Fast Turnaround Available
Quick delivery for standard assessments
What is P28?
ENA Engineering Recommendation P28 "Planning Limits for Voltage Fluctuations" defines the acceptable limits for voltage disturbances on UK distribution networks. It ensures that new connections—whether generation or load—don't cause voltage quality problems for other network users.
P28 assessment is a standard requirement for G99 grid connections, but it's also commonly requested for large industrial loads, motor starting analysis, and any connection that could cause rapid changes in power flow on the network.
Our streamlined P28 analysis process delivers accurate assessments quickly. With established modelling templates and efficient workflows, we offer faster turnaround than industry average for standard P28 studies.
P28 Assessment Types
We assess all voltage fluctuation phenomena covered by P28 depending on your application.
Rapid Voltage Change (RVC)
Assessment of step voltage changes caused by generation switching, typically limited to 3% for frequent events.
Typical limit: 3% for frequent events
Start-up Transients
Analysis of voltage disturbances during generator start-up or synchronisation sequences.
Typical limit: Depends on frequency
Flicker Assessment
Long-term and short-term flicker (Pst/Plt) calculations for variable output generation.
Typical limit: Pst ≤ 1.0, Plt ≤ 0.8
Motor Starting
Voltage dip analysis for large motor starting, common in industrial applications.
Typical limit: Typically 3-6% depending on frequency
Common P28 Applications
P28 assessment is particularly important for connections to weaker network points where impedance is higher and voltage fluctuations are more pronounced.
Our P28 Process
Data Collection
We gather network impedance data (from connection offer), equipment switching characteristics, and operational profiles.
Voltage Change Calculation
We calculate expected voltage changes for each switching event using network impedance and load/generation step changes.
Compliance Assessment
We compare calculated values against P28 limits considering event frequency and duration. Flicker calculations performed where required.
Report & Recommendations
Clear report suitable for DNO submission. If limits are exceeded, we provide practical mitigation recommendations.
P28 as a Standalone Service
While P28 assessment is included in our complete G99 packages, we also offer it as a standalone service for:
- • Projects where other studies are completed but P28 is outstanding
- • Industrial connections requiring voltage impact assessment
- • Feasibility studies before formal connection application
- • Second opinion on P28 analysis completed by others
Contact us for a fixed-fee quote based on your specific requirements.
Frequently Asked Questions
What is P28?
ENA Engineering Recommendation P28 defines the limits for voltage fluctuations on UK distribution networks. It sets requirements for rapid voltage changes (RVCs), flicker, and transient voltage disturbances to ensure new connections don't adversely affect power quality for other network users.
When is a P28 assessment required?
P28 assessment is typically required for all G99 connections as part of the compliance package. DNOs also request P28 studies for demand connections with large motors, variable loads, or equipment that causes frequent switching. It's one of the most common studies requested as part of the connection offer process.
What causes P28 issues?
The most common P28 concerns are: inverter switching in solar/BESS systems, wind turbine cut-in/cut-out, generator synchronisation, large motor starting, and arc furnace operation. Weak network connections (high impedance) are more susceptible to voltage fluctuations.
How quickly can you complete a P28 study?
For straightforward cases with good data availability, we offer fast turnaround on P28 assessments. Our streamlined analysis process means quicker delivery than many competitors. Complex cases with multiple switching scenarios may take longer—contact us for an estimate.
What if my installation fails P28 limits?
If initial assessment shows P28 limits are exceeded, we can advise on mitigation options including: modified switching sequences, soft-start equipment, power factor correction, or requesting connection at a higher voltage level. Often simple operational changes can resolve compliance issues.
Get Your P28 Quote
Send us your connection offer and project details. We'll confirm scope and provide a fixed-fee quote.