1. Introduction

An electricity interconnector is a transmission facility that connects the electricity systems of two jurisdictions or bidding zones and permits cross-border electricity flows. Interconnectors may be submarine cables, overhead lines, underground cables, or combinations of these technologies.

Because interconnectors are critical infrastructure, their availability and the legal consequences of their outages are important questions of energy law. An outage can reduce cross-border transfer capacity, create congestion, increase electricity prices, disrupt renewable-energy exports, and potentially threaten system security.

An interconnector availability and outage-liability framework therefore attempts to answer five basic questions:

What level of availability must the interconnector operator maintain?

Who decides when an interconnector may be taken out of service?

Who bears the economic consequences of an outage?

When must market participants be compensated for lost transmission capacity?

When is the operator protected from liability because the outage resulted from force majeure, emergency action, or circumstances outside its reasonable control?

European electricity law provides particularly useful examples because cross-border capacity is governed by EU internal-market rules, national regulation, transmission-system-operation rules and contractual arrangements.

2. Meaning of Interconnector Availability

Availability refers broadly to the extent to which an interconnector's technical transfer capability is capable of being used for electricity transmission.

Availability can be measured through concepts such as:

total hours available;

percentage of technical capacity available;

firm transmission capacity;

planned outage hours;

unplanned outage hours;

forced-outage rate;

derated capacity;

restoration time; and

availability during critical system conditions.

For example, an interconnector rated at 1,000 MW may technically remain operational while only 500 MW is available because of a cable fault, converter limitation or security constraint. Thus, availability is not necessarily equivalent to physical operation.

3. Legal Sources of Availability Obligations

Interconnector availability is normally governed by a combination of:

A. Primary legislation

National electricity legislation establishes:

transmission licensing;

regulatory powers;

duties of transmission operators;

security-of-supply obligations;

market-access rights; and

enforcement mechanisms.

B. EU or regional electricity legislation

For European interconnectors, cross-border electricity legislation establishes principles concerning:

access to interconnection capacity;

congestion management;

non-discriminatory access;

capacity allocation;

security of supply; and

compensation for certain curtailments.

C. Regulatory licences

The interconnector operator may be required to comply with:

availability standards;

maintenance requirements;

outage reporting;

restoration requirements;

operational-security rules; and

regulatory information obligations.

D. Grid codes and operating rules

Technical rules determine when an interconnector can be operated safely and when it must be disconnected.

E. Commercial agreements

Interconnector operators and market participants may also be subject to:

capacity contracts;

connection agreements;

transmission agreements;

balancing agreements;

allocation rules; and

market-coupling arrangements.

Consequently, outage liability is rarely determined by one legal instrument.

4. Planned and Unplanned Outages

A fundamental distinction is between planned outages and forced outages.

Planned outage

A planned outage occurs when an operator deliberately removes an interconnector from service for purposes such as:

maintenance;

inspection;

replacement;

testing;

upgrades;

repairs; or

safety work.

Operators generally have greater legal protection where the outage is properly scheduled and notified.

However, planned maintenance does not mean that the operator has unlimited discretion. Regulatory rules may require:

advance notification;

coordination with neighbouring TSOs;

minimisation of outage duration;

publication of available capacity; and

consideration of market and system-security effects.

Forced outage

A forced outage results from an unexpected event such as:

cable failure;

converter failure;

transformer failure;

fire;

extreme weather;

equipment malfunction;

accidental damage;

cyber incident;

external infrastructure damage; or

system-security events.

The liability consequences are usually more complicated because the operator's responsibility depends upon the cause and contractual allocation of risk.

5. The Principle of Maximum Available Capacity

One of the important principles of European electricity law is that available cross-border capacity should be made available to market participants subject to secure network operation.

The Court of Justice has considered rules requiring the maximum capacity of interconnections and networks affecting cross-border flows to be made available, while recognising the need for secure network operation. (EUR-Lex)

This produces an important legal balance:

Market-access principle + system-security limitation.

