Interconnection Standards

Summary

Note: Wisconsin has adopted revised interconnection rules, effective May 1, 2024. The revised rules adopt the most recent equipment standards for DG systems and inverters (IEEE Std. 1547 and UL 1741). Energy storage systems are required to be UL 9540-listed.

In February 2004, the Wisconsin Public Service Commission adopted interconnection standards for distributed generation (DG) systems up to 15 megawatts (MW) in capacity. All investor-owned utilities (IOUs) and municipal utilities are required to abide by the standard provisions. Electric cooperatives are encouraged -- but not required -- to adopt the state standards. The rules categorize DG systems by capacity and provide for several levels of interconnection review, as follows:

• Category 1: 20 kilowatts (kW) or less
• Category 2: larger than 20 kW, but no larger than 200 kW
• Category 3: larger than 200 kW, but no larger than 1 MW
• Category 4: larger than 1 MW, but no larger than 15 MW

The PSC has published two sets of standard forms for interconnection, available on the program web site. One set pertains to systems smaller than 20 kW while the second set applies to larger systems up the maximum size of 15 MW. The Wisconsin Distributed Resources Collaborative (WIDRC) has published a set of interconnection guidelines that offer some additional details on the interconnection process.

Generally speaking, Wisconsin's interconnection requirements become more stringent as the system size increases. The rules apply to all public utilities. The 20-kW dividing line between Category 1 and Category 2 installations corresponds to the maximum individual system capacity allowed under the state's net metering rules. Systems that qualify for net metering are not considered commercial ventures that require commercial liability insurance.

Minimum liability insurance of at least $300,000 per occurrence is required for systems 20 kW and smaller (Category 1) with higher amounts for larger systems based on the category of review under which they fall. However, the law also permits applicants to prove financial responsibility using a negotiated agreement with the utility in lieu of the insurance requirements. Additionally, Category 2-4 facilities must name the utility as an additional insured party in the insurance policy.