PSTN Cessation & Electricity Utilities: Protecting Vital Systems

Introduction

The UK’s PSTN switch-off is often framed as a voice migration programme. For electricity utilities, it is more accurately understood as a resilience challenge: one that directly affects substations, telemetry, alarms, and operational communications during the fault conditions when they matter most.

With analogue stop-sell already in effect and full withdrawal confirmed for 31 January 2027, electricity network operators should treat PSTN migration as an urgent operational resilience programme. Any remaining dependence on line-powered copper creates a single point of failure that will disappear; and un-audited “hidden lines” increase the risk of silent alarm or telemetry failures[1][2].

This is not a theoretical risk. Ofcom has reported a rise in significant PSTN resilience incidents, and UK Government guidance notes that 2024/25 saw over 2,600 major PSTN incidents. That combination; an ageing network plus a hard deadline, is why utilities need a structured, site-by-site migration plan now[4][3].

Did you know? Stop Sell already in effect. Openreach’s UK-wide WLR Stop Sell began on 5 September 2023. In most scenarios, new analogue (WLR/PSTN) services can no longer be ordered, so migration plans need to focus on futureproof replacements [1].

Where PSTN still exists in electricity networks

Despite ongoing digitalisation, PSTN and ISDN lines remain embedded across many electricity environments, including:

Substations and grid infrastructure: legacy RTUs/telemetry, dial-up modems, and alarm panels tied to copper lines.
Depots, control buildings, and offices: lift emergency phones, paging, and critical voice endpoints not yet migrated to IP.
Field operations: remote switching sites, environmental sensors, and ancillary monitoring that still relies on analogue signalling.
Safety and compliance systems: site alarms that escalate via PSTN because “it has always worked”.

Why PSTN switch-off introduces real operational risk

Electricity networks depend on visibility and communications to manage faults quickly and safely. PSTN cessation increases risk in three ways:

Loss of telemetry and alarms at remote sites, reducing fault localisation and extending time-to-repair.
Disruption to operational voice at the moments you most need coordination (storm response, network reconfiguration, restoration activity).
Reduced confidence in grid restoration and restart readiness if critical sites cannot reliably communicate when primary infrastructure is degraded.

Power resilience matters: Traditional analogue lines were line-powered, which is why voice and alarm circuits often kept working during local power loss. Digital voice and IP-based connectivity require local power, so migration plans should include battery-backed power (UPS or equivalent) for the router/voice layer at priority sites.

When communications fail: lessons from real incidents

On 20 March 2025, a power outage at the North Hyde 275 kV electricity substation near Heathrow led to the loss of supply to over 70,000 domestic and commercial customers, including Heathrow Airport. It is a clear reminder that localised infrastructure failures can cascade quickly; and that restoration depends on dependable communications[5].
On 28 April 2025, the power systems of Spain and Portugal experienced a major blackout that disrupted transport, payments, and telecommunications and left millions without power. Regardless of root cause, the operational lesson is consistent: if communications and control systems cannot respond quickly, impacts escalate.

From PSTN to digital voice: the role of CSL VoiceLink

Many electricity sites still need simple, dependable voice, and not necessarily a full unified communications project. CSL VoiceLink is designed to bridge that gap by converting PSTN calls to 4G VoLTE, allowing existing analogue-dependent devices and workflows to continue operating after PSTN withdrawal.

VoiceLink also includes a built-in battery backup to help maintain voice availability during short power interruptions, supporting the broader resilience requirement.

For utilities, the value is straightforward: retain essential voice at unmanned substations and remote sites, while modernising the underlying connectivity platform.

VoiceLink

Why “multi-network” isn’t enough on its own

Many solutions describe themselves as ‘multi-network’, but rely on roaming arrangements that can still fail when a local mast, backhaul, or core service degrades. Resilience is achieved through independence and active switching, not often misunderstood industry terms or marketing labels.

CSL’s approach combines resilient router connectivity with full dual-core capability (as well as dual-core rSIM technology) that can autonomously switch between independent operator profiles to help keep critical IoT services online during disruption.

The quick win

Standardise on a single, managed router layer per site and migrate telemetry and alarm paths first. Add CSL VoiceLink only where data and operational voice is required, then test under simulated outage conditions (including power loss).

A practical migration approach for electricity operators

Audit all PSTN dependencies, including ‘hidden’ alarm and lift lines.
Prioritise sites based on fault response criticality and restoration/restart requirements.
Replace analogue lines with a managed IP connectivity layer (e.g., CSL routers) for telemetry and remote access.
Deploy CSL VoiceLink where operational data and voice must remain available without PSTN.
Add battery-backed resilience at the router/voice layer for priority sites.
Test voice, alarms, and telemetry under simulated outage conditions and document outcomes for operational readiness.

Regulatory context

Utilities do not need to be telecom experts to act now and implement highly effective solutions. The key requirement is to ensure that communications supporting safety and operational control remain available beyond 31 January 2027. Government and Ofcom guidance also highlights that the legacy PSTN is already experiencing increasing fault rates, reinforcing the case for early migration planning[2][4][3].

Final thought

For electricity operators, PSTN cessation is inseparable from network resilience and outage response. By combining CSL VoiceLink for essential voice services with resilient, managed cellular connectivity (including rSIM where appropriate), utilities can protect substation communications and maintain operational control well beyond the 2027 deadline. Start with a PSTN dependency audit and a priority-site migration plan now to avoid last-minute, high-risk change[7][8][9][10].