CRU Decision on MPID 345: Fault Ride Through, Demand Caps and a 27 October Deadline

Key Takeaways

• What has been decided: the CRU has approved MPID 345 and endorsed EirGrid’s Compliance and Derogation Framework with amendments.
• Who is affected: all current and future transmission-connected Demand Facilities and not only data centres. Distribution-connected facilities are not covered but ESB Networks intends to propose a related Distribution Code modification.
• When it applies: the modification takes effect five weeks from the Decision, on 27 October 2026.
• What to do now: facilities that cannot yet comply should report their non-compliance to EirGrid and request a derogation before the effective date.

On 22 September 2026 the Commission for Regulation of Utilities (“CRU”) published its decision (CRU2026145) approving Grid Code Modification MPID 345: Fault Ride Through, Rate of Change of Frequency and Post Fault Active Power Recovery for Demand Facilities (the “Decision”).

Background: The FRT Problem

Faults on the transmission system are common and are usually isolated very quickly, with voltage recovering to its normal range within around 100 milliseconds. Most grid users ride through them but data centres generally do not. To protect their IT systems they cut their grid import and switch to back-up supply, even when the fault is far away. They can then take some time to return to normal demand. When many sites react this way at the same time, the sudden drop in demand unbalances the system and causes frequency deviations across the island. To manage this risk, EirGrid and SONI have set a 900 MW Load Rejection Limit. This is the largest sudden loss of large energy user and interconnector demand that the all-island system can securely accommodate and it equates to around 1,000 MW of data centre demand. 

What MPID 345 Requires

MPID 345 adds three technical requirements for every existing and future transmission-connected Demand Facility:

1. Fault Ride Through (FRT): a facility must stay connected and operate stably during and after a fault while the voltage at its connection point remains within the specified voltage-against-time profile.
2. Rate of Change of Frequency (RoCoF) robustness: the ±1 Hz/s RoCoF standard that already applies to generators now extends to Demand Facilities.
3. Active Power Recovery (APR): once the fault has cleared and voltage has recovered to 0.9 per unit, a facility must restore at least 90% of its pre-fault active power within 500 milliseconds.

Compliance is measured at the point of connection based on the facility’s aggregate response rather than individual loads or equipment. Behind-the-meter technology such as a co-located Battery Energy Storage System (BESS) can therefore form part of a compliance solution, subject to EirGrid’s assessment. The CRU rejected requests for a longer or staged recovery period for existing facilities and accepted the view of EirGrid and TNEI Ireland (“TNEI”), which carried out an independent technical review for the CRU, that 500 milliseconds is necessary.

The Compliance and Derogation Framework

The CRU accepts that most existing transmission-connected Demand Facilities cannot comply immediately. EirGrid’s framework provides a route to compliance over time and treats data centres and other facilities differently to reflect their different behaviour during past fault events. There are three derogation routes:

• Data centre group process: for data centres connected or connecting before the end of 2026. It offers streamlined assessment within set timelines and a 24-month derogation. A Demand Utilisation Threshold (“DUT”) applies from the effective date, a compliance plan is due within six months and status reports are due every three months.
• Non-data centre group process: for other facilities connected or connecting before the end of 2026. There is no DUT, the derogation runs for five years (up from two), a compliance plan is due within 12 months and status reports are due every three months.
• Standard (non-group) process: open to all Demand Facilities. There are no set processing timelines and the facility is treated as non-compliant until a derogation is granted. A DUT can still be imposed under this route so it is not a way to avoid one.

How DUTs work. A DUT caps the monthly average demand that a data centre may draw for its non-compliant load. Each site's DUT is its highest monthly average demand in 2025, plus a pro-rata share of any remaining headroom that the system can securely accommodate. Peaks of up to 10% above the DUT are permitted without prior approval, provided the monthly average stays within the cap; larger peaks need EirGrid's prior written approval. Exceeding the monthly average, or the DUT plus 10% threshold without approval (even accidentally), is a breach of the derogation conditions and therefore of the Grid Code. DUTs will be calculated and monitored using metering data rather than SCADA data, which the CRU has confirmed will change DUT estimates for all customers.

Key Changes from the Consultation

The final Decision largely follows TNEI’s recommendations and departs from the original proposals in several ways:

• Data centre compliance plans: deadline extended from three to six months after the effective date for both group and non-group applications.
• Non-data centre compliance plans: the 12-month deadline originally proposed for the group process now applies to all non-data centre applications including non-group applications.
• Non-data centre group derogations: extended from two to five years. The data centre group derogation remains at 24 months.
• Portfolio approach: the proposal to manage DUTs across multiple sites owned by the same parent company has been dropped.
• DUT data source: metering data replaces the proposed SCADA-based methodology.
• 10% peak allowance: subject to ongoing monitoring and may be revised by EirGrid if it creates system security risks.

Future Considerations

EirGrid must report to the CRU quarterly from the end of December 2026 on its roadmap to remove the operational constraints used to manage FRT risk, the cost of those measures, updated modelling and progress on compliance. It must also set a timeframe for that roadmap within five weeks of the Decision. An FRT Implementation Working Group will support demand customers working towards compliance and is expected to meet first in November 2026. An equivalent modification has been approved in Northern Ireland by the Utility Regulator and ESB Networks intends to propose a Distribution Code modification for distribution-connected facilities.

Next Steps for Data Centres

MPID 345 takes effect on 27 October 2026. Facilities that cannot yet demonstrate compliance should:

• Report their non-compliance to EirGrid and submit a derogation request under the appropriate route before the effective date;
• Weigh up the group and non-group routes, bearing in mind that non-group applications may not be assessed before the effective date and that a DUT can apply under either route;
• Assess the operational and commercial impact of any DUT, including on customer service level agreements and third-party contracts;
• Prepare to deliver a compliance plan within six months (data centres) or 12 months (non-data centres) of the effective date; and
• Submit their compliance self-assessment to EirGrid in good time: a facility is treated as compliant only once EirGrid has confirmed this in writing.

Conclusion

MPID 345 turns fault ride through from emerging good practice into a binding Grid Code obligation for large energy users. For data centres in particular, the DUT means that any delay in achieving compliance will translate directly into constrained growth. Early engagement with EirGrid, a realistic compliance plan and a clear view of the commercial impact of any DUT will be essential.

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