Does a Commercial Property Need a Larger Three-Phase Supply? How Inner West Businesses Can Tell

Does your commercial property need a larger three-phase supply? It does if your measured maximum demand is close to, or above, what your existing service fuses, consumer mains and main switch can safely carry, or if new equipment would push it there. The only reliable way to know is power logging combined with a maximum demand calculation under AS/NZS 3000. Many Inner West businesses discover they can stay on their current supply with better load balancing, while others genuinely need an upgrade before new machinery, ovens, coolrooms or EV chargers go in.

⚡ Quick Answers: Commercial Three-Phase Supply

• What's the first step? Power logging at the main switchboard for one to two weeks of normal trading.
• What are the warning signs? Main switch or supply fuses tripping at peak times, warm cables or breakers, dimming lights when equipment starts, and phases carrying very different loads.
• Can I just fit a bigger main switch? No. The whole supply chain has to be rated for the load.
• Who applies to Ausgrid? Your Level 2 ASP or electrician, based on the calculated maximum demand.
• How long does it take? Weeks for a simple upgrade; months if the network needs augmenting.
• Is there an alternative? Load balancing, staggered start-up and load management often avoid or delay an upgrade.

1. Why Inner West commercial properties hit their supply limit

A lot of the Inner West's commercial stock was built for a very different use. Shopfronts on King Street, Norton Street and Marrickville Road were wired for a retail counter and some lighting, not a commercial kitchen with combi ovens, induction ranges and a coolroom. Warehouses around Marrickville, St Peters and Tempe that now house breweries, roasteries, gyms and fabrication workshops were often supplied for light storage. When a new tenant moves in, the fit-out often adds far more load than the building's original supply was ever sized for.

2. Warning signs your supply is too small

• The main switch or service fuses trip during peak trading or when several machines run at once.
• Lights dim or flicker when compressors, ovens or motors start.
• Breakers, cables or the main switch feel warm or show discolouration.
• One phase is heavily loaded while the others carry very little.
• You're planning new equipment, EV chargers or an expansion and nobody has checked capacity.

Tripping on its own doesn't always mean the supply is too small. It can also be earth leakage, motor inrush or a single overloaded circuit, which is why our guide to why new machinery causes a commercial property to trip is worth reading before assuming you need an upgrade.

3. How maximum demand is actually worked out

AS/NZS 3000 Appendix C sets out methods for calculating maximum demand for non-domestic installations, based on the connected equipment and realistic diversity (not everything runs flat out at the same time). A calculation on paper is a good start, but the best evidence is measured data. A power logger installed on the main switchboard records current on each phase, voltage and power factor over normal trading, so you can see the true peak and when it happens. Our guide to why power logging should happen first explains what a logger shows.

4. Balance before you upgrade

A three-phase supply is rated per phase. If most of your single-phase equipment sits on one phase, that phase can hit its limit while the other two have plenty of spare capacity. Rebalancing circuits across phases is one of the most cost effective fixes we do for Inner West businesses, and it can buy significant headroom without touching the network connection. Staggering start-up of large equipment, fitting soft starters or variable speed drives to motors, and using load management on EV chargers can also keep peak demand down.

5. What a supply upgrade involves

• Load assessment: power logging and a maximum demand calculation including planned equipment.
• Connection application: lodged with Ausgrid for the increased supply capacity.
• Consumer mains: new, larger cables from the connection point to the main switchboard.
• Main switchboard: a new or upgraded board with a correctly rated main switch and protection.
• Metering: larger supplies may need current transformer (CT) metering rather than direct connected meters.
• Certification: Notification of Service Work and a Certificate of Compliance for Electrical Work.

For very large loads, the local network may need augmentation, which can involve network design by a Level 3 ASP and, in some cases, a new substation. That's where timeframes stretch from weeks to months.

6. Plan it before you sign the lease or order the equipment

The most expensive surprises happen when a business signs a lease or orders a new oven, kiln or compressor before anyone checks supply capacity. Ask for a supply assessment during lease negotiations, since the landlord may be responsible for the base building supply, and include the electrical upgrade in your fit-out budget and timeline. Our commercial electrical fitout service covers this planning stage.

How High Demand Electrical helps

We're a Level 2 ASP team (Licence 397193C) working with Inner West cafes, restaurants, breweries, workshops and offices. We log your actual demand, tell you honestly whether you need a bigger supply or just better balancing, and if an upgrade is needed, we handle the Ausgrid application, consumer mains, switchboard and certification in one job.

Commercial Three-Phase Supply FAQs (Inner West)

How do I know if my business needs a bigger three-phase supply?

The reliable way is power logging combined with a maximum demand calculation under AS/NZS 3000. If measured peak demand is close to or above the rating of your service fuses or main switch, or planned new equipment would push it there, an upgrade is likely needed.

Can I just fit a bigger main switch?

No. The main switch, consumer mains, service fuses and network connection all have to be rated for the load. Fitting a larger switch without upgrading the rest creates an overloaded, non-compliant installation.

How long does a commercial supply upgrade take?

A straightforward upgrade within the existing network capacity can be completed in weeks. Larger upgrades that need network augmentation, current transformer metering or a new substation can take months, so plan early.

Can load management avoid a supply upgrade?

Often, yes. Load balancing across phases, staggering equipment start times, soft starters and dynamic load management for EV chargers can keep peak demand within the existing supply.

Who applies to the network for a larger supply?

A Level 2 ASP or your electrician lodges the connection application with the distributor, which in the Inner West is Ausgrid, based on the calculated maximum demand.

Get a Commercial Supply Assessment

Planning new equipment or a fit-out? Get a power supply upgrade quote, read about our three-phase upgrades, or call 0402 559 777. We'll measure first, so you only pay for the capacity you actually need.