By 1986, the company had grown to be included among the S&P 500 list of 500 of the largest companies in the United States. By that time it had accumulated nearly $1.2 billion in long-term debt. NSP served the agriculturally-based region of its headquarters state of Minnesota, and also the neighboring states of North Dakota and South Dakota to the west. These territories were served through its subsidiary, NSP-Minnesota.
On May 28, 1996 NSP voted to split its stock two-for-one. It paid an annual 6.5% dividend yield.
NSP operated in Wisconsin to the east as well, as early as 1986.
By 1995, its other wholly-owned subsidiary, NSP-Wisconsin, served that territory, and had also added the northern neighboring Upper Peninsula of Michigan, bounded between Lake Michigan and Lake Superior.
By the end of 1995, NSP had reduced its debt to US$1.5 billion.
At that time, Richard A. Abdoo, served as Chairman, President and Chief Executive Officer of Wisconsin Energy. James J. Howard served in the same positions with Northern States Power. With the new Primergy Corporation, Howard would become Chairman and CEO, and Abdoo would serve as Vice Chairman, President and Chief Operating Officer. Further, with Howard scheduled to retire in July 2000, Abdoo would then succeed him as Chairman of Primergy.
Wisconsin Energy's two then-existing utility subsidiaries, Wisconsin Electric Power Company (WEPCO) and Wisconsin Natural Gas Company (WNG) were to be consolidated under a new subsidiary name, Wisconsin Energy Company. Under that name, it and Northern States Power Company would continue to operate as the two principal subsidiaries of Primergy Corp. Also, NSP-Wisconsin would merge into the operating subsidiary Wisconsin Energy Company. The headquarters of the two utilities would remain distinct and separate in their existing respective state locations, in Milwaukee, Wisconsin and NSP's in Minneapolis, Minnesota. Primergy headquarters were to be incorporated in Wisconsin, but located in Minneapolis. The Primergy board of directors were to be equally split, composed of six from each company. The merger deal was expected to be completed in the fourth quarter of 1996.
By 1997, approvals had been granted by the state regulatory commissions in Michigan and North Dakota, but not by the commissions in Minnesota and Wisconsin. Approvals from the Securities & Exchange Commission and the U.S. Department of Justice were still pending.
On May 16, 1997 both CEOs announced that the boards of directors of both companies had voted that day to terminate the merger plan. Howard stated that the problem was that the regulatory agencies were changing their merger policies as they were considering the companies' filing. In particular, Howard blamed the Federal Energy Regulatory Commission, which had issued a decision earlier in the week remanding the case back to the companies, for further negotiation among themselves. "There is simply no end to this process in sight," stated Howard. Abdoo said the decision to end the merger factored in that after two years of already waiting, the further likely wait of at least six months of delay would significantly reduce the benefits of the Primergy transaction.
The delay had put the merger five months behind schedule and had reduced earnings for both utilities by a total of US$58 million to that point, costs which had not been passed on to consumers. Adding to the discomfort was a growing gap between the performance of the two companies by early 1997. Wisconsin Energy's stock had by then fallen about 13% since early 1995 when the deal had been announced, due to other ongoing problems that had developed within the company, including issues with its Point Beach Nuclear Generating Station in Manitowoc County, Wisconsin. But Northern States Power's stock had risen by 6%. The case was considered to be a bellwether in the utilities industry, putting an end to the rapid pace of mergers and acquisitions that had been ongoing up to then.