SONI is Northern Ireland’s independent Transmission System Operator. Customers should note that SONI does not buy or sell electricity, but facilitates the connection of generation and large scale demand customers to the Transmission System.

We aim to deliver a reliable and efficient service to our customers. We define a customer as anyone to whom we provide a service. This includes all Demand customers, Renewable Generators and Conventional Generators who are connected to the Transmission System, Suppliers, Stakeholders and all other interested parties.

For all general enquiries please contact

Connection queries:

Supplier queries:

Interconnector queries:

Customer Complaints Procedure

In spite of our best efforts to provide a high quality service at all times, there may be occasions when the service provided does not meet the high standards that we set out for ourselves or that you as a customer might reasonably expect. It is always our intention to deliver a high standard of service to our customers. If, however, you feel that we have not performed to your satisfaction, please contact us and we will be happy to investigate the matter with the aim of quickly finding a resolution.

To make a customer complaint, please follow the complaints procedure below by contacting our Customer Relations Team.

Phone: 02890 707525


Write to: Customer and Stakeholder Relations, SONI, Castlereagh House, 12 Manse Road, BT6 9RT.

To help us resolve your complaint as quickly as possible please give us as much information as you can when you contact us. Our Customer Relations Team will make every effort to resolve the matter there and then and if unable to resolve, the team will refer it to refer it to the SONI Managing Director.

When we receive your complaint we will do the following:

  • Write to you within five working days to acknowledge we have received your complaint;
  • We will always deal with your complaint as quickly as we can. However, if we are unable to solve or settle your complaint within two weeks of receipt, we will write to tell you the progress we have made and when we aim to send you a full response;
  • If we cannot solve or settle your complaint within four weeks of receiving it, we will write to you and explain why and will tell you when we expect to be able to do so, if at all; and
  • If at any stage you are not satisfied with our action or explanation, you can ask for us to refer your complaint to the SONI Managing Director.

You can get in touch with us via this page.