The operator cannot simply withhold interconnection capacity for commercial convenience, but it may restrict capacity where necessary to maintain secure network operation.

6. Curtailment and Compensation

A particularly important aspect of outage liability concerns curtailment.

Curtailment occurs when transmission capacity that has already been allocated to market participants is subsequently reduced or withdrawn.

Under EU cross-border electricity rules, transaction-curtailment procedures are intended for emergency circumstances where rapid TSO action is required and redispatching or countertrading is not possible. The rules also provide that, except in cases of force majeure, market participants whose allocated capacity is curtailed must be compensated. (EUR-Lex)

This creates a significant liability distinction:

Thus, outage does not automatically create liability, but neither does the label "outage" automatically protect the operator.

7. Force Majeure

Force majeure is one of the most important concepts in interconnector outage liability.

Typical force-majeure events may include:

extraordinary natural disasters;

exceptionally severe storms;

earthquakes;

war;

certain governmental actions;

unforeseen external damage; and

other events beyond reasonable control.

However, whether an event constitutes force majeure depends upon the applicable legal instrument or contract.

The central questions normally include:

Was the event unforeseeable?

Was it outside the operator's control?

Could reasonable preventive measures have avoided the event?

Could the consequences have been mitigated?

Did the operator comply with notification requirements?

A failure to maintain equipment properly should not automatically become force majeure merely because the eventual consequence was unexpected.

8. Operator Negligence and Maintenance Liability

An interconnector operator may potentially incur liability where an outage results from:

inadequate maintenance;

failure to inspect equipment;

failure to replace defective components;

failure to comply with technical standards;

inadequate emergency preparedness;

failure to follow operating procedures; or

failure to notify affected parties.

The precise remedy depends upon the regulatory and contractual framework.

Possible consequences include:

compensation;

contractual damages;

regulatory penalties;

licence enforcement;

corrective orders;

increased monitoring;

loss of permitted revenue; or

reputational and investment consequences.

An important legal principle is that strict liability should not automatically be assumed. Electricity infrastructure is technically complex and some failures occur despite reasonable maintenance.

9. Distinguishing Physical Outage from Market Liability

An important analytical distinction is:

Physical liability

This concerns the physical failure of the interconnector.

Example:

A submarine cable breaks and electricity cannot physically flow.

Market liability

This concerns the consequences for market participants.

Example:

Traders purchased transmission capacity but subsequently lost the ability to use it.

Regulatory liability

This concerns breach of statutory or licence obligations.

Example:

The operator failed to comply with required outage-reporting rules.

Contractual liability

This concerns obligations established through agreements.

Example:

An interconnector operator failed to comply with a contractual availability guarantee.

These four forms of liability can exist independently.

10. Case Law: Aquind Ltd v ACER

A particularly relevant modern case is Aquind Ltd v European Union Agency for the Cooperation of Energy Regulators (ACER).

The dispute concerned the proposed Aquind electricity interconnector between Great Britain and France. Aquind sought an exemption from certain EU electricity-market requirements because of the investment risks associated with the project.

In 2023, the Court of Justice in Case C-46/21 P, ACER v Aquind Ltd upheld the General Court's conclusion concerning the proper intensity of review by ACER's Board of Appeal. The Court emphasised that the Board of Appeal had to conduct an appropriate review of ACER's decision concerning the proposed interconnector rather than merely applying a manifest-error standard. (EUR-Lex)

Although this was not an outage case, it is important to interconnector liability law because it demonstrates that:

interconnector regulation involves significant economic risk;

exemptions can affect the allocation of investment risk;

regulatory decisions concerning interconnectors are subject to judicial review; and

regulatory authorities must apply the applicable legal criteria properly.

11. Aquind v ACER — 2025 Liability Decision

The later Aquind Ltd v ACER, Case T-342/23, decided by the General Court on 11 June 2025, is particularly interesting from a liability perspective.

Aquind sought damages from ACER, alleging unlawful acts and omissions relating to the proposed interconnector.

