Hardware
What is phase imbalance with three-phase home solar in South Africa?
Phase imbalance means one leg carries far more load or generation than the others — metros and NRS-aware designs care because it stresses transformers and can trip protection or force export limits. Balance large loads and PV/inverter legs on purpose; do not park the stove, geyser and wallbox on one phase by accident.
Updated 27 October 2026 · Illustrative ranges — not a formal quote, credit decision or legal advice.
Answer first: If you are on three-phase supply, ask the designer for a phase loading sketch: which loads sit on L1/L2/L3, which inverter legs export where, and what imbalance % they design to. Single-phase hybrids on a three-phase erf need extra care — single vs three-phase · NMD / three-phase cost · NMD · inverter size.
Symptoms homeowners notice
- One phase voltage sag when the oven starts.
- Hybrid faults under “imbalance” or over-voltage on one leg when exporting.
- Metro rejection or capped export after inspection — inspection fails · export limits.
Design habits that help
| Habit | Why |
|---|---|
| Spread stove, geyser, pool, wallbox | Cuts coincidence on one leg |
| Three-phase hybrid when loads justify | Symmetric export path |
| Measure clamp currents at handover | Proof beats brochure |
| Re-check after EV add-on | Wallboxes move the imbalance — three-phase EV |
Related: DB upgrade · need a DB upgrade? · CT clamps.
SSEG and NMD link
Upsizing to three-phase or raising NMD is sometimes the clean fix when imbalance is structural. Price the metro process honestly — SSEG · timelines · SSEG cost.
Commissioning checklist
- Clamp each phase at typical evening load.
- Clamp each phase while exporting at midday.
- Photograph DB labels and inverter phase mapping.
- Confirm export limit still correct after any rebalance.
Related: read a quote · dual-supply labels · panels & inverters.
Homeowner folder to keep with the CoC
Store the quote annexures, OEM manuals, serial photos, export-limit screenshots and metro reference letters together. When a future technician or buyer inherits the plant, that folder beats scattered WhatsApps — choose installer · selling with solar · warranty transfer.
Re-check fixed charges and tariff codes after any meter change so savings models stay honest — fixed charges · 2026/27 tariffs · metro tariffs hub · bill still high.
Field notes from SA handovers
At commissioning, ask the partner to demonstrate the behaviour described on this page, photograph settings, and confirm NRS-listed SKUs match the invoice. Refuse non-listed gear and export promises that ignore your metro’s live PDF — red flags · NRS list · SSEG · read a quote.
Why transformers and metros care
Unbalanced residential clusters create neutral currents and local voltage rise on the heavy leg. That shows up as neighbour complaints, inverter over-voltage trips on sunny afternoons, and metro engineers who tighten export caps. Your “it works at my DB” test is not the network test — export limits · inspection fails · NRS 097.
Worked evening imbalance sketch
L1: oven + kettle. L2: lights + IT. L3: nothing until the 7 kW wallbox starts. A single-phase hybrid on L2 cannot rescue L1 when Stage hits. Spread permanently large loads at design time — stove / oven · three-phase EV · whole house · essentials.
Generation-side imbalance
A large single-phase hybrid exporting on one leg while the other legs import can look fine on a bill average and ugly on a instantaneous network snapshot. Three-phase hybrids or carefully limited single-phase export are the usual cures — phases · zero-export · export vs self-use.
Measurement kit at handover
- Clamp meter readings per phase at idle, at dinner peak, and at midday export.
- Voltage per phase logged if the OEM app supports it.
- Photos of DB labels mapping circuits to phases.
- CT orientation proof — CT clamps · monitoring.
When NMD / service upgrades enter
If rebalancing cannot fix coincidence peaks, upsizing NMD or converting supply arrangements may be on the table. Price metro timelines separately from hardware — NMD · upgrade cost · SSEG timelines · DB cost.
EV and heat-pump sequencing
Adding a wallbox or pool heat pump later is a classic imbalance surprise. Revisit the phase sketch before the brick arrives — pool heat pump · load management · add heat pump.
Prepaid, TOU and imbalance masking
Token buys and monthly averages hide instantaneous imbalance. After migration to conventional or while on Homeflex/TOU, look at half-hour shapes and clamp data, not only the rand total — prepaid · migration · Homeflex · Cape Town TOU · read the bill.
Commercial small shops on the same erf as a home sometimes share three-phase boards — keep residential and shop coincidence peaks in the sketch — shops · demand charges · commercial SSEG.
Decision checklist before the deposit
- Same one-page brief to every partner: 12 months of kWh or tokens, tariff code, roof/site photos, Stage essentials list.
- Two matched quotes with Incl. VAT grand totals and named SKUs.
- Export-limit and meter plan written while SSEG queues.
- CoC, dual-supply labels and OEM warranty registration named as deliverables.
- Refuse non-listed gear and export promises that ignore your metro PDF.
Cross-check: read a quote · choose installer · red flags · NRS list · SSEG · SSEG cost · fixed charges · 2026/27 tariffs · metro hub · check a quote · get quotes.
After commissioning — thirty-day habit
For the first month, skim the hybrid app every few days: self-use share, unexpected grid import on sunny afternoons, battery SoC floors before evening Stage, and any fault counts. Photograph settings after the first firmware touch. Keep metro statements beside the monitoring export so “savings” stories stay honest when fixed charges move — monitoring · bill still high · monthly savings · SoC settings · Stage strategy · selling with solar · warranty transfer · insurance.
Related reading on this desk
Imbalance shows up in DB design, EV phase choice and metro NMD upgrades. Keep those answers open while you mark L1/L2/L3 on a printed board photo — phases · three-phase EV · NMD cost · DB upgrade · CT clamps · parallel hybrids · max kW.
Practical SA homeowner notes
Write the open questions from this page onto the site-survey form before anyone quotes. South African installs fail more often on missing paperwork, wrong board placement and ignored metro rules than on brand slogans. Keep Incl. VAT totals, NRS-listed SKUs, export-limit screenshots and CoC deliverables in one folder with serial photos. If a partner cannot show those artefacts at handover, pause the final payment until they can — that discipline protects Stage cover, insurance claims and resale far better than a glossy brochure.
Revisit the live metro tariff PDF and OEM warranty sheet whenever you expand panels, add a wallbox or change prepaid status. Numbers on this desk are illustrative snapshots dated around 27 October 2026; your erf’s fixed charges, feed-in cents and inspection queue are the figures that decide the rand outcome. When in doubt, send the same one-page brief to two installers and compare their annexures line by line rather than their homepage claims.
- Photograph settings after every service visit or firmware change.
- Log Stage SoC floors for two weeks before changing reserve knobs.
- Confirm dual-supply labels still match the as-built single-line.
- Update the insurer schedule when hardware or capacity changes.
- Store monitoring passwords with the conveyancing pack for a future sale.
Quick questions
Can a single-phase hybrid sit on a three-phase home?
Yes with care, but large loads on other phases will not see that inverter’s backup — design explicitly.
Will the metro fail me for imbalance?
They can cap or reject when limits are exceeded — ask for the local imbalance rule in writing.
Does an EV wallbox make it worse?
A 7 kW single-phase wallbox on a loaded leg often does — plan the phase before the brick arrives.