SIRNSW's Balancing of Load Rule: Why Your Switchboard Might Fail an Inspection
What is the balancing of load rule, and why might it cause your switchboard to fail an inspection? The Service and Installation Rules of NSW require a three-phase installation to spread its load roughly evenly across all three phases, keeping them within 25 amps of each other. If most of your big appliances hang off one phase, that leg gets overloaded, you get nuisance tripping and voltage complaints, and the imbalance can be picked up as a defect when your installation is inspected or altered.
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1. What balancing of load actually means
A three-phase supply gives you three separate active conductors, each capable of carrying its own share of your home or business's load. Balancing means allocating your circuits across those phases so no single phase does most of the work. It is one of the quiet requirements of the Service and Installation Rules of NSW, the rulebook we introduce in what is SIRNSW and why it affects every Sydney home.
2. The 25 amp rule
Clause 1.17.3 of the Rules expects the load to be evened out so the maximum demand on each phase sits within 25 amps of the others. That single number is the difference between a compliant board and one that draws a defect: a workshop with a big single phase welder, or a home where the oven, aircon and EV charger all landed on the red phase, can blow through it without anyone noticing until something trips.
3. What an unbalanced board does in real life
The overloaded phase runs hot and trips its protection while the other two phases loaf along, which reads as random power drops. Voltage on the loaded phase sags, so lights dim when the big loads kick in. And the imbalance pushes current through the neutral, which affects supply quality beyond your own property. That is why the distributor cares about what looks like a private wiring choice.
4. When imbalance usually appears
Almost never on day one. It creeps in when installations grow: a three-phase upgrade where the old single phase circuits were never redistributed, an EV charger added to whichever phase had spare breaker space, a granny flat or pool fed from one leg, or a renovation that doubled the kitchen load. Each addition seemed small, and the imbalance was nobody's job to check.
5. How an electrician rebalances it
The fix starts with measurement and a maximum demand assessment, working out what each phase actually carries at peak. Then circuits are physically moved on the switchboard so the phases share the work, which sometimes rolls into a broader switchboard upgrade if the board is old or full. You can get a feel for your own numbers with the maximum demand calculator on this page. For how demand is calculated under the wiring rules, see how SIRNSW and AS/NZS 3000 work together.
6. What happens at inspection
When a Level 2 ASP connects, alters or reconnects your supply, they test and check the installation, and a distributor inspection can pick up imbalance as a defect requiring rectification within a set timeframe. If that letter has already arrived, our defect notice rectification team deals with both Ausgrid and Endeavour Energy paperwork. Not sure which network you are on? Check your network area in seconds with our postcode checker.
Why it's Level 2 ASP work
Rebalancing often happens alongside supply side work: a single phase to three phase upgrade, new consumer mains, or metering changes. All of that sits between your switchboard and the network, which only an accredited Level 2 ASP can carry out and certify.
How High Demand Electrical helps
We measure phase loads properly before touching anything, run the maximum demand numbers, and rebalance or rebuild the board as one job, including any Level 2 supply work and the paperwork your distributor expects. If your board trips randomly, dims the lights when the aircon starts, or copped a defect for load balance, we can usually diagnose it in a single visit and book an electrical safety inspection at the same time.
Balance Your Board Before It Becomes a Defect
We measure what each phase really carries, rebalance your circuits and handle any Level 2 supply work in one certified job, so your board passes inspection and stops nuisance tripping.
High Demand Electrical, Level 2 ASP electrical contractor, Sydney. Licence No. 397193C.
General information only. Whether your installation needs rebalancing depends on measured loads, and a site assessment by a licensed electrician is required before scope and pricing can be confirmed.
1. What are you calculating?
Choose the application — the calculator applies the matching rules from Table C1 or C2 of AS/NZS 3000:2018.
2. Add your loads
3. Results
Show the full working (line by line)
This calculator applies the maximum demand methods in Tables C1 and C2 of AS/NZS 3000:2018 (Appendix C). Appendix C is a guide — the standard permits other assessment methods, and your electricity distributor or the NSW Service & Installation Rules may impose additional requirements. Results are for estimation and education; final maximum demand assessment must be confirmed by a licensed electrician. Ratings entered in watts or kilowatts are converted at 230 V (single-phase) or 400 V (three-phase). Table C1 motors assume pf 0.86 and efficiency 0.95; Table C2 motors assume pf 1 and efficiency 0.95, per the standard's conventions.
Project information
These details appear on your PDF report.
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