The General Court reiterated the established principles of EU non-contractual liability: generally, the claimant must establish:

unlawful conduct;

actual damage; and

a causal relationship between the unlawful conduct and the damage.

The Court also considered the requirement that the breach involve a rule intended to confer rights on individuals and be sufficiently serious. (EUR-Lex)

The case is useful for understanding interconnector outage and availability liability because it demonstrates that economic loss associated with an interconnector does not automatically translate into compensable legal damage.

There must be a legally recognised breach and a sufficient causal connection.

12. Significance of the Aquind Cases

The Aquind litigation establishes an important conceptual distinction.

Investment risk

Risk that a proposed interconnector will not receive the necessary regulatory approvals or exemptions.

Operational risk

Risk that an operational interconnector will suffer outages or capacity reductions.

Regulatory risk

Risk arising from decisions of regulators or public authorities.

These risks should not automatically be transferred to consumers, TSOs or regulators.

The contractual and statutory framework must identify who bears each category of risk.

13. Inter-TSO Compensation and Cross-Border Costs

Interconnector availability also intersects with inter-transmission-system operator (ITC) compensation.

ACER monitors the ITC mechanism and has identified issues involving the treatment of electricity losses and cross-border flows. ACER has also recommended improvements to the treatment of infrastructure compensation and cross-border cost allocation. (Acer Europe)

This demonstrates that cross-border electricity regulation is not simply about deciding whether an interconnector works. It also involves allocating:

network costs;

losses;

congestion effects;

infrastructure investment;

cross-border externalities; and

compensation.

14. Availability Guarantees

Modern interconnector agreements can incorporate contractual availability guarantees.

For example, a contract could provide:

The operator shall maintain 98% annual technical availability, excluding specified force-majeure events and authorised maintenance.

The agreement could then provide a financial adjustment for availability below the guaranteed level.

A sophisticated availability regime might distinguish:

planned maintenance;

emergency maintenance;

force majeure;

operator negligence;

transmission-system emergencies;

third-party damage;

grid-security restrictions.

This produces a more predictable allocation of risk.

15. Liability Caps

Interconnector contracts frequently need to address the potentially enormous economic consequences of an outage.

Suppose an interconnector has a capacity of 2 GW. If it becomes unavailable during a period of extreme price differences between two markets, the economic losses could become very large.

Consequently, agreements may include:

aggregate liability caps;

per-event caps;

exclusions of consequential loss;

exclusions for lost profits;

liquidated damages;

availability credits; and

insurance requirements.

However, a contractual limitation may be subject to mandatory statutory and regulatory rules.

A contract cannot necessarily exclude liability for every form of regulatory breach or intentional misconduct.

16. Insurance as an Outage-Liability Mechanism

Interconnector owners may use insurance to manage risks including:

equipment breakdown;

marine cable damage;

business interruption;

construction risks;

natural disasters;

third-party liability; and

political risks.

Insurance does not eliminate legal liability. Instead, it reallocates the financial consequences of certain risks from the project company to an insurer.

17. Emergency Outages

Emergency outages create a special legal category.

A TSO may have to disconnect an interconnector immediately because continued operation could:

destabilise the grid;

violate thermal limits;

create unacceptable voltage conditions;

threaten system frequency;

worsen a cascading failure; or

endanger system security.

In such circumstances, maintaining physical availability cannot take priority over system security.

European system-operation practice emphasises coordinated remedial action and security of interconnected systems. For example, an ENTSO-E/ACER investigation into a 2021 Polish system incident highlighted rapid remedial action and neighbouring-TSO cooperation as important to maintaining the interconnected European system within security limits. (ENTSOE)

Therefore:

Availability obligations are normally subordinate to legitimate system-security requirements.

18. Regulatory Reporting Obligations

An effective framework should require an interconnector operator to report:

commencement of outage;

cause;

expected duration;

affected capacity;

restoration progress;

actual restoration time;

whether force majeure is claimed;

remedial action taken; and

final root-cause analysis.

Transparency is particularly important because an outage can affect prices and cross-border trading.

