The US general recommendation GR-1089-CORE, Issue 6 allows two different surge generators to be used for differential (metallic) Intra-Building surge testing of up to 2 pairs per port. One can use either a <2/>10 generator (Table 4-2 test #8) or a 1.2/50-8/20 generator (Table 4-2 test #10). Both generators are set to 800 V peak open circuit voltage and 100 A peak short circuit current. In the actual test situation these generators are not equivalent, the <2/>10 generator being the most stressful. To be equivalent for the times that matter the 1.2/50-8/20 generator needs to be increased in surge level. An ATIS document in development is proposing to extend the dual generator approach to cover 4 pairs for 4 pair Ethernet applications.