Free tool · ENA EREC P28 Issue 2 (2019)

P28 compliance calculator

Four checks from one set of inputs: the step voltage change against the 3% limit, whether your equipment qualifies for the simplified Stage 1 route, which rapid-voltage-change category it falls in, and whether it meets the P_st = 0.5 flicker characteristic. Every result cites the clause it comes from and shows its working.

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1 · Equipment

Equipment type

Starting method

Star-delta allows 1.5× the Annex A motor ratings (Clause A.2).

Nominal system voltage

Phases

Rated current per phase

A

Power factor

Used to estimate active input power. Annex A Tables A.1.1 and A.1.2 list a rated input (kVA) column, which is checked directly from your current and voltage — the power factor is not needed there. Table A.1.3 lists rated output (kW) only, and true shaft output also depends on motor efficiency, so that check is conservative.

2 · Supply strength

Give one of the three. A short-circuit power from your DNO is the most accurate; the generic values are for approximate calculation only.

Short-circuit power at the PCC

MVA

or supply impedance

Ω

or a generic LV supply

P28 Table 7. Actual impedances can be higher, for example on a pole-mounted transformer or a small cross-section service cable.

3 · Switching pattern

Minimum interval between switching events

s

Drives the P_st = 0.5 characteristic and selects which Annex A motor table applies. Remember a start followed by a stop counts as two voltage changes.

Events per calendar month

Selects the RVC category. 4 or fewer is Category 2; one event per three months or fewer is Category 3. Leave blank to derive it from the interval above.

4 · Stage 1 details

Declared EMC conformance

Check the manufacturer's declaration of conformity or instruction manual.

Installed at a domestic residence (allows up to 32 A under Clause 8.6.2(b)) Service current capacity confirmed as adequate with the network operator

Service current capacity

A/phase

Conditional connection details

Needed only where the equipment conforms to BS EN 61000-3-11 rather than 61000-3-3 (Clause 6.3.2.2).

Manufacturer's declared Z_max

Ω

Measured supply impedance

Ω

For single-phase this is the phase-neutral loop impedance, not the earth-fault loop impedance.

Equipment clearly marked by the manufacturer as requiring a 100 A per phase service

Advanced options and connection point

Switching current multiple

× rated

Leave blank to use our default for the equipment type — 6× for a direct-on-line motor. P28 supplies no default, so ours is an assumption. If you have the manufacturer's locked-rotor current, enter it here.

Distribution transformer rating

kVA

Enter this and the substation busbar box below is not also needed. Annex A.1.3 then applies to three-phase motors started every 10 minutes or longer, for the ratings it lists: 200, 300/315, 500, 750/800 and 1000 kVA.

Connection point

PCC is the LV busbar of a distribution substation PCC is at HV (Stage 1 will not apply — Figure 9 NOTE 5) Several items work together as one system (Clause 6.3.1)

Reset

Our calculators provide indicative assessments based on the simplified methods published in the relevant standards. They are not a substitute for a detailed study, nor for consultation with your network operator.

What this calculator checks

ENA EREC P28 Issue 2 (2019) governs voltage fluctuations caused by customer equipment connected to UK transmission systems and distribution networks. It deals with two distinct effects — flicker, and rapid voltage changes — and sets out a three-stage assessment process.

Step voltage change

A 3% general limit applies to the magnitude of percentage step voltage changes at the point of common coupling, regardless of how often they occur (Clause 5.4). This is the first thing to check (Clause 6.2).

Stage 1 eligibility

LV equipment meeting the Stage 1 criteria can be connected without reference to the network operator. For motors that means the Annex A tables; for EV chargers, heat pumps and general equipment it means conformance to BS EN 61000-3-3 or 61000-3-11, sometimes with a supply impedance condition attached.

RVC category

Rapid voltage changes are grouped into three categories by how often they occur, each with its own time-dependent envelope (Table 4, Figures 5 to 7). Category 2 and 3 carry extra conditions on frequency and separation.

Stage 2 simplified flicker

Figure B.1.2 gives the maximum permissible step voltage change against the interval between changes, at P_st = 0.5. Equipment on or below that line connects without further detailed assessment (Clause 6.3.3.2). The characteristic is capped at 3% once every 475 seconds.

Where our numbers come from

Every value this calculator uses is taken from ENA EREC P28 Issue 2 (2019) and cited to its clause, table or figure. We do not reproduce the standard's text. Where the standard is silent — the switching current multiple is the main case — we say so and label the value as our assumption.

What it does not do

It assesses one item of equipment in isolation. Combining several disturbing items at one point of common coupling, wind and PV flicker summation, energy storage, welding and furnace assessments all need a full study.

Not a substitute for a study

This is an indicative assessment based on the standard's simplified methods. Your network operator may reach a different conclusion using measured data and detailed network models.

About EREC P28

First issued 1989, as Issue 1.

Revised Once. Issue 2 was published in May 2019, thirty years later, and is a full technical revision rather than an amendment.

What changed Issue 2 extended the standard to cover rapid voltage changes, which Issue 1 did not address, and realigned it to the UK implementation of the IEC 61000 series.

Status A qualifying and licence standard under the Grid Code and the Distribution Code. Publication was approved by Ofgem.

Read from the publishing page and foreword of EREC P28 Issue 2 2019.