Failure to provide accurate outage information may itself constitute a regulatory violation even where the underlying equipment failure was not the operator's fault.

19. Regulatory Oversight

National regulators may monitor interconnector availability through:

performance indicators;

outage statistics;

maintenance records;

incident investigations;

compliance audits;

market monitoring; and

enforcement proceedings.

Where an interconnector operates between two jurisdictions, regulatory cooperation becomes essential.

The relevant regulators may need to determine:

which authority investigates;

which law applies;

which regulator imposes penalties;

how compensation is calculated; and

how disputes between operators and market participants are resolved.

20. Cross-Border Jurisdiction

A cross-border interconnector creates difficult jurisdictional questions.

For example:

A cable connects Country A and Country B, but the cable is damaged in the territorial waters of Country B while the market participant affected by the outage is located in Country A.

Potentially relevant legal systems include:

the law governing the interconnector licence;

the law governing the capacity contract;

the law of the place where the damage occurred;

international maritime law;

national electricity law; and

regional electricity-market law.

Therefore, contracts should contain carefully drafted provisions concerning:

governing law;

jurisdiction;

arbitration;

dispute escalation;

regulatory cooperation; and

emergency procedures.

21. Core Elements of a Strong Liability Framework

An effective interconnector availability framework should contain at least the following:

22. Relationship Between Availability and Energy Security

Interconnector availability is increasingly connected with energy security.

Interconnectors can:

diversify electricity supply;

provide emergency imports;

facilitate renewable-energy exports;

reduce dependence on domestic generation;

support balancing;

integrate geographically dispersed renewable resources; and

increase system resilience.

Conversely, prolonged interconnector outages can reduce these benefits.

This creates a regulatory tension:

Higher availability requirements → potentially higher infrastructure costs.

Lower availability requirements → potentially greater reliability and market risks.

Energy regulators therefore need to balance reliability, affordability, investment incentives and system security.

23. Legal Principles Emerging from the Case Law

The available case law supports several broader principles.

Principle 1: Interconnector regulation involves substantial economic interests

The Aquind litigation demonstrates that regulatory decisions concerning interconnectors can have significant consequences for project financing and expected revenues. (EUR-Lex)

Principle 2: Regulatory discretion is not unlimited

Regulatory bodies must apply the legal framework correctly and their decisions can be judicially reviewed. The 2023 Aquind judgment is particularly relevant here. (EUR-Lex)

Principle 3: Economic loss alone does not establish public-law liability

The 2025 Aquind judgment illustrates that unlawful conduct, actual damage and causation must be established before EU non-contractual liability can arise. (EUR-Lex)

Principle 4: Market participants can have compensation rights following capacity curtailment

EU cross-border electricity rules recognise compensation for certain curtailments, subject to exceptions including force majeure. (EUR-Lex)

Principle 5: System security remains fundamental

The legal framework permits operational restrictions where necessary for secure network operation. (EUR-Lex)

24. Conclusion

Interconnector Availability and Outage Liability Frameworks constitute an important part of modern electricity law because interconnectors sit at the intersection of infrastructure regulation, electricity markets, investment law and energy security.

A comprehensive framework should not simply impose an absolute obligation to keep an interconnector operating. Instead, it should establish a structured allocation of risk between:

interconnector owners;

transmission system operators;

regulators;

market participants;

consumers;

insurers; and

governments.

The central legal distinction is between ordinary operational failure, operator fault, legitimate system-security intervention, and force majeure. Each category can produce different consequences for compensation and liability.

The Aquind cases are particularly useful for understanding the wider legal environment surrounding interconnectors. ACER v Aquind (C-46/21 P) demonstrates the importance of meaningful regulatory review, while Aquind v ACER (T-342/23) illustrates the stringent requirements for establishing public-law damages and causation. (EUR-Lex)

Ultimately, the strongest legal framework is one that combines high availability standards, transparent outage reporting, clearly defined compensation rules, carefully limited force-majeure protections, appropriate liability allocation, and effective cross-border regulatory coordination.