EREC G99 and EREC G59: What are the differences and what does it mean for your generator?

9 Jan 2019
EREC G99 and EREC G59: What are the differences

Are you developing a grid connected generation project rated at 50kW or above? Engineering Recommendation (EREC) G99 applies to you!

EREC G99 was issued in July 2018, by the Energy Networks Association (ENA), following the assimilation of the EU Commission Regulation on harmonising network standards, known as Requirements for Generators (RfG), into GB Distribution and Grid Codes. It has been written to comply fully with RfG as well as including other requirements for connecting into the GB Power System.

It encompasses and replaces the long serving EREC G59 with changes to the application process, compliance requirements and commissioning requirements. G99 generators will need to be aware of the new process and requirements.

With regards to the connection application form, the ENA states that;

Whilst the old G59 application form may be used for connection applications where the connection is required before 27 April 2019, the new G99 Standard Application Form should be used for all connection applications where the connection is required on or after 27 April 2019. Please note that the ENA G99 Standard Application Form will be the only form that can be used after 27 April 2019 and the G59 Standard Application Form will be no longer accepted.

G99 alters how generators are classified and therefore affects how different types (MW rating, technology type, location) or configurations (power park modules/power generating modules/power generating facility) must demonstrate compliance.


Connection Voltage

Rated Capacity



0.8kW - 1MW



1MW - 10MW



10MW - 50 MW




The scale of requirements increases from A – D; Type A Generators will see minimal difference in how they are treated. Larger generators (Types B, C and especially D) will require:

  • Further early – stage analysis to demonstrate compliance;

  • An expanded commissioning/notification process (similar to that used by National Grid Electricity System Operator);

  • More planning and coordination with network owners and operators.

Not understanding or preparing for the changes may result in a generator facing delays and/or design challenges before connection to the network is approved. To minimise the risk of significant project costs or programme delays, the new requirements must be addressed from the outset.

From generator applications through to compliance verification, system studies, design and commissioning, TNEI can help you understand the changes and how they will impact on your project.

TNEI are offering G99 training courses throughout 2019. Please get in touch to find out more and to book your place. 

For more information please contact Callum Dell or any of our grid connection experts.

[*] Any generator connecting at 110kV or higher is classified as Type D regardless of rated capacity.

Key contact

Jonathan Oguntona

Jonathan Oguntona

Senior Consultant and Grid Connections Lead

Jonathan is a Senior Consultant and Grid Connections Lead with 10 years’ experience working as an electrical engineer and grid connection specialist. Jonathan has experience managing the delivery of grid connections for onshore wind, large biomass and battery energy storage projects within the UK. He has also overseen the delivery and construction of Contestable Works. He also has significant experience in power systems analysis specifically providing power quality grid compliance studies (P28 &Harmonics). Jonathan has good communication skills and has provided technical, commercial and regulatory advice to clients. He has significant project management experience, and a pragmatic approach to problem solving.