Modification Proposal 0222 - Amendment of IUK’s Minimum Wobbe Limit Transmission Workstream 4th September 08

Background The Wobbe Index of a unit of gas provides a measure of the energy released during combustion GS(M)R limits the range of Wobbe Index that National Grid can accept into the NTS to between 51.41 and 47.20 MJ/m3 for safety reasons Site specific limits to Wobbe Index are detailed in Network Exit/Entry Provisions The Wobbe Limits set out in IUK’s Network Entry & Exit Provisions are more stringent than the GS(M)R limits IUK have raised concerns that this is constraining the amount of gas that can enter or exit the NTS at the continental interconnector

Modification Proposal 0222 Proposal 0222 seeks to lower the minimum Wobbe Limit set out in IUK’s Network Entry & Exit Provisions to the GS(M)R limit of 47.20 MJ/m3 Benefits: A wider selection of gas would be available from Europe Security of supply would be enhanced Competition between ASEPs would be increased Analysis shows that CV shrinkage would not be impacted No UNC text modifications would be required