock by a brass washer.
All attachments were secure by identical self-threading stainless steel screws providing, at least initially, secure mechanical bonding.
This assembly was placed exposed to naturally occurring salt spray and weather above the water on the Scripps Institution of Oceanography (SIO) pier for two (2) weeks, and then recovered.
(Note that the orientation is reversed from the previous photo.)
What is immediately obvious is that the ILSCO lugs have disappeared and the screw holes where they were attached show evidence of corrosion. Also missing is the copper bonding wire that had been in direct contact with the angle stock.
The copper wire separated from the angle stock by a stainless steel washer and the tinned copper braids remain relatively intact.
More definitive tests should be made of proposed photovoltaic module bonding methods in a salt spray/coastal environment, and
While the ILSCO DB lug, of itself, is extremely durable, consideration should be given to the possibility that it may contribute to deterioration of other parts of the bonding system in a coastal environment.
Other bonding methods should be explored, including the use of tinned braid and sealing of the bonding wire-frame connection in a protected environment.
Grateful thanks are owed to Martin Learn of Home Energy Systems, Inc., who supplied the tinned copper braid, Michael Collins, also of Home Energy Systems, Inc., who assembled the components, and Ken Duff of Scripps Institution of Oceanography, who arranged for the placing and recovery of the test piece at the SIO pier.
Comments may be directed to the author:
Jim Easton, PE
P.O. Box 889
Bonita, CA 91908-0889