Maximum allowable resistance in solar PV racking system

[nagyvary]

I work for a leading solar racking manufacturer. We regularly get asked questions regarding how many grounding lugs are required for a given racking system design.

The ground path continuity test of UL2703 states a maximum resistance of 0.1 Ohm as a pass/fail criteria during certification testing. If we have a large block of PV modules on a racking system, and this racking is all electrically interconnected, we certainly have the potential to exceed the 0.1 Ohm resistance value from the UL2703 test requirements.

My question is, how is this potential issue of high resistance addressed in the NEC code requirements? Is there a limit (max allowable resistance) on how many PV racks can be connected together before running an individual ground cable for that particular racked block of PV modules?

Thank you for any clarification you may be able to offer. Typically we stay clear of providing electrical design guidance for our racking product, however it does become important to us in that we provide a certain # of grounding lugs to interconnect various blocks of racked modules together. Your information may help us to provide guidance in this matter.

 

[GoldDigger]

Thank you for any clarification you may be able to offer. Typically we stay clear of providing electrical design guidance for our racking product, however it does become important to us in that we provide a certain # of grounding lugs to interconnect various blocks of racked modules together. Your information may help us to provide guidance in this matter.

If microinverters are used, they will provide a direct GEC connection at each one as well as bonding to the panel or rack and so you would not have to worry.
The limit on interconnected racking would probably depend on how many rail-to-rail joints were crossed. A reasonable first guess would be one ground lug for each separate set of horizontal rails used in putting the racking together. How that relates to number of panels depends on design, including whether the panels are mounted portrait or landscape.
What are the maximum and minimum rail lengths in your system?