PPS Group and IPB Communications join the five incumbents, which have all been reappointed to the fresh two-year framework.
They include JBP, which PRWeek understands appealed successfully in February for the selection process to be re-run when it failed to make the first cut of 50 agencies (PRWeek, 1 March).
The others are Camargue, Grayling, Local Dialogue and Copper Consultancy, which was known as 3G Communications until it merged with Sauce Consultancy.
National Grid uses the roster to allocate comms work engaging with local communities for projects such as building connections to the electricity and gas networks from new power stations, and dealing with contaminated former gasworks sites.
Head of UK regional media relations Stewart Larque said the roster had been expanded because National Grid would be increasing the volume of work it would be undertaking on the electricity network.
'Given the amount of work we have to do over the coming years, we thought there was scope to bring in some new faces and get a bit more flexibility,' he said.
PPS, Grayling and Copper are the only agencies that qualified for all six regional lots: Scotland, Wales, and the North, South, East and West of England. Cheshire-based IPB Communications qualified for the North of England.
JBP qualified for Wales and the South, East and West of England, where it worked under the last framework, according to managing director Liam Herbert.
Herbert, who declined to confirm the agency had appealed, said: 'National Grid is a very big client for us and we have worked for it for 18 years.'
Larque said: 'One of the agencies raised a concern about the way one of the questions had been put. We clarified that and re-ran that part of the process.'